Hazardous Gas Monitoring: A Guide for Semiconductor and Other Hazardous Occupancies (Safety, Health & Hygiene)

HAZARDOUS GAS MONITORING

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HAZARDOUS GAS MONITORING A Guide for Semiconductor and Other Hazardous Occupancies

Logan T. White

Logan T. White Engineering Tucson, Arizona

Copyright 9 2000 by Logan T. White Engineering No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without permission in writing from the Publisher. Library of Congress Catalog Card Number: 00-109486 ISBN: 0-8155-1469-7 Printed in the United States Jo Ann Fite - Developmental Editor Published in the United States of America by Noyes Publications / William Andrew Publishing, LLC 13 Eaton Avenue Norwich, NY 13815 1-800-932-7045 www.knovel.com 1098765432

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Fifth Edition, Second Printing: May 2000

CONTENTS Figures & Tables ix Caveat x Acknowledgments xi Acronymns & Abbreviations xii

H A Z A R D O U S GAS MONITORING Best Industry Practice & Code Intent Prescriptive versus Performance Occupancy Classifications Research Laboratory Facilities Alterations to Existing Facilities Risk Management & Corporate Safety Standards

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REGULATED MATERIALS Concentrations Health Hazard Rating Registry of Toxic Effects of Chemical Substances Flammability Hazard Rating Reactivity Hazard Rating Material Hazard Index Refrigerant Classifications Material Safety Data Sheets Monitoring Measurements

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S U M M A R Y OF HAZARDOUS GAS MONITORING CODES Regional Model Codes Scope of the Code Sections Definition of Terms Uniform Fire Code 1997 Edition Uniform Fire Code 2000 Edition International Fire Code 2000 Edition Standard Fire Prevention Code Sunnyvale CA Toxic Gas Ordinance Santa Clara County Fire Chiefs TGO Guidelines Palo Alto CA Toxic Gas Ordinance 1999 NFPA 55 Standard for Storage, Use and Handling of Compressed and Liquified Gases in Portable Cylinders NFPA 31 8 Standard for the Protection of Cleanrooms Federal Requirements Environmental Protection Agency (EPA) Occupational Safety & Health Administration (OSHA) IEC Standard 61 508 Functional Safety- Safety Related Systems ANSI/ISA Standard $84.01 Safety Instrumented Systems for the Process Industries Underwriters Laboratories Standards

1

2 3 3 4 5 5 7 7 8 9 9 10 11 11 11 12 13 13 14 15 16 26 28 42 44 46 48 53 54 57 58 60 63 65 67

Oxygen Depletion Monitoring Refrigerant Vapor Alarm Systems Uniform Mechanical Code Requirements Uniform Fire Code Requirements ANSI/ASHRAE Standard 15 Safety Code for Mechanical Refrigeration International Fire Code Requirements Refrigeration Sensors System Testing Requirements

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HAZARDOUS GAS MONITORING SENSORS Selection Criteria Monitored Gases Sensor Suitability Sensor Sensitivity Sensor Selectivity Sensor Stability Sensor Recalibration Time Sensor Ease of Recalibration Sensor Response Time Sensor Poisoning Sensor Useful Life Sensor Diagnostic Features Sensor Susceptibility to RFI/EMI Total Cost of Ownership (TCO) Sensor Types Manufacturers Electrochemical Sensors Gas Membrane Galvanic Cell Catalytic Bead Sensors Solid State Sensors Quartz Crystal Microbalance Sensors Draeger Tube Sensors Ionization Sensors Extractive Sensing Systems Paper Tape Sensors Spectrophotometric Analysis Molecular Emission Spectrometry Sensors Acoustic Sensors Ozone Monitoring Sensors Problematic Gases Arsine Boron Trifluoride Chlorine Trifluoride Fluorine Hydrogen Nitrogen Trifluoride TEOS Recommended Sensor Locations Sample Area Interference

vi

68 69 69

70 72 74 75 77 81 81 81

82 82 82 82 83 83 83 83 83 84

84 84 85 85 85

87 88 89

90 91

92 92 94 97 98 99

100 100 100 101 102 103 104 105 105 105 108

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Alarm Set Points Using Portable Sensors Sensor Recalibration Other Sensor Considerations Sensing Reaction Byproducts Pyrolyzers Electrically Hazardous Location Requirements Obstructions Environmental Conditions Maintenance Central versus Distributed Systems

109 109 110 112 112 114 114 114 114 115 115

MONITORING, ALARM AND CONTROL SYSTEMS

117 117 117 118 120 121 121 122 122 122 123 125 125 127 129 133 135 137 138 139 140 143 145 145 148 148

System Sophistication System Safety versus Reliability System Electrical Supervision System Redundancy Dual Processors with Single I/O Dual Processors with Dual I/O and loo2 Logic Dual Processors with Dual I/O and 20o2 Logic Triple Modular Redundancy (TMR) with 2003 Logic System Diagnostics System Integration System Documentation and Data Acquisition Monitoring-Systems in General PLC-Based Monitoring Systems Triple Modular Redundancy (TMR) Fire Alarm Panel-Based Monitoring Systems Proprietary Network-Based Monitoring Systems LonWorks Network-Based Monitoring Systems System Communication Configurations Other Monitoring System Considerations Emergency Control Station Recommended Programmed Alarm Response Shutdowns Alarm Annunciation Emergency Response Chemical Delivery/Service Corridor Emergency Alarm

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MONITORING EXHAUST TREATMENT SYSTEM DISCHARGE Code Requirements Monitoring Problems Alternate Materials and Methods Direct Monitoring

vii

149 149 150 152 153

7

SYSTEM CERTIFICATION

155 155 155

Code Requirement Relevant Certification Applicable Standards Third-party Review Organizations

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156 156

CODE ENFORCEMENT System Review Third-party Review & Technical Opinion Alarm System Matrix Safety versus Reliability System Testing Compliance Checklists

159 159 160 160 161 161 162

APPENDICES AO

Table of Typically Monitored Gases

163

BD

Zellweger Protocol for Testing Toxic Gas Detectors

167

C.

UFC Table A-VI-A-1-Normalization Factor

177

DO

Safety System Suppliers

179

GLOSSARY

185

REFERENCES

195

INDEX

203

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FIGURES 1.

Simplified PLC-based gas monitoring system.

128

2.

Simplified fire alarm panel-based gas monitoring system.

132

3.

Simplified proprietary network-based gas monitoring system.

134

4.

Simplified LonWorks network-based gas monitoring system.

136

5.

Typical alarm system matrix.

144

6.

Factory Mutual system certification chart.

154

TABLES Safety Integrity Level (SIL) Standards & Classes

66

Hazardous Gases Typically Monitored in Semiconductor Facilities

163

1995 Supplement to UFC Table A-VI-A-1 -- Normalization Factor

177

ix

CAVEAT

Purpose.

This guide is intended to provide an overview of the subjects contained herein, and is intended to be used solely for general information only.

Misapplication/Misunderstanding.

The author cannot assume any liability with regard to the misinterpretation or misapplication of any code provision, monitoring system, or life-safety alarm which may result from the use of this guide.

User Responsibility.

The user is solely responsible for researching current codes and systems and application of the principles and requirements of the codes and other regulations and monitoring systems or alarms to each specific set of circumstances.

Code Compliance.

Codes and standards regulating hazardous gas monitoring are continuously revised and enacted and it is the user's responsibility to research the most current applicable regulations. Compliance plans should be discussed with, and have the approval of, the local Authorities Having Jurisdiction.

Changing Technology.

Hazardous gas monitoring technology is a rapidly changing field which demands that those using or designing monitoring systems assume responsibility for keeping abreast of the latest developments. The information in this guide is accurate to the best of our knowledge at the time of publication; however, the author does not assume any responsibility or liability for the accuracy or completeness of, or consequences arising from, such information.

Commercial Products. Reference in this guide to commercial

products does not constitute endorsement or recommendation for use by the author. It is the sole responsibility of the user to make final determination of the suitability of any information or product and the manner of that use. Anyone intending to rely upon any recommendation of materials or procedures mentioned in this guide should satisfy himself as to such suitabililty and further determine that all applicable safety and health standards are met.

ACKNOWLEDGMENTS

Grateful acknowledgment is made to the following people for their comments and input during the creation of this g u i d e . . .

Reinhard Hanselka of Advanced Industrial Designs for his critical review c o m m e n t s . . . Kelly Erin O'Brien of Envirodata for her University of California Santa Cruz course which inspired this guide . . . Dean Novy of SDN Technology, Fremont, California, for his insight into design firm c o n s i d e r a t i o n s . . . Jim Hills for sharing his wealth of e x p e r i e n c e . . . and CH2M Hill Industrial Design Corporation of Portland, Oregon. Thanks go to the many industry professionals who provided valuable information . . . Ken Eichelmann of S c o t t / B a c h a r a c h . . . Phil Alderman and Steve Pitts of MST . . . Don Bell of Edwards Systems T e c h n o l o g i e s . . . Thorn Walczak and Bill Madison of GE F a n u c . . . Ekkehard Pofahl of TUV Rheinland . .. Lou Chavez of Underwriters L a b o r a t o r i e s . . . Richard Witte of Metron T e c h n o l o g y . . . A I Carrino of P u r e A i r e . . . Kevin Williams and Les Wulf of Zellweger A n a l y t i c s . . . Gordon Simpkinson of the Palo Alto Fire D e p a r t m e n t . . . and Paris Stavrianidis of Factory Mutual.

I also thank the many colleagues and friends who offered advice and encouragement.

xi

ACRONYMS / ABBREVIATIONS (see Glossary for additional acronyms)

AHJ ECS E/E/PE EMCS ERT EVC FM FTIR HPM IDLH IFC IPA IR ISA LC~o LDL LEL LFL LOC Max TQ Mg/Kg MHI MSDS NEC NFPA NIOSH OEL OTV PEL PLC PPB PPM RFI SlL SIS SLC SRS STEL TGO TLV TWA UBC UFC UFL UL VMB

Authority Having Jurisdiction Emergency Control Station Electrical/Electronic/Programmable Electronic Energy Management Control System Emergency Response Team Equilibrium Vapor Concentration Factory Mutual Fourier Transform Infrared Hazardous Production Material Immediately Dangerous to Life & Health International Fire Code Isopropyl Alcohol Infrared International Society of Measurement and Control 50 Percent Lethal Concentration Level Lower Detection Limit Lower Explosive Limit Lower Flammable Limit Level of Concern Maximum Threshold Quantity Milligrams per Kilogram Material Hazard Index Material Safety Data Sheet National Electric Code National Fire Protection Association National Institute of Occupational Safety and Health Occupational Exposure Limit Odor Threshold Value Permissible Exposure Limit Programmable Logic Controller Part per Billion Part per Million (equivalent to Mg/Kg) Radio Frequency Interference Safety Integrity Level Safety Instrumented System Safety Life Cycle Safety Related Systems Short-term Exposure Limit Toxic Gas Ordinance Threshold Limit Value Time Weighted Average Uniform Building Code Uniform Fire Code Upper Flammable Limit Underwriters Laboratories Valve Manifold Box

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Hazardous Gas Monitoring

Codes require that air in areas that use, handle or store hazardous production materials be monitored for dangerous concentrations of these gases. Hazardous production materials (HPMs) include substances that are toxic, highly toxic, flammable, combustible, pyrophoric, reactive, corrosive or oxidizing, as well as some cryogenic and refrigeration gases. Because many of the gases used in industry have very poor physiological warning properties (odor thresholds) relative to their dangerous concentrations, monitoring systems are necessary. In addition to monitoring gas releases, codes also include requirements for containment and management of hazardous materials. These containment systems must be monitored for leaks to ensure that they are functioning properly. The need for monitoring is illustrated by the extreme toxicity of some gases to which short-term exposure of minute amounts (from ppb to ppm) can cause serious adverse effects including death. As an example of toxicity, arsine (ASH3) is used in semiconductor manufacture as a dopant. Arsine's permissible exposure limit (PEL) is 50 parts per billion--200 times lower than the PEL for hydrogen cyanide, the lethal agent commonly used for executions. The ACGIH proposes lowering the TLV for arsine to 2 ppb. Many cleanroom ion implanters contain lecture bottles that hold 40 to 50 liters of arsine. A leak of as little as two cubic feet of 100 percent arsine gas could fill a 10-foot-high, 28-foot-square room (7,840 cubic feet) with a lethal concentration (250 ppm) of this gas. While toxic and flammable gases receive the most attention, inert gases can also pose a danger. Some gases can displace ambient oxygen to the extent that the area becomes hazardous for personnel. Gas detection systems can generate alarms if the oxygen concentration drops below 1 9.5 percent. Semiconductor fabrication facilities generally contain a dedicated storage room for inert gases. Some authorities having jurisdiction require monitoring for oxygen depletion in these inert gas storage rooms.

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HAZARDOUS GAS MONITORING

The Uniform Building Code (UBC) and the Uniform Fire Code (UFC) are nationallyrecognized model codes that address hazardous gas monitoring to a certain extent and are adopted by many local jurisdictions. However, there is usually significant lag time between the use of new hazardous production materials and the development of codes specific to their regulation. Some jurisdictions modify the model codes by providing amendments addressing specific concerns of the authority having jurisdiction (AHJ). As a result, many local jurisdictions have developed codes that conflict with, or expand upon, model codes. The first step in developing a facility hazardous gas monitoring and alarm system is to determine from the local authority having jurisdiction which codes they have adopted including any modifications. Codes relating to hazardous gases are more developed in the San Francisco Bay Area (Silicon Valley) due to the concentration of semiconductor manufacturing facilities in the region. As an example, the Santa Clara County Fire Chiefs Association developed their own model toxic gas ordinance (TGO) as a guide for the cities in that county. Although many of the Bay Area municipalities did adopt Santa Clara County's model code, some cities have enacted codes that differ from Santa Clara County's TGO. The purpose of this guide is to give designers, facility owners and operators, suppliers and code officials an overview of the various code requirements and recommended applications that apply to the design and operation of hazardous gas monitoring and alarm systems. Manufacturing processes and the codes that regulate them are constantly evolving. As safety considerations are identified, code provisions are developed by industry and regulatory authorities. According to Reinhard Hanselka, a respected leading authority on semiconductor industry codes, "the semiconductor industry uses the highest standard of care of any industry anywhere in the world." The rapid development of relevant codes is the result of the young semiconductor industry pursuing a higher standard of care than long-established industries. Codes are not intended to be used as design specifications or instructional manuals, and are constantly evolving. Excerpts from various codes in the following text are for the reader's convenience and are not a substitute for research into the full body of currently-enacted applicable codes.

Best Industry Practice & Code Intent This guide includes excerpts from several codes regarding the use and monitoring of hazardous materials. Regulatory agencies develop codes to safeguard the public and property from recognized hazards. Most codes emphasize that their requirements are intended to be minimum standards. For example, the National Electrical Code states:

HAZARDOUS GAS MONITORING

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This Code contains provisions considered necessary for safety. Compliance therewith and proper maintenance will result in an installation essentially free from hazard, but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use . . . . This Code is not intended as a design specification nor an instruction manual for untrained personnel This Code prescribes regulations consistent with nationally recognized practice for the safeguarding to a reasonable degree of life and property from the hazards o f fire, explosion, and dangerous conditions arising from the storage, handling and use of hazardous materials and devices, and from conditions hazardous to life or property in the use or occupancy of buildings or premises and provisions to assist emergency responsepersonneL Codes allow the use of alternate methods and materials provided that the spirit of the code is met. Refer to the discussion of Alternate Materials and Methods in Chapter 6 of this guide. Codes are developed by committee, follow technology, may not be immediately adopted by local jurisdictions, may be locally amended, and do not necessarily require the use of the best industry practice. The real-world standard to which one would be held in a court of law is the opinion of your peers called to testify as expert witnesses for or against you. Codes are considered minimum requirements and do not necessarily provide a good design. It may be indefensible to ignore additional life-safety features in a system simply because they are not required by the authority having jurisdiction. The best industry practice is to incorporate all of the design features that will enhance life safety and minimize hazards to environment and property. Prescriptive versus Performance. Standards and codes are moving away from prescriptive requirements to be more performance-oriented. Earler codes directed the use of a specific method to achieve a result. Newer codes mandate a performance while not prescribing a specific means to achieve the result. While prescriptive rquirements may be easier to understand and to implement, performance-oriented requirements allow the use of new technologies and methods to meet an intent.

Occupancy Classifications A first step in researching code requirements is to determine the occupancy classification of every area within the facility. In the 1997 Uniform Fire Code and Uniform Building Code, semiconductor fabrication facilities were Uniform Building Code Group H, Division 6 classification.

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HAZARDOUS GAS MONITORING

1997 UBC 307.1.1 General Group H occupancies shaft include buildings or structures, or portions thereof that involve the manufacturing, processing, generation or storage of materials that constitute a high fire, explosion, or health h a z a r d . . . Division 6. Semiconductor fabrication facilities and comparable research and development areas in which hazardous production materials (HPM) are used and the aggregate quantity of materials are in excess o f those listed in Table 3-D or 3-E. Such facilities and areas shaft be designated and constructed in accordance with section 411. Occupancy classifications in other jurisdictions, such as the Standard Building Code, may differ. In addition to UBC H-6 classifications, UBC Group H, Division 3 and Division 7 may apply to storage of hazardous materials at semiconductor fabrication facilities. The 2000 International Fire Code revised occupancy classifications for hazardous Group H. Group H-1 now covers buildings and structures which contain materials that pose a detonation hazard and includes detonable pyrophoric materials. Group H-2 covers buildings and structures which contain materials that pose a deflagration hazard or a hazard from accelerated burning and includes flammable and pyrophoric gases. Group H-3 covers buildings and structures which contain materials that readily support combustion or pose a physical hazard and includes oxidizing gases. Group H-4 covers buildings and structures which contain materials that are health hazards and includes corrosives, highly toxic and toxic materials. Group H-5 covers semiconductor fabrication facilities and comparable research and development areas in which hazardous production materials are used and the aggregate quantity of materials is in excess of those listed in IFC tables 307.7(1) and 307.7(2). In previous editions of codes, semiconductor fabrication facilities were classified as Group H-6, storage of pyrophoric and flammable gases was Group H-2, and toxic and highly toxic storage was Group H-7.

Research Laboratory Facilities. Recent toxic gas ordinances in the Bay Area have addressed the problem of research laboratories falling under the same requirements as large semiconductor manufacturing facilities. Some jurisdictions now allow laboratories to meet less stringent requirements based on material quantities. The Palo Alto, California, TGO provides a section on minimum threshold quantity controls which would apply to laboratories.

HAZARDOUS GAS MONITORING

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Alterations to Existing Facilities It may be necessary to meet current code requirements when repairing, retrofitting, renovating, or adding to an existing semiconductor manufacturing facility. Although the original facility met the requirements of an earlier code in force at the time of construction, additions or alterations must comply with current codes. Alterations or additions may trigger the requirement for upgrades to existing safety systems. Early in the schematic design phase, compliance should be discussed with the code officials to determine the extent of required upgrades to the existing facility.

Risk Management & Corporate Safety Standards Corporate risk management often specifies design standards which exceed the minimum code requirements. It is advisable to coordinate with the facility loss prevention or risk management team and insurance carrier early in design. Many semiconductor manufacturers define their own safety standards, which must be incorporated into their hazardous gas monitoring systems.

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Regulated Materials

Monitoring is required when the gases used meet the definition of a hazardous production material (HPM). An HPM is a solid, liquid or gas associated with semiconductor manufacturing that has a degree-of-hazard rating in health, flammability or reactivity of Class 3 or 4 as ranked by Uniform Fire Code Standard 79-3, Identification of the Health, Flammability, and Reactivity of Hazardous Materials, and which is used directly in research, laboratory or production processes which have as their end product materials which are not hazardous.

Uniform Fire Code Standard 79-3 references the National Fire Protection Association (NFPA) Standard 704, Standard System for the Identification of the Fire Hazards of Materials, which provides the criteria for the familiar diamond placard identifying the health, flammability and reactivity of materials. NFPA Standard 49, Hazardous Chemicals Data, provides definitions for the degree of hazard.

Concentrations Exposure levels are based upon air concentration which can be measured in percent by volume, or in parts-per-million (ppm). To convert percent concentration to ppm, move the decimal point four places to the right. Gas monitoring code requirements usually refer to permissible exposure level (PEL). Gas manufacturers will provide data on exposure levels for specific gases they supply. Man.y gases used in semiconductor manufacturing are diluted mixtures. The degree of hazard can be dependent upon the concentration of the gas. When evaluating the hazard or toxicity, consider the concentration as well as the nature of the chemical.

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HAZARDOUS GAS MONITORING

Health Hazard Rating A health hazard rating of 4 is assigned to a material that on very short exposure could cause death or major residual injury, including materials too dangerous to be approached without specialized protective equipment. This degree usually includes: Materials that, under normal conditions or under fire conditions, are extremely hazardous (i.e., toxic or corrosive) through inhalation or through contact with or absorption by the skin; Materials whose 50 percent lethal concentration level (LCso) for acute oral toxicity is less than or equal to 5 ppm; Materials whose LCso for acute dermal toxicity is less than or equal to 40 ppm; Any liquid whose saturated vapor concentration at 20~ is equal to or greater than 10 times its LCso for acute inhalation toxicity, if its LC6o is less than or equal to 1,000 ppm; Gases whose LC~o for acute inhalation toxicity is less than or equal to 1,000 ppm. A health hazard rating of 3 is assigned to a material that on short exposure could cause serious temporary or residual injury, including materials requiring protection from all bodily contact. This degree usually includes: Materials that give off highly-toxic combustion products; Materials whose LC~o for acute oral toxicity is greater than 5 ppm, but less than or equal to 50 ppm; Materials whose LCso for acute dermal toxicity is greater than 40 ppm, but less than or equal to 200 ppm; Any liquid whose saturated vapor concentration at 20~ is equal to or greater than its LCso for acute inhalation toxicity, if its LCso is less than or equal to 3,000 ppm, and that does not meet the criteria for either degree of hazard 4; Gases whose LCso for acute inhalation toxicity is greater than 1,000 ppm, but less than or equal to 3,000 ppm; Materials that either are severely corrosive to skin on single, short exposure or cause irreversible eye damage.

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Additional monitoring requirements become applicable when the gases used meet the UFC definition of toxic or highly-toxic: Toxic Material A chemical or substance that has a median lethal concentration (L C5o) in air more than 2 0 0 parts per million but not more than 2 0 0 0 parts per million by volume of gas or vapor, or more than two milligrams per liter but not more than 2 0 m#ligrams per liter o f mist, fume or dust, when administered by continuous inhalation for one hour, or less i f death occurs within one hour, to albino rats weighing between 2 0 0 and 3 0 0 grams each. Highly Toxic Material A chemical that has a median lethal concentration (L C5o) in air o f 2 0 0 parts per million by volume or less o f gas or vapor, or 2 milligrams per liter or less of mist, fume or dust, when administered by continuous inhalation for one hour, or less if death occurs within one hour, to albino rats weighing between 2 0 0 and 3 0 0 grams each.

Registry of Toxic Effects of Chemical Substances (RTECS) RTECS is a database of toxicological information compiled by the National Institute of Occupational Safety and Health (NIOSH). The registry contains over 130,000 chemicals and the concentrations at which their toxicity is known to occur. Along with six types of toxicity data for each prime chemical, the database includes specific numeric toxicity values such as LCso. Information is available on-line as well as on CDROM and computer tape. See the References section of this guide for information on how to access RTECS.

Flammability Hazard Rating The degrees of flammability hazard are ranked according to the susceptibility of materials to burning. A flammability hazard of 4 is assigned to a material that will rapidly or completely vaporize at atmospheric pressure and normal ambient temperature or that is easily dispersed in air and which will burn readily. This degree usually includes: Flammable gases; Flammable cryogenic materials; Any liquid or gaseous material that is liquid while under pressure and has a flash point below 73~ and a boiling point below 100~ (i.e., Class IA flammable liquids); Materials that ignite spontaneously when exposed to air (pyrophoric).

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HAZARDOUS GAS MONITORING

A flammability hazard of 3 is assigned to a liquid or solid that can be ignited under almost all ambient temperature conditions. Materials in this degree produce hazardous atmospheres with air under almost all ambient temperatures or, though unaffected by ambient temperatures, are readily ignited under almost all conditions. This degree usually includes: Liquids having a flash point below 73~ and having a boiling point at or above 100~ and those liquids having a flash point at or above 73~ and below 100~ (i.e., Class IB and Class IC flammable liquids); Materials that due to their physical form or environmental conditions can form explosive mixtures with air and that are readily dispersed in air, such as dusts of combustible solids and mists of flammable or combustible liquid droplets; Materials that burn with extreme rapidity, usually by reason of self-contained oxygen (e.g., dry nitrocellulose and many organic peroxides).

Reactivity Hazard Rating Combustion requires a fuel, an oxidizer and a source of energy in the form of heat. Without all three components continually being available in adequate proportions and quantities, combustion cannot continue. The oxidizer most commonly comes from the oxygen (02)in the air which chemically reacts with fragmented fuel molecules under high temperature conditions. As the availability of an oxidizer increases, combustion rates (and ease of ignition) both intensify. As the oxygen concentration increases, materials that burn rapidly now burn explosively; materials that burn readily now burn rapidly, etc. In addition to atmospheric oxygen, some compounds have chemically-bonded oxygen that can become easily released and available to participate in combustion. Such materials, when burning, cannot be suppressed by smothering as they contain their own oxygen supply. Some materials can directly take the place of oxygen in the combustion process. Chlorine gas is often a stronger oxidizer than oxygen. A reactivity hazard rating of 4 is assigned to a material that in itself is readily capable of detonation or explosive decomposition or reaction at normal temperatures and pressures.

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A reactivity hazard rating of 3 is assigned to a material that in itself is capable of detonation or explosive decomposition or reaction, but which requires a strong initiating source or which must be heated under confinement before initiation or which reacts explosively with water.

Material Hazard Index Some jurisdictions have established a similar ranking of regulated materials referred to as material hazard index (MHI). Refer to the discussion of MHI in Chapter 3 of this guide under the Sunnyvale CA Model TGO.

Refrigerant Classifications Refrigerants used in cooling systems are found throughout manufacturing facilities. Some refrigerants meet the definition of a hazardous material. ANSI/ASHRAE Standard 34-1992 Number Designation and Safety Classification of Refrigerants classifies refrigerants. Class B refrigerant is one for which there is evidence of toxicity at concentrations below 400 ppm. Class 2 refrigerant is one having a lower flammability limit (LFL) of more than 0.10 kg/m 3 (0.00625 Ib/ft 3) at 21~ and 101 kPa (70~ and 14.7 psia) and a heat of combustion of less than 19,000 kJ/kg (8,174 Btu/Ib). Class 3 refrigerant is one that is highly flammable, as defined by an LFL of less than or equal to 0.10 kg/m 3 (0.00625 Ib/ft 3) at 21~ and 101 kPa (70~ and 14.7 psia) or a heat of combustion of less than 19,000 kJ/kg (8,1 74 Btu/Ib).

Material Safety Data Sheets The Material Safety Data Sheet (MSDS) should provide information regarding the toxicity, health, flammability and reactivity of a material. MSDS can be obtained from the chemical vendor, or may be found from several sources on the Internet by using the search text "material safety data sheet." The Chemical Referral Center can also provide safety and health information about chemicals. The Washington, D. C., center operates from 8:00 AM to 9:00 PM Eastern time at 800.262.8200.

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HAZARDOUS GAS MONITORING

Monitoring Measurements Several measurements are specific to hazardous gas monitoring. The American Conference of Governmental Industrial Hygienists (ACGIH) uses the terms:

Threshold limit value (TLV) 8-hour time-weighted average (TWA). The timeweighted average concentration of a substance for a normal 8-hour workday, 5 days per week, for 40 years to which nearly all workers may be repeatedly exposed without adverse effect. An occupational exposure metric pertaining to a majority of the population. National codes now refer to PEL in lieu of TLV. Threshold limit value (TLV) 15-minute short-term exposure limit (STEL). The time-weighted average concentration of a substance for a 15-minute exposure to which nearly all workers may be repeatedly exposed without adverse effect. The Occupational Safety and Health Administration (OSHA) uses both: Ceiling limit. The maximum concentration of an airborne contaminant to which one may be exposed.

Permissible exposure limit (PEL). Concentration deemed safe for 8-hour timeweighted average. The Uniform Fire Code also uses PEL. Many PELs are the same value as TLVs. The National Institute of Occupational Safety and Health (NIOSH) uses the term:

Immediately dangerous to life or health (IDLH}. A concentration of airborne contaminants, normally expressed in parts per million or milligrams per cubic meter, which represents the maximum level from which one could escape within 30 minutes without any escape-impairing symptoms or irreversible health effects. Some texts and jurisdictions also refer to:

Occupational exposure limit (OEL). A generalized term for the gas concentration considered safe for personnel. The exact definition and limit values of OELs vary between jurisdictions and countries. In the United States, the most widely used OEL is the permissible exposure limit.

9

Summary of Hazardous Gas Monitoring Codes

Code requirements for monitoring hazardous gases originate either in regional model codes or local toxic gas ordinances. This chapter is a compilation of relevant codes and design applications from communities where there is a high concentration of advanced technology manufacturers who use hazardous gases in their production processes. This compilation can serve as a useful starting point for individual designs and may save hours of searching for model hazardous gas monitoring requirements. This guide is not intended to be a comprehensive design manual. The jurisdictions referenced in this book had enacted hazardous gas monitoring and life-safety system codes at the time of publication. Because these codes may have subsequent amendments, it is important to obtain the most recent edition. An extensive bibliography of codes, standards, and recommended practices is provided in the References section of this book.

Regional Model Codes Presently, three regional model codes dominate in the United States and they will likely remain in effect for some time while jurisdictions review and adopt the new 2000 and later codes. The Uniform Fire Code, a model code originally published by the International Conference of Building Officials (ICBO), has been adopted by most jurisdictions west of the Mississippi. The National Fire Code, a model code published by the Building Officials and Code Administrators (BOCA), has been adopted by most jurisdictions in the Northeast. The Standard Fire Prevention Code, a model code published by the Southern Building Congress International (SBCCI), has been adopted by most jurisdictions in the Southeast.

13

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HAZARDOUS GAS MONITORING

The new millenium is expected to bring turmoil to the code industry. unfolding over the next few years include:

Code changes

Suspension of the National Fire Code and the Standard Fire Prevention Code and introduction of the inaugural edition of the International Fire Code. The International Fire Code (IFC) is international in name only and is the result of a cooperative effort to bring uniformity to fire codes throughout the United States. Published by the International Code Council (ICC), the codedevelopment panel included representatives of BOCA, ICBO and the SBCCI. The IFC coordinates requirements in the various fire codes developed by these organizations and is designed to be compatible with other codes such as the International Building Code, International Mechanical Code and the International Plumbing Code also published by the ICC. The Uniform Fire Code is presently sold by the Western Fire Chiefs Association (WFCA). With respect to gas monitoring requirements, the 2000 UFC is similar to the IFC and is basically the 1997 UFC plus 1998 and 1999 supplements. UFC Section 51 is similar to IFC Chapter 18, and UFC Section 80 is similar to IFC Chapter 27. Originally a member of the IFC development group, the National Fire Protection Association (NFPA) regrettably terminated their participation and now plans to develop a full Consensus Codes set of codes and standards. They have an agreement with the WFCA to produce a joint NFPA 1 - Uniform Fire Code. Successful features of the EPCOT Building Code and EPCOT Fire Prevention Code are to be incorporated. A tentative release date is mid-2002. Also being considered by the code industry are "harmonized" codes for release in 2003, and a new California code based on several existing model codes. The ideal situation for the advanced technology community would be a coordination of the codes in all areas of the United States.

Scope of the Sections Codes are organized in sections or "articles" based on the type of gas, the building occupancy classification, the quantity of hazardous material, and whether the material is being stored, used or dispensed. Specific code requirements must be evaluated with respect to the section scope. For example, the 1997 Uniform Fire Code (UFC) Article 8 0 0 3 . 3 . 1 . 6 included the wording "the gas detection shall be capable of monitoring . 9. the discharge from the treatment system." This article is part of a section on indoor storage of toxic and highly-toxic gas. Each of those criteria (indoor, storage, toxic and highly-toxic) must be met in order to require monitoring of treatment system discharge. Exhaust discharge from other areas is not required to be monitored.

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15

When reading the code, it is always critical to determine the scope of the section from which a particular requirement is taken.

Definition of Terms

Definitions of terms used in the codes must be carefully evaluated. For example, diborane (B2H6) in 100 percent concentration meets the definition of highly toxic. Many manufacturers use a 200 ppm mixture of diborane in hydrogen. This diluted mixture does not meet the definition of toxic or highly toxic. Code requirements for toxic gases may not be applicable to very diluted concentrations of gases that may otherwise be considered toxic in nondiluted form. Use the following formula to determine the LC~o of a diluted mixture" LCso of gas (ppm mixture) = 1/Toxic Component Concentration in Decimal % LC~o of Toxic Component For example, diborane in 100 percent concentration has an LC~o of 40 ppm (for a fourhour exposure) which classifies as a highly toxic. First the LCso must be normalized to one hour by using a normalization factor from Table A-VI-A-1 in UFC Supplement Appendix VI-A (refer to Appendix C of this guide). LC~o (1 Hour) = 2 x 40 ppm = 80 ppm Where 2 = the normalization factor to convert from 4 hours to 1 hour The LCso of a mixture diluted to 200 ppm (10,000 ppm = 1 percent) with hydrogen would be 4 0 0 , 0 0 0 ppm, which is greater than 2,000 and, therefore, does not meet the definition of toxic. LCso B2H6 (200 ppm mixture = 1/(0.0002/80 ppm) = 4 0 0 , 0 0 0 ppm In this example, treatment system discharge monitoring for toxics would not be required by code. However, the gas mixture is essentially hydrogen and all code requirements relating to the storage and use of hydrogen would apply.

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Uniform Fire Code 1997 Edition Where adopted, the 1997 Uniform Fire Code will likely remain in use while later codes are reviewed and approved. Considering the upheaval in the code development industry, the time required to adopt a new code may be unusually long. In general, Article 51 is devoted to Semiconductor Fabrication Facilities requirements. Article 80 also contains applicable requirements and covers Hazardous Materials in any occupancy classification. Article 51 also contains requirements for monitoring various detection systems at an emergency control station (ECS). Article 51 extensively references requirements in Article 80 and other articles. These references facilitate a more complete understanding of all of the life safety and alarm monitoring requirements for semiconductor fabrication facilities.

Regarding Emergency Control Stations Section 5101.6 requires the emergency control station to be continuously staffed by trained personnel and to be on the premises, but located outside of the fabrication area. The emergency control station location must be approved by the authority having jurisdiction. When the UFC requires emergency equipment or alarm and detection systems in a semiconductor fabrication facility, those systems are to be monitored at the emergency control station. 1997 UFC 5101.6 Emergency Control Station. An emergency control station shaft be provided on the premises at an approved location, outside of the fabrication area and shaft be continuously staffed by trained personnel The emergency control station shaft receive signals from emergency equipment and alarm and detection systems. Such emergency equipment and alarm and detection systems shaft include, but not necessarily be limited to the following when such equipment or systems are required to be provided either by this article or elsewhere in this code: 1. Automatic fire sprinkler system alarm and monitoring systems (see Section 5101.10. 1). 2. Manual fire alarm systems (see Section 5101.10. 2). 3. Emergency alarm systems (see Section 5101.10.3). 4. Continuous gas-detection systems (see Section 5101.10.4). 5. Smoke-detection systems (see Sections 1007.2.6.4, 8003.3.1.7, 8003. 6. 1.6, 8003. 7. 1.7 and 8004.2.3. 7. 7 and the Building Code). 6. Emergency power system (see Section 5101.13).

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Regarding Alarm and Detection Systems Section 5101.13 requires all of the above systems except smoke detection to be connected to emergency power. Because smoke-detection systems are usually a part of the fire alarm system, they are effectively also connected to emergency power. Alarm and detection system requirements are in Section 5101.10. 1997 UFC 5101.10 Alarm and Detection Systems. 1997 UFC 5101.10.1 Automatic fire sprinkler system. Automatic fire sprinkler systems shaft be electronically monitored and provided with alarms in accordance with Section 1003. 3. Automatic fire sprinkler system alarm and monitoring signals shaft be transmitted to the emergency control station. 1 997 UFC 5101.10.2 Manual fire alarm system. A manual fire alarm system shaft be installed throughout buildings containing Group H, Division 6 Occupancies. Activation of the alarm system shall initiate a local alarm and transmit a signal to the emergency control station. Manual fire alarm systems shaft be designed and installed in accordance with Section 1007. (Section 1007 refers to NFPA 72, The National Fire Alarm Code.) 1997 UFC 5101.10.3

Emergency alarm system.

1997 UFC 5101.10.3.1 General Emergency alarm systems shaft be provided in accordance with Sections 5101.10.3, 8003. 1.10 and 8004.4.3. The exempt amount provisions of Sections 8001.15, 8003. 1.1 and 8004. 1.1 shall not apply to emergency alarm systems required for HPM. Based on the above paragraph, emergency alarm systems are required even if stored amounts are less than exempt amounts. 1997 UFC 5101.10.3.2

Where required.

1997 UFC 5101.10.3.2.1 Service corridors. An emergency alarm system shaft be provided in service corridors, with at least one alarm device in the service corridor or as otherwise required by the chief. 1997 UFC 5101.10.3.2.2 8004.4.3.

Exit corridors and exit enclosures.

See Section

1997 UFC 5101.10.3.2.3 Liquid storage rooms, HPM rooms and gas rooms. See Section 8003. 1.10.

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1997 UFC 5101.10.3.3 Alarm-initiating devices. An approved emergency telephone system, local alarm manual pull stations, or other approved alarminitiating devices are allowed to be used as emergency alarm-initiating devices. 1997 UFC 5101.10.3.4 Alarm signals. Activation of the emergency alarm system shaft sound a local alarm and transmit a signal to the emergency control station. Section 5101.10.3 requires an "emergency alarm system" that sounds a local alarm and transmits a signal to the emergency control station in the following locations: Section 8 0 0 3 . 1 . 1 0 refers to buildings, rooms or areas used for storage of hazardous materials. An alarm-initiating device is required outside each interior exit or exit-access door and shall sound a local alarm and initiate an audible and visual signal at a constantly attended on-site location. Section 8004.4.3 refers to corridors or exit enclosures used for transport of hazardous materials having a hazard ranking of 3 or 4 in accordance with UFC Standard 79-3. An emergency telephone system, a local manual alarm station or an approved alarminitiating device is required at intervals of not more than 1 50 feet and at each exit and exit-access doorway throughout the transport route. A local audible alarm shall be initiated and the signal transmitted to the ECS. Section 5101.10.3.2.1 refers to service corridors (a fully enclosed passage used for transporting hazardous production materials and for purposes other than required means of egress). This section requires "at least one alarm device in the service corridor or as otherwise required by the chief." Note that in exit corridors also used for transport of hazardous production materials, the spacing of initiating devices is 150 feet-on-center while service corridors only require "at least one alarm initiating device" in the service corridor. The alarm initiating device can be: 9 An approved emergency telephone system. 9 A local alarm manual pull station. 9 Other approved alarm-initiating devices. The emergency alarm system is used for general emergencies and the use of a telephone system allows the person initiating the alarm to describe the nature of the emergency to emergency control station personnel as well as to receive instructions regarding proper action. The use of a listed fire alarm t w o - w a y communications system (fireman's telephone) provides a supervised system as opposed to a standard in-house telephone that does not contain system integrity monitoring.

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Article 80 exempts facilities handling hazardous production material under the exempt amounts (Tables 8001.15-A through 8001.15-D) from many of the requirements of Sections 8003 and 8004. However, Article 51 Section 5101.10.3.1 states that the exempt amount provisions shall not apply to emergency alarm systems required for hazardous production materials in a semiconductor fabrication facility.

Regarding Gas Detection 1997 UFC 5101.10.4 Continuous gas-detection systems. 1997 UFC 5101.10.4.1 General A continuous gas-detection system shaft be provided for HPM gases when the physiological warning properties of the gas are at a higher level than the accepted permissible exposure limit (PEL) for the gas and for flammable gases in accordance with Section 5101.10. 4. The 1997 UFC requires detection for flammable gases regardless of gas concentration.

Odor Threshold Values (OTVs). Although gases that have physiological warning properties such as distinctive odor threshold values (OTVs) lower than their respective permissible exposure limit (PEL) are exempted from monitoring, OTVs are not always reliable and should not be used as the only safety system, in addition, OTVs are not uniformly determined by different countries. OTVs are the result of statistical processes based on 50 percent of the members of a panel reporting a positive odor detection. Data on odor thresholds from various sources are also inconsistent. One data source is Odor Thresholds and Irritation Levels of Several Chemical Substances: A Review by Jon H. Ruth available through the Wausau Insurance Company (see References). The Santa Clara Fire Chief's Toxic Gas Ordinance (TGO) refers to Odor Thresholds for Chemicals with Established Occupational Health Standards by the American Industrial Hygiene Association (see References). There will always be a significant portion of the population with much higher personal odor thresholds that cannot depend on their own olfactory senses for hazardous gas detection. Olfactory fatigue of personnel with long-term exposure to low concentrations (under PEL) should also be considered. The best industry practice is to provide detection for hazardous gases with low OTVs even though it may not be required by code. The best industry practice would include gas detection monitoring in rooms not continuously occupied, but which contain gas. Without continuous "olfactory" monitoring by personnel, a leak could go undetected when the room is unoccupied. The following requirements indicate where gas monitoring is required. The terms areas and rooms could be interpreted as requiring breathing area monitoring. However, providing a monitor point in a tool exhaust duct could be considered providing gas detection in the room containing the tool. The local authority having jurisdiction should

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review and approve gas monitoring locations. A study may be necessary to determine the best monitoring points. The exhaust duct serving a room may be the best location to provide monitoring for a room. 1997 UFC 5101.10.4.2

Where required.

1997 UFC 5101.10.4.2.1 Fabrication areas. A continuous gas-detection system shaft be provided for fabrication areas at locations in the fabrication area where gas is used or stored. 1997 UFC 5101.10.4.2.2 HPM rooms. A continuous gas-detection system shaft be provided in HPM rooms where gas is used in the room. 1997 UFC 5101.10.4.2.3 Gas cabinets, exhausted enclosures and gas rooms. A continuous gas-detection system shallbe provided in gas cabinets, exhausted enclosures and gas rooms. 1997 UFC 5101.10.4.2.4 Corridors. When gases are transported in piping placed within the space defined by the walls of a corridor and the floor or roof above the corridor, a continuous gas-detection system shaft be provided where piping is located and in the corridor.

Exception: A continuous gas-detection system is not required for occasional transverse crossings of the corridors by supply piping which is enclosed in a ferrous pipe or tube for the width of the corridor. 1997 UFC 5101.10.4.3

Gas-detection system operation.

UFC 5101.10.4.3.1 Monitoring. The continuous gas-detection system shaft be capable o f monitoring the location where gas detection is required at or below the permissible exposure limit (PEL) or ceiling limit of the gas for which detection is provided. For flammable gases, the monitoring detection threshold level shaft be vapor concentrations in excess of 20 percent of the lower explosive limit (LEL). See also Section 8003.3. 1.6. The 1997 UFC requires gas detection capable of monitoring at PEL or ceiling limit. It also requries activation of alarms and gas shutoffs at short-term hazard conditions. Short term hazard is not defined in the UFC, but could be interpreted as IDLH. 1997 UFC 5101.10.4.3.2 Alarms. The gas-detection system shaft initiate a local alarm and transmit a signal to the emergency control station when a shortterm hazard condition is detected. The alarm shaft be both visual and audible and shaft provide warning both inside and outside the area where the gas is detected. The audible alarm shaft be distinct from all other alarms. Refer to the discussion of Alarm Set Points in Chapter 4 of this guide.

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Regarding Gas Shutoff The following gas shutoff requirements could also be interpreted as directing monitoring of specific locations to control specific shutoff valves. 1997 UFC 5101.10.4.3.3 Shut off of gas supply. The gas-detection system shall automatically close the shutoff valve at the source of gas supply piping and tubing related to the system being monitored for which gas is detected when a short-term hazard condition is detected. Automatic closure of shutoff valves shaft be in accordance with the following:

Exception: When the gas-detection sampling point initiating the gas-detection system alarm is at a use location or within a gas valve enclosure of a branch line downstream of a piping distribution manifold, the shutoff valve in the gas valve enclosure for the branch line located in the piping distribution manifold enclosure shaft automatically close. 0

B

0

When the gas-detection sampling point initiating the gas-detection system alarm is within a gas cabinet or exhausted enclosure, the shutoff valve in the gas cabinet or exhausted enclosure for the specific gas detected shaft automatically close. When the gas detection sampling point initiating the gas-detection system alarm is within a room and compressed gas containers are not in gas cabinets or exhausted enclosures, the shutoff valves on all gas lines for the specific gas detected shaft automatically close. When the gas-detection sampling point initiating the gas-detection system alarm is within a piping distribution manifold enclosure, the shutoff valve for the compressed gas container of specific gas detected supplying the manifold shaft automatically close.

Regarding General Scope of UFC Article 80 1997 UFC 8001.1.3 Application. Article 80 shaft apply to all hazardous materials, including those materials regulated elsewhere in this code, except that when specific requirements are provided in other articles, those specific requirements shaft apply. See Section 101.6. Based on the above scope statement, the requirements of UFC 8001 are not contingent on the occupancy classification or the aggregate quantity of hazardous material exceeding the exempt amounts set forth in UFC 8001.1 3. 1997 UFC 8001.4.4 Equipment, machinery and alarms. Equipment, machinery and required detection and alarm systems associated with the use, storage or handling of hazardous materials shaft be listed or approved.

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The 1997 UFC Section 8001.4.4 covers the detection and alarm systems which may not be "fire alarm" systems, but which are required and regulated by the code. The location of this requirement in UFC Article 80 makes it applicable to all systems which are required when handling hazardous materials. Since UFC Article 80 applies to all hazardous material installations, it will cover all of the necessary detection and alarm systems. The requirement states that the detection and alarm systems shall be listed or approved. The authority having jurisdiction can approve gas detection systems that incorporate PLCs and other individual components that may not be listed specifically for gas detection use by a nationally recognized testing laboratory such as Underwriters Laboratories. Most authorities having jurisdiction do not have the resources necessary to review complex life safety systems and, therefore, rely on third-party organizations to certify system safety and functionality. Refer to Chapter 7 System Certification of this guide. The authority having jurisdiction should be consulted for local interpretation regarding this requirement at the start of a project. The requirement for maintenance is contained in Section 8001.4.7.1. 1 997 UFC 8001.4.7.1 General Equipment, machinery and required detection and alarm systems associated with hazardous materials shaft be maintained in an operable condition . . . . Required detection and alarm systems shaft be replaced or repaired where defective. See also Section 8001.4.4. The 1997 UFC Section 8001.4.7.1 requires maintenance of detection and alarm systems which may not be "fire alarm" systems, but are required by the code. Additionally, it requires the removal from service of faulty equipment, followed by the decision of whether to repair or replace the equipment.

Regarding Regulations for Specific Hazardous Materials in Quantities Not Exceeding Exempt Amounts 1997 UFC 8001.16.2.1 Emergency Shutoff. Compressed-gas systems conveying flammable gases shaft be provided with emergency shutoff capability in accordance with Section 8004. 1.12.

Regarding the Scope of UFC 8003 1997 UFC 8003.1.1 Applicability. Storage of hazardous materials where the aggregate quantity is in excess of the exempt amounts set forth in Section 8 0 0 1 . 1 5 shall be in accordance with Sections 8001 and 8003. Storage of hazardous materials where the aggregate quantity does not exceed the exempt amounts set forth in Section 8001.15 shall be in accordance with Section 8001.

HAZARDOUS GAS MONITORING

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Regarding Indoor Storage of Toxic and Highly-Toxic Gas 1997 UFC 8003.3.1.6 Gas Detection. A continuous gas-detection system shaft be provided to detect the presence of gas at or below the permissible exposure limit (PEL) or ceiling limit. The detection system shaft initiate a local alarm and transmit a signal to a constantly attended control station. The alarm shaft be both visual and audible and shaft be designed to provide warning both inside and outside of the storage area. The audible alarm shaft be distinct from all other alarms. Exceptions: 1. Signal transmission to a constantly attended control station need not be provided when not more than one cylinder is stored. 2. A continuous gas-detection system need not be provided for toxic gases when the physiological warning properties for the gas are at a level below the accepted PEL for the gas. The gas-detection system shaft be capable of monitoring the room or area in which the gas is stored at or below the PEL or ceiling limit and the discharge from the treatment system at or below one-haft the IDLH limit.

Because the gas detection requirement is in Article 8003, monitoring is not required unless the quantities of HPM gas exceed the exempt amounts in the tables of Section 8001.15. Research and other facilities with only small quantities of hazardous gas could be exempt from monitoring requirements. However, the City of San Jose 1994 California Fire Code Amendments require gas detection systems for the indoor storage of toxic gases in amounts exceeding 10 ft 3 per control area and for highly toxic gases in any amount. This local requirement illustrates the need to review jurisdictional code amendments prior to design. Refer to Chapter 6 of this guide, Monitoring Exhaust Treatment System Discharge, for a review of treatment system discharge monitoring.

Regarding the Scope of UFC 8004 1997 UFC 8004.1.1 Applicability. Use, dispensing and handling of hazardous materials where the aggregate quantity is in excess of the exempt amounts set forth in Section 8 0 0 1 . 1 5 shaft be in accordance with Sections 8001 and 8004. Use, dispensing and handling of hazardous materials where the aggregate quantity does not exceed the exempt amounts set forth in Section 8 0 0 1 . 1 5 shaft be in accordance with Section 8001. For flammable, oxidizing and pyrophoric gases, see also section 8001.16.

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Regarding Use, Dispensing and Handling 1997 UFC 8004.1.7 Supervision. Manual alarm, detection and automatic fireextinguishing systems required by other provisions of Section 8004 shall be supervised by an approved central, proprietary or remote station service or shall initiate an audible and visual signal at a constantly attended on-site location. 1997 UFC 8004.1.12 Emergency Shutoff for Flammable, Oxidizing and Pyrophoric Gases. Flammable, oxidizing and pyrophoric gas systems shall be provided with approved emergency shutoff systems that can be activated from each point of use and at each source.

Regarding Indoor Dispensing and Use in Closed Systems 1997 UFC 8004.2.3.2 Use. Systems shaft be suitable for the use intended and shaft be designed by persons competent in such design. Where nationally recognized good practices or standards have been established for the processes employed, they shaft be followed in the design. Controls shaft be designed to prevent materials from entering or leaving process or reaction systems at other than the intended time, rate or path. When automatic controls are provided, they shaft be designed to be fail safe. The section above refers to conformance to "nationally recognized good practices or standards." The International Society for Measurement and Control (also known as ISA) has developed standards for oxygen and combustible gas sensors and is working on standards for other gases. In addition, both ISA and the International Electrotechnical Commission (IEC) have developed standards for safety instrumented systems. Refer to the discussion of these standards in this chapter and in Chapter 7 of this guide.

Regarding Special Requirements for Highly-Toxic and Toxic Compressed Gases in Closed Systems 1997 UFC 8004.2.3.7.6 Gas Detection. Gas detection shaft be provided in accordance with Section 8003.3. 1.6. Activation of the monitoring system shaft automatically close the shutoff valve on highly-toxic or toxic gas supply lines related to the system being monitored. There is an exception to the above requirement relating to reactors utilized for the production of toxic or highly-toxic gases. Sections 8004.2.3.7.6 and 8004.3.6.5 refer to Section 8003.3.1.6. This section calls for the gas detection system to detect the presence of gas at or below the PEL, but does not specifically indicate at what level alarms and gas valve shut offs are to occur.

HAZARDOUS GAS MONITORING

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Regarding Special Requirements for Toxic and Highly-Toxic Compressed Gases in Outdoor Dispensing and Use 1997 UFC 8004.3.6.5 Gas Detection. Gas detection shaft be provided in gas cabinets and exhausted enclosures in accordance with Section 8003.3. 1.6. Activation o f the monitoring system shaft automatically close the shutoff valve on highly-toxic or toxic gas supply lines related to the system being monitored. There is an exception to the above requirement relating to reactors utilized for the production of toxic or highly-toxic gases.

Regarding Use, Dispensing and Handling 1997 UFC 8004.1.12 Emergency shutoff for flammable, oxidizing and pyrophoric gases. Flammable, oxidizing and pyrophoric gas systems shall be provided with approved emergency shutoff valves that can be activated at each point o f use and at each source. This requirement is referenced in 8001 with respect to flammable (8001.1 6.2.1) and pyrophoric (8001.1 6.4.1) gases and, therefore, applies regardless of quantity.

Regarding Ozone Gas-Generating Equipment UFC Appendix I1-1applies to equipment having a maximum ozone-generating capacity of one-half pound or more over a 24-hour period. 1997 UFC 4.3 Ozone-generator Rooms. Ozone-generator rooms shaft be mechanically ventilated with a minimum of six air changes per hour. Exhausted air shaft be directed to a treatment system designed to reduce the discharge concentration of gas to one half o f the IDLH value at the point o f discharge to the atmosphere or ozone-generator rooms shaft be equipped with a continuous gas-detection system which will shut off the generator and sound a local alarm when concentrations above the permissible exposure limit occur . . . . Section 6. Automatic Shutdown: Ozone generators shaft be designed to automatically shut down under the following conditions: . . . 4. Failure o f the gas-detection system. Section 7. Manual Shutdown: Manual shutdown controls shaft be provided at the generator and if in a room, within 10 feet of the main exit or exit-access door. Note that the UFC requires ozone generators to automatically shut down if the gas detection system fails. Although there is no similar requirement for other gas detection systems, consideration should be given to implementing this feature in all gas detection systems.

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Uniform Fire Code 2 0 0 0 Edition When the idea of the International Fire Code (IFC) was conceived, the intent was to incorporate all of the requirements of the various fire codes in use throughout the United States into one commonly accepted model code. The IFC was designed to replace the Uniform Fire Code as well as model codes prevalent east of the Mississippi. However, during meetings of the cooperating code development groups, differences of opinion could not be reconciled and the UFC was reborn. The 2000 edition of the Uniform Fire Code was initially developed by the Western Fire Chiefs Association (WFCA) with input from the International Association of Plumbing and Mechanical Officials (IAMPO). The 2000 UFC is basically the 1997 UFC with 1998 and 1 999 Supplements incorporated and a few minor changes developed in the limited time available. In December 1 999, the WFCA reached an agreement with the National Fire Protection Association (NFPA) to develop an integrated family of codes and standards including fire, plumbing, mechanical, electrical and life safety. Presently referred to as Consensus Codes, their target publication date is 2003. There is also an agreement to produce a joint NFPA 1 - Uniform Fire Code which will incorporate successful features of the EPCOT Fire Prevention Code and the EPCOT Building Code. The tentative release date is mid-2002.

Regarding Occupancy Classifications Because the WFCA/NFPA Concensus Codes will not be available until 2003, there is a code coordination issue regarding building occupancy classifications. The 1 997 UFC referred to the Uniform Building Code (UBC) occupancy classifications. With the suspension of the UBC, the 2000 UFC defines the Group H Occupancies in a more generic manner in order to coordinate with other codes such as the International Building Code. Semiconductor fabrication facilities classified as H-6 by previous editions of the UFC are classified as H-5 by the new International codes. Occupancies containing oxidizing gases classified as H-2 by previous editions of the UFC are now classified as H-3 by the International codes. Occupancies containing toxic and highly toxic materials classified as H-7 by previous editions of the UFC are now classified as H-4 by the International codes. The 2000 UFC Article 51 now refers to Group H Occupancies in lieu of H-6 Occupancies:

HAZARDOUS GAS MONITORING

27

2000 UFC Group H Occupancies shaft include buildings or structures, or portions thereof that involve the manufacturing, processing, generation or storage of materials that constitute a high fire, explosion or health hazard. Group H Occupancies shaft be classified in accordance with the Building Code adopted by the jurisdiction.

Regarding Other Requirements There are no other differences between the 2000 and 1997 UFC regarding hazardous gas monitoring. Refer to the discussion in this guide of the 1997 UFC for relevant requirements for hazardous gas monitoring which are continued in the 2000 UFC.

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Intemational Fire Code 2 0 0 0 Edition The inaugural edition of the International Fire Code (IFC) is international in name only and is the result of a cooperative effort to bring uniformity to fire codes throughout the United States. Published by the International Code Council, the code-development panel included representatives of" Building Officials and Code Administrators International (BOCA) International Conference of Building Officials (ICBO) Southern Building Code Congress International (SBCCI) The IFC coordinated requirements in the various fire codes developed by these organizations and is designed to be compatible with other codes such as the International Building Code, International Mechanical Code and the International Plumbing Code. Originally a member of the IFC development group, the National Fire Protection Association (NFPA) regrettably terminated their participation. The ideal situation for the advanced technology community would be a coordination of codes in all areas of the United States. Currently, the Uniform Fire Code dominates the western jurisdictions, BOCA's National Fire Code dominates in the northeast, and SBCCI's codes prevail in the southeast. The IFC 2000 chapters that apply to hazardous gas monitoring are:

Chapter 18, Semiconductor Fabrication Facilities, covers issues related only to semiconductor fabrication facilities and comparable research and development areas that handle hazardous production materials. These areas previously classified as Use Group H-6 are now designated Use Group H-5 by recent editions of national codes. Chapter 27, Hazardous Materials- General Provisions, covers the prevention, control and mitigation of dangerous conditions related to storage, dispensing, use and handling of hazardous materials in all occupancies. Chapter 30, Compressed Gases, covers storage, use and handling of compressed gases in compressed gas containers, cylinders, tanks and systems including those gases regulated elsewhere in the IFC. Chapter 31, Corrosive Materials, covers the storage and use of corrosive materials. Chapter 35, Flammable Gases, covers storage and use of flammable gases. The requirements in this chapter apply to all quantities of flammable gases. The storage and use of flammable gases in amounts exceeding the maximum quantity in a control area indicated in Section 2703.1 shall be in accordance with Chapter 35 as well as with Chapter 27.

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Chapter 37, Highly Toxic and Toxic Materials, covers the storage and use of highly toxic and toxic materials. Section 3704 covers highly toxic and toxic compressed gases. Chapter 40, Oxidizers, covers storage and use of oxidizers. Chapter 41, Pyrophoric Materials, covers the storage and use of pyrophoric materials. Section 4106 specifically covers silane gas. Regarding Applicability of Code Requirements Chapter 1, Administration, contains general administrative provisions which can have an effect on design of hazardous gas monitoring and alarm systems. IFC 102.1 Construction and design provisions. The construction and design provisions o f this code shaft apply t o : . . . 4. Existing structures, facilities and conditions which, in the opinion of the code official, constitute a distinct hazard to life or property. The above provision gives the code official authority to require facilities to retrofit existing systems to comply with the 2000 IFC.

Regarding Permits IFC 104.1 General The code official is hereby authorized to enforce the provisions o f this code and shaft have the authority to render interpretations of this code, and to adopt policies, procedures, rules and regulations in order to clarify the application of its provisions. Such interpretations, . . . shaft be in compliance with the intent and purpose of this code and shaft not have the effect o f waiving requirements specifically provided for in this code. IFC 105.3.6 Compliance with code. The issuance or granting of a permit shaft not be construed to be a permit for, or an approval of, any violation of any of the provisions of this code or of any other ordinance o f the jurisdiction. Permits presuming to give authority to violate or cancel the provisions of this code or other ordinances of the jurisdiction shaft not be valid . . . . The IFC makes it clear that the code official does not have any liability for approving systems that do not comply with the Code. IFC 104.7.2 Technical assistance. To determine the acceptability of technologies, processes, products, facilities, materials and uses attending the design, operation or use of a building or premises subject to the inspection of the department, the code official is authorized to require the owner or agent to provide, without charge to the jurisdiction, a technical opinion and report. The opinion and report shaft be prepared by a qualified engineer, specialist,

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laboratory or fire safety specia/ty organization acceptable to the code official and shaft analyze the fire safety properties of the design, operation or use of the building or premises and the facilities and appurtenances situated thereon, to recommend necessary changes. The code official is authorized to require design submittals to be prepared by, and bear the stamp of, a registered design professional

These requirements are similar to previous editions of model fire codes. The required report could be similar to the safety system documentation required by OSHA, IEC 61 508 and ANSI/ISA Standard $84.01. IFC 104.8 Modifications. Whenever there are practical difficulties involved in carrying out the provisions of this code, the code official shaft have the authority to grant modifications for individual cases, provided the code official shaft first find that special individual reason makes the strict letter of this code impractical and the modification is in compliance with the intent and purpose of this code and that such modification does not lessen health, life and fire safety requirements. The details of action granting modifications shaft be recorded and entered in the files of the fire department. IFC 104.9 Alternative materials and methods. The provisions of this code are not intended to prevent the installation of any material or to prohibit any method of construction not specifically prescribed by this code, provided that any such alternative has been approved. The code official is authorized to approve an alternative material or method of construction where the code official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this code in quality, strength, effectiveness, fire resistance, durability and safety. Any variances from the code that seem to be allowed by Sections 104.8 and 104.9 should be well documented due to the wording of IFC 104.1 and 105.3.6. Those t w o sections seem to relieve the code official of any liability in approving systems that do not strictly conform to the code. IFC 105.7.2 Compressed gases. When the compressed gases in use or storage exceed the amounts listed in Table 105.6.9, a construction permit is required to install, repair damage to, abandon, remove, place temporarily out of service, or close or substantially modify a compressed gas system. Table 105.6.9 requires a permit for any amount of highly toxic or toxic compressed gases. Flammable compressed gases in excess of 200 cubic feet also require a permit.

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Regarding Maintenance and Testing IFC 107.1 Maintenance of safeguards. Whenever or wherever any device, equipment, system, condition, arrangement, level of protection, or any other feature is required for compliance with the provisions of this code, or otherwise installed, such device, equipment, . . . shaft thereafter be continuously maintained in accordance with this code and applicable referenced standards. IFC 107.2 Testing and operation. Equipment requiring periodic testing or operation to ensure maintenance shaft be tested or operated as specified in this code. IFC 2703.2.6 Maintenance. In addition to the requirements of Section 2703.2.3, equipment, machinery and required detection and alarm systems associated with hazardous materials shaft be maintained in an operable condition . . . . Required detection and alarm systems shaft be replaced or repaired where defective. Safety system testing is necessary to verify the integrity of the entire safety system including sensors, logic solver, final control elements, and alarm indicating devices. Refer to the discussion of System Testing Requirements in Chapter 3 of this guide.

Regarding System Listing IFC 2703.2.3 Equipment, machinery and alarms. Equipment, machinery and required detection and alarm systems associated with the use, storage or handling of hazardous materials shaft be listed or approved. Because hazardous gas monitoring systems are typically custom installations, it is difficult to have an installed system listed. Local jurisdictions may be reluctant to approve complex systems without a review by a competent, independent third party.

Regarding Gas Sampling Intervals The definitions in IFC Chapter 2 refer to IFC Chapter 18 for a definition of a continuous gas-detection system that may have an impact on the gas detection technology allowed. IFC 202 & 1 802.1 Continuous Gas Detection System. A gas detection system where the analytical instrument is maintained in continuous operation and sampling is performed without interruption. Analysis is allowed to be performed on a cyclical basis at intervals not to exceed 30 minutes. The 30-minute cycle interval may have an impact on the gas sensing technology or system. The ACGIH has proposed a 2.0 ppb TLV for arsine, a very low concentration. The Zellweger Analytics System 16 using paper tape technology requires a sample

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time of up to 600 seconds to detect a one-half TLV level of 0.7 ppb. The System 16 has the capability to cycle through 16 sample points. Several arsine sample points could slow this system down to the point that a complete cycle takes more than the allowed 30 minutes. A sensing system that provides continuous monitoring would be a more practical monitoring method for low levels of arsine.

Regarding the Emergency Control Station The IFC requirement for the emergency control station is identical to the wording in the 1997 UFC. IFC 1803.1 Emergency control station. An emergency control station shaft be provided on the premises at an approved location outside of the fabrication area, and shaft be continuously staffed by trained personnel The emergency control station shaft receive signals from emergency equipment and alarm and detection systems. Such emergency equipment and alarm and detection systems shaft include, but not be limited to, the following where such equipment or systems are required to be provided either in this chapter or elsewhere in this code:

1. 2. 3. 4. 5. 6.

Automatic sprinkler system alarm and monitoring systems. Manual fire alarm systems. Emergency alarm systems. Continuous-gas detection systems. Smoke detection systems. Emergency power system.

Regarding Gas-Detection Systems in Semiconductor Fabrication Facilities IFC 1803.13 Continuous gas detection systems. A continuous gas detection system shaft be provided for HPM gases when the physiological warning properties of the gas are at a higher level than the accepted permissible exposure limit (PEL) for the gas and for flammable gases in accordance with this section. Refer to the discussion on odor threshold values (OTVs) earlier in this chapter in the section on the 1997 UFC. IFC 1803,13.1.1 Fabrication areas. A continuous gas detection system shaft be provided in fabrication areas when gas is used in the fabrication area. The 2000 IFC requires gas detection only when gas is used in the fabrication area. The 1997 UFC requires gas detection in the fabrication area where gas is used or stored.

HAZARDOUS GAS MONITORING

33

IFC 1803.13.1.2 HPM rooms. A continuous gas detection system shaft be provided in HPM rooms when gas is used in the room. IFC 1803.13.1.3 Gas cabinets, exhausted enclosures and gas rooms. A continuous gas detection system shaft be provided in gas cabinets and exhausted enclosures. A continuous gas detection system shaft be provided in gas rooms when gases are not located in gas cabinets or exhausted enclosures. IFC 1803.13.1.4 Exit access corridors. When gases are transported in piping placed within the space defined by the walls of an exit access corridor and the floor or roof above the exit access corridor, a continuous gas detection system shaft be provided where piping is located and in the exit access corridor.

Exception: A continuous gas detection system is not required for occasional transverse crossings of the corridors by supply piping which is enclosed in a ferrous pipe or tube for the width of the corridor. The wording in Section 1803,13.1.4 refers to exit access corridors, whereas the 1997 Uniform Fire Code referred to corridors in general. IFC 1803.13.2 Gas detection system operation. The continuous gas detection system shaft be capable of monitoring the room, area or equipment in which the gas is located at or below the permissible exposure limit (PEL) or ceiling limit of the gas for which detection is provided. For flammable gases, the monitoring detection threshold level shaft be vapor concentrations in excess of 20 percent of the lower flammable limit (LFL). Monitoring for highly toxic and toxic gases shaft also comply with Chapter 37. The 1997 UFC calls for monitoring the location where gas detection is required. The 2000 IFC better defines the location. IFC 1803.13.2.1 Alarms. The gas detection system shaft initiate a local alarm and transmit a signal to the emergency control station when a short-term hazard condition is detected. The alarm shaft be both visual and audible and shaft provide warning both inside and outside the area where the gas is detected. The audible alarm shaft be distinct from all other alarms. IFC 1803.13.2.2 Shut off of gas supply. The gas detection system shaft automatically close the shutoff valve at the source on gas supply piping and tubing related to the system being monitored for which gas is detected when a short-term hazard condition is detected. Automatic closure o f shutoff valves shaft comply with the following:

Exception: Where the gas-detection sampling point initiating the gas detection system alarm is at the use location or within a gas valve enclosure of a branch line downstream of a piping distribution manifold, the shutoff valve for the

34

HAZARDOUS GAS MONITORING

branch line located in the piping distribution automatically close. o

D

o

manifold enclosure shaft

Where the gas-detection sampling point initiating the gas detection system alarm is within a gas cabinet or exhausted enclosure, the shutoff valve in the gas cabinet or exhausted enclosure for the specific gas detected shaft automatically close. Where the gas-detection sampling point initiating the gas detection system alarm is within a room and compressed gas containers are not in gas cabinets or exhausted enclosure, the shutoff valves on all gas lines for the specific gas detected shaft automatically close. Where the gas-detection sampling point initiating the gas detection system alarm is within a piping distribution manifold enclosure, the shutoff valve supplying the manifold for the compressed gas container of the specific gas detected shaft automatically close.

For a discussion on short-term hazard, refer to the section on Alarm Set Points in Chapter 4 of this guide. The IFC sections on gas shutoff are identical to the 1997 UFC. These gas shutoff requirements could be interpreted as specifying locations where gas detection is required.

Regarding Gas-Detection Systems for Indoor Storage & Use of Highly Toxic & Toxic Gases Chapter 37 covers requirements for highly toxic and toxic materials. Highly toxic and toxic compressed gases must also comply with Chapter 30, Compressed Gases. The gas monitoring requirements in Chapter 37 are very similar to those in Chapter 18, Semiconductor Fabrication Facilities. IFC 3704.2.2.10. Gas detection system. A gas detection system shaft be provided to detect the presence of gas at or below the permissible exposure limit (PEL) or ceiling limit of the gas for which detection is provided. The system shaft be capable of monitoring the discharge from the treatment system at or below one-haft the IDLH limit.

Exception: A gas detection system is not required for toxic gases when the physiological warning properties for the gas are at a level below the accepted PEL for the gas. Ceiling limit is an OSHA term and is defined as the maximum concentration of an airborne contaminant to which one may be exposed. OSHA introduced the concept of ceiling values and excursion factors around the time-weighted average values to reduce conflict or confusion with the maximal values in the ANSI Standards. An OSHA C listing indicates ceiling value and is given to those fast-acting substances

HAZARDOUS GAS MONITORING

35

thought likely to be injurious if the concentration exceeded the limit value by more than a designated factor for a relatively short period (about 1 5 minutes). The factor varies between 3 and 1.25, depending inversely upon the magnitude of the TLV. The concept is discussed in depth in the preamble to OSHA 29 CFR Part 1 910.1000. Table Z. 1, Limits for Air Contaminants, in 29 CFR Part 1 910.1000 lists maximum concentrations. Most values are given as PELs in 8-hour Time Weighted Averages, but some are listed as ceiling values. Some current ceiling values for commonly-used gases in the semiconductor industry are: Boron trifluoride Chlorine Chlorine trifluoride Hydrogen chloride

1.0 1.0 0.1 5.0

ppm ppm ppm ppm

These chemical ceiling limits are identical to their generally-accepted PELs. IFC 3704.2.2.10.1 Alarms. The gas detection system shaft initiate a local alarm and transmit a signal to a constantly attended control station when a short-term hazard condition is detected. The alarm shaft be both visual and audible and shaft provide warning both inside and outside the area where gas is detected. The audible alarm shaft be distinct from all other alarms. Exception: Signal transmission to a constantly attended control station is not required where not more than one cylinder of highly toxic or toxic gas is stored. Alarm annunciation is discussed in Chapter 5 of this guide. IFC 3 7 0 4 . 2 . 2 . 1 0 . 2 Shut off of gas supply. The gas-detection system shaft automatically close the shutoff valve at the source on gas supply piping and tubing related to the system being monitored for whichever gas is detected. Exception: Automatic shutdown is not required for reactors utilized for the production of highly toxic or toxic compressed gases where such reactors are: lm

o

3.

Operated at pressures less than 15 pounds per square inch gauge (psig) (103.4 kPa). Constantly attended. Provided with readily accessible emergency shutoff valves.

IFC 3 7 0 4 . 2 . 2 . 1 0 . 3 Valve closure. Automatic closure of shutoff valves shaft be in accordance w/th the following: o

When the gas-detection sampling point initiating the gas detection system alarm is within a gas cabinet or exhausted enclosure, the shutoff valve in the gas cabinet or exhausted enclosure for the specific gas

36

HAZARDOUS GAS MONITORING

B

8

detected shaft automatically close. Where the gas-detection sampling point initiating the gas detection system alarm is within a gas room and compressed gas containers are not in gas cabinets or exhausted enclosures, the shutoH valves on all gas lines for the specific gas detected shaft automatically close. Where the gas-detection sampling point initiating the gas detection system alarm is within a piping distribution manifold enclosure, the shutoff valve for the compressed container of specific gas detected supplying the manifold shall automatically close.

Exception: When the gas-detection sampling point initiating the gas-detection system alarm is at a use location or within a gas valve enclosure of a branch line downstream of a piping distribution manifold, the shutoff valve in the gas valve enclosure for the branch line located in the piping distribution manifold enclosure shall automatically close.

It is interesting that IFC 3705.5 requires automatic shutdown of ozone gas-generators if the ozone gas-detection system fails, but the IFC does not require automatic shutdown of highly toxic or toxic gas valves if that gas-detection system fails. Facility safety departments should consider what action to take if gas-detection system diagnostics determine that the gas-detection system has failed. Gas-detection system designs should include sufficient redundancy to maintain system operation should some system components fail.

Regarding Gas Detection for Outdoor Conditions IFC 3704.3.2.7 Gas detection system. The gas detection system requirements set forth in Section 3704.2.2. 10 shaft apply to highly toxic or toxic gases located outdoors.

Regarding Emergency Power Chapter 18, Semiconductor Fabrication Facilities, covers requirements for Group H-5 occupancy emergency power systems. IFC 1803.1 5.1 Required electrical systems. Emergency power shaft be provided for electrically operated equipment and connected control circuits for the following systems: . . . .

6. 7. 8.

HPM gas detection systems. Emergency alarm systems. Manual fire alarm systems. Automatic sprinkler system monitoring and alarm systems . . . .

HAZARDOUS GAS MONITORING

37

Where stored quantities of hazardous materials exceed the maximum allowable quantity, the provisions of Section 2704 apply. IFC 2704.7 Standby or emergency power. When mechanical ventilation, treatment systems, temperature control, alarm, detection or other electrically operated systems are required, such systems shaft be connected to an emergency electrical system or a standby power system in accordance with Section 604. The wording in Section 2704.7 is repeated as Section 2705.1.5 with respect to use, dispensing and handling of hazardous materials in amounts exceeding the maximum allowable quantity per control area. Section 2704.7 refers to alarm systems while Section 2705.1.5 refers to manual alarm systems. Section 604 covers emergency power systems in general. Section 3704.2.2.8 covers emergency power for the indoor storage and use of highly toxic and toxic materials. IFC 3704.2.2.8 Emergency power. Emergency power in accordance with the ICC Electrical Code shaft be provided in lieu of standby power where any of the following systems are required: o

2. 3. 4. 5. 6. 7.

Exhaust ventilation system. Treatment system. Gas detection system. Smoke detection system. Temperature control system. Fire alarm system. Emergency alarm system.

Exception: Emergency power is not required for mechanical exhaust ventilation, treatment systems and temperature control systems where approved fail-safe engineered systems are installed. IFC 3704.3.2.6 Emergency power. The requirements for emergency power set forth in Section 3704.2.2.8 shaft apply to highly toxic or toxic gases located outdoors. Because gas detection systems are microprocessor based, emergency power systems should incorporate battery backup (UPS systems) to maintain gas detection and alarm system power during the time between loss of power and generator startup and power transfer to a generator.

38

HAZARDOUS GAS MONITORING

Regarding Hazardous Materials in General Chapter 27, Hazardous Materials- General Provisions, covers the prevention, control and mitigation of dangerous conditions related to storage, dispensing, use and handling of hazardous materials. Chapter 27 applies to all hazardous materials, including those materials regulated elsewhere in this code, except that when specific requirements are provided in other chapters, those specific requirements shaft a p p l y . . . Chapter 27 is further divided into Section 2703 General Requirements, Section 2704 Storage and Use, and Section 2705 Dispensing and Handling. Section 2701 General applies to all hazardous materials regardless of quantity. When exceeding the maximum allowable quantity, Section 2703 applies. IFC 2703.1.3 Quantities not exceeding the maximum allowable quantity per control area. The storage, use and handling of hazardous materials in amounts not exceeding the maximum allowable quantity per control area indicated in Tables 2703. 1.1(1) through 2703. 1.1(4) shall be in accordance with Sections 2 701 and 2 703. IFC 2703.1.4 Quantities exceeding the maximum allowable quantity per control area. The storage and use of hazardous materials exceeding the maximum allowable quantity per control area indicated in Tables 2703. 1.1 (1) through 2 703. 1.1(4) shaft be in accordance with this chapter. Section 1803.1 3.2.2 indirectly describes shutoff valve locations for HPM gases in a semiconductor fabrication facility. Section 3704.2.2.10.3 indirectly describes shutoff valve locations for highly toxic and toxic gases. Section 2703.2.2.1 Item 3 lists required shutoff valves for all hazardous materials. Regarding Shutoff Valves IFC 2703.2.2.1 0

Design and construction . . . .

Readily accessible manual valves, or automatic remotely activated failsafe emergency shutoff valves shaft be installed on supply piping and tubing at the following locations: 3. 1 The point of use. 3.2 The tank, cylinder or bulk source.

Section 3503.1.3 covers shutoff valves for all quantities of flammable gases. IFC 3503.1.3 Emergency shutoff. Compressed gas systems conveying flammable gases shaft be provided with approved emergency shutoff valves that can be activated at each point of use and each source.

HAZARDOUS GAS MONITORING

39

Section 2704 Storage covers storage of hazardous materials in amounts exceeding the maximum allowable quantity per control area. Storage of amounts not exceeding the maximum allowable quantity per control area shall be in accordance with Sections 2701 and 2703.

Regarding Fail-Safe Controls for Indoor Dispensing & Use of Hazardous Materials in Closed Systems IFC 2705.2.2.1 Design. Systems shaft be suitable for the use intended and shaft be designed by persons competent in such design. Controls shaft be designed to prevent materials from entering or leaving the process or reaction systems at other than the intended time, rate or path. Where automatic controls are provided, they shaft be designed to be fail safe.

Regarding Fail-Safe Controls for Use & Handling of Compressed Gases IFC 3005.2 Controls. Compressed gas system controls shaft be designed to prevent materials from entering or leaving process or reaction systems at other than the intended time, rate or path. Automatic controls shaft be designed to be fail safe. The above two requirements could be interpreted as requiring gas valve shutoff controls to be fail safe.

Regarding Alarm Systems for Storage of Hazardous Materials Exceeding Maximum Allowable Quantity Per Control Area IFC 2704.9 Emergency alarm. An approved manual emergency alarm system shaft be provided in buildings, rooms or areas used for storage of hazardous materials. Emergency alarm-initiating devices shaft be installed outside of each interior exit or exit access door of storage buildings, rooms or areas. Activation of an emergency alarm-initiating device shaft sound a local alarm to alert occupants of an emergency situation involving hazardous materials. IFC 2704.10 Supervision. Emergency alarm, detection and automatic fireextinguishing systems required by Section 2704 shaft be supervised by an approved central, proprietary or remote station service or shaft initiate an audible and visual signal at a constantly attended on-site location. For semiconductor fabrication facilities, the constantly attended on-site location is the emergency control station (ECS) described in Section 1803.1. The wording of Section 2704.10 on supervision is basically repeated in Section 2705.1.6 with respect to use, dispensing and handling of hazardous materials in amounts exceeding the maximum allowable quantity per control area.

40

HAZARDOUS GAS MONITORING

IFC 2705.4.4 Emergency alarm. Where hazardous materials having a hazard ranking o f 3 or 4 in accordance with NFPA 704 are transported through corridors or exit enclosures, there shall be an emergency telephone system, a local manual alarm station or an approved alarm-initiating device at not more than 150-foot (45, 720 ram) intervals and at each exit and exit access doorway throughout the transport route. The signal shall be relayed to an approved central station, proprietary supervising station or remote supervising station or a constantly attended on-site location and shall also initiate a local audible alarm.

Regarding Treatment Systems for Highly Toxic and Toxic Material Releases Chapter 37 covers the storage and use of highly toxic and toxic materials. This chapter includes requirements for treatment systems to handle the accidental release of highly toxic and toxic gases from indoor storage rooms. The treatment system requirements do contain the following exception for toxic gases. IFC 3704.2.2.7 Exceptions: 2. 2.1 2.2

Treatment systems . . . .

Toxic gases - use. Treatment systems are not required for toxic gases supplied by cylinders when the following are provided: A gas detection system with a sensing interval not exceeding 5 minutes. An approved automatic-closing fail-safe valve located immediately adjacent to cylinder valves. The fail-safe valve shaft close when gas is detected at the permissible exposure limit (PEL) by a gas detection system monitoring the exhaust system at the point of discharge from the gas cabinet, exhausted enclosure, ventilated enclosure or gas room. The gas detection shaft comply with Section 3704.2.2.10.

Note that this exception pertains only to toxic gases, not to highly toxic gases. Section 3704.2.2.10 calls for the gas-detection system to be capable of monitoring the discharge from the required treatment systems for indoor storage and use of highly toxic and toxic compressed gases (Section 3704.2.2.7). Refer to Chapter 6 in this guide for a discussion of treatment system discharge monitoring.

Regarding Ozone Gas-Generators Ozone gas-generators with a maximum ozone-generating capacity of one-half pound or more over a 24-hour period are required to be located in approved cabinets or rooms. IFC 3705.3.2 Ozone gas generator rooms. Ozone gas generator rooms shaft be mechanically ventilated in accordance with the International Mechanical Code with a minimum of six air changes per hour. Ozone gas generator rooms

HAZARDOUS GAS MONITORING

41

shaft be equipped with a continuous gas detection system which will shut o f f the generator and sound a local alarm when concentrations above the permissible exposure limit occur. IFC 3 7 0 5 . 5 Automatic shutdown. Ozone gas generators shaft be designed to shut down automatically under the following conditions: 2. 3. 4. 0

When the process using generated ozone is shutdown. When the gas detection system detects ozone. Failure of the ventilation system for the cabinet or ozone-generator room. Failure of the gas-detection system.

Note that for ozone generation systems if the gas detection system fails, the generator is automatically shut down. Presently, there is no similar requirement for other gases, even for highly toxic gases. IFC 3 7 0 5 . 6 Manual shutdown. Manual shutdown controls shaft be provided at the generator and, where in a room, within 10 feet (3048 mm) of the main exit or exit access door.

42

HAZARDOUS GAS MONITORING

Standard Fire Prevention Code Southem Building Code Congress Intemational (SBCCI)

This code, presently adopted by most states in the Southeast, does not have future editions in development. As a member of the group publishing the new "International" codes, the SBBCI now offers the International Fire Code. Most jurisdictions will likely continue to use the Standard Fire Prevention Code for some time while reviewing and adopting a new code.

Regarding Chapter 22 Hazardous Materials (Under Exempt Amounts) The Standard Fire Prevention Code (SFPC) requires gas monitoring for quantities under the exempt amounts. SFPC 2 2 0 3 . 3 . 1 . 1 0 Gas Detection. A continuous gas detection system shaft be provided to detect the presence of gas at or below the permissible exposure limit (PEL) or ceiling limit. The detection system shall initiate an alarm at or below PEL and transmit a signal to a constantly attended control station. The alarm shaft be both visual and audible and shaft be designed to provide warning both inside and outside of the storage area. The audible alarm shaft be distinct from all other alarms. Exceptions: 1. Signal transmission to a constantly attended control station is not required when one cylinder is stored. 2. A continuous gas detection system shaft not be required for toxic gases when the physiological warning properties for the gas are at a level below the accepted PEL for the gas, as found in the National Institute o f Occupational Safety and Health (NIOSH) Pocket Guide to Chemical Hazards. The gas detection system shaft be capable of monitoring the room or area in which the gas is stored at or below the PEL or ceiling limit and the discharge from the treatment system at or below one-haft the IDLH limit.

Regarding Chapter 42 HPM Facilities (Over Exempt Amounts) SFPC 4 2 0 2 . 1 . 5 Gas Detection System. When HPM gas is used or dispensed and the physiological warning properties for the gas are at a higher level than the accepted permissible exposure limit for the gas, a continuous gas monitoring system shaft be provided to detect the presence of a short-term hazard condition. When dispensing occurs and flammable gases or vapors are liberated in quantities in excess of 20% o f the lower explosive limit, a continuous gas monitoring system shaft be provided. The monitoring system shaft be connected to the HPM emergency control station.

HAZARDOUS GAS MONITORING

43

Note that Chapter 22 calls for alarm at or below PEL and Chapter 42 requires detection of short-term hazard. Short-term hazard could be interpreted as IDLH, a much higher concentration than PEL.

Regarding Special Requirements for HPM Gases SFPC 4202.2.2.2 Gas Detection. Storage cabinets for hazardous gases shall be provided with a continuous gas monitoring system in accordance with 4202. 1.5 whether dispensing occurs or not. Activation of the monitoring system shaft automatically shut the valves on all HPM gas lines from the cabinets and initiate an alarm to the HPM emergency control station.

44

HAZARDOUS GAS MONITORING

Sunnyvale, Califomia, Toxic Gas Ordinance 1996 The Sunnyvale (jurisdiction within Santa Clara County) ordinance classifies hazardous gases with a material hazard index (MHI) designating the maximum concentration of a substance in air that will not cause serious health effects in the majority of the population. It further classifies materials into Class I materials (e.g., arsine and chlorine trifluoride) which pose the greatest potential hazard, and Class II (e.g., boron trichloride and hydrogen fluoride) and II! lesser hazards. The degree of required controls is dependent upon the gas class. The MHI and Class may normally be found in tables available from most fire departments enforcing this type of toxic gas ordinance. Appendix A of this guide provides the class of many gases used in semiconductor manufacture. The MHI formula is expressed as follows: MHI = Equilibrium .Vapor Concentration @ 25 ~ Level of Concern (ppm) The MHI concept is being deleted from Silicon Valley TGOs in future editions. Regarding Class I Gas Controls

Sunnyvale TGO 1 6.53.130 (b)(l) P i p i n g . . . Secondary containment shaft be provided for piping for Class I materials. The secondary containment shaft be capable of directing a sudden release into an approved discharge treatment system, and shaft be monitored continually with a continuous gas-monitoring system approved by the department of public safety. Secondary containment for piping is provided by double-walled coaxial piping. The outer wall of coaxial piping can be connected to the sheet metal enclosure of an exhausted gas cabinet. Gas cabinet exhaust produces a negative pressure in the void between the double-walled piping. Any leaks from the inner pipe will be drawn to the gas cabinet where it can be drawn across a gas sensor at the gas cabinet. Some facilities monitor the integrity of piping secondary containment by closing off both ends of the outer containment pipe, pressurizing it with nitrogen, and then monitoring the pressure with a pressure switch. A leak in the primary containment will cause a drop in nitrogen pressure. However, closing both ends of the outer containment prevents directing releases into a treatment system. Sunnyvale TGO 1 6.53.1 30 (b)(2) Automatic Shut-off. An automatic shut-off valve which is of a "fail-safe to close" design shaft be provided. Each of the following shaft activate automatic shut-off: gas detection; manually from remote locations; failure of emergency power; seismic activity upon a seismic event within 5 seconds of horizontal sinusoidal oscillation having a peak

HAZARDOUS GAS MONITORING

45

acceleration of O. 15 g and a period of 0.4 seconds; failure of primary containmenU activation of manual fire alarm.

Regarding Class II Controls Sunnyvale TGO 1 6.53.130 (c)(5) Gas Detection. A continuous gas-detection system as required by the Fire Code shaft be provided to detect the presence of gas at or below the PEL. The detection system shaft initiate a local alarm and transmit a signal to a continually staffed remote location to provide an immediate response to an alarm. The alarm shaft be both visual and audible and shaft be designed to provide warning both inside and outside of the storage, use or handling area. The audible alarm shaft be distinct from all other on-site alarms.

46

HAZARDOUS GAS MONITORING

Santa Clara County Fire Chiefs Association Toxic Gas Ordinance Consensus Guidelines 1996 Several jurisdictions within Santa Clara County, California, have adopted toxic gas ordinances (TGOs). Because these ordinances varied somewhat, the county fire chiefs developed a consensus guideline to summarize the common features.

Item A. Materials R e g u l a t e d . . . 7. Dilute toxic gas mixtures are regulated by the TGO. However, when the concentrations are such that they are less than the standards required by a specific control, the material may be exempted from that particular control (e.g., concentrations less than PEL). . . . Halogenated, non-carbon-based gases may hydrolyze to their base mineral acid upon contact with moisture. Therefore, the TGO requirements (i.e., monitoring, treatment, compatibility, etc.) for these gases shaft apply to their decomposition products. B

Item F. Seismic Protection Automatic shut-down shaft be required for the toxic gas sources in the event of seismic activity at 0.3G, or lower, as specified by each jurisdiction. Item G. Gas D e t e c t i o n . . . 10. Monitoring systems shaft be tested at the point of use. 11. The interval time for "continuous" gas detection shaft be determined by the Fire Chief in each jurisdiction. The maximum interval time shaft be 30 minutes, as defined by the UFC. 12. Automatic shut-down shaft occur upon gas detection at or below PEL in occupied areas, and at or below 1/2 IDLH in unoccupied areas. 13. Continuous gas detection may not be required to detect the presence of gas at or below the PEL when the upper range of the odor threshold limit is less than the PEL, as determined by the critiqued and approved data published by the American Industrial Hygiene Association, "Odor Thresholds for Chemicals with Established Occupational Health Standards" (1989, or as amended thereafter). That notwithstanding, monitoring may be required to provide for the proper function of the treatment system and other emergency controls. Moreover, this exemption may apply only in those j u r i s d i c t i o n s . . , which provide an exception based on the physiological warning properties of certain gases. Item J. Secondary Containment 1. Secondary containment systems shaft be approved and tested on a caseby-case basis by individual jurisdictions. New types of systems shaft be evaluated by the TGO Committee as they are proposed. 2. Secondary containment may not be required for systems operating

HAZARDOUS GAS MONITORING

47

under sub-atmospheric conditions (i.e., vacuum piping systems) i f it is demonstrated that equivalent protection is provided (e.g., when the system is equipped with an alarm and a fail-safe-to-close valve activated by a loss in vacuum pressure). Item M. Existing Ammonia Refrigeration Systems 1. For facilities where ammonia refrigeration systems store more than the Maximum Threshold Quantity (Max T. Q. = 12,500 Ibs.) in a single vessel, automatic valves shaft be used to isolate zone areas or equipment areas to less than the Max T. Q. Isolation shaft be achieved by shutting off the liquid supply to an area within the system. The isolated area shaft then be evacuated by suction from the compressor. b. Automatic isolation shaft be provided for: L Seismic, fire or other remote location alarm; i~. Ammonia detection at 100 ppm, or at a concentration acceptable to the individual jurisdiction, not to exceed 250 ppm; iii. Emergency power failure; iv. Exhaust system failure. Redundant ammonia gas detection shaft be used to monitor non-welded connections located within non-exhausted enclosures. b. Sensors shaft automatically isolate zone or equipment areas upon detection at 100 ppm, or at a concentration acceptable to the individual jurisdiction, not to exceed 250 ppm. c. Gas sensors shaft be tested, at the discretion of the individual jurisdiction. B

Note the reference to redundant gas detection in Item M, 2.

48

HAZARDOUS GAS MONITORING

Palo Alto, Califomia, Toxic Gas Ordinance 1 9 9 9 Local jurisdictions throughout Santa Clara County, California, have modified their toxic gas ordinances (TGOs) to be similar within the county. These excerpts from the City of Palo Alto 1999 TGO provide examples of typical hazardous gas monitoring requirements in California's Silicon Valley. The Palo Alto TGO differs slightly from other municipal TGOs within Santa Clara County. The following comparison illustrates the importance of carefully reviewing the TGO of a specific project's jurisdiction. Mountain View, another city within Santa Clara County, requires exhaust system flow monitoring and if exhaust flow stops, Class I hazardous gas valves are to automatically close. Palo Alto does not require exhaust flow monitoring. This is a significant difference in code requirements between cities within the county.

Regarding Hazardous Material Classifications The Palo Alto TGO defines three classes of hazardous materials. Palo Alto TGO 9101.2 Class I Material is a material that has a m e d i a / l e t h a l concentration (LC~) in air o f 2 0 0 parts per million or less by volume o f gas or vapor, or 2 milligrams per liter or less of mist, fume or dust, when administered by continuous inhalation for an hour, or less i f death occurs within one hour, to albino rats weighing between 2 0 0 and 3 0 0 grams each. This is the same definition used in the Uniform Fire Code for Highly Toxic Material. Palo Alto TGO 9101.2 Class II Material is a material that has a medial lethal concentration ( L C ~ in air more than 2 0 0 parts per million but n o t more than 3 , 0 0 0 parts per million by volume of gas or vapor, or more than 2 milligrams per liter but not more than 30 milligrams per liter o f mist, fume or dust, when administered by continuous inhalation for an hour, or less if death occurs within one hour, to albino rats weighing between 2 0 0 and 3 0 0 grams each. This is similar to the Uniform Fire Code definition of Toxic Material except that the upper limit for a Toxic Material is 2,000 ppm for gas and 20 mg for mist, fume or dust. Palo Alto TGO 9101.2 Class III Material is a material that has a medial lethal concentration (LCr~) in air more than 3 , 0 0 0 parts per million but n o t more than 5 , 0 0 0 parts per million by volume of gas or vapor, or more than 3 0 milligrams per fiter but not more than 50 milligrams per liter o f mist, fume or dust, when administered by continuous inhalation for an hour, or less if death occurs within one hour, to albino rats weighing between 2 0 0 and 3 0 0 grams each.

HAZARDOUS GAS MONITORING

49

The Uniform Fire Code does not have a classification similar to the TGO Class II1. The TGO does not require gas monitoring for Class III materials.

Regarding Hazardous Material Quantities Gas monitoring requirements are dependent upon the quantities of hazardous material in question. Palo Alto TGO 9101.2 Minimum Threshold Quantity (Min. T.Q.) means the aggregate quantity of a single regulated material in a control area which, due to the minimal aggregate quantities present, need only comply with specific control requirements established in sections 9102 and 9108 of this article, and not with the specific requirements for Class I, II or III regulated materials. Min. T.Q. for mixtures shaft be based on the aggregate weight (in pounds) of the regulated components. For all regulated materials: Min. T.Q. = 2 Ibs. or less. Minimum threshold quantity controls are set forth in section 9108 of this article. Section 9103.2 defines exempt amounts. Palo Alto TGO 9103.2 Exempt Amounts. Except as provided in section 9103.2. I below, any single material which would otherwise be regulated is exempt from regulation under this article if: 0

0

The aggregate quantity of any single material in a control area does not exceed the Min. T.Q.; and The aggregate quantity of all regulated materials in a control area or exterior storage does not exceed the exempt amounts specified in Article 80 of the currently adopted edition of the California Fire Code; and (a) The quantity of the material in a single vessel does not exceed 1 pound; or The concentration of material in the vessel is less than the (b) Permissible Exposure Limit (PEL), for each constituent.

Regarding Nationally-Recognized Standards Section 9104.2 could refer to any of the standards developed by various organizations and especially to those adopted by ANSI. Palo Alto TGO 9104.2 Nationally recognized standards. All control equipment for materials regulated by this article shaft meet appropriate nationally recognized standards, if any, approved by the Fire Chief or his designee.

50

HAZARDOUS GAS MONITORING

Regarding Reaction Byproducts Palo Alto TGO 9104.3 Gases which hydrolyze or decompose. Halogenated, non-carbon based gases may hydrolyze to their base mineral acid upon contact with moisture. Therefore, the monitoring and compatibility requirements of this article shaft apply to their decomposition products. For information on hydrolysis, see discussion of Sensing Reaction Byproducts in Chapter 4 of this guide.

Regarding Class I Gas Controls Palo Alto TGO 9105.1 Requirements applicable to Class I materials. Persons responsible for any facility where Class I materials are present shaft comply with all of the requirements of this section and with sections 9102, 9106, 910 7, and 9108 of this article. Class I controls includes section 9102 General Provisions, 9106 Class II Controls, 9107 Class III Controls, and 9108 Minimum Threshold Quantity Controls. Palo Alto TGO 9105.2.1 Secondary containment. Secondary containment sha# be provided for piping for Class I materials. The secondary containment shall be capable of directing a sudden release to an approved discharge treatment system, and shaft be monitored continually with a continuous gas monitoring system approved by the Fire Chief. Secondary containment includes, but is not limited to, double walled piping.

Exception: The chief may waive the requirement for secondary containment for piping under sub-atmospheric conditions if the piping is equipped with an alarm and cylinder fail-safe-to-close valve activated by a loss of vacuum. Secondary containment for piping is provided by double-walled coaxial piping. The outer wall of coaxial piping can be connected to the sheet metal enclosure of an exhausted gas cabinet. Gas cabinet exhaust produces a negative pressure in the void between the double-walled piping. Any leaks from the inner pipe will be drawn to the gas cabinet. The gas cabinet exhaust sensor should be able to detect presence of leaks. This method does not differentiate between leaks inside the gas cabinet and leaks in the coaxial piping. An additional gas sensor could be provided to sense the coaxial piping void directly. Palo Alto TGO 9105.3 Automatic Shut-off. An automatic shutoff valve which is of a "fail-safe to close" design shaft be provided. Each of the following shaft activate automatic shut-off:

HAZARDOUS GAS MONITORING

0

w

3. 4.

w

6.

51

Gas detection at PEL in occupiable areas; at 1/2 IDLH (or 0.05 LCso i f no established IDLH) in unoccupiable areas. Manual activation of emergency shutoff, from remote locations. Failure of emergency power. Seismic activity, upon a seismic event within 5 seconds of horizontal semisoidal oscillation having a peak acceleration of 0.3g (= 2.94m/sec 2) and a period of 0.4 seconds. Failure of primary containment. Activation of manual fire alarm.

Palo Alto TGO 9105.4 Emergency Control Station. Signals from emergency equipment shaft be transmitted to an emergency control station which is continually staffed by trained personnel Regarding Class II Controls Palo Alto TGO 9106.1 Requirements applicable to Class II materials. Persons responsible for any facility where Class II materials are present shaft comply with all of the requirements of this section and with sections 9102, 910 7, and 9108 of this article. Class II controls includes section 9102 General Provisions, 9107 Class III Controls, and 9108 Minimum Threshold Quantity Controls. Palo Alto TGO 9106.3 Local Gas Shut-oH. Manual activation controls shall be provided at locations near the point of use and near the source, as approved by the Fire Chief. Manuafy activated shut-oH valves sha# be of "fail safe to close" design. The Fire Chief may require additional controls at other places, including, but not limited to, the entry to the building, the area in the building where regulated materials are stored or used, and emergency control stations. Palo Alto TGO 9106.4 Emergency Power. Emergency power sha# be provided for: 1. Exhaust ventilation, including the power supply for treatment systems. 2. Gas-detection systems. 3. Emergency alarm systems. 4. Temperature-control systems which comply with the Fire Code. Palo Alto TGO 9106.6 Gas Detection. A continuous gas-detection system shaft be provided to detect the presence of gas at or below the permissible exposure limit in occupiable areas and at or below 1/2 IDLH (or 0.05 LCso i f no established IDLH) in unoccupiable areas. The detection system shaft initiate a local alarm and transmit a signal to a continually staffed remote location to provide an immediate response to an alarm. The alarm shaft be both visual and

52

HAZARDOUS GAS MONITORING

audible and shaft be designed to provide warning both inside and outside of the storage, use or handling area. The audible alarm shaft be distinct from all other on-site alarms. Section 9107 on Class III Controls does not contain any gas monitoring provisions. Section 9108 on Minimum Threshold Quantity Controls does not contain any gas monitoring provisions.

HAZARDOUS GAS MONITORING

53

NFPA 55 Standard for the Storage, Use and Handling of Compressed and tiqoified Gases in Cylinders 1998 Edition This National Fire Protection Association (NFPA) standard is not an adopted code in most jurisdictions. However, many insurers and corporate risk managers recommend use of NFPA standards to mitigate hazards.

Regarding General Requirements for Toxic Gases NFPA 55 3-1.1 Indoor storage areas used to store toxic gases shaft be equipped with a continuous gas detection system that provides an alarm to warn o f the presence of toxic gases in levels that present a hazard to life. Exception: A continuous gas detection system shaft not be required for toxic gases with a health rating of 3 when the upper range of the odor threshold limit o f the gas is at a level below the Permissible Exposure Level o f the gas.

NFPA 55 Appendix A3-1.1 See Odor Thresholds for Chemicals with Established Occupational Health Standards for an odor threshold rating of gases.

54

HAZARDOUS GAS MONITORING

NFPA 3 1 8 Standard for the Protection of Cleanrooms 1 9 9 8 Edition This National Fire Protection Association (NFPA) standard is not a code in most jurisdictions; however, it does provide good guidelines for safe practices in cleanrooms. It may be possible to demonstrate to the local authority having jurisdiction that the cleanroom-specific procedures and systems in this standard are acceptable alternatives to more general codes.

Regarding Alarm Systems NFPA 31 8 2-2.2 Where the potential exists for flammable gas concentrations to exceed 20 percent of the lower flammable limit (LFL), a continuous gasdetection system shall be provided. NFPA 318 articles 6-4 and 6-5 describe an exterior storage method for silane (Sill4) and silane mixtures. The silane storage area is open on at least three sides, with cylinders secured to steel frames and separated from each other by a steel plate.

Regarding Detection Systems for Silane NFPA 31 8 2-3.3 Detection shaft be provided at silane gas cylinders in open dispensing systems described in Sections 6-4 and 6-5. Activation of the detectors shaft result in closing of the cylinder automatic shutoff valves described in 6-1.2. The detection means is not specified. There has been limited research dealing with silane-air mixtures. One phenomenon is that silane (Sill4), while classified as a pyrophoric, does not always ignite immediately when released into the air. This can potentially lead to a vapor cloud explosion (VCE); however, most clouds in exterior storage areas disperse without ignition. Tests conducted by Y oukiehi Urano (see References) showed that even at concentrations well below 1 percent silane, spontaneous ignition and reaction are possible without the detection of flames. Studies have also shown that ignition may not occur even with 100 percent silane at high release rates, but may occur after the velocity of the non-burning stream is reduced. A silane release usually ignites and burns smoothly, but in a partially confined space it may explode. Open air with adequate space and air movement should cause a silane leak to react immediately. In the past, silane was stored in gas cabinets. Based on more recent tests, most authorities now recommend unconfined exterior storage. Current design practice for exterior silane storage facilities is to incorporate continuously operating air fans directing high volumes of air across the silane cylinder valves and piping fittings. These large volumes of air dilute any leaks, thereby making detection difficult. One gas supplier has reported successfully detecting silane leaks at exterior storage areas using electrochemical sensors.

HAZARDOUS GAS MONITORING

55

Environmental conditions must be considered during the selection, location and installation of detection systems. Consider variables that may impact sensors and controllers in outdoor silane storage locations such as high or low ambient temperatures, changes in humidity, and contact with rainwater or fire sprinkler water (most silane installations also incorporate fire sprinkler deluge systems). Gas suppliers are currently proposing silane delivery systems which typically include a bulk storage container, such as an ISO-module (International Organization of Standardization) or tube trailer that can store from three to six metric tons of product. Seemingly, increased quantities of silane would proportionately increase risk in the case of a leak. However, suppliers maintain that the highest risk of leak occurs when cylinders are changed out; therefore, reducing the number of change-outs decreases risk. Flame detectors have been used to detect silane because silane ignites under many conditions. Standard infrared (IR) flame detectors working in the 4.3 micron emission band cannot be used to detect non-hydrocarbon fires such as silane (Sill4), hydrogen (H 2) or ammonia (NH3) which produce emissions in the 2.9 micron range. Standard ultraviolet (UV) flame detectors can go into alarm if their cone of vision detects sunlight (a UV source). The positioning and aiming of UV detectors is critical to detect flame without detecting innocuous but alarming UV sources. Glass and Plexiglas windows significantly attenuate UV radiation and must not be located between the detector and a potential flame source. A hydride monitor can also be placed over the dispensing end manifold or in a valve manifold box (VMB) exhaust. In order to alarm, standard combination UV and IR flame detectors require detection of flame emissions in both the UV (2,000 to 2,900 angstroms) and the IR (4.3 micron) bands. Omniguard Sensors Division offers a combination UV/IR flame detector that looks for emissions in the UV region and both the 4.3 and 2.9 micron IR ranges. This detector has received Factory Mutual approval for detection of hydrogen, silane and hydrazine flames. RK! offers a silane detector incorporating two sensor types. A conventional electrochemical silane sensor is combined with an ionization chamber that detects silicon dioxide particulates produced from combustion of silane. Chapter 7 covers bulk silane systems and 7A 1 specifically covers tube trailer systems. NFPA 318 7-1.2 Automatic fixed water spray protection shaft be provided to the tube trailer storage . . . . The flame water spray system shaft be activated by approved optical flame detectors that will respond to the flame signature of silane. NFPA 31 8 7-1.3 Activation of the water spray system shall close emergency shutoff valves (ESOVs).

56

HAZARDOUS GAS MONITORING

Section 7-2 specifically covers silane cylinder pack systems. NFPA 318 7-2.2 Approved optical flame detectors that will respond to the flame signature of silane shall be provided to close ESO Vs and to actuate water spray systems, if provided, upon alarm. NFPA 318 7-2.3 A gas detection system shaft be provided to close all cylinder ESOV upon activation.

Regarding Flammable or Toxic Gases NFPA 318 6-6.1 Toxic or flammable gases in use shaft be contained in cabinets provided with exhaust ventilation. Cabinets shaft be provided with gas detection and automatic shutdown of the gas supply. Exhaust ventilation shaft be continuous or activated automatically by gas detection. NFPA 318 6-6.2 Exhaust ventilation shaft be provided where there is potential for gas release and for the area containing valves, fittings or connections, transfer station, or vacuum pumps. Detection of toxic or flammable gases shaft activate a local alarm and shut down the gas supply. Alarms shaft be monitored continuously.

Regarding Production and Support Equipment Interlocks NFPA 318 7.2.4 Tools utilizing hazardous chemicals shaft be designed to accept inputs from monitoring equipment. An alarm signal from the monitoring equipment shaft automatically stop the flow of hazardous chemicals to the tool

Regarding Production and Support Equipment NFPA 31 8 8-2.4 Tools utilizing hazardous chemicals shaft be designed to accept inputs from monitoring equipment. An alarm signal from the monitoring equipment shaft automatically stop the flow of hazardous chemicals to the tool

Regarding Seismic Interlocks NFPA 318 contains appendices that are not a part of the requirements of the NFPA document, but which are included for information only. Appendix B covers seismic protection. NFPA 31 8 Appendix B-1.2 An approved seismically activated valve should be provided for automatic shutoff of piping systems that convey hazardous chemicals during significant seismic events. It should generate a signal to activate emergency shutoff valves on gas cabinets, hazardous gas supply lines, and appropriate utility services, such as natural or LP-gas.

HAZARDOUS GAS MONITORING

57

Federal Requirements Several federal agencies govern hazardous gas monitoring and publish standards as Codes of Federal Regulations (CFRs). The Environmental Protection Agency (EPA) covers hazardous chemical releases in Title 40, Protection of Environment, Part 68 (40 CFR 68) Chemical Accident Prevention Provisions. The Occupational Safety and Health Agency (OSHA) addresses hazardous gas monitoring in 29 CFR 1910.119 Process Safety Management of Highly Hazardous Chemicals. Federal standard 29 CFR 1910.120 Hazardous Waste Operations and Emergency Response could be applicable to wastes or to releases of hazardous materials. Note that chemicals and threshold quantities differ between these standards; e.g., EPA's list of chemicals includes 100 toxic substances, 51 of which are not included on OSHA's list. In addition, facilities that may not be required to meet OSHA requirements may fall under EPA requirements. These standards were mandated by the Clean Air Act and all are uniform in requiring a formal, written hazard assessment and prevention program. The federal standards require safety systems to be designed in accordance with accepted standards. This directive could be interpreted as requiring conformance to ISA or IEC standards. Refer to the discussion of system certification in Chapter 7 of this guide. Many federal documents are available on the Internet and the OSHA and EPA Web sites contain search engines that allow material to be retrieved by document number or by text. Refer to the References section of this guide.

58

HAZARDOUS GAS MONITORING

Environmental Protecdon Agency (EPA) Requirements The Environmental Protection Agency's hazardous gas monitoring requirements are covered in 40 CFR 68. Subpart F, Section 68.13, Regulated Substances for Accidental Release Prevention, lists EPA-regulated substances with designated threshold quantities in pounds. Following is a comparison of selected substances commonly used in semiconductor manufacturing regulated by EPA and/or OSHA. It is interesting that the agencies do not regulate the same substances or agree on threshold limits.

EPA Hazardous Substance Ammonia (anhydrous) Arsine Boron trichloride Boron trifluoride Bromine Chlorine Diborane Dichlorosilane Dimethyldichlorosilane Fluorine Hydrogen chloride Hydrogen fluoride Methyl mercaptan Ozone Phosgene Phosphine Silane Trichlorosilane

EPA Threshold 10,000 Ibs 1,000 Ibs 5,000 Ibs 5,000 Ibs 10,000 Ibs 2,500 Ibs 2,500 Ibs 10,000 Ibs 5,000 Ibs 1,000 Ibs 5,000 Ibs 1,000 Ibs 10,000 Ibs Not Regulated 500 Ibs 5,000 Ibs 10,000 Ibs Not Regulated

OSHA Threshold Not Regulated 100 Ibs 2,500 Ibs 250 Ibs Not Regulated 1,500 Ibs 100 Ibs 2,500 Ibs Not Regulated Not Regulated 5,000 Ibs 1,000 Ibs Not Regulated 100 Ibs 100 Ibs 100 Ibs 1O0 Ibs 5,000 Ibs

Subpart C of Section 68.48, Safety Information, outlines a prevention program with the following requirements: (a) The owner or operator shall compile and maintain the following up-to-date safety information related to the regulated substances, processes and equipment: (1) Material Safety Data Sheets that meet the requirements of 29 CFR 1910. 1200 (g) . . . . (5) Codes and standards used to design, build, and operate the process. (b) The owner or operator shaft ensure that the process is designed in compliance with recognized and generally accepted good engineering practices. (c) The owner or operator shall update the safety information if a major change occurs that makes the information inaccurate.

HAZARDOUS GAS MONITORING

59

Subpart G of Section 68.170, Prevention Program, outlines the requirements of a Risk Management Plan (RMP). Along with other requirements, the RMP shall include the following information: 9

0

=

4.

The date of the most recent review or revision of the safety information and a list of federal or state regulations or industry-specific design codes and standards used to demonstrate compliance with the safety information. The date of the most recent compliance audit and the expected date of completion of any changes resulting from the compliance audit. The date of completion of the most recent hazard review or update. The hazard review containing: a. Major hazards identified. b. Process controls in use. c. Mitigations systems in use. d. Monitoring and detection systems in use. (i.e., gas monitoring) e. Changes since the last hazard review.

Facility RMPs are posted by the EPA at http://www.epa.gov:9966/srmpdcd/owa/rmpcmnc $ .startup.

60

HAZARDOUS GAS MONITORING

Occupational Safety and Health Administration (OSHA) Requirements 29 CFR 1910.119 Process Safety Management of Highly Hazardous Chemicals This standard is summarized in OSHA Fact Sheet No. OSHA 93-45 and contains OSHA's requirements for preventing or minimizing the consequences of catastrophic releases of toxic, reactive, flammable, or explosive chemicals. This standard applies to processes involving chemicals at or above specified threshold quantities as well as processes involving flammables in one location in a quantity of 10,000 pounds or more. Understanding OSHA's definition of "process" is important. "Process" means any activity involving a highly hazardous chemical including any use, storage, manufacturing, handling, or the on-site movement of such chemicals, or combination o f these activities . . . . any group o f vessels which are interconnected and separate vessels which are located such that a highly hazardous chemical could be involved in a potential release shaft be considered a single process.

Section (c) outlines employer requirements to compile and distribute to employees process safety information pertaining to the hazards of the highly hazardous chemicals used, the technology of the process, and the equipment in the process. The safety information i s also to include design codes and standards employed and safety systems such as interlocks and detection or suppression systems. The employer shall document that equipment complies with recognized and generally accepted good engineering practices. Section (e) covers the employer's process hazard analysis. The analysis shall address engineering and administrative controls applicable to the hazards and their interrelationships such as appropriate application of detection methodologies to provide early warning of releases. (Acceptable detection methods might include process monitoring and control instrumentation with alarms, and detection hardware such as gas sensors.) Section (f) directs the employer to develop and implement written operating procedures that provide clear instructions for emergency shutdown including the conditions under which emergency shutdown is required in a safe and timely manner. The employer must annually certify that these operating procedures are current and accurate. Section (i) addresses the employer's pre-startup safety review. New facilities and facilities modified to the extent that changes in the process safety information are required are subject to review. Prior to the introduction of highly hazardous chemicals to a process, the review shall confirm that construction and equipment is in accordance with design specifications and that safety, operating, maintenance and emergency procedures are in place and are adequate.

HAZARDOUS GAS MONITORING

61

Section (o) directs that a compliance audit be performed at least every three years to determine that procedures and practices developed under this standard are adequate and are being followed. Appendix C, paragraph 14, mandates an audit of the process safety management system and program including an evaluation of its design and effectiveness and a field inspection of the safety and health conditions and practices. 2 9 CFR 1 9 1 0 . 1 2 0 Hazardous Waste Operations and Emergency Response This section applies to any industry that has emergency response operations for release (or substantial threat of release) of hazardous substances without regard to the location of the hazard.

(g) Engineering controls, work practices, and personal protective equipment (PPE) for employee protection. Engineering controls, work practices, personal protective equipment, or a combination of these shaft be implemented in accordance with this paragraph to protect employees from exposure to hazardous substances and safety and health hazards. (1) Engineering controls, work practices and PPE for substances regulated in subparts G and Z. (i) Engineering controls and work practices shaft be instituted to reduce and maintain employee exposure to or below the permissible exposure limits for substances regulated by 29 CFR part 1910, to the extent required by subpart Z, except to the extent that such controls and practices are not feasible. (2) Engineering controls, work practices and PPE for substances not regulated in subparts G and Z. An appropriate combination of engineering controls, work practices and personal protective equipment shaft be instituted to reduce and maintain employee exposure to or below published exposure levels for hazardous substances and health hazards not regulated by 29 CFR part 1910, subparts G and Z. Engineering controls could be interpreted to include gas monitoring systems that shut off gas valves upon detection of hazardous gas leaks.

(h) Monitoring-(1) General (i) Monitoring shaft be performed in accordance with this paragraph where there may be a question of employee exposure to hazardous concentrations of hazardous substances in order to assure proper selection of engineering controls, work practices andpersonal protective equipment so that employees are not exposed to levels which exceed permissible exposure limits, or published exposure levels if there are no permissible exposure limits, for hazardous substances.

62

HAZARDOUS GAS MONITORING

(ii) Air monitoring shaft be used to identify and quantify airborne levels of hazardous substances and safety and health hazards in order to determine the appropriate level of employee protection needed on site. (2) Initial entry. Upon initial entry, representative air monitoring shaft be conducted to identify any IDLH condition, exposure over permissible exposure limits or published exposure levels, exposure over a radioactive material's dose limits or other dangerous condition such as the presence of flammable atmospheres or oxygen-deficient environments. (3) Periodic monitoring. Periodic monitoring shall be conducted when the possibility of an IDLH condition or flammable atmosphere has developed or when there is indication that exposures may have risen over permissible exposure limits or published exposure levels since prior monitoring. The above sections require air monitoring for hazardous gases. The following sections outline some of the requirements for an employee alarm system.

(I) Emergency response by employees at uncontrolled hazardous waste sites. (3) Procedures for handling emergency incidents. (vi) An employee alarm system shaft be installed in accordance with 29 CFR 1910. 165 to notify employees of an emergency s i t u a t i o n ; . . . 29 CFR 1 9 1 0 . 1 6 5 Employee Alarm System This section applies to all emergency employee alarms installed to meet a particular OSHA standard. (b) General requirements. (3) The employee alarm shaft be distinctive and recognizable as a signal to evacuate the work area or to perform actions designated under the emergency action plan. (d) Maintenance and testing. (4) The employer shaft assure that employee alarm circuitry installed after January 1, 1981, which is capable of being supervised is supervised and that it will provide positive notification to assigned personnel whenever a deficiency exists in the system. The employer shaft assure that all supervised employee alarm systems are tested at least annually for reliability and adequacy. Employee alarms for each emergency condition must be distinct from other alarms. The alarm system circuitry is required to be electrically supervised similar to requirements for fire alarm systems.

HAZARDOUS GAS MONITORING

IEC Standard 6 1 5 0 8

63

Functional Safety - Safety Related Systems

Although this standard developed by the International Electrotechnical Commission (IEC) does not specifically address hazardous gas monitoring, it contains requirements for any control system related to safety. Standard 61 508 outlines a generic approach for all activities concerning safety systems comprised of electrical and/or electronic and/or programmable electronic (E/E/PE) components. The standard addresses all phases of the life safety system including development of the system requirements or scope, design of hardware and software, testing, commissioning, operation, maintenance and modifications. The standard describes a structured approach outlining the steps to be taken and documentation to facilitate reviews, maintenance and future modifications. A method to rank risk and the reliability of the safety system to mitigate risk is developed. The allowable risk depends on factors such as severity of injury, the number of people exposed to danger, and the frequency and duration of the exposure. Properly designed safety systems reduce the frequency or probability of the hazardous event and/or the consequences of the hazardous event. The concept of safety integrity is developed as a means to rank the probability of a safety-related system (SRS) satisfactorily performing its required safety functions under all stated conditions within a specific time period. The use of redundancy to improve safety system integrity is outlined. Standard 61 508 is divided into the following parts: Part 1 specifies general requirements applicable to the other parts. Parts 2 & :3 provide additional and specific requirements for safety-related system hardware and software. Part 4 gives definitions and abbreviations used throughout the standard. Part 5 provides guidelines on the application of Part 1 in determining safety integrity levels (SILs) and includes examples of the various methods. Part 6 provides guidelines on the application of Parts 2 and 3. Part 7 is an overview of techniques and measures outlined in the standard. It is important to note that this standard covers not only the design of safety systems, but also system operation, testing and maintenance. It outlines the need for periodic functional safety audits, procedures for initiating modifications, and approval procedures. Documentation of all activities is highly stressed. Both EPA and OSHA standards mandate that "the employer document that equipment complies with recognized and generally accepted good engineering practices." This could be interpreted as requiring safety systems to conform to standards such as IEC 61 508. Factory Mutual, UL and TUV use IEC 61 508 as a criterion in certifying safety systems.

64

HAZARDOUS GAS MONITORING

This standard develops the concept of the safety life cycle model to identify and provide guidance for all activities that affect the functional safety of E/E/PE safety related systems. One performance criterion in the standard is the safety integrity level (SlL) which is related to the probability of the E/E/PE SRS to fail to function. The overall objective of the standard is to identify the hazards, the required safety functions, establish their SlLs and implement them in an E/E/PE SRS in order to achieve the desired safety level for the process. This standard also mandates the development of a safety management plan, maintenance and system modification procedures, requires extensive documentation of all safety activities that affect functional safety, and proposes validation and verification activities throughout the safety life cycle. The basic steps required to comply with this standard are: 9

2. 3. 4. 5. =

7. 8. 9. 10. 11. 12. 13. 14. 15.

Establish the safety target level of the process. Perform a hazard analysis. Perform a risk analysis of the process to quantify process risk. Identify hazardous events that do not meet the safety target level. Evaluate potential risk reduction using SRSs or other technology (mechanical devices) and external risk reduction facilities (e.g., scrubbers). Identify safety function(s) implemented in an E/E/PE SRS. Determine the safety integrity level of the E/E/PE SRS's safety function(s). Define the specification requirements of the E/E/PE SRS's safety function(s). Integrate E/E/PE SRS safety functions in an E/E/PE SRS safety related system. Establish a procedure for reliability modeling of the E/E/PE SRS. Perform a Failure Mode and Effects Analysis (FMEA) on the E/E/PE SRS. Develop a reliability model for the E/E/PE SRS. Evaluate the SlL of the E/E/PE SRS. Evaluate process risk reduction due to the use of the E/E/PE SRS. Make the required modifications and analysis to make certain that SRS meets the risk reduction (SlL) requirements.

Step 1 establishes the safety target level of the process. Steps 2 trough 9 focus on the risk analysis of the process and the identification of safety functions and their SlL in order to achieve the safety target level. Steps 10 through 13 discuss the hardware and software reliability modeling requirements and techniques to evaluate and certify reliability of the safety related system. Steps 14 and 15 provide evidence of compliance to the standards. This standard is under revision.

HAZARDOUS GAS MONITORING

65

ANSIIISA Standard S84.01 Application of Safety Instrumented S y s t e m s for the Process Industries This standard developed by the International Society for Measurement and Control is based on IEC Standard 61508, but does not include sensors and final control elements and is narrower in scope in that it only applies to safety systems in process industries. OSHA and EPA require safety systems to comply with recognized, generally accepted good engineering practice. Because this ISA standard has been adopted as an ANSI standard, it could be interpreted as being an OSHA and EPA requirement. From an economic standpoint, complying with recognized national standards (such as ANSI) helps avoid or mitigate claims of negligence in design or operation. Punitive sanctions of OSHA or EPA are insignificant when compared to potential lawsuits. This standard uses the concept of the safety life cycle and safety integrity level (SIL) developed in IEC 61 508. The ISA standard defines safety integrity in three levels, 1 through 3. The higher the SlL, the more available the safety function must be. Availability performance is improved by the addition of redundancy, more frequent testing, the use of diagnostic fault detection, and the use of diverse sensors and final control elements. A SlL of 2 requires more diagnostics than SlL 1 and typically includes redundancy of the logic solver and sensors, with redundancy of final control elements being necessary. A SIL of 3 typically requires two separate and diverse 1ool arrangements, each with their own sensor, logic solver and final control element. The l o o l arrangements would be connected in a loo2 voting scheme. Diverse separation, redundancy, and exhaustive diagnostic capabilities are considered significant aspects of a SlL 3 system. Among the requirements for safety instrumented systems (SIS) defined by ISA S84.01 are the following: A control valve from the Basic Process Control System (BPCS), as opposed to a valve that is a dedicated part of the safety system, shall not be used as the only final control element for a SlL of 3. A formal safety review shall be required to use a BPCS single control valve as the only final element for a SiL of 1 or 2. The safety system shall be designed such that once it has placed the process in a safe state, it shall remain in the safe state until a reset has been initiated. Manual means, independent of the logic solver, shall be provided to actuate the safety system final control elements.

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HAZARDOUS GAS MONITORING

Safety system input/output power circuits shall be separated from circuits used for any other purpose, except where the sensor or final control element is shared with other systems. Energized-to-trip discrete input/output circuits shall apply a method (e.g., endof-line monitor) such as pilot current continuously monitored to insure circuit continuity (electrically supervised). The operator shall be alerted to the bypass of any portion of the safety system via an alarm and/or operating procedure. Bypassing o f any portion of the safety system shall not result in the loss of detection and/or annunciation of the conditions being monitored. A written procedure shall be in place to initiate, document, review the change, and approve changes to the safety system other than replacement in kind. ISA publishes a handbook, Safety Shutdown Systems: Design, Analysis and Justification, that expands on procedures outlined in ISA Standard S84.01. Safety integrity level is addressed by different organizations under various schemes. This table compares several classes and standards.

i

Percent Availability

Probability of Failure on Demand (PFD)

ANSI/ISA S84.01

IEC 61508

TUV Class

(SIL)

(SIL)

(AK)

DIN V 19250

i

99.999

0.00001 i

ii

99.99

4

0.0001

AK8

8

AK7

7

i

i

i

99.90

0.001

3

3

AK6AK5

6-5

AK4AK3

4-3

i

99.00

0.01

i

i|l

90.00

0.1

AK2AK1 i

2-1

i

HAZARDOUS GAS MONITORING

67

Underwriters Laboratories Standards Underwriters Laboratories (UL)is a product safety testing and certification organization that evaluates products for public safety. Companies and products must pass UL tests and achieve specified levels of safety and performance in order to receive a UL label, commonly called a listing. Both the Uniform Fire Code and the International Fire Code require detection and alarm systems associated with the use, storage or handling of hazardous materials to be listed or approved. The words listed and approved are synonymous with certified by an accepted testing laboratory--the phrase used in the SEMI Standard $2-0200, Safety Guidelines for Semiconductor Manufacturing

Equipment. Underwriters Laboratories listing standards related to gas sensors and safety systems include:

UL 2075 Gas Detectors and Sensors. This draft standard includes requirements for the evaluation of fire and shock hazards as well as product performance. The UL listing category is CCN "FTAM." This category does not cover detectors for use in atmospheres containing ignitable mixtures of flammable vapors or hazardous (as defined by NFPA 70) locations or portable gas detectors. UL 1998 Safety-Related Software. This standard applies to software whose failure could result in a risk of injury to persons or loss of property. It is intended to supplement applicable end-product or component standards and is not intended to serve as the sole basis for investigating the risks of injury or property loss associated with equipment. The UL 1998 requirements include an integral investigation of the acceptability of the controlling hardware to perform its specified safety-related protective function. This is conducted in accordance with UL 991, Standard for Tests for Safety-Related Controls Employing Solid-State Devices, or as specified in the end-product standard. Overall life cycle requirements including hazard and risk analysis are an integral part of UL 1998. Extensive measures to address hardware failures and malfunctions, including examples of acceptable required hardware fault/error coverage, are included. UL 991 Standard for Tests for Safety-Related Controls Employing Solid State Devices. This standard applies to controls that employ solid-state devices and are intended for specified safety-related protective functions. UL 991 contains standardized test methods for investigating the performance of an electronic control when subjected to particular environmental stresses.

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Oxygen Depletion Monitoring While highly-toxic and flammable gases receive the most attention, inert gases can also pose a danger. Personnel have lost consciousness after entering rooms containing nitrogen-purged wafer storage cabinets. A slight nitrogen purge is maintained in these cabinets to protect product from ingress of particles. If a cabinet has a slight leak and will not maintain positive pressure, an expedient solution is to increase the nitrogen gas flow. However, an increased flow of nitrogen into a small room could replace sufficient oxygen to present a hazard. Oxygen is the only constituent of breathable air that is capable of supporting life. Oxygen concentrations should be in the range of 19.5 percent to 23 percent. Normal concentration in the atmosphere is 21 percent. Any gas, if provided in large enough concentration, can displace or dilute the existing air supply. Oxygen concentrations of 19.5 percent or less can greatly increase the hazard of asphyxiation. OSHA defines oxygen deficiency as concentrations of oxygen below 19.5 percent. As the oxygen concentration is progressively lowered, the physiological effects are giddiness, mental confusion, loss of judgment, incoordination, weakness, nausea, loss of consciousness, and death. Oxygen-deficient atmospheres may cause an inability to move and a semiconscious lack of concern about work surroundings. In cases of sudden entry into an area containing deficient oxygen, the individual usually has no warning symptoms, but is quick to lose consciousness. Senses cannot be relied upon to alert or warn one of atmospheres that are deficient in oxygen. An asphyxiant is a vapor or gas that can cause unconsciousness or death by suffocation (lack of oxygen). Most simple asphyxiants are harmful to the body only when they become so concentrated that they reduce (displace) the available oxygen in the air (normally about 21%) to dangerous levels (1 8% or lower). Examples of simple asphyxiants are carbon dioxide, nitrogen, hydrogen and helium. Chemical asphyxiants like carbon monoxide (CO) reduce the blood's ability to carry oxygen, or like cyanide, interfere with the body's utilization of oxygen.

Monitoring Requirements Although not presently a code requirement, the best industry practice is to monitor interior storage rooms for nitrogen or argon and Dewar fill stations for oxygen depletion. In addition, if bulk nitrogen or argon distribution piping is located within an exit corridor, the local authority having jurisdiction may require oxygen depletion monitoring within the corridor. Some facilities provide oxygen depletion monitoring in rooms containing cryogenic gases such as scanning electron microscopes. If monitors detect a dangerous condition, a local alarm should be annunciated and an alarm message sent to the emergency control station. Oxygen depletion monitoring systems should provide a warning alarm when the oxygen concentration in air is reduced to around 19.5 percent. A full alarm should be generated when the oxygen concentration is reduced to 18 percent or less.

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Section 11.13.2.1 of the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) Standard 15-1994, Safety Code for Mechanical Refrigeration, addresses oxygen monitoring in refrigeration machinery rooms. ASHRAE 1 5-11.13.2.1 For Group A 1 refrigerants, machinery rooms shaft be equipped with an oxygen sensor to warn of oxygen levels below 19.5 volume percent since there is insufficient odor warning. The sensor shaft be located in an area where refrigerant from a leak is likely to concentrate and shaft actuate an alarm. Another useful guide for oxygen depletion monitoring is ISA-RP92.04.02, Part I1-1 996, Recommended Practice for Installation, Operation, and Maintenance o f Instruments Used to Detect Oxygen-Deficient~Oxygen-Enriched Atmospheres. The presence of acid gases can have adverse effects on most oxygen measuring cells. When selecting oxygen measuring systems for use in areas where acid gases may be present, review potential problems with the sensor manufacturer.

Refrigerant Vapor Alarm Systems Refrigerant vapor monitoring and alarm systems are required in refrigeration machinery rooms (chiller plants) when the chiller system is large enough to meet the definition of a "refrigeration machinery room" in the Uniform Mechanical Code (UMC). In addition, Uniform Fire Code Article 63 and International Fire Code Section 606 on Refrigeration contain many requirements for monitoring systems. Requirements of these codes relate to the flammability or toxicity of the refrigerant. Uniform Mechanical Code 1997 Edldon Requirements Uniform Mechanical Code requirements are outlined in sections 1106, 1107, and 1108. In addition to a vapor detection and alarm system, ventilation fans must be interlocked with the detection system to turn on when the refrigerant vapor concentration in air is 25 percent of the lower flammable limit (LFL) or not greater than 50 percent of the IDLH for the refrigerant, whichever is less.

UMC 1106.4 Refrigerant-vapor Alarms. Machinery rooms shaft have approved refrigerant-vapor detectors, located in an area where refrigerant from a leak is likely to concentrate, and shaft activate visual and audible alarms. Alarms shaft be activated at a value not greater than one half the immediately dangerous to life or health (IDLH), or measurement consistent therewith; the PEL, or measurement consistent therewith; or 25 percent of the LFL, whichever is less. UMC 1107.4 Intermittent Control of the Ventilation Systems. Fans providing refrigeration machinery room temperature control or automatic response to refrigerant gas in order to maintain concentrations below the PEL may be

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automatically controlled to provide intermittent ventilation as conditions require. UMC 1107.5 Emergency Control of the Ventilation Systems. Fans providing emergency purge ventilation for refrigerant escape shaft have a clearly identified switch of the break-glass type providing on-only control immediately adjacent to and outside of each refrigerant machinery room exit. Purge fans shaft also respond automatically to the refrigerant concentration detection system set to activate the ventilation system at no more than 25 percent of the LFL or 50 percent of the IDLH or a measure equivalent thereto, whichever is less. An emergency purge control shaft be provided with a manual reset only. UMC 1107.6 Central Control of Ventilation Systems. Mechanical ventilation systems shall have switches to control power to each fan. The switches shall be key operated or within a locked glass-covered enclosure at an approved location adjacent to and outside of the principal entrance to the machinery room. Necessary keys shall be located in a single approved location. Switches controlling fans providing continuous ventilation shall be of the two position, on-off type. Switches controlling fans providing intermittent or emergency ventilation shall be of the three position, automatic on-off type. Switches shall be labeled identifying both function and specific fan controlled. Two colored and labeled indicator lamps responding to the differential pressure created by airflow shall be provided for each switch. One lamp shall indicate flow, the other shall indicate no flow. The following exception provides a method for existing refrigeration rooms to conform to requirements for a separation wall between chillers and boilers. UMC 1106.7 Exception 3. Existing nonconforming installations may be allowed if approved by the building official when the combustion system is interlocked with the refrigerant detection system to shutoff at the PEL and the risks to the equipment life arising from dissociation products are acknowledged in writing by the owner. Uniform i~re Code 1997 Edidon Requirements

1997 UFC 6310.4 Refrigerant-vapor Alarms. Machinery rooms shaft have approved refrigerant-vapor detection or detectors. The detector, or a sampling tube that draws air to the detector, shaft be located in an area where refrigerant from a leak is likely to concentrate. The detector shaft activate visual and audible alarms at a value not greater than one half IDLH, or measurement consistent therewith, the PEL, or measurement consistent therewith, or 25 percent of the LFL, whichever is less.

1997 UFC 6310.7 Special Requirements. Open flames or devices having an exposed surface exceeding 800~ (427~ are prohibited in refrigeration machinery rooms.

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Exceptions: 3. Existing nonconforming installations may be allowed if approved by the building official when the combustion system is interlocked with the refrigerant detection system to shutoff at the PEL and the risks to the equipment life arising from dissociation products are acknowledged in writing by the o wner. The UFC exception 3 is identical to the UMC exception 3. The installation of walls separating boilers and chillers in existing heating and cooling plants may not be required if a refrigerant detection system is installed and interlocked with the boiler combustion system. UFC Section 631 6 outlines the actual requirements for detection and alarm systems. 1997 UFC 6313.1 General When required by this article, approved refrigerant vapor-detection devices shaft be connected to alarm systems utilizing listed fire alarm signaling devices capable of generating a sound level of at least 15 dB above the operating ambient sound pressure level of the space in which they are installed and providing an approved, distinctive audible and visual alarm. See Sections 6314. 1 and 8003. 1.10. 1997 UFC 6313.2.1 Alarm. Refrigerant vapor alarms shaft be activated whenever the refrigerant vapor PEL is exceeded. 1997 UFC 6313.2.2 Automatic shutdown. In other than machinery rooms, such systems shall also automatically stop the flow of refrigerant to evaporators within the space and stop the flow of refrigerant in all supply lines leaving the machinery room whenever the refrigerant vapor concentration is detected at or above 50 percent of the IDLH or 25 percent of the LFL. Detection of refrigerant vapor concentrations at or above 25 percent of the LFL shall automatically de-energize electricalpower within the space which does not meet the requirements for a Class I, Division 1, Group D electrical installation. 1997 UFC 6313.3 Power and Supervision. Detection and alarm systems shaft be powered and supervised as required for fire alarm systems in accordance with UFC Standard 10-2. (Standard 10-2 is NFPA 72.) Notice that this section of the UFC specifically requires the refrigerant gas detection and alarm systems to use listed fire alarm signaling devices and to be supervised as required for fire alarm systems. UFC Articles 51 and 80 do not specifically call for electrical supervision of hazardous gas detection systems, but Article 8004.1.8 can be interpreted as requiring supervision. The 1996 Code Supplement requirement for "listed" gas detection systems does not outline what functions are required for a "listed" system. Future editions of the UFC will probably require all hazardous gas detection systems to be powered and supervised as required for fire alarm systems.

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1997 UFC 6313.4 Monitoring andAnnunciation. Detection and alarm systems shall be remotely annunciated at an approved constantly attended location as required for fire alarm systems in accordance with Article 10. UFC Article 10 covers Fire-Protection Systems and Equipment. 1997 UFC 6313.5 Installation and Maintenance. Detection and alarm systems shall be installed and maintained as required for fire alarm systems in accordance with Article 10 and UFC Standards 10-2 and 10-4. Also see Section 6320. 1. UFC 6320 covers acceptance testing and periodic testing of detection and alarm systems "in accordance with the manufacturer's instructions and as required by the chief." 1997 UFC 6314.2 Electrical Electrical equipment and installations shaft comply with the Electrical Code. The refrigeration machinery room shaft not be required to be classified as a hazardous location for electrical equipment except as provided in the Mechanical Code and Article 63. 1997 UFC 6314.4 Emergency Control A clearly identified switch of the break-glass type providing off-only control of electrically energized equipment and devices within the refrigeration machinery room shaft be provided immediately adjacent to and outside of each refrigeration machinery room means of egress. In addition, emergency shutoff shall also be automatically activated when the concentration of refrigerant vapor exceeds 25 percent of the LFL. 1997 UFC 6311.4 Emergency Control of Ventilation Systems. Fans providing emergency purge ventilation for refrigerant escape shall have a clearly identified switch of the break-glass type providing on-only control immediately adjacent to and outside of each refrigerant machinery room means of egress. Purge fans shaft also respond automatically to the refrigerant concentration detection system set to activate the ventilation system at no more than 25 percent of the LFL or 50 percent of the IDLH or a measure equivalent thereto, whichever is less. An emergency purge control shaft be provided with a manual reset only. ANSI/ASHRAE Standard 1 5 - 1 9 9 4 Safety Code for Mechanical Refrigeration The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 15, Safety Code for Mechanical Refrigeration, addresses requirements for air monitoring within refrigeration rooms. This 1994 standard was current at the time of publication of this guide. ASHRAE 1 5-7.4.2, Rule 3 For refrigerating systems of 100 hp (74.6 Kw) or less, when the quantity of refrigerant in each system exceeds Table 1

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quantities, the rules for commercial occupancy shaft apply unless the following OCCUFS:

(d) Detectors (refrigerant, oxygen, etc.) are located in areas where refrigerant vapor from a leak will be concentrated so as to provide warning at a concentration not exceeding the refrigerant(s) TL V-TWA (detectors are not required for ammonia due to its self-alarming character);

Section 7.4.2 provides a means for refrigeration system designers to reduce some of their system requirements if a detection system is provided. ASHRAE 1 5-8.1 3.2 Each machinery room shaft contain a detector, located in an area where refrigerant from a leak will concentrate, which shaft actuate an alarm and mechanical ventilation in accordance with 8. 13.4 at a value not greater than the corresponding TL V-TWA (or toxicity measure consistent therewith). The wording of 8.13.2 applies to all refrigerants in all safety groups and to all refrigeration equipment rooms. ASHRAE 15-8.13.6 No open flames that use combustion air from the machinery room shaft be installed where any refrigerant is used. The use of matches, lighters, halide leak detectors, and similar devices shaft not be considered a violation of 8. 13. 6. Combustion equipment shaft not be installed in the same machinery room with refrigerant-containing equipment except under one of the following conditions: (b) A refrigerant vapor detector is employed to automatically shut down the combustion process in the event of refrigerant leakage. Section 8.13.6 is similar to Uniform Mechanical Code Section 1106.7, Exception 3, and to Uniform Fire Code Section 6310.7, Exception 3, and it allows boilers and chillers to be in the same room if a refrigerant detection system is provided and is interlocked with the combustion process. ASHRAE 1 5-8.14 Machinery Room, Special Requirements. In cases specified in the rules o f 7.4.2, a refrigerating machinery room shaft meet the following special requirements in addition to those in 8. 13: (h) When ammonia is used, the machinery room is not required to meet Class 1, Division 2 of the National Electrical Code providing (1) the mechanical ventilation system in the machinery room is run continuously and failure o f the mechanical ventilation system actuates an alarm or (2) the machinery room is equipped with a vapor detector that will automatically start the mechanical ventilation system and actuate an alarm at a detection level not to exceed 1,000 ppm.

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intemational Fire Code 2000 E(Btion Requirements Section 606.6 requires refrigerant detection and alarm systems to be tested. IFC 606.6 Testing of equipment. Refrigeration equipment and systems having a refrigerant circuit containing more than 220 pounds (100 kg) of Group A 1 or 30 pounds (14 kg) of any other group refrigerant shaft be subject to periodic testing in accordance with Section 606.6. 1. IFC 606.6.1 Periodic testing. The following emergency devices or systems shaft be periodically tested in accordance with the manufacturer's instructions and as required by the code official 9 4. Detection and alarm systems. Section 606.8 describes the detection system. IFC 606.8 Refrigerant detector. Machinery rooms shaft contain a refrigerant detector with an audible and visual alarm. The detector, or a sampling tube that draws air to the detector, shaft be located in an area where refrigerant from a leak will concentrate. The alarm shaft be actuated at a value not greater than the corresponding TL V- TWA values shown in the International Mechanical Code for the refrigerant classification. Detectors and alarms shaft be placed in approved locations.

Exception: Detectors are not required for ammonia systems where the machinery room complies with Section 1106.8 of the International Mechanical Code.

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Refrigeradon Sensors To put refrigerant leaks in refrigeration rooms into perspective, one pound of refrigerant will evaporate to occupy 3 to 4 cubic feet of volume at atmospheric pressure. This will provide a concentration of 100 ppm in a 3 0 , 0 0 0 to 4 0 , 0 0 0 cubic foot room. Refrigerant monitors are available using IR, CMOS (solid state) and catalytic technology. Catalytic sensors have traditionally been applied to detection of combustible hydrocarbon gases, but are not selective. Catalytic sensors have the following functional problems: Catalytic poisons (silicone, hydrides, lead, mercury, etc.) can coat the catalytic elements. Halogen compounds can etch the catalytic elements. Performance is affected in oxygen-depleted atmospheres Performance is affected by a constant hydrocarbon background concentration. Once the sensor has been exposed to high concentrations of hydrocarbon gases, it must clear before it can be used again. After a high dose, another sensor would have to be brought in to determine if the area was clear. This may delay bringing a facility back into operation after an incident. Performance of catalytic sensors is problematic after high pressure wash downs. Some cleaning solvents and paints or paint thinner may be an interferent to catalytic or solid state sensors. CMOS sensors are less expensive than IR technology, but are also sensitive to other halocarbons or volatile hydrocarbons that may be present in refrigeration rooms. Some cleaning solvents or paint thinners may cause CMOS sensors to alarm if a sufficient local concentration reaches a sensor. IR sensors can be highly selective. Some IR sensing systems use an extractive system to pull sampled air from sensing points through tubing to the sensor head. The same design and installation concerns discussed with respect to semiconductor facility use of extractive systems also apply in refrigeration rooms. Refrigerant sensors should be located where leaked fumes would potentially collect or be carried by air movement within the space. At least one sensor should be provided for each 2 0 , 0 0 0 to 4 0 , 0 0 0 cubic feet of refrigeration room volume, or one sensor point fewer than the total number of chillers. If fans in the refrigeration room run continuously, a sensor should be located downstream of potential leak sources.

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Refrigerants are heavier than air and tend to concentrate near the floor. Sensors should be located 1 8 to 24 inches above the floor and in depressions such as sumps near the potential leak sources. Sensors should be located away from roll-up doors or boiler blowdown discharge that could provide rapid changes in ambient conditions around the sensor. DetTronics PointWatch infrared hydrocarbon gas detector model PIR9400 and Thermal Gas Systems Haloguard IR are sensors suitable for this application.

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System Testing Requirements Life safety system testing is necessary to verify the system is functioning as needed and that the design meets the system requirements. Safety systems will fail and tests are required to find faults that would prevent the system from detecting dangerous conditions, responding with programmed equipment shutdowns, and initiating evacuation alarms. Life safety system acceptance testing is necessary to ascertain that the system is functioning as designed and as required by code at the time of transfer from the contractor to owner. Acceptance testing also substantiates that the system was functioning properly at the time the owner took possession and responsibility for the system. Records indicating successful completion of testing are also required by most authorities having jurisdiction. The Uniform Fire Code requires that alarm systems be maintained in an operable condition. It is not possible to determine if the detetion and alarm system is operating properly unless it is tested periodically. 1997 UFC 8001.4.7.1 Equipment, machinery and required detection and alarm systems associated with hazardous materials shaft be maintained in an operable condition . . . . Required detection and alarm systems shaft be replaced or repaired where defective. The OSHA, EPA, IEC and ISA standards all require testing and documentation of testing. OSHA 29 CFR 1910.119, Process Safety Management, requires employers to "establish maintenance systems for critical process related equipment including written procedures, employee training, appropriate inspections, and testing of such equipment to ensure ongoing mechanical integrity." This OSHA standard also requires that "inspection and testing procedures shall follow recognized and generally accepted good engineering practices." OSHA 29 CFR 1 910.1 65, Employee Alarm System, requires that "the employer shall assure that all supervised employee alarm systems are tested at least annually for reliability and adequacy." ISA S84.01-1996, Application of Safety Instrumented Systems for the Process Industries, contains several testing requirements including the following: S84.01 7.9.1 The design shaft allow for the testing of the overall system. It shaft be possible to test final element actuation in response to sensor operation.

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S84.01 9.7.2. The entire Safety Instrumented System shallbe testedincluding the sensor(s), the logic solver, and the final element(s) (e.g., shutdown valves, motors). ISA S91.01-1 995 Identification of Emergency Shutdown Systems that are Critical to Maintaining Safety in Process Industries includes the following requirement: S91.01 4.2.1 All emergency shutdown systems and safety critical controls shaft be periodically tested and maintained in accordance with user system test procedures taking into account system manufacturer recommendations. ISA S84.01 is an internationally-accepted standard that has also been adopted as an ANSI standard; it couldtherefore be interpreted as being an OSHA requirement.

Regarding Fire Alarm Emergency Voice Alarm Testing The National Fire Alarm Code (NFPA 72) Chapter 7-3 requires that fire alarm emergency voice alarm communications equipment be tested at least semiannually. If fire alarm voice alarm communications equipment is utilized for broadcasting hazardous gas alarms, it must be tested in accordance with NFPA 72.

Regarding Testing Procedures Most codes do not dictate how gas detection systems shall be tested. methods required by fire alarm codes could be used as a guide.

Testing

SBBCI-SFPC F-501.3 All fire protection systems shaft be tested in accordance with the requirements of this code and the building code listed in Chapter 44. The tests shaft be conducted by the owner or an authorized representative thereof and in the presence of the code official All tests required by this code and the standards referenced in this code shaft be conducted at the expense of the owner or the owner's representative. NFPA 72 contains an entire section regarding testing of fire alarm systems. These testing requirements could be used as a general guide for hazardous gas monitoring and alarm system testing. NFPA 72 7-1.2 The owner or owner's designated representative shaft be responsible for inspection, testing, and maintenance of the system and alterations or additions to this system. The delegation of responsibility shaft be in writing, with a copy of such delegation made available to the authority ha ving jurisdiction. NFPA 72 7-1.6.1 Initial Acceptance Testing. All new systems shaft be inspected and tested in accordance with the requirements of this chapter.

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NFPA 72 7-1.6.2.1 Reacceptance testing shall be performed after system components are added or deleted; after any modification, repair, or adjustment to system hardware or wiring; or after any change to software. All components, circuits, systems operations, or site-specific software functions known to be affected by the change or identified by a means that indicates the system operation changes shaft be 100 percent tested. In addition, 10 percent of initiating devices that are not directly affected by the change, up to a maximum of 50 devices, also shaft be tested and proper system operation shaft be verified. A revised record of completion in accordance with 1-7.2. 1 shaft be prepared to reflect any changes. NFPA 72 1-7.2.1 A record of completion (see Figure 1-7.2. 1) shallbe prepared for each system . . . . A preliminary copy of the record of completion shaft be given to the system owner and, where requested, to other authorities having jurisdiction after completion of the installation wiring tests, and a final copy shaft be provided after completion of the operational acceptance tests.

Testing. Testing shaft be performed in accordance with the schedules in this chapter or more frequently where required by the authority ha ving jurisdiction. Exception: Devices or equipment that is inaccessible for safety considerations (e.g., continuous process operations, energized electrical equipment, radiation, excessive height) shaft be tested during scheduled shutdowns where approved by the authority having jurisdiction but not more than every 18 months. NFPA 72 7-3.2

Regarding Testing Documentation NFPA 72 Table 7-3.1 Visual Inspection Frequencies and Table 7-3.2 Testing Frequencies both indicate that during initial acceptance testing, all functions and devices are required to be tested. NFPA 72 7-5.2.2 A permanent record of all inspections, testing, and maintenance shaft be provided that includes the following information of periodic tests and all the applicable information requested in Figure 7-5.2.2 (a) Date; (b) Test frequencw (g) Designation of the detector(s) tested; (h) Functional test of detector; (i) Functional test of required sequence of operations; Other tests as required by equipment manufacturers; (0 (m) Other tests as required by the authority having jurisdiction; (n) Signatures of tester and approved authority representative; NFPA Section 7-5.2.2 outlines the documentation required for fire alarm tests. detection system l~esting should follow a similar format.

Gas

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ISA S84.01 Section 9.8.1 states "A description of all tests performed shall be documented. The user shall maintain records to certify that tests and inspections have been performed." Having the tester, the approved authority representative, and an owner's representative sign the test report form alleviates questions as to what was tested and who witnessed the test. Sufficient records should be maintained to allow an independent audit in case of an accident. After acceptance tests are completed, an owner's representative should sign a release of liability indicating that the system has been tested and is in proper working order. Operator training should also be documented. As part of project completion, operations and maintenance manuals should indicate recommended and code-required testing frequencies and methods. Substantial time is required for proper testing and liability transfer. Sensor recalibration is discussed in Chapter 4 of this guide. A protocol for testing gas detection sensors, developed by Zellweger Analytics, is included for reference as Appendix B of this guide.

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Hazardous Gas Monitoring Sensors

The number of gases used in the semiconductor industry make the detection of hazardous gases a complex problem. No single type of sensor will monitor all of the different gases most effectively, and most gas sensors are not 100 percent selective to a single gas. Hazardous gas detection includes monitoring for toxic, highly toxic, flammable, combustible, pyrophoric, reactive, and corrosive or oxidizing gases, as well as some cryogenic and refrigeration gases. Gases such as toxics are normally monitored in the ppm or ppb range, while other gases such as combustibles are associated with high concentrations in the percent lower explosive limit (LEL) range. Many gases are both toxic and combustible. Often, bottles of compressed gas are very diluted mixtures in a carrier gas. For example, a 200-ppm mixture of diborane is mixed with hydrogen. Locations fed by this gas bottle could be monitored for both hydrogen and diborane. Alternatively, the gas with the more stringent criteria LEL or PEL could be monitored. An alarm would indicate the presence of both gases.

Selection Criteria Not only are there many different sensor technologies currently available, but new products continually enter the rapidly-changing field. No single technology will work reliably for all gases used in a typical fabrication facility. Semiconductor Equipment and Materials International (SEMI) Standard 2 705, Safety Guidelines for the Selection of Toxic and Flammable Gas Detection Instruments, addresses gas sensing system selection criteria. As a minimum, the following criteria should be considered in the selection of sensor technology for each specific application. Monitored Gases In addition to target gases, also consider all possible interferents, byproducts, and gases that may be formed as the result of leaked gas reaction with ambient or process air. The designer should work closely with the process engineers and tool suppliers to identify all monitoring requirements.

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Sensor Suitability Consider the sensor monitoring location and environment. Sensor resistance to temperature, humidity, RF interference, etc., should be evaluated carefully. Some sensors may have physical constraints which limit their location or mounting.

Sensor Sensitivity Sensivity refers to the sensor's capability to consistently detect a specific gas concentration. Combustible gas sensors are designed to detect gases at the lower flammable limit (LFL). Other sensors may be designed to detect gas concentrations around the permissible exposure level (PEL), which may be in the parts per billion. Sensors will not function properly if exposed to gas concentrations outside their designed sensitivity range. Electrochemical sensors exposed to concentrations more than 10 to 20 times their designed operating range can become saturated and inoperative (poisoned) for a long time period. Choice of the appropriate concentration range to be monitored is very important. Monitoring gases for worker protection typically requires a full scale range of 0.25 to 10 times the PEL of the gas. The PEL for a gas is defined as a safe level which workers can be exposed to for the entire work day. Thus, it is wise to choose a full scale range which is higher than the PEL to enable setting alarm points at concentration ranges above the PEL. For combustible monitoring, a range of 2 percent to 100 percent LEL is typically chosen.

Sensor Selecdvity Sensor selectivity (as opposed to cross-sensitivity) relates to the ability of the sensor to differentiate between various gases. Sensor manufacturers can provide data for each sensor indicating the concentration of an interference gas that is required to create a sensor response equivalent to the response obtained from a given concentration of the target gas. This is an important criterion for a sensor that is cross-sensitive to other gases that may be in the same area. Sensor Stability How a sensor's response varies with time (weeks or months) is characterized in terms of zero drift and span drift. Zero drift relates to a sensor's response over time with no (hence zero) target gas present. Less than 10 percent drift per year during continuous operation is acceptable zero drift. Span drift refers to degradation of sensor output over time with respect to a continuous, constant concentration of target gas. Acceptable span drift over a one-year period is plus or minus 20 percent.

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Sensor Recalibradon Time Time between recalibration or maintenance also relates to sensor life. Some sensor technology requires frequent calibrations. Some sensor cells must be refilled with electrolyte and recalibrated periodically, while other sensors are factory sealed. Some sensing systems require maintenance of moving parts such as air pumps, moving valves, etc. Maintenance that takes the system off-line is a costly interruption of production.

Sensor Ease of Recalibration The recalibration or testing process should be easily accomplished to minimize costly production downtime. For sensors requiring several hours to regain sensitivity after refilling with electrolyte, the facility should keep a spare set of sensor cells for rotation into use while the originals are refilled or recalibrated. Consider whether recalibration takes special skills that might not be readily available. Also consider whether the integrity of the system can be properly maintained by the facility's personnel. Documentation of proper training of facility personnel to maintain or recalibrate a gas detection system is necessary. For efficiency, liability abatement and safety, it may be advisable to purchase factory-calibrated replacement parts.

Sensor Response Time Sensor response time is the time between the sensor's exposure to a gas and generation of an alarm signal. Sensor response time is proportional to the concentration of gas. For extractive systems that draw air samples through tubing to a remote sensor, response time also includes the time for air to move through the tube from the sensing location to the sensor. A fast response time is important not only for safety, but also to minimize costly contamination of the work place.

Sensor Poisoning Sensor poisoning refers to sensor saturation from exposure to high concentrations of either the target gas or an interferent. Once exposed to high levels of gas, the sensor loses its sensitivity until it recovers in a clean atmosphere. Recovery time is proportional to the gas concentration exposure: the higher the concentration, the longer the recovery time.

Sensor Useful Life Evaluate how long a sensor system will provide useful service. Some systems contain sensor cells that must be replaced or refilled with electrolyte every six months. Welldesigned systems allow replacement of only the part with a limited life.

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Sensor Diagnostic Features Sensors or sensor controllers should contain diagnostics that monitor sensor presence and performance. For example, both Scott/Bacharach and EcoSys MST sensor controllers test for an electrical connection between the sensor and the controller. If the signal ceases, a "missing sensor" alarm is generated. Scott/Bacharach controllers test and display the amount of gain applied to the sensor when it is calibrated and use this information to predict sensor life. During calibration, Ecosys MST's Satellite controllers calculate a self-test signal to duplicate the sensor response during calibration. This self-test signal is then generated once every 24 hours and compared to sensor response. If self-test response is below the configuration output by the programmed threshold amount, a warning alarm is generated. Extractive sampling systems should monitor the air pump or venturi mechanism as well as the gas sensors.

Sensor Susceptibility to RFIIEMI Some gas sensors are susceptible to interference from radio frequency and magnetic fields. Sensors and cables connecting sensors to controllers or other monitoring equipment handle signals of very low magnitude. Especially at the low end of the sensor's sensitivity scale, the signal-to-noise ratio is very low and electromagnetic interference (EMI) or radio frequency interference (RFI) can cause false alarms if sensors, controllers and cables are not shielded. Many users report gas alarms triggered by use of hand-held radios. Some process equipment also generates RFI and EMI. The European Union (an economic collaboration of European countries) has developed an Electromagnetic Compatibility (EMC) Directive that sets standards for shielding of components and systems from RFI and EMI. The EMC Directive addresses t w o levels of shielding, light industrial and heavy industrial. Testing of components or systems for compliance to the EMC Directive is completed by their manufacturers on the honor system. It is important to note that even if components meet the EMC Directive, an interconnected system may not. Sensors and controllers can be shielded by using grounded, conductive enclosures. Interconnecting cabling should always be shielded and enclosed in metallic raceway. Equipment built for the European market should be CE Marked to indicate that it is EMC compliant.

Total Cost of Ownership (TCO) The total cost of ownership (TCO) is an important criterion in selecting a sensor system or technology. In addition to first purchase cost, carefully consider the cost of expendable parts, maintenance replacements, integration with other systems, expandability, and downtime due to maintenance and false-alarms. A TCO evaluation of sensor systems should also compare response and repeatability.

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Sensor Types Manufacturers

Mergers and acquisitions over the last year have brought new names to the industry. TeloSense has been acquired by Advanced Technology Materials, Inc. (ATMI) under their Ecosys Division. They are now referred to in the text as Ecosys TeloSense and can be found in Appendix D under TeloSense Ecosys. MST has also been acquired by ATMI's Ecosys Division and are referred to in the text as Ecosys MST and can be found in Appendix D under MST Ecosys.

EIT has been acquired by Scott/Bacharach and is now referred to in the text as Scott/Bacharach and can be found in Appendix D under Scott/Bacharach. Due to the rapidly developing nature of the industry, expect continued change in the future.

Bectrochemical Sensors

A typical electrochemical sensor consists of a sensing electrode, a counter electrode and a reference electrode separated by a thin layer of electrolyte. Gas which comes in contact with the sensor first passes through a diffusion barrier which is designed to limit the amount of gas entering the sensor. Gas diffusing through the barrier reacts at the surface of the sensing electrode by either oxidation or reduction. Reactions are catalyzed by electrode materials specifically developed for the gas of interest. Gas selectivity is achieved through the choice of the electrode material, electrolyte, operating voltage and through selective filtration. Sensor design and features vary from manufacturer to manufacturer. Some of the generalizations in this guide may not apply to all manufacturer's products. Electrochemical sensors are available for the detection of approximately 15 to 20 gases. Other electrochemical sensors detect a family of gases, such as hydrides (arsine, phosphine, silane, diborane). Refer to the "Other Sensor Considerations" section in this Chapter for a discussion regarding monitoring for many gases by detecting products of reaction with air. Electrochemical sensor response is relatively quick and monitoring is continuous. Extractive sensing systems that sample several areas sequentially by drawing air samples through a tube to a centrally located analyzer could potentially take longer to sense a leak. First cost is comparatively less than other systems and electrochemical sensors have no moving parts to maintain. Draeger Safety's Polytron 2 system features remote transmitters with EEPROM memory that stores all sensor-specific information including type of sensor, production

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date, zero value, sensitivity and the last calibration date. Integrated self-test functions continuously monitor the sensor for quality and useful life. The same remote transmitter can be used with 15 different sensors. Ecosys MST offers similar systems. Some sensors respond to interferent gases as well as to the target gas they are designed to measure. Such sensors should not be used in areas where interferents could be present. In many applications, such as gas cabinets, this is not an issue because interferents are not present. Filters are available to block some interferents and careful positioning of gas sensors during design and installation can also prevent interference problems. Sensor manufacturers can provide information on interferents for specific sensors. Some sensor electrolytes are affected by hydrogen. Many electrochemical sensor electrolyte fluids are affected by isopropyl alcohol (IPA) which is commonly used for cleaning. Such cross-sensitivities can make it difficult to determine the cause of an alarm. Electrochemical sensors can also be contaminated by other chemicals requiring replacement of the sensor. Ecosys MST and Zellweger Analytics recommend installation of charcoal filters with some of their electrochemical sensors to mitigate interference from IPA. Electrochemical sensors tend to lose sensitivity quickly in a chlorine or hydrogen chloride environment and, therefore, need to be checked periodically for proper operation. Electrochemical sensors for detecting methyl fluoride (CH3F), a relatively new gas to the semiconductor industry, can only take 4 to 5 hits before they are poisoned and require replacement. When methyl fluoride is heated in a pyrolyzer, it is reduced to hydrogen fluoride (HF). Using a sampling system consisting of an extractive pump to pull a sample through a pyrolyzer and then sensing for hydrogen fluoride is an alternative method to sense for low levels (1,000 ppm or less) of methyl fluoride. This system adds the cost of an extractive pump and pyrolyzer to the electrochemical cell, but has a longer life than a simple electrochemical cell sensing for methyl fluoride. Ecosys MST and RKI Instruments make a similar extraction pump with pyrolyzer system for use in detecting nitrogen trifluoride (NF3). Electrochemical sensors require periodic recalibration. Electrolyte fluids have a finite life span. Some fluids have to be replaced every 3 to 6 months. Some sensors are sealed and are not refillable. After changing the fluid, the cell has to come to an equilibrium by passing gas through it. After reaching equilibrium, the sensor must be calibrated prior to use. Ecosys MST's approach to sensor maintenance is to provide new sensor cells every 6 months. Sensor electrolytes are generally hygroscopic, meaning the amount of water in the electrolyte tends to reach equilibrium with that in the surrounding air. Because water is a key part of the electrochemical reaction, in very dry (and very hot) areas sensor lifetime will be diminished. Similarly, in environments with very high continuous

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relative humidity (monitoring wet scrubber discharge) sensors will have a shortened life. Electrochemical sensors should not be used in areas prone to sudden changes in humidity. Dramatic sensor output changes can be expected under such conditions. Because of the effect humidity has on electrochemical cells, calibration gas should be humidified to the same percentage as the area being monitored by the sensor. Rapid air flow past a sensor cell can change gas diffusion characteristics, which can affect sensor performance. In addition, high air velocities can reduce sensor lifetime by drying out the sensor more rapidly. These types of applications should be reviewed with the sensor manufacturer. Some manufacturers have developed new sensors for high air flow applications. RKI Instruments, a sensor manufacturer popular in Japan, recommends using an extractive pump (sample draw system) to pull samples from high velocity exhaust systems to a sensor in a separate enclosure. RKI contends this method provides better sampling, repeatability and longer life for the sensors. Scott/Bacharach offers a perforated shield or cap that prevents air from directly hitting the sensor face. Response time for electrochemical sensors is a logarithmic function. The first molecules of gas to diffuse through the membrane cause a very rapid change in response. As the sensor's output approaches the actual ambient gas concentration, the rate of change of response slowly decreases. The inverse of the response curve determines a sensor's recovery time after being exposed to gas. Exposures to high concentrations require a long recovery time. After leaks are repaired, time is required for all gas to leave the cell to allow it to reset. The affected tool usually cannot be reactivated and the fab repopulated until the gas detection system is in operation, i.e., the local sensor has recovered and the system reset. Electrochemical sensors should not be exposed to high concentrations of target gas for long time periods as their useful life will be dramatically reduced. Some electrochemical sensors require a fixed bias to be maintained across the sensor electrodes. This bias is one of the key determinants of sensor performance. After the bias is applied, the electrolyte typically requires time to reach equilibrium. For some electrochemical sensors this warm-up period is 4 to 8 hours. Some manufacturers (Scott/Bacharach 4600 Series) offer sensors with an integral battery to maintain bias. Ecosys MST, Scott/Bacharach and Draeger can provide a battery-powered "burn-in box" to apply bias and warm up a sensor. After reaching equilibrium, the sensor head can be transferred from the burn-in box to the controller in the field. This system can be warmed up and calibrated in a maintenance area and then transferred to the cleanroom while the battery maintains bias. Regular maintenance, calibration, and spares represent the majority of cost for electrochemical sensors over the lifetime of a facility.

Gas Membrane Galvanic Cell. These sensors are a type of electrochemical sensor that consists of t w o different electrodes, an internal electrolyte and a gas-permeable hydrophobic membrane. The selection of membrane media and electrodes determines

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the sensitivity of the cell to different gases. When a gas permeates the membrane, oxidation-reduction reactions take place on the working and counter electrodes creating an electric current through the electrodes in accordance with Faraday's law. This electrochemical process is designated amperometry and differs from most other sensor cells that require an externally-applied current. A thermistor can be provided to compensate for ambient temperature fluctuations. This cell type has high sensitivity, quick response and recovery, and is resistant to poisoning. It is also unaffected by high humidity, allowing installation in wet scrubber discharge. Bionics Instrument Company uses this technology for ammonia, hydrogen chloride, hydrogen fluoride, diborane, silane and disilane. Generally, this type of acid-gas sensor is not specific to a single gas, but responds to many acid gases including hydrogen chloride and hydrogen fluoride. This sensor can be applied to the detection of hydrides such as diborane, silane, and disilane, but will respond to all hydrogen compounds as well. This technology does provide a very specific hydrogen sensor that can operate in an oxygen-free environment, and which does not respond to other hydrocarbons which is a common problem with catalytic bead sensors.

Catalytic Bead Sensors A catalytic bead sensor consists of an active element and a reference element. Each element consists of an oxidizing metal dispersed on a porous ceramic substrate. At the core of each of the elements is a heated platinum coil whose resistance varies with temperature. In the presence of gas below the upper flammable limit (UFL), the active element will oxidize the gas on its surface thereby raising the temperature of its platinum coil. Oxidation can be enhanced by providing a catalytic coating on the sensing element surface and by operating the sensor at an elevated temperature. The reference element has negligible response to all gases, but compensates for effects of changes in ambient temperature and humidity. The differential created in the resistances of the two elements acts to produce a signal proportional to the gas concentration. Catalytic sensors must be used in environments containing oxygen because they operate on the combustion principle. For most combustible gases, an oxygen level of at least 15 percent is sufficient. Catalytic bead sensors require periodic calibration. Calibration interval varies with the application and environment, but once a month is typical. Catalytic bead sensors are typically used for flammable gas detection where toxicity is of no concern. They are nonspecific, respond to a wide variety of combustibles, and only respond well to higher gas concentrations from 1,000 ppm up to percent LEL levels. At exposures above the LEL, the high current passing through the coils can result in weak points that could eventually open the circuit. This sensor type has fast response, excellent repeatability, high accuracy, and resistance to temperature and humidity variations. Once this sensor is exposed to the upper flammable limit (UFL), it will no longer function properly because the gas will no longer combust in air. This will lead to a

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negative reading from the sensor which can provide erroneous results. This is especially a problem for sensors located in confined spaces where concentrations can reach the UFL. When using catalytic sensors, the oxygen content in that area must also be monitored. Some sensor systems will contain a catalytic bead sensor in combination with an oxygen sensor (and sometimes a carbon monoxide or hydrogen sulfide sensor). If the oxygen sensor detects concentrations outside acceptable limits, this indicates that the catalytic sensor will not operate correctly. Catalytic sensors are also subject to poisoning by silicones, chlorinated or fluorinated hydrocarbons, lead, chlorine, sulfur, hydrides and methyl fluoride. This leads to a short life for the detector, even as short as a few weeks in certain applications. These poisoning substances are found in many applications and the problems of catalyst poisoning are increasing. Newer sensors are available that are more resistant to poisoning. Sensor poisoning is only detectable by calibrating the sensor. If poisoning is suspected, frequent calibration is recommended. Selection criteria for sensors should include a review of gases in the area that could poison sensors. Catalytic sensors can be affected by corrosion which mechanically breaks down sensor structure. The attacking chemical can be either the component of interest (e.g., ammonia) or a combustion byproduct such as fluoride derived from halogenated hydrocarbons. This corrosion can cause a baseline drift indicating increased resistance in the circuitry. Once the baseline correction has been made by calibration, the sensor should operate properly. Molecular sieves can be provided that significantly reduce response to selected gases. RKI offers a catalytic sensor with molecular sieve for specific hydrogen detection. Solid State Sensors Solid state sensors (also called metal oxide semiconductor sensors) consist of t w o electrodes embedded into a solid state metal oxide material. The presence of target gas changes the resistance of the material by displacing the oxygen in the metal oxide, with the magnitude of change indicating the gas concentration. The resistance change is measured through the sensor's circuitry. Oxygen is required for the solid state sensor to operate properly. The specific operating temperature of the sensor is maintained by applying a heater voltage. The magnitude of heater voltage is critical in determining the response characteristics of the sensor. By varying this voltage and by using different materials and processing techniques, sensors can be made which are more sensitive to one gas or group of gases and less sensitive to others. Sensor signal output is non-linear (logarithmic) and inversely proportional to the target gas concentration. In general, solid state sensors are not as specific as other available technologies. Some manufacturers provide membrane filters to improve selectivity. Changes in humidity, temperature and oxygen concentration affect performance.

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Solid state sensors are available to detect more than 1 50 toxic gases and can detect combustible gases in concentrations as low as several ppm or as high as 100 percent LEL, they have long life expectancies, are not generally subject to poisoning, are quite rugged, have no moving parts, and are relatively inexpensive. Depending on the application, calibration intervals range from 1 to 6 months. Calibration compensates for a drifting zero point. Solid state sensors would be applicable in a research laboratory where specificity is not of concern and where regular maintenance and recalibration is unreliable. Solid state sensors used for chlorine or hydrogen chloride tend to be sensitive and sometimes have problems with false alarms. Solid state sensors are generally not selective enough for hydride gas applications. In typical applications, there are many chemicals in the area (including members of the alcohol family) that will cause the solid state sensor to go into alarm. Sensor manufacturers can provide cross-sensitivity data for each sensor. Certain types of solid state sensors that are not exposed to the target gas for an extended period of time may oxidize and "go to sleep," resulting in a lack of response to leaks. Solid state sensor calibration is more difficult and time consuming than calibration of electrochemical sensors because the sensor output is not linear. Molecular sieve coatings on the sensing element can reduce response to some gases, thereby producing a more specific sensor. Solid state and electrochemical sensors require sensor controllers to operate the sensor and integrate the sensor's signal into a usable format. The controller is usually mounted close to the sensor to facilitate calibration and testing. Controllers typically have alarm output contacts, sensor controller failure alarm contacts, as well as a 4 to 20 milliamp analog signal. The analog signal can be monitored for data logging purposes. Some sensor/controller manufacturers can provide serial interface with programmable logic controllers (PLC) such as Modbus protocol. Considerations for sensor controller locations include accessibility for calibration, protection from tampering, Class I, Division 1 (explosion-proof) requirements, and protection from the elements.

Quartz Crystal Microbalance Sensors This device, developed by the EcoSys Monitoring Systems Division of ATMI, Inc., is based on the use of a quartz crystal microbalance (QCMB) coated with gas-speciesselective thin films. Similar quartz oscillators are commonly found in wristwatches and radios. When a piezoelectric material is exposed to an oscillating electric field, the material will vibrate mechanically. An oscillator circuit, incorporating feedback control, is used to drive the crystal at a stable, resonant frequency. The resonance frequency of the quartz oscillator depends primarily on the mass of the crystal.

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Thin film coatings of gas-selective adsorbents are deposited onto the surface of the QCMB. As gases flow over the surface, target gases chemisorb onto the thin film. The change in mass of the crystal will be mirrored by a measurable frequency shift. The frequency shift can be directly correlated to the concentration of an absorbent in the gas stream. The sensor manufacturer has incorporated a reference crystal into the device to provide t w o functions. Primarily, it operates as a hygrometer to correct for any ambient changes in relative humidity. It also compensates for other potential interferences such as particles or vapor phase contaminants (e.g., IPA or diesel fumes). This technology detects hydrides and acid gases as low as 25 percent of TLV/TWA and is capable of responding to TLV levels of these gases in less than 30 seconds. This sensor does not differentiate between individual gases within a gas family, it simply detects a specific gas family. By incorporating multiple crystal arrays, a sensor system can detect and differentiate between acid gases (including diatomic halides) and hydrides. Eco-Sys has also developed a hydrogen-selective QCMB capable of detecting hydrogen in either an ambient or inert atmosphere from 10 to 100 percent of LEL. The QCMB sensor is used in an extractive sampling system. The on-board sample pump has sufficient draw to overcome exhaust system negative pressures. Recommended maximum sampling tubing length is 30 feet. Sample pump power is monitored to ensure operation. Should a sample point be blocked, the pump will exhibit increased power consumption. If a sample tube has been breached, the pump's power requirement will diminish. The system is microprocessor controlled and incorporates discrete contacts, analog channels and digital network connectivity. Self-diagnostics continually insure that the sampling train is not breached, that communications channels are functioning, that the crystal coatings remain reactive, and that the microprocessor is operational. An RS485 communications port allows the user to monitor nearly any operations parameter, to configure for target gas and warn/alarm settings, to clear alarms and to place the sensor into maintenance mode (i.e., disables alarm contacts). ATMI advises that the QCMB sensor has a six-month lifetime, but does recommend replacement if it is exposed to a high concentration of target gas. The QCMB sensor requires no field calibration.

Draeger Tube Sensors A gas sample is drawn into a tube where it reacts with chemicals. If a hazardous gas is present, the chemical will change color. This system is only useful for portable testing and emergency response, not for continuous monitoring. Portable testers are valuable in finding the source of the leak because they can be moved throughout the space.

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Ionizadon Sensors Flame-ionization and photo-ionization sensors are generally used to detect flammable gas, although some toxics (volatile organics and arsine and phosphine) will work with this technology. Ionization sensors can also be used to detect products of combustion from silane flames. When TEOS or TEOA is drawn through a pyrolyzer, it will create Si02 particulates which can be detected by an ionization sensor.

Extractive Sensing Systems Extractive sampling gas monitoring systems (commonly called sample draw) use air pumps or venturi-driven systems to draw air samples through tubing from the sampling location to a remote-mounted sensor. Extractive systems are useful when the sampling location is not readily accessible for sensor recalibration and maintenance or when an active sampling technique is preferred. The sensor cell or system can be located where it is easily accessible with tubing running to the desired sampling location. Some manufacturers, such as Ecosys MST and Zellweger Analytics, offer single-point extractive sampling systems incorporating either a venturi or a small air pump with a sensor cell or Chemcassette detector. Extractive sampling is also used with centralized sensor technologies such as Chemcassette-based systems (Zeilweger Analytics System 1 6 and CM4), FTIR (Ecosys TeloSense ACM), molecular emission spectrometry (Ecosys TeloSense TGM), and acoustic (Ecosys TeloSense H2M). With these systems, a central sensing console monitors from 4 to 40 separate points through tubing. Sensing systems incorporating pyrolyzers use extractive air pumps to draw air samples through the pyrolyzer where it is heated to facilitate chemical reactions which produce reaction byproducts that are more easily monitored. A few gases which are generally inert will not readily react with moisture in the air at ambient temperatures and require a heat source to produce the desired byproducts. An example of a gas which is more easily detected through pyrolysis is nitrogen trifluoride (NF~). Extractive sampling systems used to monitor exhaust ducts must be well positioned to avoid turbulent air flows that can dry out many cells. By controlling the flow rate, the drying effect can be reduced, but the flow rate must be sufficient to pull against vacuum in the monitored exhaust duct and cause a sensing system response. If extractive sampling systems are not designed and installed following some simple rules, they can be applied incorrectly and may not function properly. If the incorrect sampling tubing material or size is used, some gases can be adsorbed by the walls of the tubing material during transport from the monitoring location to the sensor. Potential sample adsorption is increased by longer tubing lengths which provide more surface area for adsorption. Sample flow through the tubing that is neither turbulent or laminar can minimize the amount of inner tubing wall in contact with the sample. Ecosys TeloSense controls flow rate with port orifices, while Zellweger uses a flow

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balancing technique. Ecosys TeloSense recommends 1/4-inch I.D. tubing, while Zellweger uses a 1/8-inch I.D. Tubing fitting materials exposed to gas samples should also be selected considering potential chemical interactions that could affect sensing system readings. Sensor manufacturers recommend different tubing types and maximum lengths for their various products. Studies performed by Ecosys TeloSense, Zellweger Analytics and PureAire/Bionics have determined that various tubing materials have differing adsorption characteristics relative to individual gases. The PureAire/Bionics tests investigated the percentage of sample loss for CI2, HCI and HF that occurred with three different types of Teflon tubing (PTFE, PCTFE and PFA). The tests indicate that PTFE had no sample loss for chlorine, but had significant loss for HCI and HF. PCTFE appears to be best suited for use with HCI although there was some sample loss (5 percent) regardless of sample line length. The PFA tubing adsorbed 100 percent of the HCI sample. The tests also indicated that tubing length is a big factor in the amount of sample loss. Zellweger Analytics has performed more extensive tests using the FEP Teflon tubing they supply with their systems and have determined adsorption with that tubing material is in a 0 to 10 percent range. In tests at user sites and at their factory using the 100 percent polypropylene tubing they supply with their systems, Ecosys TeloSense has found negligible adsorption for the gases their equipment is recommended to detect, in some cases, Ecosys TeioSense does recommend the use of FEP Teflon tubing. RK! Instruments recommends PTFE Teflon tubing for use in their extractive sampling systems. RKI provides a table that recommends maximum sampling tubing lengths for the following gases: HCI, HF, SiH2CI2, DCS, BCI3, POCI3, CIF3, WF 6, BF3, NH3 BCI2, HBr, F2, TEOS, NF3 Sill 4, PH3, AsH3

5 Meters 10 Meters 30 Meters

These tests indicate that tubing diameter, material and length must be considered when using extractive sampling systems. Extractive tubing material and layout should be discussed with the gas sensing system manufacturer. Gases with potential adsorptive problems include boron trichloride, boron trifluoride, fluorine, hydrogen bromide, hydrogen fluoride and tungsten hexafluoride. Some manufacturers of extractive sampling systems recommend that filters be placed on the tubing at the sampling location to keep particulates out of the sensing system. This is especially important for vacuum pump enclosures that may contain oil mist.

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Paper Tape Sensors The most widely used paper tape sensing system is manufactured by MDA/Zellweger Analytics. In this system, air containing hazardous gas reacts with a paper tape impregnated with a specially formulated chemical to produce a colored stain. The intensity of the stain is proportional to the gas concentration. An electro-optical detection system measures reflectance off the tape. The rate of change of reflectance measures changes in gas concentrations. Air samples from the fab are drawn through Teflon tubes to the analyzer where chemically-treated tape is exposed to the air sample. If no color change occurs after a period of time, the tape advances to a new position. The tape must advance because it dries out by being exposed to the air sample. If a gas is detected and the tape becomes discolored, the signal is converted to a digital format, matched to the gas response curve stored in the machine's permanent memory, and documented as the actual concentration value. When concentrations exceed programmed alarm levels, the date, time, and concentration are printed out in hard copy format. Alarm relay contacts are provided for each monitored point as well as an RS-422 or RS-485 interface (depending on the model). The Zellweger Analytics standard monitoring system provides pressure sensors that can sense gross changes in pressure indicating a possible kink or break in the sampling tubing. A Sample Line Integrity Option provides a check valve at the end of the sensing tubing. At programmed intervals, sampling will cease, and the line is pressurized and monitored to determine if there are any small holes in the sample tubing. Zellweger Analytics calls the module containing the paper tape a Chemcassette. Chemcassette tapes are formulated to react only to the target gas family; they will not react to other gases or substances such as solvents or hydrocarbons. Chemcassette systems detect hydrides, mineral acids, chlorine, nitrogen trifluoride and ammonia. Each gas family requires a different chemically-treated tape and each gas causes different color spots. A hydrides or mineral acids Chemcassette can be programmed to respond to a specific gas within that gas family. The mineral acids Chemcassette is formulated for sensitivity and specificity to the following mineral acids: hydrogen fluoride hydrogen chloride hydrogen bromide hydrogen iodide nitric acid phosphoric acid

HF HCI HBr HI HN03 H3PO4

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Gases or vapors which react with ambient moisture to form acids are also detectable with the mineral acids Chemcassette. Refer to the Other Sensor Considerations section for a list of gases that hydrolyze to form byproducts that can be more easily monitored. The mineral acids Chemcassette will not respond to ammonia, arsine, carbon tetrachloride, chlorine, diborane, phosgene, phosphine, silane or hydrogen. The hydrogen chloride (HCI) Chemcassette is formulated for sensitivity and specificity to hydrogen chloride. Other compounds which form hydrogen chloride upon contact with ambient air containing moisture can also be detected using the hydrogen chloride Chemcassette. Refer to the list of gases that hydrolyze in the Other Sensor Considerations section in Chapter 4. Hydrogen peroxide (H202) is a possible interferent to the hydrogen chloride chemcassette. Because it forms a greenish-yellow stain color instead of the typical blue color at ppm levels, it can be distinguished from hydrogen chloride. Hydrogen fluoride in ppm concentrations has a bleaching effect on the hydrogen chloride chemcassette, resulting in no concentration readings. High humidity levels (> 70 percent) also have a bleaching effect. The hydrides Chemcassette will respond to the following gases: arsine phosphine diborane silane germane disilane hydrogen selenide hydrogen sulfide dichl or osila ne trichlorosilane hydrogen bromide

AsH 3 PH3 B2H6 Sill4 GeH4 Sill 6 H2Se H2S Si H2CI2 SiHCI3 HBr

Zellweger Analytics uses a Luft IR Analyzer to detect nitrogen trifluoride (NF3), carbon monoxide (CO) and carbon dioxide (CO2). This analyzer consists of two cells and a membrane separated gas-filled detector. Infrared energy is pulsed by a rotating shutter and is divided equally between a sample cell and a reference cell. The air sample passes through the sample cell. If the target gas is present, infrared energy is absorbed and less energy reaches the sample side of the gas-filled detector than on the reference side. The membrane dividing the detector will then move since its two sides are unequally heated. A capacitance circuit on either side of the membrane detects this movement and quantifies the gas level. Zellweger Analytics has also developed a pyrolyzer that heats air samples prior to exposing to the Chemcassette tape which can be used to detect nitrogen trifluoride.

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It takes time to cycle through each sampling point. The 2000 International Fire Code and some local toxic gas ordinances (TGOs) limit time between samples for the same point to 30 minutes in order to meet the definition of "continuous" monitoring. Other jurisdictions require a monitoring cycle of once every 5 minutes or less to meet the definition of continuous monitoring. Depending on the gases monitored, the older Zellweger Analytics System 16s may not be able to cycle through all 16 points in five minutes. Zellweger analyzation of silane requires 30 seconds per point and germane requires 4 minutes. Drawing air samples through long lengths of tubing also requires time. It takes approximately 24 seconds for a Zellweger unit to draw an air sample through 100 meters of tubing. The Zellweger Analytics System 16 has plug-in sampling modules that handle 4, 8, 1 2 or 16 individual sampling points. A built-in thermal printer records monitoring events including concentration alarms, instrument faults and power losses. An RS-422 output is available to connect to a Zellweger remote alarm documentation module which provides the same information and format as the onboard printer. The newer Zellweger model CM4 provides continuous monitoring of four points on the same Chemcassette tape. A serial communications interface, alarm output contacts, and 4-20 milliamp outputs are provided for connection to PLC control/monitoring systems. Because a serial interface cannot be electrically supervised, it should not be used for initiating life safety alarms. Onboard data logging of concentrations for up to 30 days for future retrieval is also provided. Up to seven model CM4s can be rack mounted in a single enclosure. Zellweger Analytics also manufactures single-point sensors for portable use such as trouble shooting and ERT response. Paper tape technology is affected by changes in humidity. The ambient moisture is part of the reaction of the gas sample with the paper tape. in cleanrooms with tightly controlled humidity, this is not an issue. Areas without humidity control should be reviewed with the equipment manufacturer. Chemcassette tapes do require special maintenance in handling. The tapes have a limited life span and must be stored properly in temperature-controlled rooms. Some tapes must be stored in a freezer. After a tape package is opened, it should be replaced within 6 weeks. A standard play tape lasts for 7 days of continuous monitoring. An extended play tape will last for 30 days of continuous monitoring. Mechanical failure is an issue because the cassette drive can jam, the optics can foul, pumps can fail, filters can plug, and flows through sampling tubes can become unbalanced. The Chemcassette monitoring system eliminates the need for sensor cell replacement and calibration with hazardous gas mixtures and is more sensitive than sensor cell systems. The Chemcassette cannot be permanently "poisoned" because the tape is advanced for each sample.

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Spectrophotometric Analysis Individual compounds absorb infrared radiation in a characteristic pattern. A graph of infrared light absorption versus wavelength (the spectrum) may be used to identify components in a gas mixture by their spectra. The quantity of light absorbed is proportional to the concentrations of the individual components, providing quantitative as well as qualitative analysis. The Ecosys TeloSense Air Composition Monitor (ACM) uses a Fourier transform infrared (FTIR) spectrometer to determine the concentration of airborne chemicals by examining their interaction with a beam of infrared light. An integral computer automatically converts the information produced by the FTIR analyzer into concentrations of chemicals using an encoded qualitative database of reference spectra. A typical air sample scan for concentrations down to 1 ppm requires between 20 and 30 seconds and can look for up to 13 gases per sample port scan. Analysis down to 0.1 ppm is possible but requires analysis of up to 5 minutes. Due to this increased analysis time, the ACM is not recommended for safety alarm monitoring of arsine, phosphine, or diborane. This technology will not work on atomic or diatomic gases that do not absorb infrared radiation (oxygen, chlorine, hydrogen and nitrogen). Air samples are drawn into the monitor through 3/8-inch O.D. polypropylene tubing. The Ecosys TeloSense ACM sensor is not subject to interference from other chemicals or gases. The ACM will identify all phases of a gas going through hydrolysis; it isn't necessary to first determine if the gas or the gas byproduct of a reaction with moist air must be sensed. The ACM can be utilized to analyze discharge from treatment systems. Samples from wet scrubbers should be drawn through a hydrophobic filter to remove excess moisture prior to analysis. A source of nitrogen is required to purge the sample cell between samples. The ACM monitors the integrity of the air sampling tubing. One-way check valves can be provided at the end of each sample tube. Once every 24 hours, the sample tube is pressurized with clean dry air. If the tube holds pressure, the sample tube integrity is verified. If the tube does not hold pressure, a trouble alarm is generated indicating maintenance is required. The ACM was modified in 1986 to upgrade the Michaelson interferometer and reduce maintenance requirements. This revised system requires little maintenance and no periodic calibration. However, if the system does require repair, specially trained personnel are required and historically, parts and trained technicians may not be readily available in some areas. Ecosys TeloSense handles this with modular replacement of the interferometer and off-site repair. The Ecosys TeloSense ACM is available in models to monitor 20, 40 or 60 sample ports. The ACM has alarm relays and a serial interface port. Initial purchase cost may be high, but the life cycle cost may be lower than other technologies when comparing systems of 40 points.

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Ecosys TeloSense recommends the ACM for the following gases: ammonia boron trichloride carbon monoxide dichlorosilane hydrogen chloride hydrogen fluoride nitric acid nitric oxide nitrous oxide nitrogen dioxide nitrogen trifluoride ozone silane silicon tetrachloride silicon tetrafluoride sulfur hexafluoride trichlorosilane tungsten hexafluoride organic solvents

NH3 BCI3 + HCI CO SiH2CI 2 + HCI HCI HF HNO3 NO N20 NO2 NF3 03 Sill 4 SiCI4 + HCI SiF4 + HF SF8 SiHCI 3 + HCI WF B + HCI

Molecular Emission Spectrometry Sensors This detection device uses a pump to draw an air sample through polypropylene tubing into a continuous hydrogen flame in a reaction chamber. The gas molecules are raised to excited states in the flame and emit light of characteristic wavelengths in returning to their natural states. The emitted radiation is proportional to the concentration of the gas. Optical filters are used to isolate the wavelengths involved and to subtract contributions from interferences. Selectivity is obtained by measurement of radiation emitted at wavelengths selected for the compound of interest. Ecosys TeloSense calls this technology Molecular Emission Spectrometer (MES) and the equipment the Toxic Gas Monitor (TGM). The first analysis of a sample by the TGM simply determines if there is toxic gas. The TGM then uses highly selective "getters" to scrub the sample prior to subsequent analysis. Using a series of getters, the toxic material is identified through a process of elimination. Gas identification (down to 0.25 TLV) and alarm validation requires four seconds for a single gas and up to three gas types may be identified at each point. The system's computer reports and logs the concentration of the identified substance and initiates alarm contact closures and serial communications with other devices. This technology is extremely fast (2 seconds in most cases) and detects concentrations down to 0.25 TLV and even in the ppb concentration for some gases. It is not cross-sensitive to solvents or acid gases. Preventive maintenance requires

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four hours off line and is recommended twice a year. A calibration is recommended once a year. This system requires a source of hydrogen (1 50-300 cc/min). During an emergency event, bulk gases may be shut off. If remote bulk hydrogen is used, a backup source of bottled hydrogen should be provided near the machine. The TGM is available in a 20 monitoring point system. Due to reduced maintenance compared to other systems, the life cycle cost per point may be less than other systems when comparing systems of 20 points. Ecosys TeloSense recommends the TGM for the following gases: ammonia arsine diborane dichlorosilane germane nitrous oxide nitrogen dioxide nitrogen trifluoride phosphine phosphorous oxychloride silane tetraethoxysilane trichlorosilane tungsten hexafluoride

NH 3 AsH3 B2H8 SiH2CI 2 + HCI GeH4 NO NO2 NF3 PH~ POCI3 Sill4 TEO S SiHCI3 WF 6

The TGM is not recommended for chlorine or fluorine.

Acoustic Sensors

Ecosys TeloSense has developed the H2M sensor that tests air for hydrogen and methane with pulses of ultrasound. The speed of sound through a chamber filled with an air sample is compared to a reference cell. Low levels of hydrogen in the sampled air greatly alter the time-of-flight of acoustic waves, making it easy to detect hydrogen at low levels. Helium is nearly as light as hydrogen and causes a similar (but lesser) change to the acoustic waves. The Ecosys TeloSense device distinguishes hydrogen from helium by using a palladium getter. Hydrogen is readily removed by palladium, but helium and other gases are not. A sample can be tested in only 2 seconds. The acoustic sensor/analyzer is completely drift-free which eliminates the need for calibration. Semiannual preventive maintenance is recommended. This is an extractive system incorporating an air pump with a capacity of 20 points. Considering the life and replacement costs of catalytic bead sensors, the life cycle cost of this technology is favorable if there are at least 10 or 15 monitoring points.

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Ozone Monitoring Sensors Ozone is produced in lithographic optical systems (wafer steppers) using an excimer laser source. Ozone is used in a wide variety of semiconductor processes including CVD, dry ashing, wet bench cleaning and ultrapure water. Ozone is a human health hazard in concentrations over 1 ppm for prolonged exposure. There are five ozone monitoring methods: Ultraviolet analyzers offer absolute measurement, are selective, quick and reliable, but do respond to interference from some organics and mercury. Semiconductor sensors are selective for ozone, inexpensive and compact, but require periodic calibration. Electrochemical sensors are also inexpensive and compact, but are slow, unstable and less selective than other technologies. Chemical titration is inexpensive, but not selective and not a continuous monitoring process. Chemiluminescent analyzers are selective, but need fuel and are expensive. Of the five methods, UV absorption is recognized by the EPA, ASTM and NIST as the reference method for ozone in air measurements. Ozone sensors should be located around ozone generators, contact chambers, ozone destruct units and enclosed pipe galleys. The OSHA permissible limit for ozone is 0.1 ppm. There is a natural background concentration of ozone in air of 0.03 ppm. Because ozone decays as it is drawn through sample tubing, long lengths of tubing in such systems should be avoided.

Problematic Gases Many gases used in semiconductor manufacturing present particular problems for detection. In order to minimize their impact, discuss problematic gases with the hazardous gas monitoring system supplier prior to design.

Arsine Arsine (ASH3) is used in several processes in semiconductor manufacturing. The American Conference of Governmental Industrial Hygienists (ACGIH) is proposing lowering the TLV for arsine from its current level of 50 ppb to 2 ppb. OSHA and many other agencies use the term PEL in lieu of TLV (refer to the Glossary). Many arsine sensing systems were developed based upon the current TLV and typically are not sensitive enough to detect the proposed 2 ppb TLV. Most sensor manufacturers are researching modifications to their equipment that would allow detection of arsine at 2 ppb.

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Sensing systems have an inherent signal-to-noise ratio. If the electronic signal from the gas sensor is low due to low concentrations of the target gas, inherent noise may mask the signal. Ecosys MST has developed signal conditioning techniques for their electrochemical cell that will allow detection of 2 ppb concentrations of arsine. EcoSys TeloSense has modified their TGM MES detector to achieve a lower detectable limit (LDL) of 2 ppb for arsine. Typical paper tape signal-to-noise ratios are on the order of 15 ppb to 20 ppb. Zellweger Analytics has developed new hydrides calibrations with heightened responses to allow 2 ppb arsine detection without the risk of false alarms. The combination of software revisions and a more sensitive paper tape should allow the Zellweger Model CM4 to respond to a 2 ppb concentration in 100 seconds. This new technology will provide a LDL of 0.3 ppb. Sensors detect gas concentrations at the sensor location. Sensors are typically located in exhausted enclosures or ducts. High air flows through these enclosures will dilute target gas concentrations. The farther the sensor is from the actual leak point, the greater the dilution. High velocity air flows also tend to minimize dispersion of the target gas throughout the enclosure or duct. If the sensor is not in just the right location, target gas could flow by the sensor without entering the sensing device. This problem is amplified when trying to detect very minute concentrations. Another problem with sensing systems used to detect very diluted concentrations is field calibration and testing. Some vendors offer target (or interferent) gases in small cylinders for use in calibration and testing. One manufacturer advises they offer a 0.5 ppm phosphine concentration for use as an interferent in testing arsine sensors. The accuracy of this bottled concentration is +/- 5 percent. If the calibration gas is only + / - 5 percent accurate, how accurate is the field calibration of a sensor at 2 ppb? Accurate, dependable detection of arsine at 2 ppb concentrations in semiconductor fabs will be difficult at best.

Boron Tdfiuoride

Boron trifluoride (BF3) is used in semiconductor manufacturing as a P-type dopant in ion implanters. Due to inherent problems with this gas, the gas supply bottle is required to be near the process tool. Implanters use small quantities of dopant gas. From an economical standpoint, it is preferable to use small lecture bottles of gas at the implanter than to dispense gas from a remote gas storage room and fill long lengths of piping with the gas. Implanters are designed with an integral exhausted enclosure for a small lecture bottle of boron trifluoride. To meet safety standards such as SEMI S2, Safety Guidelines for Semiconductor Manufacturing Equipment, the gas bottle enclosure has very high exhaust rates (500-700 cfm) to contain a worst-case

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leak. Boron trifluoride is stored in lecture bottles at a relatively low pressure, which produces a potentially slow leak. This slow leaking rate combined with the high exhaust rates leads to very diluted concentrations which are difficult to detect. Gas sensing systems are typically programmed to alarm at one-half TLV, which is 0.5 to 1 ppm for boron trifluoride. However, a 0.5 cc/minute leak in a typical implanter lecture bottle enclosure exhausted at a rate of 500 cfm dilutes the concentration to only 0.035 ppm. While leaks below TLV may not be a safety code problem, facility personnel will want to know of any leaks which can cause equipment corrosion or failure as well as process gas loss. Studies by Zellweger Analytics have determined that their Model CM4 Chemcassette technology can be used to detect concentrations of boron trifluoride as low as 20 ppb at the sensing instrument. Studies by Ecosys MST determined that their HF electrochemical cell can be used to detect the fluoroboric and boric acid produced in the hydrolization of 10 ppm boron trifluoride. The basic reaction principle of Ecosys MST's HF cell is a change of the system Ph value. Scott/Bacharach advises their tests determined that TLV concentrations of BF3 are not reliably detected by their electrochemical sensors. The Ecosys MST research also indicated that boron trifluoride has a high adsorption tendency in Teflon sampling tubes. The measured concentration of boron trifluoride through a 25 meter Teflon tube was approximately 80 percent lower than that sampled through a 20 cm tube. Ecosys MST research suggests sampling tubing length for boron trifluoride monitoring should be minimized. Studies by Zellweger have detected adsorption of BF3 by TEDLAR plastic bags typically used in gas sensor testing and calibration. This adsorption can affect the accuracy of calibration.

Chlorine Tdfluodde Chlorine trifluoride (CIF3) is used in semiconductor manufacturing as a chlorine/fluorine source for plasma etch and as a chamber-cleaning agent to remove excess deposition products from chemical vapor deposition (CVD) reactors and diffusion furnaces. The cleaning method previously used induced a plasma in a nitrogen trifluoride (a global warming chemical problem) atmosphere to create silicon and tungsten fluorides which could be removed by the chamber vacuum pump. Using the CIF3 cleaning method reduces environmental impact as well as costly downtime, and eliminates the plasma generator from the tool. Chlorine trifluoride is a powerful oxidizing agent and is the most reactive of the halogen fluoride compounds. The TLV for CIF3 is 0.1 ppm, which requires a very sensitive detection system. Exposure above the IDLH limit of 20 ppm can lead to extremely severe chemical and thermal burns.

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Reaction byproducts of CIF3 are dependent on conditions such as relative humidity, temperature, and presence of other chemicals. Typical byproducts include hydrogen fluoride (HF), hypochiorous acid (HOCI), oxygen (02), chlorine (CI), and chlorine dioxide (CIO2). From a monitoring standpoint, reaction byproducts available for detection are also dependent on the distance between the leak and the sensor: the greater the distance, the more time available for reactions with water vapor and other ambient chemicals. Reaction byproducts HF and C102 pose a greater health hazard than CIF3. Detection systems for CIF3 can sense for reaction byproducts such as CI and Hr. Using electrochemical sensors for HF may be problematic due to typical interference with tungsten hexafluoride (also commonly used in CVD tools for metalization), and the limited sensitivity of the HF sensor to CIF3 or its reaction byproducts. Based upon balanced chemical reactions for CIFz and water vapor, HF is produced in a 3"1 ratio with respect to CIF 3. The Uniform Fire Code requires gas detection systems to "be capable of monitoring at PEL or ceiling limit." PEL for CIF3 is 0.1 ppm. This would require an HF sensor capable of detection at concentrations of 0.3 ppm (3"1 ratio), less than the lower detection limit (LDL) of most electrochemical HF sensors. The 1997 UFC requires alarming if gas concentrations reach "short-term hazard conditions." IDLH for CIF3 is 20 ppm, well within the range of most electrochemical sensors. If there are no other potential fluoride sources in the monitoring location, such as in a valve manifold box, HF detection may be acceptable. Some users have noted interference problems from atmospheric ozone where large quantities of outside air may reach the sensor, such as gas storage rooms. Zellweger Analytics recommends detection of CIO2 and offers a Chemcassette calibration that provides a range of detection of 30 to 1000 ppb, well below the TLV. Most other manufacturers recommend sensing for Hr. Sensor positioning should consider that CIF3 is three times heavier than air. In addition, sensor location is dependent on whether CIF3 or its reaction byproducts is monitored. Because CIF3 is highly reactive, the concentrations of CIF3 rapidly decrease as distance from the leak source increases. If the detection system is sensing CIF3 directly, the sensor location or sample tubing should be placed near the potential leak source. Ruorine

Fluorine (F) is used in semiconductor manufacturing in deep ultraviolet excimer lasers. Fluorine is the most reactive element known, the most electro-negative element and, therefore, is a strong oxidizing agent. Fluorine is extremely hazardous with a TLV of 1 ppm. Fluorine produces hydrogen fluoride (HF) as a reaction byproduct when exposed to moisture in the air. The quantity of HF formed and the rate of the reaction is a function of temperature and humidity. Scott/Bacharach performed tests to determine which of three electrochemical sensor types, fluorine/chlorine, oxidant, or hydrogen fluoride, is best suited to detect fluorine

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leaks. These tests indicated that either of the three sensor types may be used to detect fluorine leaks. There was no evidence of rapid hydrolysis of the fluorine to hydrogen fluoride gas. All three sensors responded when exposed to fluorine gas in a container of humidified air (approximately 40 percent RH).

Hydrogen Hydrogen (H) is widely used in semiconductor manufacturing diffusion, epitaxy, and CVD processes and in emissions abatement equipment. It is used as a carrier gas and etching agent and can be a byproduct waste gas in ion implant and other processes. Hydrogen is flammable in concentrations between 4 percent and 75 percent by volume in air. Hydrogen is lighter than air and can collect in the tops of enclosures and rooms that are poorly ventilated. Isopropyl alcohol (IPA) and other organic vapors can be interferents with some sensing technologies. Catalytic sensors can be used to detect the presence of higher concentrations of hydrogen; however, catalytic sensors only detect the presence of combustible gas, they are not gas-specific. In areas where other flammable gases are not present, this technology may be appropriate. Electrochemical sensors can be used to detect hydrogen and offer some selectivity compared to catalytic sensors. Disadvantages to electrochemical sensors are their required recalibration and periodic maintenance. Solid-state sensors can be used to detect hydrogen in low-level concentrations; however, they may be subject to interference from IPA. Some manufacturers offer activated carbon filters to mitigate IPA interference. Ecosys TeloSense offers an acoustic sensing technique that is described earlier in this chapter. Their acoustic technology offers a specific detection method not subject to interference. Placement of operator breathing space sensing points is dependent on air flow patterns in the area with respect to potential gas leak points. High speed, laminar air flows in fabs limit the dispersion of gas leaks. Plumes from leaks tend to flow in tight linear patterns in the direction of air flow until some obstruction creates turbulence. Air flow patterns in the area should be analyzed using cleanroom foggers prior to placement of sensors. The high air volumes moving through a cleanroom will rapidly dilute any gas leaks to concentrations that may not be detectable. Gas sensors located too far from potential leak points may not detect a high enough concentration to initiate alarms. Sensing cleanroom operator breathing space for hydrogen is complicated by the fact that hydrogen is lighter than air. Hydrogen's buoyancy will fight the cleanroom laminar air flow causing some dispersion. There is no universally-accepted sensor location in the industry. There are three schools of thought regarding operator breathing space sensor placement for hydrogen:

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Sensors should be placed above potential leak points because hydrogen rises. Sensors should be placed downstream from potential leaks because hydrogen will be carried along with the laminar air flow. Hydrogen will disperse rapidly due to buoyancy fighting air flow and dilution, thereby reducing concentrations to below a detectable concentration. The only consensus is that hydrogen sensing points should be located near potential leaks.

Nitrogen Trifluoride Nitrogen trifluoride (NF3) is used in semiconductor manufacturing as a reactor cleaning agent in plasma and thermal etch/clean processes. Nitrogen trifluoride is a strong oxidizing agent, but is stable at typical ambient conditions. Nitrogen trifluoride can be detected directly using FTIR spectroscopy or by sensing reaction byproducts HF and NO, created with the use of a pyrolyzer. Several manufacturers offer sensing systems incorporating HF detection with a pyrolyzer. Freon compounds in the area can be an interferent because they also form HF as a byproduct of the pyrolysis reaction. Freon filters for sensors or sensor tubing are available that can mitigate the Freon interference problem. PureAire offers a detection system that does not monitor for HF and, therefore, does not have an interference problem with Freon.

TEOS TEOS (tetraethoxysilane) is a commonly used liquid dopant in semiconductor manufacture. TEOS hydrolyzes into OH which can be detected with an alcohol sensor. However, isopropyl alcohol (IPA), commonly used in semiconductor manufacturing facilities for cleaning, is an interferent for this detection method. PureAire offers a monitoring technique that converts TEOS to silicon dioxide (SiO2) which is then sensed. The EcoSys/Telosense MES sensor can be used for TEOS detection.

Recommended Sensor Locations Codes typically do not dictate specific locations for sensors. However, the Uniform Fire Code (UFC) does require sensors at gas cabinets for HPM gases and the 1997 edition lists general sensor locations. The 2000 International Fire Code can be interpreted to require monitoring of treatment system discharge from storage rooms containing toxic and highly-toxic gases. Refer to the section on Exhaust Treatment System Monitoring in Chapter 6 of this guide. Sensor locations should be reviewed with the local authority having jurisdiction as well as with the facility safety and risk managers. The Palo Alto, California Toxic Gas Ordinance (TGO) provides guidelines

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for sensor locations. This local gas ordinance categorizes gases into Class I and I1. Only Class I double-containment and Class II gases are required to be monitored by the TGO. However, most semiconductor fabs monitor all hazardous gases. Sensors are typically provided in the following locations: Gas cabinets (usually in the exhaust). Any place where fittings are not welded, such as valve manifold boxes (VMB) and tool gas jungles or pump enclosures. Annular space of double-containment gas lines (can be monitored by gas cabinet or valve box sample point if the annular space empties into that exhausted enclosure which has negative pressure). Tool exhaust. Operator breathing zones (some codes do not require breathing zone monitoring). Chemical delivery/service corridors. Gas purifier cabinets and ozonators. Exhaust treatment system discharge (problematic due to sensor clogging). Gas storage rooms. Vacuum pump enclosures. As part of the gas monitoring and alarm system, the gas detection system should also monitor excess flow switches in gas cabinets and valve manifold boxes. Detection of excess flow should close gas valves. Codes require locations where leaks typically occur to be in exhausted enclosures to keep any leaked hazardous gas away from personnel. Sensors are typically placed in the exhaust ducts connected to gas cabinets and valve manifold boxes. A 1992 study by the University of Southhampton, Highfield, England, studied optimum sensor locations with respect to gas leak mixing and local flow behavior within the duct. The study developed the following recommendations for sensor placement. Rectangular duct diameter is defined as 4 times duct cross-section area divided by the duct perimeter length. Duct Feature Bend or Elbow Flow Constriction Connection to Exhausted Cabinet Combining Junction

Min. Distance From Duct Feature to Gas Sensor 1 Diameter Upstream, 2 Diameters Downstream 1 Diameter Upstream, 6 Diameters Downstream 4 to 6 Diameters Downstream 60 to 150 Diameters Downstream

Sensor placement within a gas cabinet is not recommended because sensors could be located where there is little mixing air flow and gas leaks could be exhausted from the cabinet bypassing the sensor. If space allows, sensors monitoring exhausted enclosures should be mounted in the exhaust duct approximately 6 to 10 duct diameters away from the duct connection to the exhausted enclosure. Where sensors are grouped in a common duct, the minimum separation should be 4 times the length of the protrusion into the duct.

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Some semiconductor facilities personnel report that sensor placement only 2 duct diameters downstream of any duct bend or fitting adequately disperses and mixes gases to allow detection at 0.5 to 1 TLV concentrations. Zellweger Analytics recommends that sample tubing should be inserted at least 2.0 inches into an exhaust duct. in normal gas bottle replacement operations, gas lines are purged to remove hazardous gases entrapped in fittings and piping within the gas cabinet. The discharge from this purging is connected to the gas cabinet exhaust duct above the cabinet. Sensors monitoring gas cabinets should be mounted between the top of the gas cabinet and the connection of the cabinet purge discharge. Otherwise, the sensor may detect gases released during normal purging operations. The number of required sensors is dependent on the gases present and the sensor technology used. Tools may employ more than one hazardous gas. Some technologies may have the capability to monitor more than one gas with a single sensor. Some monitoring devices can monitor a "family" of gases such as mineral acids or hydrides. In gas-detection systems using vacuum pumps to draw air samples into an extractive detection chamber, sensor locations should be tested to determine if the sample pump has sufficient capacity to draw a sample against the back pressure from air flow through the tool, duct or gas cabinet at that location. Polypropylene tubing or stainless steel probes should not be used in mineral acid or corrosive gas sensing systems that draw air samples through tubing. Mineral acids and corrosive gases are adsorbed by stainless steel and many plastics, diluting the sample reaching the analyzer. Gas sensors should be located in the most likely path a gas leak will follow. Potential leak sources and the air flows around those sources must be considered. Gas density will also impact the path leaked gas will take. Gases lighter than air will rise, and gases heavier than air will sink. However, high exhaust rates or laminar air flows may change those typical flow patterns. If sensors or their controllers have temperature operation limits, they may have to be remotely located and gas samples drawn through tubing from the desired sampling point to the sensor in a more controlled environment. For example, discharge from thermal oxidizers (burn boxes) may be too hot for direct contact with the sensor itself. Most sensors are sensitive to excessive moisture. Water traps or filters may be necessary, or select a sensor type that is unaffected by moisture. Sensors must be located where they are accessible for maintenance, testing and calibration, If the desired sampling location is not easily accessible, an extractive sample system may be necessary. With this system, a sampling tube can be run from an accessible sensor location to the inaccessible sampling location.

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Cleanroom laminar air flow is interrupted by process tools. In addition, process tool exhaust can cause horizontal air currents. These variations in the laminar air flow can carry the gas cloud in an unplanned path. Air turbulence within exhausted enclosures can also influence the sample point location within the enclosure. Sensor locations should be modeled and tested to insure that sensors are placed downwind of probable leak sources. Cleanroom foggers are available to help locate airflow patterns. (See MSP Corporation and PWC Technologies in Appendix B of this guide for fogger availability). Liquid nitrogen or dry ice in hot deionized (DI) water will produce a visible plume that can be used as a guide to where air flow may carry gas leaks. Selection of proper sensor locations in equipment requires engineering evaluation along with experimentation. Sensor location is addressed in the Semiconductor Equipment and Materials International (SEMi) Standard S2-0200, Safety Guidelines for Semiconductor Manufacturing Equipment. SEMI $ 2 - 0 2 0 0 , Paragraph 23.6 Equipment that uses hazardous gases may require continuous detection and, if so, should have sample points mounted in the equipment, or have recommended sampling points identified in the equipment installation instructions. Where the gas supply is part of or controlled by the equipment, the equipment should be able to accept a signal from an external monitoring device and shut down the supply of the gas. Review manufacturer's equipment literature for recommended sensor locations or contact the manufacturer and request sensor location information. Many detected leaks are due to operator error, e.g., opening chambers before purging is complete. The high air volume moving through a clean room will usually dilute small hazardous gas leaks that escape into operator breathing zones making detection difficult. Some companies and jurisdictions may still require monitoring of operator breathing zones. Providing a monitoring point and data logging the information can provide a record that the company is meeting safety guidelines for personnel exposure to hazardous materials.

Sample Area Interference Some types of gas sensors are subject to interference that can cause false alarms and even "poison" the sensor thereby rendering it inoperable until the gas is gone and the sensor resets. Chlorine and hydrogen can also cause some sensors to false alarm. Carbon monoxide exhaust from a truck or forklift can cause false alarms in some types of sensors. Isopropyl alcohol (IPA), used extensively for cleaning in fabs, is an interferent that affects most gas sensors. The interference problem is mitigated by using charcoal filters at the sensors, but these filters must be changed regularly. The filter will only absorb so much IPA and once it saturates, it can pass a more concentrated dose of

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IPA through to the sensor thereby poisoning it. Recovery time for electrochemical sensors is proportional to the gas concentration. A heavy dose of IPA could put an electrochemical sensor out of operation for an extended period, leaving an area unmonitored. Sensor locations should be reviewed for possible interferents and their presence should be considered when selecting sensor types. Sensor manufacturers can provide data on possible interferents for each sensor type. The wiring connecting sensor heads to sensor controllers and monitoring systems is subject to radio frequency interference (RFI). The cables are generally shielded, but can still be affected by process tools, cellular telephones, handheld radios, etc. Malfunctioning high-voltage equipment can cause arcing which can generate RFI. The RFI generated by some process tools (sputter and ion implant) is shielded, but malfunctions can emit RFI beyond the tool enclosure. This RFI can impress a false signal on the sensor wire causing the system to go into alarm. Because of interferents, the emergency response team (ERT) must look for gases other than those the sensors are designed to identify. When the ERT enters the fab to determine the source of an alarm, they must be informed of processes and specific materials in use at the time of the alarm.

Alarm Set Points In general, gas detection systems must be capable of detecting hazardous gases at or below the permissible exposure limit (PEL). For flammable gases, the monitoring detection threshold level is 20 percent of the lower explosive limit (LEL). Both the UFC and the IFC state that alarms are generated when a short-term hazard condition is detected. The definition of PEL is the concentration deemed safe for 8-hour time-weighted average. That does not meet the definition of short-term hazard. Short-term hazard more closely meets the definition of immediately dangerous to life and health (IDLH): a concentration of airborne contaminants which represents the maximum level from which one could escape within 30 minutes without any escape-impairing symptoms or irreversible health effects. While the codes can be interpreted as not requiring alarm until IDLH levels, many facilities set alarms at PEL or one-half PEL. Many facilities set alarm levels for flammable gases at one-eighth to one-half the LEL.

Using Portable Sensors An improperly operated portable sensor can produce erroneous results. The portable sensor must be turned on, reach equilibrium and be calibrated before being used. In addition, the sampling tubes can become clogged and blocked. The sample pump may

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run but be unable to draw a sample into the device. It is important to be able to measure flow through the device to insure that air samples are actually being drawn into the machine. Because the pump is running and the sensor is reading zero concentration, an erroneous assumption can be made that there is no problem, when, in fact, the device may not be drawing air into the sample chamber. When using portable systems to detect leaks, the time required for the air sample to travel from the end of the sample tube into the machine and to be processed must be considered. If the sample tube is moved too fast, it may not be possible to determine the source of the gas, or not enough of the contaminated air can be drawn into the sample hose. The response time and characteristics of the detector must be known in order to properly use the device. Several manufacturers offer pocket-sized gas detectors that incorporate a sensor, controller, LCD display, audio and visual alarm signals and a battery. These gas detectors are available using the various sensing technologies described in this Chapter. These portable sensors generally do not provide selectivity between various gases.

Sensor Recalibration Gas sensor recalibration typically is scheduled in accordance with the sensor manufacturer's recommendations, with user corporate safety policies, or upon warning alarms from the sensor or sensor controller diagnostics. Many manufacturers recommend a recalibration interval of three months. Sensor location and periodic exposure to gas affect the need for recalibration. Electrochemical cells exposed to high air flows or high temperatures may tend to dry out faster, leading to more frequent replacement and recalibration. Electrochemical cells exposed to high concentrations of target gas may become saturated (poisoned). Because returning to cell equilibrium takes time and the facility cannot be repopulated until the gas detection system is fully functional, many users will replace the poisoned cell, calibrate the new cell, and return the facility to production. The removed cell can be tested off line, recalibrated, and reused later. Some electrochemical oxidant sensors can "go to sleep" if not periodically exposed to gas. The cell electrodes can become coated by oxidation with the electrolyte. Passing target gas over the face of the cell during recalibration reverses the reaction toward the other electrode, effectively cleaning the electrode. Solid state sensors have a similar problem if not periodically exposed to target gas during recalibration. This is not a problem with reducing-type cells. Calibrations usually require exposing the gas detection instrument to target gas. Zellweger Analytics paper tape instruments can be calibrated electronically with an optics calibration card. Using the card, the instrument automatically calculates and

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executes all zero and span adjustments. Some user safety departments or local code officials may require the use of target gas for calibration. Very small cylinders (lecture bottles) of target gas in known concentrations (usually 8hour TLV) are available for testing and calibration. The actual gas concentrations are usually +/- 5 or 10 percent of labeled contents; therefore, calibrations may only have an accuracy of + / - 5 or 10 percent. Lecture bottles are used for ease in mobility and for safety in case there is some problem and target gas is released from the cylinder. Complete discharge of a lecture bottle of TLV-concentration toxic gas would be quickly diluted and not become a personnel hazard. For gases considered too hazardous for use in testing (such as arsine), a gas with instrument cross sensitivity (interferent) may be used. With the exception of FTIR types, most sensors have cross sensitivities to other gases and manufacturers publish tables providing information on cross-sensitive gases and their effects on the target gas readings. In addition to lecture bottles of an appropriate gas, a O-gas source is also required for calibration. A O-gas is a gas known to not contain any target or interferent gas. Draeger offers selective filters with absorption agents to provide O-gas for calibration. The instrument zero (0) setting is first calibrated. The cell is exposed to O-gas until the instrument measured value stabilizes, which is about 2 or 3 minutes for most instruments. The zero potentiometer is adjusted to indicate 0 target gas concentration. The span potentiometer is set after the zero setting is completed. The sensor, or sensing tubing for extractive systems, is exposed to target gas. Most gas sensing instrument manufacturers provide cups that fit over the sensor or fittings for use in calibrations. For extractive systems, a plastic bag with ambient air and a "T" fitting is used. One end of the T connects to the extractive sampling tubing, another end to the target gas cylinder tubing, and the other end open to the inside of the plastic bag. Gas flow is controlled by a regulator. Manufacturer calibration instructions may provide a gas flow rate. The sensing instrument is exposed to gas until the measured value stabilizes. The span potentiometer is then adjusted to the known concentration of the target gas. In addition to quarterly recalibration, some facilities perform "bump" tests (tests without calibration) to expose the sensing instrument to target gas to determine if it will respond and generate an alarm. If no alarm is generated, the sensor is recalibrated. If the system alarms, no calibration is performed until the next regularly scheduled recalibration. Portable sensors are usually tested and recalibrated more often. Sensing instruments used for confined-space entry are required to be tested before each entry into confined spaces. If the instrument is not within 10 percent calibration, it must be recalibrated prior to entry into the confined space.

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If the gas sensing instrument is sensing for reaction byproducts of the target gas, a plastic bag with air containing the same humidity as the monitored space should be used during recalibration. Humid air will be required for the reaction byproducts to be produced. The humidity inside the test bag must be the same as the ambient air in the sensed area in order to properly calibrate for normally sensed air. Semiconductor fabrication facilities in the United States are generally 40 to 45 percent RH, while those in Southeast Asia can be much higher. Calibration of gas sensing instruments also requires logistic planning including: obtaining work permits from fab managers, scheduling access into the cleanroom, and scheduling tool downtime to perform testing. The system that monitors gas detection instrument alarms must also be bypassed so that instrument alarms during calibration do not initiate facility evacuation alarms. Safety protocol may require t w o - w a y communication between personnel performing instrument calibration and personnel monitoring alarms at the emergency control station. Zellweger Analytics has developed a protocol for testing gas detector sensors. Their protocol is included as Appendix B to this guide.

Other Sensor Considerations Sensing Reaction Byproducts Because some gases will react with air, the reaction byproduct must sometimes be sensed in lieu of the gas itself. Boron trichloride (BCI3) is an example. Boron trichloride hydrolyzes to hydrogen chloride (HCI) and boric acid (H3BO3) when exposed to moisture in air. Sensors for hydrogen chloride can be used to detect leaks of boron trichloride if there is sufficient humidity in the air for hydrolysis. This also relates to testing the sensors. Some hydrogen fluoride (HF) sensors can be used to monitor boron trichloride releases, but hydrogen chloride sensors are more generally used. National Draeger recommends using their hydrogen chloride electrochemical sensor to detect boron trichloride, hydrogen bromide (HBr), dichlorosilane (SiHzCI2) and trichlorosilane (SiHCI3) as well as hydrogen chloride. The following compounds are detected directly or they can be detectable as a mineral acid upon reaction with moisture in ambient air. Compounds which hydrolyze to hydrogen bromide (HBr): boron tribromide phosphorous tribromide

BBr3 PBr3

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Compounds which hydrolyze to hydrogen chloride (HCI): arsenic trichloride boron trichloride dichlorosilane he xa chl or od isila ne phosphorous oxychloride phosphorous trichioride phosphorous pentachloride phenyl trichlorosilane silicon tetrachloride (tetrachlorosilane) trichlorosilane

AsCI3 BCI3 SiH2CI2 Si2ClB POCI3 PCi3 PCI5 SiCI3Ph SiCI4 SiHCI3

Compounds which hydrolyze to hydrogen fluoride (HF): arsenic trifluoride arsenic pentafluoride boron trifluoride carbonyl fluoride chlorine trifluoride fluorine phosphorous trifluoride phosphorous pentafluoride silicon tetrafluoride sulfur pentafluoride sulfur tetrafluoride tetrafluorosilane tungsten hexafluoride

AsF3 AsF5 BF3 COF2 CIF3 F2 PF3 PFs SiF4 S2Flo SF4 SiF4 WF6

Once chlorine trifluoride, a highly toxic gas, contacts air it reacts rapidly with oxygen and moisture to form a series of products. Most of these products are also toxic and corrosive. Following are the common breakdown products. chlorine trifluoride chlorine dioxide fluorine chlorine oxygen difluoride hydrogen fluoride hydrogen chloride

CIF3 CIO2 F2 CI2 OF2 HF HCI

One semiconductor manufacturer recommends using electrochemical sensors calibrated to chlorine dioxide for sensing chlorine trifluoride leaks. Refer to the discussion on chlorine trifluoride in the Problematic Gases section of this chapter.

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Boron trifluoride (BF3), a dopant used in the semiconductor industry, forms hydrogen fluoride (HF), boric acid (HB03) and fluoroboric acid (HBF4) as by-products in a reaction with ambient moisture. Zellweger Analytics recommends using their Mineral Acids Chemcassette calibrated to hydrogen fluoride to detect boron trifluoride leaks.

Pyrolyzers Some gases that are difficult to monitor decompose into more easily-detected components when subjected to heat in a pyrolyzer. A pyrolyzer is basically a tube coiled around a heating element which heats gas drawn through the tube. Pyrolyzers can be combined with extractive sampling systems to add heat to the sampling tube path. The pyrolyzer converts halide gases to more easily detected and measured mineral acid gases such as hydrogen fluoride or hydrogen chloride. Pyrolyzers are typically used for detection of nitrogen trifluoride (NF3), methyl fluoride (CH3F), methylene chloride (CH2CI2), and tetraethoxysilane (TEOS detected as silicon dioxide). The use of pyrolyzers can be problematic in areas containing refrigerant fumes from environmental chamber maintenance. Freon compounds generate hydrogen fluoride as a reaction byproduct which can be an interferent to some sensing systems. Zeilweger Analytics offers an optional Freon scrubber for their pyrolyzer that removes commonly-used Freons before pyrolysis.

Bectrically Hazardous Locadon Requirements Some areas containing combustible gases that require monitoring are classified as "hazardous areas" by the National Electrical Code (NEC). Electrical equipment to be placed within hazardous areas must be constructed and rated for that use. The NEC has developed classifications (Class 1 Division 1, Zone 1 or Zone 2 ) f o r electrical equipment identifying suitability for use in areas containing combustible gases. Many electrochemical sensor heads are suitable for use within hazardous areas, but their controllers are not, so they must be located outside the hazardous area zone. Ol~tmctio~ Sensor inlet obstructions may be a problem in some applications. If filters become wet or covered with oil mist, they can block gas passage to the sensing element. Corrosion or reaction byproducts can also block access to the sensing element. Sensors that become wet during fire sprinkler discharge should be checked or replaced.

Environmental Con(Etions All equipment is limited by the environmental conditions under which it will properly function. Sensors, sensor controllers and interconnecting wiring installations should be in compliance with the recommended environmental limits stated by the manufacturer. For example, gas detection systems at exterior silane storage areas in the desert Southwest may be subject to temperatures over the limitation of the sensor

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or sensor controller. Sensors also have humidity limitations and may not function properly in applications such as sensing wet scrubber discharge or in extremely humid Southeast Asia. Sensors must also be placed far enough downstream of burn boxes (local, small incinerators that heat exhaust to break down the effluent) for the exhaust stream to cool down to the acceptable temperature limitations of the sensor. Sensors and sensor controllers mounted in exterior locations should be provided with weatherproof enclosures. Some damaging environments may be modified to accommodate sensors, e.g., treating scrubber exhaust to remove particulates and moisture prior to exposing sensors. To prevent tampering or unauthorized modifications, gas sensor controls and alarm monitoring panels should be located in restricted access areas. Maintenance

System maintenance costs as well as the high cost of false alarms triggered by interferent materials must be considered during design. Electrochemical cells are initially cheaper, but can be poisoned or go out of specification causing expensive process shutdowns. Also, these sensors have a limited life due to drying of the electrolyte. It is possible for shelf time to exceed the life of the electrolyte resulting in a non-functioning sensor even before installation. Some paper tapes can lose sensitivity if they are improperly stored or become too old. Some gas sensor manufacturers offer maintenance programs that include supplying recently-calibrated sensor cells on a regular schedule for exchange. Also consider the availability of repair parts and qualified maintenance personnel. To reduce downtime and limit liability, carefully maintain written records of all maintenance performed. Central versus Distributed System

Consider the following when selecting a central system TeloSense) versus individual distributed sensors: 9

0

(Zellweger or Ecosys

A central system's single point of failure compromises several detection points, whereas distributed sensors are affected individually. Long sections of sample tubing from a sampling point back to a central system may allow problems such as adsorption of acid target gases onto walls of tubing; exposing tubing to damage; increasing sample time; and limiting distance (usually a maximum of 300 feet) between the sample points and the central system. Always review sample tubing lengths with the gas sensor supplier.

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Additions of sampling points to central systems must be done in blocks usually numbering between 8 and 40 points.

4D

However, central systems are usually less susceptible to interference from gases other than target gases and are, therefore, more specific than distributed individual sensors.

5 I

Central systems provide one central reporting and maintenance location.

II

Monitoring, Alarm and Control Systems

The means used to transmit alarm data from the gas sensors to the emergency control station (ECS) and display alarms is critical. Due to the serious health, safety, environmental and economic concerns of a hazardous material release, the system that monitors the gas sensors, processes information, generates evacuation alarms, and shuts down equipment and gas valves must be of the highest integrity yet easy to use. The system should also be expandable as the facility is modified for different products over its lifetime.

System Sophistication All alarm systems monitor the state of sensors. Less sophisticated sensors may simply provide a contact closure indicating that a threshold has been reached. More sophisticated sensors may provide analog data on sensed levels. Most monitoring systems are evolving towards the use of analog sensors. Originally, fire alarm systems monitored contacts of manual pull stations, smoke detectors, and fire sprinkler flow switches. Newer systems now include analog smoke sensors. Some fire alarm system manufacturers are developing modules to monitor any sensor with a 4 to 20 milliamp analog signal output. Many vendors offer monitoring and control systems with widely varying levels of sophistication, dependability, supervision, ease of use, and ease of modification. All of these factors must be considered when selecting from the many systems capable of monitoring sensors and affecting controlled devices.

System Safety versus Reliability There are t w o general safety system failure modes: nuisance trips and the failure to respond to a true demand. Because safety systems are required to be configured in a fail safe mode, the failure of a component should shut down the manufacturing process. Not only are process shutdowns in the semiconductor industry extremely expensive, but frequent nuisance shutdowns cause personnel to lose confidence in the system and ignore or bypass safety systems.

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The other safety system failure mode is even more disastrous. Failure to respond to a true demand is termed covert failure, hidden failure, or fail-to-danger (versus fail safe). The safety system does not function when necessary. Safety system diagnostics and periodic testing is the only sure method to detect hidden failures. Modeling safety systems be somewhat subjective. include: Mean time to probability of failure on

to predict failure modes is a complex science that can also Terms developed to compare the reliability of safety systems failure (MTTF), mean time between failures (MTBF), and demand (PFD). This topic is covered in depth in Safety Shutdown Systems: Design, Analysis and Justification, authored by Paul Gruhn and Harry L. Cheddie (refer to References).

Safety systems that are simple, have few components, and are configured in a fail safe mode are generally the safest for personnel protection. As the number of components and system complexity increases, there are more potential points of failure. Studies in other industries have found that 90 percent of safety system problems can be associated with field devices (sensors and final control elements). However, simple safety systems such as hard-wired relay systems are generally more difficult to modify and expand as the facility processes are changed or the fab is enlarged. A more complex programmable system is easier to revise to accommodate constantly changing semiconductor manufacturing. To improve reliability, redundant components and diagnostics can be added. If a system is configured to remain operational unless t w o redundant sensors both indicate a problem (2o02), process operation is less susceptible to costly nuisance trips. However, the system is less safe: if one of the redundant components fails to respond, the system would never shutdown because it is not receiving input from that sensor. If the redundant system is configured to shut down if either component detects an unsafe condition, the system is safer. However, one failed component could shut down the process. The greater number of redundant components, the greater probability that a component will fail. Triple redundancy systems with two-out-of-three (2oo3) voting can address both safety and reliability concerns, but are even more complex and contain even more components. Triple redundant systems are discussed later in this chapter.

System Electrical Supervision The rapid development of new microchip technologies requires constant renovation of semiconductor fabs. This continual demolition and construction exposes alarm circuitry to damage or disconnection. If the hazardous gas alarm system wiring is not monitored for integrity, portions of the system may malfunction unnoticed. Wiring for monitoring and alarm systems should be protected inside conduits. Locating conduits

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tight against the structure as opposed to hanging from ceiling support wires will provide some protection during building renovations. Conduits and outlet boxes should be identified with labels or painted bright colors. Fire alarm systems were one of the first widely-used life safety systems and are, therefore, one of the most developed and regulated systems. Several things can happen to a life-safety monitoring and control system to cause it to fail. Codes require fire alarm systems to include backup subsystems and electrical supervision that provides notification when problems with circuits or components are detected. Many of the hazardous gas monitoring systems now in use do not include electrical supervision. Since 1994, the Uniform Fire Code has required refrigerant gas monitoring systems to incorporate the features of fire alarm systems. Hazardous gas monitoring codes are evolving to require electrical supervision. The Uniform Fire Code and the International Fire Code require hazardous gas monitoring systems to be "listed" or "approved." Most third-party certification agencies will likely require electrical supervision for certification of life safety systems. The electrical supervision is required for monitoring, alarm and control circuits. A listed gas monitoring system cannot rely on a separate process control system to shut gas valves unless the process control system is also listed as compatible with the fire alarm or life safety system. The NFPA text Fire Alarm Signaling Systems defines supervision as: 9 monitoring of the circuit, switch, or device in such a manner that a trouble signal is received when a fault that would prevent normal operation of the system occurs.

Section 1-5.8 of NFPA 72, The National Fire Alarm Code, covers monitoring integrity of fire alarm system conductors and power supplies. NFPA 72-1-5.8.1 All means of interconnecting equipment, devices, and appliances and wiring connections shaft be monitored for the integrity of the interconnecting conductors or equivalent path so that the occurrence o f a single open or a single ground fault condition in the installation conductors or other signaling channels and their restoration to normal shaft be automatically indicated within 200 seconds. Note: The provisions of a double loop or other multiple path conductor or circuit to avoid electrical monitoring is not acceptable.

NFPA 72-1-5.8.6.1 All primary and secondary power supplies shaft be monitored for the presence of voltage at the point of connection to the system. Fire alarm control panels monitor the connecting wiring for open and short circuits and provide trouble alarms when wiring problems are detected. Some fire alarm circuitry

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is connected in a loop configuration so that communications will not be lost with a single open circuit. Some programmable logic controller-based monitoring systems can be configured to sense for system faults and generate trouble alarms. Hazardous gas releases can be far more dangerous than fires which can be detected by sight and smell, but many gases are odorless and invisible even at lethal concentrations. Some authorities having jurisdiction may not require hazardous gas alarm systems to be electrically supervised, but the best industry practice is to provide all of the reliability and safety features currently required for fire alarm systems. It is the nature of safety systems to be dormant for extended periods of time. If the system is not fully supervised and does not contain diagnostic features, it's failure can go unnoticed. It is necessary, therefore, to conduct periodic complete system testing to find and repair latent failures.

System Redundancy Because system components will fail at some time, carefully consider the consequences of failed components. Safety systems should be designed so that when sensors or control devices fail, the facility is still safe. If a simplex safety system is connected in a fail-safe mode, failed components will not endanger personnel, but can cause a loss of product due to a false trip. Properly configured redundant safety systems can both increase safety and reduce false alarms. In general, redundancy means providing t w o or more components that perform the same function. In systems with t w o components, failure of one of the components indicates that there is a disagreement, but without more information, it is not certain there is an alarm condition. In systems utilizing three components, it is unlikely that more than one component will fail so an alarm is more reliably the result of an adverse condition. Diverse redundancy means that the redundant components are not identical, but perform the same function. Redundancy is improved if the components are installed so that the same failure mode cannot cause the redundant components to fail, or so that the components employ different measurement or control principles. A safety system should incorporate the appropriate levels of redundancy from the sensors, through the communication to the processor, the processors themselves, the control and alarm circuitry, and the control and alarm devices to ensure safety and reliability. The following terms describe the functionality of a control system. Fail safe. When a component fails, if a system goes to a predefined safe state as opposed to going to a dangerous state, it is said to be fail safe. Reliability. The probability that a component or system will perform its required function under stated conditions for a stated period of time. The ability of a system to perform its function upon demand.

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Availability.

The percentage of time over which a system is capable of performing its intended function. If a safety system fails due to a faulted component, the system is not available. Availability is a function of reliability.

Fault tolerance. The ability of a control system to sustain a failure in a single component yet maintain correct, continued operation of the system. Voting. Taking signals from multiple sensors or control devices and comparing them to execute logic or control. Solid state and programmable systems are difficult to implement in a fail safe mode. Mechanical relays and hard-wired logic can be configured so that a failed component will take the system to a predetermined state. Solid state systems can fail in a dangerous mode. A dangerous failure is one where the system fails in such a way that the system being controlled cannot be shut down if required. The use of solid state components in semiconductor processing equipment safety interlocks is addressed in SEMI Standard S2-0200. Evaluation for suitability may include reliability, self-monitoring and redundancy as addressed in standards such as NEMA ICS 1.1, UL 991, IEC 61 508 and ISA S84.01. SEMI S2-0200 . . . solid-state devices and components may be used, provided that the safety interlock system, or relevant parts of the system are evaluated for suitability for use. The simplest control system utilizes a single processor with single I/O devices (simplex system). If any single component fails, the system fails. Commonly used control system redundancy architectures include the following: Dual Processors with Single I10. In this architecture there is no redundancy in input sensors or output control elements. The only redundancy provided by this configuration is in the processor. A second processor is connected in a hot backup mode. Sensor inputs are read by both the primary and backup processors. If the primary processor fails and the failure is diagnosed by the backup unit, the backup unit takes control. For safety applications, the two processors should be programmed to initiate a shutdown to a safe state if a disagreement develops between the two processors. This is required because in many failure modes, the hot backup processor cannot determine which processor is correct. Dual Processors with Dual IIO and One-out-of-Two (loo2) Logic. In this architecture, each input sensor is connected to an input point in each processor. Alternatively, each processor could have separate, redundant input sensors. Each processor processes the information and produces an output. With loo2 voting, either system can initiate the programmed control function. This logic is prone to frequent false trips since either sensor or processor can initiate control. The availability of the safety system is improved, but the reliability is suspect.

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Dual Processors with Dual IIO and Two-out-of-Two (2oo2) Logic. This configuration can reduce the false trip rate, but decreases the safety of the system. As in the 1 002 system, each input sensor is connected to an input point in each processor. To reduce false trips, both systems are required to produce the same output in order for the system to initiate the control function. The reliability of this architecture is good, but the availability is poor because if one component fails, the system will not function. Triple Modular Redundancy (TMR) with Two-out-of-Three (20o3) Logic.

In this architecture, there are three processors and each input sensor is connected to an input point in each processor. Two out of the three sensors or control signals must agree for action to take place. If one sensor fails, there are still two sensors available and the programmed response can function. A faulty component can be identified by virtue of its not agreeing with the majority and it can be flagged for repair by a diagnostic routine that looks for discrepancies. Some TMR systems will allow repair of faulted components while the safety system is still operational. A safety system can utilize a combination of these architectures. In locations where a false trip can have severe safety or economic consequences, a higher level of redundancy is called for. In locations where the consequences are not as severe, a lower level of redundancy may be adequate.

System Diagnostics Safety systems must be tested periodically to ensure they will operate when needed. The intervals for testing can be lengthened if the safety system incorporates automatic diagnostics. In addition to providing notification of malfunctioning equipment, automatic diagnostics provide the following benefits: 9 Lower costs for preventive testing. 9 No downtime during automatic diagnostics (compared to manual testing). 9 Less human error introduced by testing procedures. It is advisable to transmit measured gas concentrations to the ECS as opposed to only monitoring alarm contact closures. Analog signals from field sensors generally allow for much improved monitoring and diagnostics of internal and external faults. The term "measurement diagnostics" applies to any of the methods used to verify the validity of a measurement by applying knowledge of its expected characteristics. For example, the range of measured gas concentrations is typically known. If the sensing system reports a value out of this expected range, there is probably an error. Other measurement diagnostics include trend analysis and comparison of redundant or diverse measurements. Analog instruments that use a 4 to 20 milliamp signal typically indicate failure modes as specified by NAMUR:

HAZARDOUS GAS MONITORING

Less than 3.6 mA 3.6 m A - 3.8 mA 3.8 m A - 4.0 mA 4.0 mA - 20.0 mA 20 mA - 20.5 mA 20.5 m A - 21.0 mA More than 21 mA

123

Open circuit or failed transmitter or loop power supply Failed transmitter (downscale indication) Normal under range Normal operating range Normal over range Failed transmitter (upscale indication) Shorted wires or failed transmitter

If diagnostics indicate the gas detection system is not operating and there is no redundancy built into the system to provide protection, the affected gas valves should be shut off. This is a code requirement for ozone monitoring systems, but presently is not required for other hazardous gas monitoring systems.

System Integration The hazardous gas monitoring system is only one of several monitoring and control systems in a typical manufacturing facility. Other monitoring and control systems include fire alarm, security, HVAC, and process. In some installations, information is passed between different systems. For example, upon detection of fire or hazardous gas, some facilities send a signal to the security system to unlock doors in the affected area. This facilitates evacuation and emergency response team (ERT) response. Because hazardous gas alarms are only one of many alarm systems in a semiconductor manufacturing facility, providing a separate annunciating panel for each alarm system would require valuable space and would be difficult for monitoring personnel to operate. An integrated life-safety monitoring and alarm system could monitor and control fire alarm, fire sprinkler monitoring, smoke exhaust, hazardous gas monitoring, chemical delivery corridor emergency alarm, chemical double-containment leak sensing, seismic sensor (for shutdown of hazardous gas and chemicals), and monitoring of firesuppression systems integral to process equipment. Fire alarm panels can be configured to monitor other non-fire alarm systems. 72, National Fire Alarm Code, addresses this issue.

NFPA

NFPA 7 2 3-8.14.1 Fire alarm systems shaft be permitted to share components, equipment, circuitry, and installation wiring with non fire alarm systems. NFPA 72 3-8.14.2 Where common wiring is employed for combination systems, the equipment for other than fire alarm systems shaft be permitted to be connected to the common wiring of the system. Short circuits, open circuits, or grounds in this equipment or between this equipment and the fire alarm system wiring shaft not interfere with the supervision of the fire alarm system or prevent alarm or supervisory signal transmissions.

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This last code reference is open to interpretation. An open circuit on an addressable device communications loop that serves both fire and non-fire detectors could interfere with the fire alarm systems. However, connecting non-fire detectors to that communications loop would not seem to increase the likelihood of a short or open circuit. Typically, addressable monitoring and control modules provide the actual interface between the fire alarm system device communications loop and the monitored or controlled device. Malfunctions between the addressable device and the monitored device should not affect operation of the device communications loop. However, separate communications loops with their loop controllers could be provided for non-fire alarm equipment to meet a strict interpretation of this code requirement. Section 3-1 1 of NFPA 72 covers interconnection of fire alarm control units with other fire alarm systems and auxiliary functions. Gas detection and other life safety features could be interpreted as auxiliary functions. NFPA 72 3-1 1 Fire alarm systems shaft be permitted to be either integrated systems combining all detection, notification, and auxiliary functions in a single system or a combination of component subsystems. NFPA 7 2 3-1 1.1 The method of interconnection of control units shaft be by the following recognized means: (a) Properly rated electrical contacts (b) Compatible digital data interfaces (c) Other listed methods and shaft meet the monitoring requirements of NFPA 70 1-5.8 and the requirements of NFPA 70, National Electrical Code, Article 760. The interconnection of alarm systems in an important issue. The terms recognized means, compatible interfaces and listed methods all indicate that the manufacturers of the systems must recognize the interface as compatible and non-interfering. A malfunction within one system should not adversely affect the operation of other interconnected systems. Many facility operators prefer separate systems for their fire and non-fire alarm systems in any case. Gas detection systems are continually undergoing modification and detection circuits temporarily bypassed during maintenance and testing. A separate fire alarm system may be less likely to be inadvertently put out of commission due to gas detection system modifications. A common fire voice alarm could still be used for annunciation of non-fire alarm emergency conditions. A personal computer with CRT (UL listed for use with the fire alarm system) could monitor both fire and non-fire alarm systems to provide an integrated operator interface. Malfunctioning of the operator interface should not affect the programmed responses in each separate alarm system. A second backup operator interface should be provided at a separate, remote backup emergency control station location.

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System Documentation and Data Acquisition An essential part of any monitoring system is its ability to document all important monitoring events and accumulate this information for later analysis. Information should be logged to a database. From the database, users can retrieve the information for reports or troubleshooting activities. The operator can select the items to be logged and the conditions under which they are logged. Reports tailored to specific requirements can be developed using the query features of the database to retrieve specific data. Some of the more important monitoring data include: Alarm Conditions. The date, time, location and concentration of any point that exceeds programmed alarm levels.

Non-zero Concentrations. In most semiconductor operations, the presence of any hazardous gas is cause for concern, even if concentrations do not exceed programmed alarm levels. The system must be able to calculate and store 8hour time weighted averages (TWA). Calibration and Testing Records. A complete record including time, date and results of all calibrations and testing. Monitoring Interruptions. The date and time of any planned or unplanned interruptions to monitoring system operation.

Monitoring Systems in General Most gas sensors must be connected to a local sensor control panel. The local control panel must be relatively close to the sensors due to limitations in wiring or sensor tubing length or testing and calibration concerns. Alarm signals are transmitted from the local control panel to the emergency control station (ECS) which can be a significant distance away. Running a dedicated pair of wires from each set of contacts in a local alarm control panel to the ECS is expensive, requires physical space and is not conducive to sensor revisions or alarm response changes. Energy management and fire alarm systems historically encountered similar problems with connecting sensors, actuators and controls to a master control system monitored from a remote location. They evolved to a system of addressable devices connected to local control panels networked over a communication bus consisting of twisted, shielded pair cables. This greatly reduced wiring installation costs and provided great flexibility through programming. Similarly, an addressable monitoring module can monitor the alarm output contacts of a hazardous gas sensor control panel (or any other device with output contacts). Each alarm contact can have a discrete address. Fire alarm systems also have electrically-supervised addressable control relays that can be utilized for equipment shutdown and gas valve closure.

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Some gas sensor manufacturers have developed hardware and software to monitor their sensors using a personal computer. In addition to providing discrete alarm signals, the computer can display a graph of real time readings for each sensor. The archived data of each sensor can be plotted for any given time period for use as a troubleshooting tool. Reviewing archived sensor data during an alarm can help determine if the alarm was initiated by an interferent instead of an actual gas leak. If the detected concentration is a "spike" in lieu of a gradual rise in concentration, it is possibly a false alarm. Correlating the time of the gas alarm with the gases being used in the tool can help determine which gas was detected. Many of these systems lack electrical supervision and redundancy and are not designed for life safety use. In a multi-building campus, each building should contain a stand-alone monitoring system. Each building's system should be capable of monitoring sensors, generating local alarms and equipment shutdowns within that building. The various building panels should be networked into a campus-wide peer-to-peer configuration to share information, transmit alarms to the ECS, transmit equipment shutdown commands and transmit general evacuation alarms. In addition to alarm contacts, some sensors produce an analog 4 to 20 milliamp or 1 to 5 volt signal that can be connected directly to a computerized monitoring system such as a programmable logic controller (PLC) or a vendor's gas alarm management system. Simplex has developed an addressable module to monitor 4 to 20 miiliamp analog devices as well as software to display and archive actual analog levels. Other fire alarm manufacturers will likely offer similar functionality in the near future. A program matrix can be developed to initiate local audible and visual alarms, close gas valves, and control ventilation systems based on discrete alarm inputs. Once hazardous gas at the programmed high-level alarm point is detected, audible and visual alarms can be initiated and valves controlling the detected gas automatically closed. Audible alarms for different monitoring systems are required to be distinct from all other alarms. Programmable safety systems offer benefits not obtained with the older, hard-wired relay-based systems. System diagnostics can detect component failures. However, many microprocessor-based systems fail in unpredictable patterns and must be specifically configured for safety systems. Standards are available for software used in safety applications. Selection of a monitoring system depends on several factors related to specific gases, manufacturing process and facility requirements. Specificity of the system to particular gases is critical to avoid false alarms and to limit very costly disruption of manufacturing processes. Accuracy, sensitivity, fast response time and redundancy are essential features of a good hazardous gas monitoring system. Reliability of the monitoring system for long-term operation without frequent maintenance and downtime, as well as ease of operation and simple routine calibrations, is important from a production perspective. Codes allow the use of alternate materials and

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methods provided the intent of the code is met. Refer to the discussion of Alternate Materials and Methods in Chapter 6. Studies in other industries indicate that there are more nuisance shutdowns during process startup, shutdown and testing. System design, operation and testing procedures should consider those operational modes as well as normal production.

PLC-Based Monitoring Systems Standard programmable logic controllers (PLCs) can be applied in fault-tolerant and failsafe configurations to monitor gas sensors, archive data, and control valve closure and equipment shutdown. These are custom configurations not generally listed as a packaged system for life safety use. The 1997 Uniform Fire Code (UFC) requires the use of listed or approved gas monitoring and control systems. Review by regulatory agencies for approval requires personnel knowledgeable in configuration and programming of PLCs. Software-based safety systems are used in other industries for shutdown systems. These safety systems do not depend on a single system or a single type of system; protection is provided in many layers. Regulators need a basis to review software-based safety systems for safety and reliability in addition to meeting safety code performance criteria. Safety system integrators need detailed standard methods and tools to use in meeting performance criteria and need to know that if they follow the standard methods and criteria that regulators will approve their systems. When software engineering standards are not used, it is difficult to demonstrate to regulators that systems are reliable and safe. The International Electrotechnical Commission (IEC), headquartered in Geneva, Switzerland, develops recommended standards on electrical products, components and software. Their recommendations include references to safety and performance. The IEC does not perform any system testing. IEC Standard 61 508, Functional SafetySafety-Related Systems, identifies process issues, techniques and measures applicable to all aspects of functional safety. Some portions of this standard identify software validation, verification and test requirements. (This standard was in revision at the time of publication.) ANSI/ISA-S84.01, Application of Safety Instrumented Systems for the Process Industries, covers the definition and use of safety integrity levels (i.e., risk) for electrical, electronic and programmable electronic systems in the process industries. It provides information on design, installation, commissioning, startup, operation, maintenance and decommissioning. Refer to Chapter 3 of this guide for a discussion of IEC and ISA standards.

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PLC-based safety systems can be configured with hot backup or dual or triple redundancy to provide a system that is fault tolerant so that any single fault can be isolated, diagnosed and repaired quickly before a second fault occurs. Benefits of redundancy must be balanced with increased maintenance or downtime due to additional system components. Comprehensive diagnostics should be provided to identify component problems so they can be repaired before their redundant counterparts also malfunction, causing nuisance shutdowns.

Tdple Modular Redundancy (TMR) GE Fanuc and SiiverTech, a system integrator in England, developed software for a fault-tolerant, triple modular redundant (TMR) PLC-based system to monitor and control safety systems requiring conformance to IEC 61 508 and ISA S84.01 such as those used on ocean oil drilling platforms. It is imperative that safety shutdown systems function properly on oil drilling platforms because of the safety hazards (evacuation is difficult and possibly dangerous). These systems must also be dependable, fault tolerant, and redundant to avoid remote service calls. Because their TMR system utilizes functionality of GE Fanuc Genius I/O blocks, it is designated Genius Modular Redundancy (GMR). The GMR system normally consists of one to three identical CPUs (GE Fanuc 90-70 PLC) running identical application software. Each PLC receives all inputs and performs voting for discrete inputs and mid-value selection for analog outputs. For a typical input, three sensors are monitored by three different !/O blocks connected to different communications buses. It is possible to monitor one input sensor with three separate I/O blocks. However, having only one sensor provides a weak link in the life safety system. It is more typical and provides higher reliability and fault tolerance for each location to utilize three separate sensors. The GMR system compares the state or analog value of the three sensors and provides a 2-out-of-3 voted input to the application program. If there is a discrepancy between the original input data for an input and the voted input state, the GMR software automatically places an error message in the I/O fault table, where it is available to the software and application program. If a failure (discrepancy fault, autotest fault, or Genius fault) occurs, the GMR software adapts to reject the faulty data. Discrepant signals are filtered for a configurable time period to eliminate transient discrepancies caused by timing differences or transients. When GMR software compares analog input data, it checks each channel against discrepancy limits provided as a part of the system configuration for that input group. Any channel that varies by more than a configurable percentage from the intermediate value is reported as an error condition.

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In a voted input group, if only one input is available, the result of the voting depends on how the group is configured during startup. Either the one input value can be used, or the system can go to a default state. The GMR software will automatically test selected discrete inputs for the ability of the input electronics to recognize both the on and off state. GMR software cannot autotest analog I/O blocks. Input autotesting also detects circuit-to-circuit shorts. For applications such as fire and gas detection, normally-open inputs are generally monitored for open circuits on the lines, since an open circuit represents an alarm that would not be detected by the life safety system. GMR output voting is performed at the output block groups. Each controlled device is connected to a 4-block output group. Two Genius source outputs are connected in parallel on one side of the actuator and two Genius sink outputs are connected in parallel on the other side. Each block in the group receives outputs from each of the three separate PLC processors over three separate Genius communications buses. This type of grouping creates a fault-tolerant system where any single point of failure does not cause the system to lose control of a critical load. A GMR output group compares corresponding output data for each point as received from each of the three PLCs. If all three PLCs are online, the data from at least t w o must match. The block group sets each output load to match the state commanded by at least t w o of the PLCs. If communications with all PLCs are lost, the block outputs go to their default state as configured during setup at each block group. Output discrepancy monitoring is the process of monitoring the block output voting function to detect both processor discrepancies and lost communications between the block and other processors. All PLCs periodically monitor all blocks' discrepancy status. On interrogation by any PLC, the block responds with a discrepancy message indicating the discrepant output and the disagreeing PLC. The system uses output discrepancy checking to determine if the output data sent from each of the PLCs agrees with the voted output state. If a discrepancy check reveals that a PLC is sending incorrect output data to a block, the GMR system logs an output discrepancy fault in the I/0 fault table and sets the appropriate fault contacts. Genius I/0 blocks in GMR mode can detect on, off, short circuit, or open wire conditions on circuits set up as tristate inputs. A zener diode (a diode which limits voltage) is inserted in the circuit to detect short circuits.

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GMR safety systems have a higher initial cost than simplex or dual PLC-based systems. A GMR system requires 3 PLCs with 3 communication buses, 3 Genius input blocks for each sensor input and 4 output blocks for each controlled device along with the associated programming. However, reducing the number of costly false alarms can easily recover the higher initial expense. Certain configurations of GE Fanuc PLCs with Genius I/0 blocks and GMR software are approved for use in safety-relevant applications, such as emergency shutdown, by Technischer Uberwachungs-Verein (TUV), a German technical inspection agency similar in function to Underwriters Laboratories. A TUV site application approval consists of use of approved components, a review and check of the system (hardware, software and configuration) as installed and commissioned at the final site by a TUV site engineer. TUV requirements include" 9

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Triconex Corporation offers a TMR safety system similar in function to the GE system. However, the Triconex system is specifically designed and configured to be triple modular redundant: the three independent, parallel control systems with extensive diagnostics are integrated into a common set of hardware. The configuration is fully triplicated with three main processors and triplicated I/O modules with triplicated communications links to the I/0 modules. The Triconex TMR controller also provides capability to hot repair a failed I/O module without affecting system operation. This is accomplished by having a primary and spare I/O slot which is connected to the I/O terminations. If the primary I/O module develops a fault, the user can insert a replacement module in the spare slot. After the replacement module takes control of the I/O operation and the faulty module becomes inactive, the faulty module can be removed for repair. Output modules contain a fault tolerant output voter that insures a correct output even in the presence of a voter fault. Each output point on the module is generated by six switches, which are driven from the data received from the three processors. The output circuit is fault tolerant and will continue to output the correct value even if one of the switches is shorted or open. Another important feature of the output module is the integrated Ioopback circuit that allows the output module to run diagnostics on the output voter circuit so that output module failures can be detected and repaired quickly.

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Triconex developed their TMR system based on years of worldwide experience in safety and critical control in the petrochemical industry. The TMR architecture is completely transparent, all voting and diagnostics are automatic. A single sensor connects to a TMR input module which divides the signal into three separate paths for processing by the three control systems. Simplex and dual I/O modules are also available. The Triconex TMR system is certified by TUV as suitable for safety-related applications according to requirement classes AK1-AK6 (DIN V Standard 19250, section 05.94). TUV Class AK6 is equivalent to the IEC Safety Integrity Level (SlL) 3.

Fire Alarm Panel-Based Monitoring Systems The programmable logic controller (PLC) system described above utilizes i/O buses that are connected in a radial fashion. An addressable fire alarm system can provide most of the monitoring and control functions of such a system. Fire alarm I/O blocks are designated addressable modules or sub-panels. Some manufacturers can provide fire alarm I/0 buses configured in a Class A, Style 7 loop configuration that will still provide total communication if the bus sustains a single open or short circuit. The Style 7 I/O bus and the fact that the system is Underwriters Laboratories listed as an alarm system provides an advantage over the PLC-based system. With newly-available 4 to 20 milliamp addressable modules, a fire alarm system can now also log analog sensor data. Due to current Underwriters Laboratories listing requirements, most fire alarm systems do not communicate with non-fire alarm systems over a serial communications link. Any communication with or control of other systems is usually handled via monitored relay contacts. Fire alarm systems may be used to monitor and annunciate other hazards as long as the other systems do not interfere with the supervision of the fire warning system or prevent alarm or trouble signal operation. Alarm signals for evacuation due to gas detection are required to be separate and distinct from other alarms (such as fire alarms). This requirement can be addressed by using a voice alarm system listed for use in fire alarm systems. Different prerecorded messages can be used for the different alarm conditions. The use of a fire alarm system to monitor gas detection systems and annunciate evacuation alarms should be reviewed with the local authority having jurisdiction. Refer to the discussion on System Integration earlier in this chapter.

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Proprietary Network-Based Monitoring Systems Some sensor manufacturers develop proprietary network-based monitoring systems to connect sensors and control modules to a common network. When reviewing these systems, it is important to consider the following" Redundancy. The capability to interface with other manufacturer's equipment. Supervision of input and output circuit conductors. Listing as a complete life-safety system. Detector Electronics Corp (DetTronics) has developed the Eagle 2000, a hybrid monitoring and control system. The Eagle 2000 system I/O blocks can monitor 2 output contacts and an analog signal, and contain a control contact. The I/O blocks are connected to the host PLC with a Class A loop I/O bus. I/O bus fault isolation circuitry can allow uninterrupted communication in the event of a single open or short. The host PLC can communicate with other PLC systems over a serial bus. The Eagle 2000 system is Underwriters Laboratories listed as a NFPA 72 alarm system. Draeger Safety offers a system to monitor their Polytron 2 sensors. Draeger's Regard Highway Addressable Remote Transducer (HART) system allows sensor analog data to be transmitted over the same pair of wires that handle digital communication with the gas sensors. Sensor data, along with information about the sensing head, is communicated to a Draeger Regard Controller. Each Regard HART card can communicate with up to eight Polytron 2 sensor heads. A Regard Master Card can address up to 99 different sensing heads and distributes data to the Regard Modbus Card. The Regard Modbus Card enables the Regard System to communicate with computer equipment via RS232 and industry standard Modbus protocol. At this level, the system can be interfaced with data acquisition software such as Intellution's FIX system.

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LonWorks Network-Based Monitoring Systems LonWorks is an open, interoperable, peer-to-peer control network that distributes the processing throughout the network. No central controller is needed. Sensor modules communicate directly with control modules. This lowers the overall installation and life cycle costs, allows the use of devices from more than one vendor, increases reliability by minimizing single points of failure, and provides the flexibility to adapt the system to a wide variety of applications. The heart of the LonWorks system is the neuron chip that contains a configurable application program. The program includes a variety of function blocks (process and instrumentation diagram, analog function, discrete sensor, and type translators) that are configured using a PC or laptop and the installation tool LonMaker for Windows. The neuron chip can process sensor status, execute actuator control programs and communicate with other neuron chips. LonWorks allows networks to be configured in loop, star, or branched wiring configurations. Each subdomain or channel can contain up to 500 meters of wire. As control systems increase in size and complexity (requiring subdomains), LonPoint interface, scheduler and router modules can be added to provide I/O processing, application resources, time-keeping, logging and routing. These interface modules integrate sensors, actuators, and controllers into peer-to-peer, interoperable networks. The LonWorks control system can be combined with remote control systems or a remote supervisory station to form a wide-area control system. Gateways are available to bridge LonWorks networks with PLCs or other controllers. LonWorks is compatible with Wonderware's In Touch and National Instruments' Lab View humanmachine interface systems. Some gas sensor manufacturers (Ecosys MST, RKI and Zellweger) have incorporated the neuron chips into their sensors. The neuron chip has the capability to interface with sensors to allow remote troubleshooting and changing sensor setpoints or other features. Echelon has developed LonPoint interface modules that can interface sensors and actuators without integral LonWorks neuron chips into the control system. The advantage of using sensors with integrated neuron chips over the LonPoint interface modules is the ability to program and troubleshoot sensors over the network in addition to monitoring the sensor's digital or analog outputs. Several manufacturers offer relays and actuators with integral LonWorks neuron chips that can be incorporated into the hazardous gas monitoring system network to handle equipment shutdown or control. Distributed, intelligent devices provide several diagnostic benefits. Failures can be precisely pinpointed and communication errors can be isolated from device errors.

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Incorporating neuron chips into sensors allows the addition of specific diagnostics to the device. Safety-critical functions can be provided with redundancy and diagnostics to provide a strong system with high availability. LonWorks-based systems should incorporate the following features to improve safety: 9

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The LonPoint system is presently UL and CUL (Canadian use) listed under Standard 91 6, Energy Management Equipment. LonWorks systems are not specifically listed for gas detection monitoring, alarm and control systems. Refer to Chapter 7 of this guide on System Certification. Third-party review and certification of the LonWorks gas monitoring and control system is strongly recommended.

System Communication Configurations Fire alarm panels in a network configuration communicate over signaling line circuits defined as a circuit or path between any combination of circuit interfaces, control units, or transmitters over which multiple system input signals or output signals, or both, are carried. The National Fire Alarm Code (NFPA 72) categorizes the different types of signaling line circuits as "styles" based on their performance capabilities under abnormal (fault) conditions as follows. Style 0.5. This type of signaling line circuit does not provide any functionality for transmitting alarms under abnormal conditions. It can, however, report a trouble indication when there is a circuitry problem. This is also called a Class B system. Style 2. To meet the criteria for Style 2, a signaling line circuit must have the capability to maintain communications under the following abnormal circuit conditions: single open, single ground, or single open and ground. In the past, this configuration was designated Class A and was connected as a loop.

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Style 7. To meet the criteria for Style 7, a signaling line circuit must have the capability to maintain communications under the following abnormal circuit conditions: single open, single ground, wire-to-wire short, or single open and ground. From the standpoint of dependability, a Style 7 is more immune to abnormal conditions than a Style 2. This configuration also meets the requirements for a Class A loop.

Token Ring. A token ring is a loop (ring) configuration. A token is a string of data that travels around the loop from node to node. Only the panel (node) with the token can communicate to the network. Other nodes read the token (data) and respond to the received information. The token is then passed to the next node. During normal operation, the token moves in one direction. During a fault condition, the token moves in one direction up to the fault condition. Then the token reverses direction. Multiple faults result in each group of nodes establishing a separate network. A peer-to-peer token ring network consists of several stand-alone monitoring and control panels connected over a token ring network. Each panel can function as a separate system, but communicates status and control functions to other panels on the network. If communication between panels is lost, each panel can function as an independent system. Programmable logic controller (PLC) systems communicate over a bus which is left unconnected at each end (not in a loop configuration). If a fault occurs on the bus, communication with devices downstream of the fault is lost. This basic configuration could be considered a Class B signaling line circuit if electrical supervision features are provided. Redundant systems can be provided to integrate standby central processing units (CPUs) and redundant buses. A hot standby CPU (a CPU connected and running in the background) enables applications to continue even if there is a failure in the online CPU. The CPU normally controlling the system is designated the active unit; the redundant CPU is designated the standby unit. If certain system failures are detected in the active unit, control is transferred to the standby unit and redundant bus. For the complete PLC-based system to meet listed system functionality, circuits to monitored or controlled devices (sensors or control relays) must be electrically supervised. In some systems, communications with host devices and other PLCs can be carried over local area networks (LANs) such as Ethernet. Sharing information between the various monitoring and control systems in a facility can be very desirable; however, care should be taken to insure that faults in other systems will not affect the operation of the life-safety system (refer to NFPA 72, Section 3-8.14.2).

Other Monitoring System Considerations Each building should contain at least one life-safety monitoring and control system panel that will provide a stand-alone system for that building. Using a fire alarm panel-

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based system, the various control panels can be networked in a Token Ring configuration to provide a system that can be monitored and controlled from the emergency control station. Each building's life-safety alarm system should function independently if the Token Ring network is damaged. Hazardous gas monitoring sensor control equipment and life-safety monitoring and alarm panels should be located in easily accessible dedicated alarm rooms adjacent to the hazardous gas storage rooms. These equipment rooms should have a minimum 2hour fire rating to provide prolonged survivability during fires or hazardous gas releases. The alarm system should be both flexible and expandable through field programming. Communication loops should have the capability to add devices. Under the initial installation, the communication loops should only be loaded to 85 percent capacity. The entire monitoring and alarm system should be powered through an uninterruptible power system (UPS). This includes gas cabinet controllers, toxic gas sensors and their controllers, the system that monitors the toxic gas sensors, alarm indicating devices and gas valve shutdown systems. Equipment shut down circuits should be connected in a fail-safe mode. A well-designed hazardous gas monitoring system allows maintenance and testing of tools without affecting fab production. Alarm points should be combined in groups that relate to a particular tool. The alarm system should be programmable to put that tool group in a bypass mode. in bypass mode, alarms will be sent to the emergency control station, but will not automatically close gas valves or initiate audio/visual evacuation alarms in the fab. The ECS operator can verify with maintenance personnel working on the tool that the received alarm is from their maintenance/testing work. If not, the ECS operator can release the bypass and allow the system to activate shutoffs and alarms in accordance with the regular program. When the monitoring/alarm system is in bypass mode, a "system trouble" indication should be evident. Hazardous gas monitoring systems should also monitor flame or heat detectors inside gas cabinets handling pyrophoric gases. Some facilities also monitor excess flow switches in HPM gas piping. In Japan, pressure switches are used in lieu of excess flow switches. These sensors should be interlocked with the gas cabinet controller to close gas valves upon detection of flame, heat or excess flow (loss of pressure).

Emergency Control Station Codes require that gas-detection systems be monitored by an emergency control station (ECS), a continuously-attended location on site manned by properly trained personnel. In practice, the ECS is usually housed in the site security office. During an emergency, the ECS will be the command center for the on-site emergency response

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team and the fire department. The ECS should be housed in a dedicated secure room with minimum one-hour fire rated walls. A direct exterior exit will improve egress during emergency conditions. Emergency power should be provided for all ECS operational functions. The International Society for Measurement and Control, otherwise known as ISA, has developed the following recommended practices for the design of a control center which are applicable to an ECS. These standards could be used as a guide in developing an emergency control station. ISA RP60.1-1990 Recommended Practice - Control Center Facilities. ISA RP60.2-1995 Recommended Practice - Control Center Design Guide and Terminology. ISA RP60.3-1985 Centers.

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OSHA regulations in 29 CFR 1910.119 Appendix C, Compliance Guidelines and Recommendations for Process Safety Management Paragraph 13, provides recommendations for an emergency control center. The emergency control center should be sited in a safe zone area so that it could be occupied throughout the duration o f an emergency. The center would serve as the major communication link between the on-scene incident commander and plant or corporate management as well as with the local c o m m u n i t y officials. The communication equipment in the emergency control center should include a network to receive and transmit information by telephone, radio or other means. It is important to have a backup communication network in case o f p o w e r failure or one communication means fails. The center should also be equipped with the plant layout and c o m m u n i t y maps, utility drawings including fire water, emergency lighting, appropriate reference materials such as a government agency notification list, company personnel phone list, SARA Title III reports and material safety data sheets, emergency plans and procedures manual, a listing with the location of emergency response equipment, mutual aid information, and access to meteorological or weather condition data and any dispersion modeling d a t a . . 9. Employers at a minimum must have an emergency action plan which will facilitate the prompt evacuation o f employees when an u n w a n t e d release of highly hazardous chemical occurs. This means that the employer will have a

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plan that will be activated by an alarm system to alert employees when to evacuate. The intent of these requirements is to alert and move employees to a safe zone quickly. Delaying alarms or confusing alarms are to be avoided. The use o f process control centers or similar process buildings in the process area as safe areas is discouraged. Recent catastrophes have shown that a large life loss has occurred in these structures because of where they have been sited and because they are not necessarily designed to withstand overpressures from shockwaves resulting from explosions in the process area.

Based on Appendix C, an emergency control station should not be located in or adjacent to a semiconductor fabrication building. OSHA requirements for training personnel involved with hazardous substances could be interpreted to mean not employing ordinary security guards to monitor the emergency control station. ECS monitoring personnel should thoroughly understand the potential facility hazards and be trained specifically for hazardous materials monitoring and emergencies. The 1996 edition of NFPA 72, the National Fire Alarm Code, chapter on Protected Premises Fire Alarm Systems requires a fire command center that meets the following requirements. NFPA 7 2 3-1 2-6.5.1 A fire command center shaft be provided near a building entrance or other location approved by the authority having jurisdiction. The fire command center shaft provide a communications center for the arriving fire department and shaft provide for control and display of the status of detection, alarm, and communications systems. The fire command center shaft be permitted to be physically combined with other building operations and security centers as permitted by the authority having jurisdiction. NFPA 7 2 3-1 2.6.5.2 . . . All controls for manual initiation of voice instructions and evacuation signals shaft be located or secured to restrict access to trained and authorized personnel NFPA 72 3-1 2.4.2 The fire command center and the central control unit shaft be located within a minimum 1-hour fire resistive area and shaft have a minimum 3-ft. clearance about the face of the fire command center control equipment. The 1997 Uniform Fire Code requires that signals from the manual fire alarm system in a Group H- Division 6 occupancy facility (semiconductor fabrication facility) be received at the emergency control station. It can, therefore, be interpreted that the emergency control station must meet the above NFPA 72 requirements for restricted access and fire resistive areas.

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Recommended Programmed Alarm Response Presently, codes require alarm annunciation inside the facility and transmission to the emergency control station upon detection of a hazardous gas. Codes also require gas shutoff. The 1997 Uniform Fire Code Article 5101.10.4.3.3 outlines specific gas shutoff requirements. Shutoff of the gas supply is a recommended design practice regardless of whether it is a code requirement. Other programmed responses are negotiated between the facility operations personnel and the authority having jurisdiction (usually the fire department). The programmed response will depend on where the gas is detected and at what concentration. Once hazardous gas at the PEL or IDLH level (refer to UFC Article 80 versus Article 51 IDLH/PEL discussion in Chapter 3) is detected, audible and visual alarms should be initiated and valves controlling the detected gas closed. This audible alarm is required to be distinct from all other alarms. To minimize production interruptions, monitoring systems usually provide a warning alarm when concentrations of one-half the high level alarm are detected. This warning advises that there is a leak, but that the concentration is not immediately dangerous to health. Maintenance personnel are alerted to investigate and fix the source of the leak. If necessary or deemed prudent, maintenance personnel can manually shut off the gas. This type of shutdown may sometimes be done in a controlled manner to limit loss of product. Gas cabinet or double-containment piping annular space low-level alarms usually only notify the ECS and maintenance personnel who respond to search for the leak, but the gas is not shut down. Maintenance can decide to shut down the gas. A high-level alarm inside a gas cabinet should alarm inside the gas storage room and shut down all gas inside that cabinet. The Palo Alto TGO requires that gas be shut off upon failure of primary containment. A high-level detection inside the tool should notify the ECS, initiate an alarm in that area of the facility and shut down the gas supplying that tool. A facility breathing zone high-level alarm should notify the ECS, initiate a general alarm and shut down all hazardous gases serving that area of the facility. A gas storage room breathing zone high-level alarm should shut down all gases in the storage room, generate a local alarm and notify the ECS. Many facilities provide manual switches near exits to shut down all hazardous gases serving that part of the facility. If facility operating personnel believe a leak has occurred, they can manually shut off hazardous gas. Upon detection of an earthquake or fire, all hazardous gas valves should be shut down.

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A matrix correlating monitored inputs with alarm and control functions should be developed during design. The facility operator, in-house safety department, and the authority having jurisdiction should review and indicate approval of the matrix by signing it prior to completing system design. A typical matrix is shown in Fig. 5.

Shutdowns The life-safety monitoring and alarm system can utilize addressable control modules or I/0 blocks with the capability to shut down systems, turn on fans, etc. The circuitry from the alarm panel to the controlled device should be electrically supervised for system integrity. Provisions should be made to shutdown systems automatically via programming, or manually as the result of the operation of a local switch monitored by the system. Codes require the following systems to have shutdown capability: Power to work stations using flammables if exhaust is lost. Toxic and highly-toxic gas cabinets and valves upon fire alarm, hazardous gas leaks, earthquake or operator initiation. Bulk chemical distribution systems. An emergency button is provided outside bulk chemical storage rooms. Also automatic shutdowns upon general fire alarm evacuation, earthquake or detected leak. Also, capability to shut down manually by switch at the ECS. Exhaust systems via manual switches located outside the facility and outside each HPM storage room exit door. Facility makeup and recirculation air via manual switch located outside facility. Refrigeration room equipment (a Uniform Mechanical Code requirement) via manual switch located adjacent to the door into refrigeration room. Computer room HVAC (a National Electrical Code requirement). Flammable, oxidizing and pyrophoric gas systems at each point of use and at each source.

Alarm Annunciation The Uniform Fire Code and the International Fire Code do not provide requirements for the gas alarm other than that it be distinct from other alarm systems on site. However, other codes and standards do address general alarm system requirements. OSHA 29 CFR 1 910.119, Appendix C, Compliance Guidelines and Recommendations for Process Safety Management, paragraph 1 9 states: Employers at a minimum must have an emergency action plan which will facilitate the prompt evacuation of employees when an unwanted release of highly hazardous chemical (occurs). This means that the employer will have a

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plan that will be activated by an alarm system to alert employees when to e v a c u a t e . . . The intent of these requirements is to alert and move employees to a safe zone quickly. Delaying alarms or confusing alarms are to be avoided. The typically high levels of ambient noise in semiconductor fabrication facilities from air handling systems and machinery require an alarm system capable of high sound pressure levels in order to properly warn employees. Conversely, alarms that are painfully loud may cause employees to disable or modify alarm devices in their work areas. Chapter 6 of NFPA 72, the National Fire Alarm Code, addresses "minimum requirements for the performance, location and mounting required for notification appliances for fire alarm systems for the purpose of evacuation or relocation of occupants." While NFPA 72 does not specifically apply to hazardous gas monitoring systems, it provides the most concise criteria for similar alarm systems insuring audibility and visibility of alarms as well as backup power and electrical supervision of devices and circuits. NFPA 72 audible alarm system criteria include: A sound level of not less than 75 dBA at two feet or not more than 1 30 DBA. A sound level of at least 15 dBA above the average ambient sound level or 5 dBA above the maximum sound level having a duration of at least 60 seconds measured 5 feet above the floor in the occupiable area. NFPA 72 does not address the frequency of audible signals, but ISO Standard 7731, Danger Signals for Work Places--Auditory Danger Signals, recommends components in the 300 to 3,000 Hertz range and inclusion of sufficient energy in the frequency range below 1 5,000 Hertz to meet the needs of personnel with hearing loss. It is important that the alarm system be capable of properly notifying employees of the alarm condition. The use of horns or bells to annunciate alarm conditions can lead to confusion. During emergency situations, employees may be unable to recall whether a specific sound is associated with fire, gas or other alarm. This confusion can foster panic, delay in response, or incorrect action. Using voice alarm systems in lieu of bells or horns provides the capability to broadcast various tones along with short voice messages to impart critical information regarding evacuation routes or mustering areas (designated evacuation areas). If needed, messages can be broadcast in more than one language. Alarm tones can be selected that are in a different frequency than the ambient noise. A voice alarm system can also be used to broadcast information to emergency response personnel. If speakers are placed in mustering areas, the voice alarm system can be used to direct employees to move to another area, leave the facility, or return to their work area.

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Because voice alarm systems can be used for several alarm conditions, there is a cost savings when compared to installation of separate, distinct alarm annunciating systems for fire, gas, etc. Redundancy can be incorporated into the alarm system by providing more than one speaker circuit controlled by different amplifiers to each area. Present codes do not specifically require hazardous gas alarm annunciating systems to be electrically supervised, but the best industry practice is to incorporate all of the reliability and safety features currently required for fire alarm systems. It is only a matter of time before codes will require electrical supervision and backup systems for hazardous gas alarm systems. Inside cleanrooms with perforated raised floors, consider locating speakers under the raised cleanroom floor. This will allow cleanroom wall relocation without having to relocate speakers. Ensure that speakers are suitable for use inside cleanrooms. Some cleanroom managers limit equipment within the circulating air stream to types that will not generate particles that can affect the product. Typical speakers are painted with a particle-generating paint and have particle-generating back-boxes and paper cones.

Signaling Devices for the Hearing Impaired, ISO 11429 Ergonomics--System of Auditory and Visual Danger and Information Signals, and the NFPA 72, UL 1971

Americans with Disabilities Act also address installation requirements and location of visible signaling devices. Visible alarm notification devices are required only in public areas. Some authorities having jurisdiction and some facility safety or risk managers may require the use of visible devices in other than public areas. A visual alarm signal can be provided for hearing-impaired individuals to supplement audible alarm indicating devices. Strobe lights similar to those used for fire alarm systems should be used in lieu of rotating beacons which have historically been used for hazardous gas alarm systems. Motorized rotating beacons are difficult to electrically supervise and use much more power than a strobe light requiring larger UPS backup systems. There are several different alarm systems in a semiconductor manufacturing facility that require distinctive alarm signals. These include fire alarm, hazardous gas detection alarm, HPM storage room emergency alarm, and service (chemical delivery) corridor emergency alarm. Some designers provide a different color strobe light for each alarm system. In areas that require several different alarms, this could lead to a confusion of different colored strobe lights. A better solution is to provide only one color strobe light for visual alarm. Personnel with hearing disabilities would be alerted by the strobe light that there is an emergency condition. Other personnel without hearing disability could explain the type of emergency condition. Some facilities provide digital pagers with a vibrating call feature for their hearing-impaired personnel. A different message for each alarm condition could be broadcast to these pagers. Strobe lights inside lithography areas should have yellow lenses to eliminate interference with lithography processes.

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Emergency Response Upon detection of a leak, the emergency response team (ERT) and equipment engineers must try to locate the source. There may be visual clues, such as corrosive gases like hydrogen chloride or dichlorosilane causing corrosion at the leak point. When a Class I (Palo Alto TGO designation) gas is detected, codes require that the gas source be shut off. By the time the emergency response team mobilizes, dons Level A suits, warms up and stabilizes portable detection equipment and enters the fab, the fab ventilation system has probably exhausted the leaked gas and the ERT w o n ' t be able to detect the leak source. In this case, the ERT must determine whether a hazardous gas or an interferent material was sensed. Without data acquisition and archiving of sensed gas levels, it is more difficult to review the incident and determine the cause. The gas-monitoring data can be compared with process run data to match detection time with gases being used in that area of the fab. If the hazardous gas monitoring system archives gas concentrations, that information can be compared to process events and times when specific gases are being used in the particular process tools near the suspected leak. This information can be compared over time to help troubleshoot the alarm source. Reviewing archived information can also identify sensors that are drifting out of tolerance so that preventive maintenance can be performed prior to false alarms. Hazardous gas monitoring control equipment should be located in separate rooms that will allow access by ERT personnel during an emergency and provide some resistance to fire to maintain the monitoring system as long as possible during a fire.

Chemical Delivery/Service Corridor Emergency Alarm The chemical delivery/service corridor emergency alarm can be handled by a fireman's telephone system such as those used in high-rise buildings. The fireman's telephone provides an electrically-supervised UL listed life-safety alarm system to communicate details of chemical spills and other emergency conditions to the emergency control station. Using UL listed fire alarm systems provides electrically-supervised circuits. Fireman's telephone handsets in enclosures with clear, hinged doors can be provided in service corridors at the corridor exits (and at 1 50-foot intervals along the corridor if also classified as an exit corridor). Audible and visual alarms can be handled by lifesafety alarm speakers and strobe lights located in the service corridors. Fireman's telephone handsets should also be located at the bulk gas pad. Removing the telephone handset should automatically initiate the service corridor alarm strobe light and recorded warning message over the speaker system. The person removing the handset would be connected to the emergency control station and could describe the nature of the emergency and receive instructions.

9

Monitoring Exhaust Treatment System Discharge

Code Requirements Codes require that hazardous materials not be released into the environment. Accurate records of environmental releases must be maintained, and the authority having jurisdiction must be notified when there is an unauthorized discharge. The 1997 Uniform Fire Code (UFC) addresses the issues as follows.

Regarding Unauthorized Discharges 1997 UFC 8001.5.2.1 Records. Accurate records shaft be kept of the unauthorized discharge of hazardous materials by the permittee. 1997 UFC 8001.5.2.2 Notification. The chief shall be notified immediately when an unauthorized discharge becomes reportable under state, federal or local regulations. It can be reasoned that exhaust treatment system discharge would have to be monitored to determine if any hazardous gas is released into the atmosphere. The Uniform Fire Code and International Fire Code require monitoring of the discharge from exhaust treatment systems serving storage rooms for toxic and highly-toxic gases. The following excerpts are from the 1997 Uniform Fire Code.

Regarding Indoor Storage of Toxic and Highly-Toxic Compressed Gases 1997 UFC 8003.3.1.6 Gas Detection. A continuous gas-detection system shaft be provided to detect the presence of gas at or below the permissible exposure limit or ceiling l i m i t . . . .

149

150

HAZARDOUS GAS MONITORING

The gas-detection system shaft be capable of monitoring the room or area in which the gas is stored at or below the permissible exposure limit or ceiling limit and the discharge from the treatment system at or below one-haft the IDLH limit.

Regarding Toxic and Highly-Toxic Compressed Gases in Closed System Indoor Dispensing and Use 1997 UFC 8004.2.3.7.6 Gas Detection. accordance with Section 8003. 3. 1.6 . . . .

Gas detection shall be provided in

This requirement is also contained in the 2000 International Fire Code (IFC).

Regarding Indoor Storage and Use of Highly Toxic and Toxic Compressed Gases IFC 3704.2.2.10 G e n e r a l . . . The system shaft be capable of monitoring the discharge from the treatment system at or below one-haft the IDLH limit. Exception: A gas-detection system is not required for toxic gases when the physiological warning properties for the gas are at a level below the accepted permissible exposure limit for the gas.

The exception regarding physiological warning properties is only for toxic gases, not for highly toxic gases. The EPA also has requirements regarding discharge from treatment systems, but may not require continuous monitoring of actual discharge.

Monitoring Problems Treatment system discharge is one of the most challenging semiconductor monitoring applications. A wet scrubber exhaust stream contains extremely high humidity as well as trace amounts of several gases which can adversely affect the operation of sensors and sensing systems. Most sensor cells cannot function properly in high humidity. Electrochemical sensors generally utilize hygroscopic electrolytes, meaning that the amount of water in the electrolyte tends to reach equilibrium with the amount of water in the surrounding air. Typical electrochemical sensors in high humidity applications will have a shortened life. High temperatures in the discharge from burn boxes can dry out electrochemical sensor cells thereby shortening their useful life. High moisture content in an air sample exposed to paper-tape sensing technology changes the color of the paper tape which could cause an alarm. It is possible that by

HAZARDOUS GAS MONITORING

151

the time maintenance personnel investigating the alarm check the paper tape, the tape may have dried out leaving no indication of a hazardous material detection. High humidity levels can also have a bleaching effect on the paper tape, thereby affecting the sensor detection. Zellweger Analytics advises that excessive moisture in the sampled air can cause glycerol vapors from the hydrides Chemcassette tape to pass through the monitor console internal particulate filter and collect at the check valves inside the air pump head. This can negatively affect air pump performance and sample flow. Some manufacturers offer sensing systems that extract an air sample from the exhaust stream and condition it prior to exposure to the sensor. The sample conditioning dries the air to a point more suitable for exposure to sensors. However, this conditioning can also dilute the concentration of toxics causing the sensed concentration to inaccurately represent the actual discharge. Gas sensing systems that extract water-saturated air samples from scrubber discharge through tubing may be subject to inaccuracies. Water vapor can condense inside the tubing as the sample is drawn toward the sensor. Highly reactive gases can then react with the water inside the tubing, creating reaction byproducts which may affect sensing. Highly reactive gases may also be adsorbed by long lengths of sample tubing changing the gas concentrations reaching the sensor. Exhaust treatment system discharge can also contain hydrogen which is an interferent to some sensors. Monitoring of exhaust treatment system discharge has been so problematic that the Uniform Fire Code committee deleted the requirement for semiconductor facility treatment system discharge monitoring from the 1997 Uniform Fire Code. The 1997 Uniform Fire Code consolidated many of the general requirements of Article 80 into Article 51 which is specific to semiconductor facilities. Section 5101.10.4 identifies the areas requiring gas detection and does not list treatment system discharge. However, the requirement to monitor treatment system discharge is still a part of Section 8003.3.1.6. It can be argued that because Article 51 is specific to semiconductor facilities, monitoring of treatment system discharge at semiconductor facilities is not a code requirement. Other facilities regulated by Article 80 would be required to monitor treatment system discharge. However, the scope of Article 51 requires compliance with other applicable provisions of the Uniform Fire Code. 1997 UFC 5101.1.1 . . . The use, storage and handling of hazardous materials in semiconductor fabrication facilities classified as Group H Occupancies shaft be in accordance with Article 51, other applicable provisions of this code and the Building Code.

152

HAZARDOUS GAS MONITORING

The 2000 International Fire Code and 2000 UFC contain similar wording. It can be interpreted that the discharge from treatment systems handling toxic and highly toxic gases is required to be monitored.

Alternate Materials and Methods For applications that do require monitoring of treatment system discharge, it may be possible to provide an alternate means to determine if an unauthorized release has occurred. The 1997 Uniform Fire Code contains the following provision regarding the use of alternate methods. 1997 UFC 2.301 (a) The chief is authorized to modify any of the provisions of this code upon application in writing by the owner, a lessee or a duly authorized representative where there are practical difficulties in the way of carrying out the provisions of the code, provided that the spirit of the code shaft be complied with, public safety secured and substantial justice done. 1997 UFC 2.302 To determine the acceptability of technologies, processes, products, facilities, materials and uses attending the design, operation or use of a building or premises subject to the inspection of the department, the chief is authorized to require the owner or the person in possession or control of the building or premises to provide, without charge to the jurisdiction, a technical opinion and report. The opinion and report shaft be prepared by a qualified engineer, specialist, laboratory or fire-safety specialty organization acceptable to the chief and the owner and shaft analyze the fire-safety properties of the design, operation or use of the building or premises and the facilities and appurtenances situated thereon, to recommend necessary changes. The 2000 International Fire Code contains similar wording in Section 104.7.2. Both codes require the treatment system discharge to be not more than one-half IDLH.

Regarding the Design of Treatment Systems for Indoor Storage of Toxic and HighlyToxic Compressed Gases 1997 UFC 8003.3.1.5.2 Design. Treatment systems shaft be capable of diluting, adsorbing, absorbing, containing, neutralizing, burning or otherwise processing the entire contents of the largest single tank or cylinder or gas stored or u s e d . . . 1 997 UFC 8003.3.1.3.5.3 Performance. Treatmentsystems shallbe designed to reduce the maximum allowable discharge concentration of the gas to onehaft IDLH at the point of discharge to the atmosphere. When more than one gas is emitted to the treatment system, the treatment system shaft be designed to handle the worst-case release based on the release rate, the quantity and the IDLH for all the gases stored or used.

HAZARDOUS GAS MONITORING

153

Treatment system technology and sizing are based on the quantities and concentrations of the chemicals or gases used and the volume of air being exhausted. In facilities that exhaust huge quantities of air, it is not uncommon for the one-half IDLH dilution to be achieved by dilution with air running through the exhaust fan. Treatment system operation should be monitored to determine that there is proper air and water flow and that the scrubber sump Ph is in the proper range. If it can be shown by engineering calculations that a treatment system reduces the concentration of hazardous materials to less than one-half IDLH and treatment system monitoring indicates that the treatment system is functioning properly, then, theoretically, it is not possible for there to be an unauthorized release from the treatment system. Therefore, direct monitoring of the treatment system discharge would not be required if the functioning of the treatment system was monitored and alarmed. Alternate means to meet the intent of code approved by the authority having jurisdiction. exhaust treatment system discharge monitoring and efficiency and dilution of a release based exhaust system.

requirements must be reviewed and A submittal for alternate means for should include data on scrubber design on the volume of air handled by the

New plasma etching and chemical vapor deposition (CVD) technologies use significantly greater amounts of nitrogen trifluoride than earlier processes. It is possible that changes in the process chemistry can overload existing treatment discharge systems. Discharge treatment systems designed based on previous process chemistries may not be able to successfully treat all of the effluent leading to discharge of toxic or highly toxic gases. Direct monitoring of treatment system discharge may be warranted to ensure the treatment system is keeping up with process changes.

Direct Monitoring For those applications where scrubber monitoring is desired or required, PureAire Monitoring Systems developed a system specifically designed for in-situ monitoring of wet corrosive scrubber discharge. The scrubber monitoring sensor cell is an electrochemical type designed to operate even in 100 percent relative humidity conditions. As a result, there is no requirement for air sample extraction or air sample conditioning systems. PureAire's hydrogen chloride, chlorine, fluorine and hydrogen fluoride sensor cells are not cross-sensitive and are not susceptible to poisoning by hydrogen or other common scrubber system gases. Scott/Bacharach offers an electrochemical gas sensor for scrubber discharge monitoring which it markets as operating continuously in a condensing gas stream without blinding or loss of sensitivity. Presently, this sensor is only available for chlorine, chlorine dioxide, fluorine, bromine, ozone, hydrogen and oxygen.

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9

System Certification

Code Requirement The 1 997 Uniform Fire Code section 8001.4.4 and the 2000 International Fire Code Section 2703.2.3 specifically require that detection and alarm systems associated with the use, storage or handling of hazardous materials be listed or approved. To be listed, equipment is reviewed by a nationally recognized testing laboratory for conformance to one or more standards. This requirement for third-party certification is an important element of hazardous gas monitoring systems.

Relevant Certification Underwriters Laboratories (UL), Factory Mutual (FM) and TUV are among several thirdparty certification organizations in the United States. These organizations develop standards and test products for conformance to standards. Requirements vary between certifiers and each organization applies its own identifying label to products meeting their requirements. However, a product carrying a certification label may not be specifically tested for use in hazardous gas monitoring applications. It is necessary to determine the listing category or standards used in certification and decide if the product was tested under relevant use. For example, combustible gas sensors are typically listed for use in flammable atmospheres, a listing which only considers fire or explosive hazards. That listing is not relevant to their use as a hazardous gas sensor in a life safety system. Underwriters Laboratories has developed a category applicable to hazardous gas use (UL 2705, Gas and Vapor Detectors and Sensors) which includes requirements for sensor performance and evaluation of fire and shock hazards.

155

156

HAZARDOUS GAS MONITORING

Other organizations have developed standards of recommended practices for hazardous materials safety systems. The International Electrotechnical Commission (IEC) and the International Society for Measurement and Control (otherwise known as ISA) publish standards that expand on the requirements in OSHA's CFR 1910.119 Process Safety Management Rule and the EPA's 40 CFR 68 Risk Management Program.

Applicable Standards The following standards relate specifically to design and installation of life safety systems. Life safety systems could include hazardous gas detection and alarm systems. ANSl/ISA-S92.04.01 Performance Requirements for Instruments Used to Detect Oxygen-Deficient/Oxygen-Enriched Atmospheres. IEC 61508 Functional Safety- Safety Related Systems. (In revision at time of publication.) IEC SC65A WG9 1990 Software for Computers in the Application of Industrial Safety-Related Computer Systems. ISA-S84.01 1996 Application of Safety Instrumented Systems for the Process Industries. ISA-RP92.04.02 Installation, Operation and Maintenance of Instruments Used to Detect Oxygen-Deficient/Oxygen Enriched Atmospheres. UL 991 Safety-Related Controls Employing Solid-state Devices. UL 1998 Safety-Related Software. (Applies to software whose failure could result in a risk of injury to persons or loss of property.) UL 2075 Gas and Vapor Detectors and Sensors.

Third-party Review Organizations Review of safety systems for third-party certification or approval by the authority having jurisdiction is complex. Standards such as those above are generally performance-based and do not specify system configuration. They do not mandate any particular technology, level of redundancy, or testing methodology or interval. The safety system equipment vendors can only be responsible for certification of the equipment they supply: the logic box, sensors and actuators. It is possible for a system integrator to use certified equipment and connect the components in such a

HAZARDOUS GAS MONITORING

157

manner that the overall system will not meet the intended safety functions or recognized standards. Typical semiconductor fabrication facility gas detection and alarm systems are custom installations that would require review of the installed system to certify for conformance with the ISA and IEC standards. Depending upon the size and complexity of the system, field certification could cost between $100,000 and $250,000. Local authorities having jurisdiction may not have the resources for this complex review and approval process and may require third-party certification. Third-party certification offers benefits to designers, owners, users, and vendors as well as authorities having jurisdiction. A safety system complying with standards such as those above should minimize the number of nuisance trips (shutting down fabrication production) and minimize the probability of system failure. In addition, by the act of reviewing and certifying the system, the third-party absorbs some liability for the proper operation of the system. A component of OSHA 29 CFR 1910.7, Accreditation of Testing Laboratories, is the program to accredit Nationally Recognized Testing Laboratories (NRTL) to test and evaluate equipment and materials for workplace safety and to determine conformance with appropriate U. S. national regulatory standards. TUV Product Services (TUV-PS) is associated with Technische Uberwachungs Verein (TUV), a German organization of testing laboratories similar to Underwriters Laboratories in the United States. TUV-PS is the leading testing and certification body for safety instrumented systems worldwide (the U. S., Japan, Europe and the Pacific area) with 8,500 employees in more than 60 engineering disciplines. TUV-PS is a Nationally Recognized Testing Laboratory accredited by OSHA and has developed a "Safety in Electronics" program to review and certify safety systems such as those used for hazardous gas monitoring. The TUV-PS review process addresses the following verification and validation segments for safety-related electronic systems: 9 Functional Safety to a certain Safety Integrity Level (SIL). (SlL is an ANSl/ISA-S84.01 criterion.) 9 Safety of the hardware and software. 9 Safety indications in the user manuals. 9 Basic safety including electrical shock and fire hazard. 9 Susceptibility to environmental stress. 9 Electromagnetic compatibility. 9 Quality engineering in production, field observation and revision handling. The TUV-PS review includes conformance to several OSHA, IEC and ISA standards.

158

HAZARDOUS GAS MONITORING

Factory Mutual Research Corporation (FMRC) recently formed the Risk Engineering and Reliability Certification group to handle review and certification of safety-related systems. Services offered by FMRC to safety system designers, vendors, installers and facility owners include: Risk Assessment. Identifies hazards and risks in a facility or process. A review of the system or facility for compliance to recognized standards is available. Figure 6 summarizes the elements covered in a typical risk assessment program. Reliability, Availability and Maintainability (RAM). Utilizes modeling to evaluate the performance of safety systems. Cost-effective alternatives are reviewed to improve the performance of the systems.

Safety Instrumented System Compliance. Certification of safety systems for compliance with ANSI/ISA $84.01 and IEC 61 508. TUV-PS and FMRC have recently agreed to work jointly to offer certification and commissioning services for safety systems consistent with IEC 61508 and ANSI/iSA S84.01.

9

Code Enforcement

Building officials, risk managers, planning and zoning commissions, and fire departments view the monitoring of hazardous gases from a code enforcement rather than compliance perspective. Although this chapter is written for them, it is also useful to designers and facilities to self-evaluate their systems. Code officials should be involved early in the design concept whether a facility is being built from the ground up or undergoing retrofit, renovation or expansion, in the best case, a community's zoning provides the first level of protection for the public in industrial areas where hazardous materials may be used. Good designers are aware of zoning and safety codes and present their concepts to the local authorities having jurisdiction long before construction plans are submitted for permit.

System Review The following basic issues need to be addressed when reviewing a hazardous gas monitoring and alarm system. Much of this information should be supplied in the facility's Hazardous Materials Management Plan (HMMP), Hazardous Materials Inventory Statement (HMIS), Process Hazard Analysis (PHA) or Risk Management Plan (RMP). THe 1997 UFC Sections 8001.3.2 and 8001.3.3 give the authority having jurisdiction the ability to require an HMMP and HMIS. These documents are similar to RMPs and PHAs required by EPA and OSHA. Gas storage locations with lists of all gases, concentration and quantities. Gases to be monitored (including reaction by products). Gas concentrations used for warning and high-level alarms. Gas use locations. Gas piping routing, valve manifold boxes and shutoff locations. Hazardous areas (with respect to the National Electrical Code Article 500). Gas sensor locations.

159

160

HAZARDOUS GAS MONITORING

Sensor suitability for a specific gas and monitoring location. Visible and audible alarm indicating device locations. Alarm zones (with respect to air handling zones). Actions to be taken if gas is detected. Monitoring and alarm system single-line diagrams. Redundancies and emergency power. Gas sensing instrument data sheets correlated to specific use locations. Process equipment data sheets indicating recommended gas sensor locations. System testing.

Third-party Review & Technical Opinion The 1 997 Uniform Fire Code Section 8001.4.4 requires detection and alarm systems associated with the use, storage or handling of hazardous materials to be listed or approved. Hazardous gas monitoring and alarm systems are highly complex and review with respect to code compliance is a tedious process for which many jurisdictions may not have the resources to perform. UFC Section 103.1.1 allows the authority having jurisdiction to require a technical opinion and report by an acceptable third party to analyze the fire-safety properties of the design. Where listings of components or the safety system architecture are not available, the third party can review the system for conformance to accepted standards. Methods to evaluate the safety of critical control systems were developed by the petrochemical and nuclear industries. Standards for safety systems have been developed by the International Society for Measurement and Control (ISA) and the International Electrotechnical Commission (IEC). ISA Standard S84.01, Application of Safety Instrumented Systems for the Process Industries, has been adopted as an ANSI standard. Review of safety systems with respect to accepted standards is one method to evaluate the acceptability of safety systems. Refer to Chapter 3 of this guide for a discussion of these standards.

Alternate Materials & Methods. The 1997 UFC Article 103.1.2 allows the authority having jurisdiction to review and approve alternate materials or methods that could address developments in technology or processes not specifically covered by codes.

Alarm System Matrix A matrix format can be used to correlate the actions to be taken upon the detection of hazardous gas with the sensor locations. The column headings across the top of the matrix are typically actions taken. The row headings are typically the general sensor locations. A sample matrix and discussion of equipment shutoffs is included in Chapter 5 of this guide. Although an alarm system matrix is not required by code, most facilities generate one and it is a useful tool for visualizing the general relationship between types of sensors and outputs (alarms and shutdown).

HAZARDOUS GAS MONITORING

161

Safety versus Reliability Safety systems that are simple, have few components, and are configured in a fail safe mode are generally the safest for personnel protection. As the number of components and system complexity increases, there are more potential points of failure. However, simple safety systems such as hard-wired relay systems are generally more difficult to modify and expand as the facility processes are changed or the fab is enlarged. A more complex programmable system is easier to revise to accommodate constantly changing semiconductor manufacturing. To improve reliability, redundant components and diagnostics can be added. If a system is configured to remain operational unless t w o redundant sensors both indicate a problem (20o2), process operation is less susceptible to costly nuisance trips. However, the system is less safe: if one of the redundant components fails to respond, the system would never shutdown because it is not receiving input from that sensor. If the redundant system is configured to shut down if either component detects an unsafe condition, the system is safer, but a single failed component could shut down the process. The greater number of redundant components, the greater probability that a component will fail. Triple redundancy systems with two-out-of-three (2oo3) voting can address both safety and reliability concerns, but are even more complex and contain even more components. Triple redundancy is discussed in Chapter 5. Although increased reliability decreases false alarms and costly emergency response, reliability cannot be equated with safety.

System Testing Safety systems should be tested at initial installation, after modifications and periodically during their lifetime. Although the Uniform Fire Code does not require specific safety system testing, IEC and ISA standards contain specific and comprehensive testing requirements. Fire alarm system testing requirements in NFPA 72 could also be used as a guide for testing hazardous gas monitoring systems. OSHA and EPA require safety systems to be installed in accordance with accepted standards. Accepted standards require both initial and periodic testing. Sections 8 and 9 of ISA Standard S-94.01 (see Chapter 3) cover installation, commissioning and testing of safety instrumented systems. They recommend a full functional test of sensors, logic and final control elements to ensure performance in accordance with the design to determine that: Sensors trip at the setpoints outlined in the design. Proper shutdown sequence is activated. Alarm annunciation system provides the proper alarm signal/message in the

162

HAZARDOUS GAS MONITORING

proper area. Alarms are sufficiently visible and audible. System reset functions work properly. Bypass and bypass reset features work properly. 9The system alerts the operator when bypass is activated. 9 Bypass does not result in the loss of detection and or annunciation at the emergency control center. Operation of manual shutdown stations function properly. Testing is documented to substantiate completion of all testing. Testing is satisfactorily completed prior to the introduction of hazardous production materials into the fab. System testing should also include functionality under emergency power conditions. To insure system fuctionality, gas sensors should be exposed to the target gas as a part of testing. The UFC requires automatic controls to be designed as fail safe. Thorough testing would include checking functionality of the safety system with failed components to insure the system fails to a safe condition. System testing requirements are covered in Chapter 3 of this guide.

Compliance Checklists Experienced jurisdictions have created comprehensive checklists for evaluating compliance with hazardous gas monitoring codes. Santa Clara County, California, has an excellent compliance checklist describing typical toxic gas system inspection violations on their Website at www.unidocs.org. Typical compliance issues include" Failure to monitor the room or area where the gas is stored. Failure to monitor treatment system discharge. Failure to provide audible and visible alarms inside and outside the storage, use or handling area. Failure to provide a seismically activated shut down. Failure to provide continuous monitoring of secondary containment. Failure to provide automatic fail-safe-to-close shutoffs for the following: 9 Gas detection. 9 Failure of primary containment. 9 Activation of fire alarm. 9 Failure of emergency power. Failure to transmit alarm signal to emergency control station. Failure to provide emergency alarm system. Failure to perform annual maintenance of all safety control systems. Failure to maintain records of maintenance and testing. Failure to provide emergency power for gas detection and emergency alarm systems. Failure to use logic devices and software listed or approved for safety applications.

HAZARDOUS GAS MONITORING

163

APPENDIX A HAZARDOUS GASES TYPICALLY MONITORED IN SEMICONDUCTOR FACILITIES

The following table of gases commonly used in semiconductor manufacturing was compiled from several sources. Not all sources provided the same results for each gas: entries set in parentheses were found in only one source; other entries were found in at least t w o sources. Each project's Hazardous Materials Management Plan (HMMP) or Risk Management Plan (RMP) should contain complete information for the designer's use. The following table simply offers a general overview of the hazards of materials to be considered during design. It is good engineering practice to obtain this data from more than one source, to search for the most recent data, and to verify HMMP or RMP data with the authority having jurisdiction before beginning design.

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Gas Name

HAZARDOUS GAS MONITORING

167

APPENDIX B This Technical Note from Zellweger Analytics provides a documented procedure for testing gas monitors. It is useful for the majority of available gas sensing technologies.

Protocol for Testing Toxic Gas Detectors TIN 1998-0219 Rev. 1 06-98

Introduction

Teflon, and Tedlar are registered trademarks of E.I. DuPont de Nemoirs & Co. Kynar is a registered trademark of Pennsalt Chemical Corp. 9Copyright 1998, Zellweger Analytics, Inc.

This publication is not intended to form the basis of a contract, and the company reserves the right to amend the design and specificaUon of the insg'uments without noUce.

Zellweger Analytics, Inc. 405 Barclay Blvd. Lincolnshire, IL 60069 For more information, contact Zellweger Analytics during normal business hours at:

(800) 323-2000 or (847) 634-2800

This protocol provides a comprehensive method to evaluate the performance of toxic gas detectors. A worksheet is included; this is a useful guide in recording the performance of gas detection sensors. It is also useful as part of a maintenance log for complete gas detection systems. To fully understand the merits of specific gas detection equipment, several parameters must be tested. These factors include response time, environmental conditions, effects of temperature, accuracy, sensitivity to potential interfering substances, recovery time, failure indication, stability (drift) and repeatability over time. Test conditions must simulate the real world; therefore the test conditions must simulate the working environment (temperature and humidity). Supplies and materials must be selected accordingly.

Equipment and Test Gas: Schematics of the recommended gas generation and dilution system are provided in Figures 1 and 2.

Figure 1 shows a typical single stage dilution gas generation rig. This is best utilized when diluting concentrated cylinders at ratios below 1000-to-1.

Rotometer 20 L/min

V--

valve 20 psi

Source Gas

=~.

=

Do Not Vent to Atmosphere

Referee ] Instrument or Gas Bag L Test Inslmment

Water Bubbler

Rotometer 0-1000 cc/min (or MFC)

I Sample Lines

Humidified Air 20 IJmin (or MFC)

~=

Diluted Gas

' " ','

Mixing Jar (Vented to

Atmospheric

RH Sensor

Pressure)

Note: When a dilution ratio of > 1000 to I is required, a double stage system should be used.

Figure 1. Single Stage Dilution Gas should be supplied from a reliable source. To achieve accuracy and consistency, it must be assured that the source is stable and within date code (eg. for cylinders and permeation tubes). Whenever possible, primary target gases should be used for calibration. Cross-calibrants (non-target gases which can cause a quantifiable response, but that are typically easier to handle) should be used only when gas detection manufacturers confirm accuracy of response. It is better if these cross-calibrants be used for semi-quantitative or qualitative work, eg.: triggering alarms and relays.

Protocol for Testing Toxic Gas Detectors courtesy of Zellweger Analytics, Inc.

Figure 2 shows a typical double stage dilution rig. This is utilized for diluting cylinders at ratios greater than 1000-to-1. Double stage dilution is the best method when generating low level mixtures is required.

Compressed Air Line 20 psi

Rotometer

20 L/min (or MFC)

Vent to Hood

Rotometer Rotometer

20 L/rain

20 L/min (or MFC)

/Water

20 psi

Rotometer Source Gas

Rotometer

O-1000cc/min (or MFC) Referee Instrument or Gas Bag Test Instrument

l,oJl

Humidified Air

Bubbler

0

0-1000 cc/min (or MFC) [ Sample Lines.

20 IJmin (or MFC)

Mixing Jar (Vented to

Atrnospher~

Diluted Gas

RH Sensor*

Pressure)

*RH Sensor is monitored and water bubbler pinch valve is adjusted to provide -45% _+5% RH.

Figure 2. Double Stage Dilution

If cylinder gas is used, a =referee" method must be used to ensure that accurate concentrations are being produced. Even certified cylinders may not provide the expected gas concentration, especially after storage. Good laboratory practice indicates the use of a referee method. It should also be noted that high quality permeation devices can provide excellent accuracy for many gases. For most applications, the sample gas should be prepared using humidified dilution air (to approximately 30.-60% RH; with 45% RH being optimal). This simulates real world conditions that are likely to be encountered dudng an actual event.

Protocol for Testing Toxic Gas Detectors courtesy of Zellweger Analytics, Inc.

All materials must be selected to ensure that any "wetted" surfaces in contact with the supplied gas are inert to the compound being tested. For example, when supplying HCI, tubing, fittings and all other wetted surfaces should be constructed of FEP Teflon; stainless steel is not appropriate, since it will react with HCI and other common industrial gases at ppm concentrations. Active, sample-draw instruments often pull high volumes of sample (several liters per minute). The volume of test gas generated must exceed the monitor's sample flow intake. When using low volume permeation devices to test these instruments, it will be necessary to collect several liters of sample gas in a Tedlar~ bag; then draw the sample gas from the bag. This bag could typically be 100 Liters in size. For several of the reactive, adsorptive gases the sample bag should be preconditioned to establish equilibrium between the sample gas and the surfaces of the bag. This will help to ensure that the concentration of the generated gas is maintained. The material of the bag should be suitable for the target gas; since some reactive gases may be adsorbed onto some materials. The bag should be checked with a referee method to ensure appropriate concentrations and efficient transfer from the source. For passive (non-sample draw) sensors, the manufacturer's recommended calibration cap (flow-through housing) should be used. In order to simulate typical field conditions, NIOSH protocol suggests a minimum face velocity. The face velocity is calculated by dividing the flow rate by the cross-sectional area of the flow housing. Concentration (ppm) -Cylinder Flow (cc/min) * Cylinder Concentration~oDm~ Total Flow [Cylinder +Dilution Flow] (cc/min) Note: Multiplygas concentration (ppm) by 1000

for cylinder concentration (ppb) Table 1 provides guidance when selecting gas generation equipment. The gases that are listed are commonly found or used in industrial environments. Information on these compounds is included to satisfy the need for cross-interference testing.

Protocol for Testing Toxic Gas Detectors courtesy of Zellweger Analytics, Inc.

If cross-interferents are present in ambient air or in the diluent air, another source of clean, humidified air or nitrogen should be used. The mass flow controlled output should be verified against an independent flow calibrator. A primary standard bubble flowmeter can be utilized for this purpose.

The gases utilized in this verification are very toxic. It is therefore essential that a thoroughly trained safety engineer or industrial hygienist be responsible for the generation of these gases and that the gas be generated in a well-ventilated area.

Table 1. Calibration Considerations for Common Gases (continued) j

Gas

Tubing and other materials in contact with sample gas

Source(s) i

Hydrogen Bromide (HBr)

i

|

i

i

Aluminum cylinders; 316 stainless steel regulator with Teflon gasket and stainless steel mass flow conlmfler.

iml

i

i i

Special

considerations i

FEP Teflon, polypropylene, Kynar, Tedlar Stainless steel and most other metals are not acceptable

iiii

iiiii

Refer to Note 1. Diffusion vials are recommended.

Permeation device |

Hydrogen Chloride (HCI)

ii

i

ii

i

ii

Aluminum cylinders; coated brass regulator with internal Monel parts; Monel mass flow controller

iii,

iii

i

ii

FEP Teflon polypropylene, Kynar, Tedlar

i

Refer to Note 1.

Stainless steel and most other metals are not acceptable

Diffusion vials are recommended.

Permeation device i

Hydrogen Fluodde (HF)

,

Aluminum cylinders; Monel, Iconel,| nickel or copper regulator with Teflon packing; Monei mass flow cortroll~r.

ii

i

i

i

FEP Teflon polypropylene, Kynar, Tedlar

i.i

i

ii

ii

Refer to Note 1.

Stainless steel and most other metals are not acceptable

Permeation device i

Ammonia (NH3)

i

Aluminum cylinders ; stainless steel regulator or Monel mass flow controller

llll

i

i

i

FEP Teflon, polypropylene, Kynar, Tedlar

i

iii

Refer to Note 1.

Permeation device ii

ill

i i i

i

ill

Note 1. Permeation devices have low volume output. Gas bags need to be used to accumulate the large sample volumes needed for gas testing. Fill and flush bags several times for reactive gas conditioning.

Protocol for Testing Toxic Gas Detectors courtesy of Zellweger Analytics, Inc.

,

,i

i

Tubing and other materials in contact with sample gas

Gas

Source(s)

Amine (AsH3)

Aluminum cylinders, N 2 balance, stainless steel regulator with TeflorP gasket; stainless steel mass flow controller

Phoshine (PH3)

Aluminum cylinders, Nzbalance, stainless steel regulator with Teflon gasket; stainless steel mass flow controller

Silane (Sill 4)

Aluminum cylinders, N2 balance, 8tainless steel regulator with Teflon gasket; stainless steel mass flow controller

Diborane

FEP Teflon polypropylene, Kynar, Aluminum cylinders, N2 balance, Tedlar, Monel, brass stainless steel regulator with Teflon gasket;, stainless steel or Monel mass flow controller

i

i

ii

i

i1=

i

FEP Teflon polypmpylene, Kynar, Tedlar, Monel, brass

i

i

(B=H~)

ii

FEP Teflon polypropylene, KynaP, Dilulion using mass flow TedlaP, Monel, brass

,,,

i

i

i

Special considerations

i,,

FEP Teflonpolypropylene, Kynar, Tedlar, Monel, brass

Difficult to achieve high volumes with permeaUon devices.

i

i

i

FEP Teflon, Kynar, Tedlar

Aluminum cylinders; stainless steel regulator; stainless steel or Monel mass flow controller

Chlorine

(c~)

Stainless steel and most other metals are not acceptable.

See Note 1.

Permeation device IB

Carbon Monoxide

(co) Hydrogen (Hz)

Aluminum cylinders; stainless steel regulator; stainless steel or Monel mass flow controller Aluminum cylinders; stainless steel regulator; stainless steel or Monel mass flow controller

FEP Teflon, polypropylene, Kynar, Tedlar, Monel, brass

i

Isopropyl Alcohol (IPA)

Nbte I. ~ ~ s

ii

II

FEP Teflon, polypropylene, Kynar, Tedlar, Monel, brass

i

~tion

i

i

i

Syringe injection into gas bag

~OeS

Concentration in cylinders may not be stable.

i

i

i

FEP Teflon, polypropylene, Kynar, Tedlar, Monel, brass

have low ~ cxCput. Gas ba:js need to be used to ~ E~llardflu~]mgs~altfmmf=rreac~gas~.

Readily available liquid

the lazoje ~ e

Protocol for Testing Toxic Gas Detectors courtesy of Zellweger Analytics, Inc.

Response Time Response time may be measured in three basic ways. 1. One method of response time specification is provided as follows: eg." Tgo = x seconds

eg.: Tso = y seconds

The term Tgo provides the amount of time in which 90% of the actual concentration is reported. The term Tso provides the amount of time required in which 50% of the actual concentration is reported. By reporting the response time in this manner, the illusion of quick response is given; but it may hide a significantly slower, partial response. In essence a T~oo time would provide the time it takes to indicate the true concentration of gas present. 2. A second method of providing response time is the amount of time required to indicate a 1 TLV concentration of gas when a 1.6 level of gas has been applied. This is the standard method of specifying response times in Japan. 3. The third way is to simply state the response time. This generally indicates the amount of time required to display an accurate reading of the actual concentration (similar to the T~oo concept described above). This provides a straightforward specification for accurate response indication. It is important to test for speed of response throughout the useful life of the sensor. In other words, the response time of a sensor may become significantly longer as the detector ages. It is not enough to simply test a sensor after the initial installation date; the sensor should be tested just prior to the calibration or replacement of the existing sensor. This test indicates, before adjustment, how well a sensor has been performing during the time it has been in service.

Protocol for Testing Toxic Gas Detectors courtesy of Zellweger Analytics, Inc.

Note: Some detectors may need to be "conditioned" before they will reasonably respond to gas. It is important that if a sensor has not been gased for several weeks, the response time should be noted for the first application of gas. Under field conditions there is normally no target gas present, so it is important to replicate this by taking the data upon the first exposure of the sensor to the target gas.

Accuracy, Drift and Repeatability:

Accuracy is tested by comparing a known concentration against the stabilized reading of the sensor with a known concentration of test gas. This test should be performed before calibration and several months after calibration to ensure that the instrument will perform acceptably throughout its life. Any calibration adjustments that are made to the sensor are primarily done to ensure accuracy at the time of calibration. On occasion the sensor may be adjusted to provide a quicker response by sacrificing accuracy; the instrument will read higher than the actual concentration.

Drift occurs when, under a no-gas condition, any non-zero readings are observed. Drift can add to, or subtract from, the reported concentration. Excessive drift can cause false alarms, false negative readings, or instrument faults.

Repeatability describes how closely a sensor can read to a gas concentration that it previously reported. This test does not necessarily ensure accuracy.

Lowest Detectable Limits: The Lowest Detection Limit (LDL) is important. Several manufacturers provide a published range of detection, but they do not provide this minimum detection limit, due to their inability to detect low concentration levels. The capability to detect low level concentrations under operating conditions means earlier detection, before a small leak becomes a significant problem.

Protocol for Testing Toxic Gas Detectors courtesy of Zellweger Analytics, Inc.

Cross-Sensitivity to Potential Interferents: Many areas that require toxic and combustible gas detection have the potential for other, non-target gases to be present. These potential interferents include solvents (eg.: acetone, isopropyl alcohol), ammonia, hydrogen, hydrogen peroxide and carbon monoxide. These compounds should be applied to the cell to determine positive (false alarm) or negative (masking) effects, as well as the potential for permanent poisoning of the sensor. These should be applied to the sensor when testing for the target gas to observe their effect on the response to the target gas in the presence of potential interferents. For example, if IPA is a negative interferent, the response to the target gas will be lower than anticipated. The possibilities of permanently poisoning some types of sensors should also be considered. As previously indicated, potential interferents which are easy to handle and which are not highly toxic are sometimes used to calibrate sensors. A correlation factor is applied, based on empirical, controlled laboratory testing. Again, this may not be an accurate method of calibrating, since the correlation factor may depend on the characteristics of the individually manufactured sensor.

Life Testing: Several of the above sections include testing for performance characteristics that need to be checked upon initial installation. These parameters should also be checked just prior to maintenance. It is important to check these parameters before and after maintenance. The detector should perform virtually as well, 3 or 6 months after calibration, as it did during its last calibration.

Other Performance Considerations: Performance considerations are not limited to those outlined above. Other features of the gas detector which should be considered include real-time failsafe fault/failure warnings, verifiable proof of the gas release, ownership cost, interruption of normal operations during calibration, permanent sensor poisonability at high concentrations, impact of false alarms due to cross interference or drift, EMI/RFI susceptibility and others.

Protocol for Testing Toxic Gas Detectors courtesy of Zeliweger Analytics, Inc.

Gas Testing Checklist Hill

i

i

Sensor Sedal Number/I.D.:

Location9, ii

i

i

i

Gas Typeii

i

Testing to be repeated I ~ o m recalibmtion on (date): i i

i

,

Results

Test Procedure

Results

Results

After Calibration

After Calibration

Im~dB~Sj Immediately 3 Months Before Calibration ,

Results 6 Months

After Calibration

i

Date: Tested By: Verified By: Zero Reading: Response time: i

75O T90 T100 J

~me ( . c ) ~

m m

1 TLV

ivenl.6 TLV as: Accuracy: Actual Gas Concemation~ % de~ation:. . . . . Recovery Time: .time (sec) to mlum to zero after test as is removed: Interferents.~~..,...,,_~~~ Potential Gas 1 i

i

Gas 3

c,",

Proof of Gas Presence? (Y or N): !Lowest Detectable Limit: Resolution (Ppb or ppm),: ,EMI/RFI Susceptibility? (Y or, N): Self-d ia~ nostice/Failsafe t;apabHity: . .

.

.

Note: The last four items may not be easily verified in the field. Individual manufacturers may need to be consulted.

Protocol for Testing Toxic Gas Detectors courtesy of Zellweger Analytics, Inc.

HAZARDOUS GAS MONITORING

177

APPENDIX C 1 9 9 5 S U P P L E M E N T T O T H E UFC T A B L E A - V I - A - 1 -- N O R M A L I Z A T I O N F A C T O R

Time (Hours) 0.5 1.0 1.5 2.0 3.0

Multiply By 0.7 1.0 1.2 1.4 1.7

Time (Hours) 4.0 5.0 6.0 7.0 8.0

MultiDIv Bv 2.0 2.2 2.4 2.6 2.8

Toxic and highly-toxic gases include those gases which have an LCso of 2,000 ppm or less when rats are exposed for a period of 1 hour or less. To maintain consistency with the definitions for these materials, exposure data for periods other than 1 hour must normalized to 1 hour. LC6o data which are for other than 1-hour exposures need to be normalized to 1 hour by multiplying the LCso data for the available time by the factor indicated in Table A-VI-A1. The preferred mammalian species of LC6o data is the rat, as specified in the definitions of toxic and highly toxic in UFC Article 2 (refer to Glossary).

To classify mixtures of compressed gases which contain one or more toxic or highly-toxic components, the L Cso of the mixture must be determined. For mixtures of two components where the hazardous component is diluted with a nontoxic gas such as an inert gas, use the following formula to determine the LCso of the diluted mixture:

LC6o of Gas Mixture (in ppm) = 1 / Concentration of Toxic Component in Decimal Perc.ent LCso of Toxic Component

For example, diborane in 100 percent concentration has a LC6o of 40 ppm (for a 4-hour exposure) which classifies as a highly toxic. First the LCso must be normalized to 1 hour by using a normalization factor from Table A-VI-A-1.

LC6o(1-hour) = 2 x 4 0 p p m

=

80ppm

Where: 2 = the normalization factor to convert from 4 hours to 1 hour.

178

HAZARDOUS GAS MONITORING

The LCso of a mixture diluted to 200 ppm with hydrogen would be 400,000 ppm which is greater than 2,000 and therefore does not meet the definition of toxic. However, the gas mixture is essentially hydrogen and code requirements relating to storage and use of hydrogen would apply.

LCso of B2H6 (200 ppm mixture)

1 / 0.0002 80 ppm

= 400,000 ppm ( > 2 0 0 0 non-toxic)

For a multicomponent mixture where more than one component has a listed LCso, the LC6o of the mixture is estimated by use of the following formula:

LC6om = 1 /(Cil/LC6oil) + (Ci2/LC6oi2) + (Cin/LCsoin)

The calculations for determining the LC6o of diluted mixtures require access to gas data for the project, LC6odata from handbooks and a general understanding of chemistry. Most authorities having jurisdiction require these calculations to be submitted with the Hazardous Materials Management Plan for the project.

HAZARDOUS GAS MONITORING

179

APPENDIX D SAFETY SYSTEM SUPPLIERS The following manufacturers are not recommended or approved by the author, but are simply listed as a design resource.

AIM Safety USA 1624 Headway Circle, Austin TX 78754 Telephone: 800.275.4246 Internet: www.aimsafety.com

Carbon Monoxide Sensors Chlorine Sensors

ATMI (see MST EcoSys and TeloSense EcoSys) Bacharach (see Scott/Bacharach) Bionics Instrument Co. (PureAire Monitoring Systems) 5420 Newport Dr #57, Rolling Meadows IL 60008 Telephone: 888.788.8050 Facsimile: 847.788.8080 Internet: www.bionics instrument.corn E-mail: PureAirl @aol.com

Electrochemical Sensors

Bio Systems 651 S Main St, Middletown CT 06457 Telephone: 800.711.6766 Facsimile: 860.344.1068 Internet: www.biosystems.com E-mail: [email protected]

Catalytic Bead Sensors Oxygen Depletion Sensors

CEA Instruments, Inc. 16 Chestnut St, Emerson NJ 07630 Telephone: 888.893.9640 Facsimile: 201.967.8450 Internet: www.ceainstr.com/main, html E-mail: [email protected]

Electrochemical Sensors

CSE Corporation 600 Seco Rd, Monroeville PA 15146-1428 Telephone: 800.245.2224 Facsimile: 412. 856. 9203

Catalytic Bead Sensors Electrochemical Sensors Personnel Monitors

180

HAZARDOUS GAS MONITORING

Detector Electronics Corp (DetTronics) 6901 W 1 1 0 S t Minneapolis, MN 55438 Telephone: 800.765.3473 Facsimile: 612.829.8750 Internet: www.detronics.com

Catalytic Combustible & Infrared Hydrocarbon Gas Sensors, Refrigerant Gas Sensors, Flame Detectors, Eagle 2000 Monitoring Network

Draeger Safety, Inc. P O Box 120, Pittsburgh PA 15230-0120 Telephone: 800.922.5518 Facsimile: 800.922.5519 Internet: www.draeger-usa.com

Catalytic Bead Sensors Electrochemical Sensors Infrared Combustible Gas Sensors Monitoring Systems

Echelon Corporation (LonWorks) 4015 Miranda Ave, Palo Alto CA 94304 Telephone: 650.855.7400 Facsimile: 650.856.61 53 Internet: www.ionworks.echeion .corn/Ins E-mail: [email protected]

Network Services Architecture

EcoSys Monitoring Systems (see MST and TeloSense) Edwards Systems Technologies 6411 Parkland Dr, Sarasota FL 34243-4037 Telephone: 800.226.2333 Internet: www. est. net/

Fire alarm systems with gas monitoring capability.

EIT (see Scott/Bacharach) Enmet Corporation P O Box 979, Ann Arbor MI 48106-0979 Telephone: 734.761.1270 Facsimile: 734.761.3220 Internet: www.enmet.com/

Electrochemical Sensors

Foxboro P O Box 500, East Bridgewater MA 02333 Telephone: 888.369.2676 Facsimile: 508.378.5505 Internet: www.foxboro.com/

Gas Chromatograph

GE Fanuc Automation P O Box 8106, Charlottesville VA 22906-8106 Telephone: 800.648.2001 Facsimile: 610.437.5212 Internet: www.gefanuc.com Internet: GESemiconductor.com

PLC-based Monitoring & Control Systems

HAZARDOUS GAS MONITORING

181

GasTech 8407 Central Ave, Newark CA 94560-3431 Telephone: 877.427.8324 Facsimile: 510.794.6201 Internet: www.gastech-inc.com

Catalytic Bead Sensors Electrochemical Sensors Infrared Sensors

Genesis International, Inc. 1040 Fox Chase Industrial Dr, Arnold MO 63010 Telephone: 636.282.0011 Facsimile: 636.282.2722 Internet" www. genesis-international, corn E-mail: MAIL@Genesis-international. com

Refrigerant Gas Sensors Oxygen Depletion Sensors

INTEC Controls P O Box 12506, La Jolla CA 92039 Telephone: 858.578.7887 Facsimile: 858.578.4633 Internet: www.inteccontrols.com

Combustible Gas Sensors Solid State Refrigerant Gas Sensors Solid State Sensors

International Sensor Technology 3 Whatney, Irvine CA 92618-2824 Telephone: 800.478.4271 Facsimile: 949.452.9009 Internet: www.intlsensor.com

Catalytic Bead Sensors Electrochemical Sensors Infrared Sensors Photoionizaation Detectors Solid State Sensors

Interscan Corporation P O Box 2496, Chatsworth CA 91313-2496 Telephone: 800.458.6153 Internet: www. gasdetection.com/

Electrochemical Sensors

In USA, Inc. 87 Crescent Rd, Needham MA 02194 Telephone: 800.798.4029 Facsimile: 781.444.9229 Internet: www.inusaozone.com

Ozone Sensors

Invensys P O Box 2940, Loves Park IL 61132-2940 Telephone: 81 5.877.0241

Refrigerant Gas Sensors

LonWorks (see Echelon) Manning Systems, Inc. 11511 W 83 Terrace, Lenexa KS 66214 Telephone: 913.894.1185 Facsimile: 913.894.1296 Internet: www.manningsystems.com

IR Refrigerant Gas Sensors

182

HAZARDOUS GAS MONITORING

Matheson Tri-Gas 625 Wool Creek Drive, San Jose CA 95112 Telephone: 408.971.6500 Facsimile: 408.275.8643 Internet: www.mathesontrigas.com

Combustible Gas Sensors Electrochemical Sensors

MDA (Zellweger Analytics) 405 Barclay Blvd, Lincolnshire IL 60069-1405 Telephone: 800.323.2000 Facsimile: 708.634.1371 Internet: www.zelana.com

Combustible Gas Sensors Electrochemical Sensors Paper Tape Sensors

MiI-Ram Technology, Inc. 2360 Qume Dr Ste C, San Jose CA 95131 Telephone: 888.464.5726 Facsimile: 408.324.1661 Internet: www.mil-ram.com

Electrochemical Sensors

MSA P O Box 427, Pittsburgh PA 15230 Telephone: 800.672.2222 Facsimile: 41 2.967.3451 Internet: www.msanet.com

Combustible Gas Sensors Electrochemical Sensors IR Refrigerant Gas Sensors

MSP Corporation 1313 E Fifth St SE #206, Minneapolis MN 55414 Telephone: 612.379.3963 Facsimile: 612.379.3965

Cleanroom Fogger

MST (Ecosys MST) 975 Deerfield Pkway, Buffalo Grove IL 60089 Telephone: 800.547.2900 Facsimile: 847.808.9976 Internet: www.mst-us.com

Combustible Gas Sensors Electrochemical Sensors Satellite MonitoringNetwork

Omniguard Sensors Division/Meggitt Avionics 10 Ammon Dr, Manchester NH 03103-7466 Telephone: 800.842.4291 Facsimile: 603.669.0931 Internet: www.meggittavi.com E-mail: [email protected]

Silane Flame Detectors

On-line Technologies 87 Church St, East Hartford CT 06108 Telephone: 888.384.7888 Facsimile: 860.289.7975 Internet: www.online-ftir.com

FTIR Spectroscopy Monitors

HAZARDOUS GAS MONITORING

183

PWC Technologies, Inc. 13270 SW 6 St, Beaverton OR 97005 Telephone: 800.677.6109 Facsimile: 503.646.9975 Internet: www.pwctech.com

Cleanroom Fogger

Perkin Elmer MS 10, 761 Main Ave, Norwalk CT 06859-0010 Telephone: 800.762.4000 Facsimile: 203.762.4228 Internet: www.pecorporation

Mass Spectrometer

PureAire Monitoring Systems, Inc. 5420 Newport Dr #57, Rolling Meadows IL 60008 Telephone: 888.788.8050 Facsimile: 847.788.8080 E-mail: [email protected]

Ambient & Extractive Monitoring Systems Electrochemical Sensors

RKI Instruments, Inc. 1855 Whipple Rd, Hayward CA 94544 Telephone: 800.754.5165 Facsimile: 510.441.5650

Catalytic Bead Sensors Electrochemical Sensors Infrared Sensors, Solid State Sensors Paper Tape & Extractive Sensors

Scott/Bacharach Instruments 251 Welsh Pool Rd, Exton PA 19341 Telephone: 800.872.8008 Facsimile: 41 2.963.2091 E-mail: info@scottbacharach, com Internet: www.scottbacharach .com

Catalytic Bead Sensors Combustible Gas Sensors Electrochemical Sensors Hydrogen Sensors Oxygen Depletion Sensors

SenTech Corporation 5745 Progress Rd, Indianapolis IN 46241 Telephone: 888.248.1988 Facsimile: 317.248.2014 Internet: www.sentechcorp.com

Refrigerant Gas Sensors

Sensidyne 16333 Bay Vista Dr, Clearwater FI_ 33760 Telephone: 800.451.9444 Facsimile: 727.539.0550 Internet: www.sensidyne.com

Electrochemical Sensors

Sensor Electronics 5500 Lincoln Dr, Minneapolis MN 55436 Telephone: 800.285.3651 Facsimile: 612.938.9617 Email" [email protected] Internet: www. sensorelectronic.com

Catalytic Sensors Combustible Gas Sensors Electrochemical Sensors Oxygen Depletion Sensors Solid State Sensors

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Sierra Monitor Corporation 1991 Tarob Ct, Milpitas CA 95035 Telephone: 800.727.4377 Facsimile: 408.262.9042 Internet: www. sierramonitor.com/

Combustible Gas Sensors Electrochemical Sensors Hydrogen Sensors Oxygen Depletion Sensors

Simplex Simplex Plaza Gardner, MA 01441-0001 Telephone: 800.746.7539 Internet: www.simplexnet.com

Fire alarm systems with gas monitoring capability.

TeloSense (EcoSys TeloSense) 5369 Randall PI, Fremont CA 94538 Telephone: 510.490.2087 Facsimile: 510.490.6485 Internet: www.telosense.com

Acoustic (Hydrogen) Sensors FTIR Spectrometer Sensors Flame Emission Spectrometry Sensors

Thermal Gas Systems P O Box 803, Roswell GA 30075 Telephone: 770.667.3865 Facsimile: 770.667.3857 E-mail: [email protected] Internet: www.thermalgas.com

Refrigerant Gas Sensors Oxygen Depletion Sensors

Toxalert, Inc. P O Box 159, Mound MN 55364 Telephone: 612.472.4541 Facsimile: 612.472.4960

Refrigerant Gas Sensors

Triconex Corporation 15091 Bake Parkway, Irvine CA 92618 Telephone: 949.699.2100 Facsimile: 949.768.6601 Internet: www.triconex.com

PLC-based Monitoring & Control Systems

Zellweger Analytics (MDA) 405 Barclay Blvd, Lincolnshire IL 60069-1405 Telephone: 800.323.2000 Facsimile: 708.634.1371 Internet: www.zelana.com

Combustible Gas Sensors Electrochemical Sensors Paper Tape Sensors

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GLOSSARY ACRONYMS / ABBREVIATIONS ADA AHJ BLEVE CVD DOT ECS E/E/PE EMCS EMI ERT EVC FM FTIR HMI HPM IDLH IPA IQSE IR ISA ISO LC6o LDL LEL LFL LOC Max TQ Mg/Kg MHI MSDS NEC NFPA NIOSH OTV PEL PHA PLC PPB PPE PPM REL

Americans with Disabilities Act Authority Having Jurisdiction Boiling Liquid Evaporating Vapor Explosion Chemical Vapor Deposition Department of Transportation Emergency Control Station Electrical/Electronic/Programmable Electronic Energy Management Control System Electromagnetic Interference Emergency Response Team Equilibrium Vapor Concentration Factory Mutual Fourier Transform Infrared Human/Machine Interface Hazardous Production Material Immediately Dangerous to Life & Health Isopropyl Alcohol Institute for Quality and Safety in Electronics Infrared International Society of Measurement and Control International Organization of Standardization 50 Percent Lethal Concentration Level Lower Detection Limit Lower Explosive Limit Lower Flammable Limit Level of Concern Maximum Threshold Quantity Milligrams per Kilogram Material Hazard Index Material Safety Data Sheet National Electric Code National Fire Protection Association National Institute of Occupational Safety and Health Odor Threshold Value Permissible Exposure Limit Process Hazard Analysis Programmable Logic Controller Part per Billion Personal Protective Equipment Part per Million (equivalent to Mg/Kg) Recommended Exposure Limit

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RFI RTECS SARA SEMI SIL SIS SLC SLDC SRS SSA STEL TGO TLV TUV TWA UBC UFC UFL UL UMC UPS UV VCE VMB

HAZARDOUS GAS MONITORING

Radio Frequency Interference Registry of Toxic Effects of Chemical Substances Superfund Amendments and Reauthorization Act Semiconductor Equipment and Materials International Safety Integrity Level Safety Instrumented System Safety Life Cycle Single Loop Digital Controller Safety Related Systems Semiconductor Safety Association Short-term Exposure Limit Toxic Gas Ordinance Threshold Limit Value Technische Uberwachungs V erein Time Weighted Average Uniform Building Code Uniform Fire Code Upper Flammable Limit Underwriters Laboratories Uniform Mechanical Code Uninterruptible Power Supply Ultra Violet Vapor Cloud Explosion Valve Manifold Box

DEFINITIONS

Adsorption. The adhesion in an extremely thin layer of molecules to the surfaces of solid bodies (extractive tubing) or liquids with which they are in contact. Alarm Signal. An audible or visual signal, or both, indicating the existence of an emergency fire condition. Audible devices may be bells, horns, chimes, speakers, or similar devices. Voice alarms and their messages shall be approved by the chief. (From the Uniform Fire Code.) Alarm System. A combination of approved compatible devices with the necessary electrical interconnection and energy to produce an alarm signal in the event of system activation. (From the Uniform Fire Code.) Amperometry. Chemical analysis by techniques which involve measuring electric currents. Approved. Refers to approval by the chief as the result of investigation and tests conducted by the chief or by reason of accepted principals or tests by national authorities, or technical or scientific organizations. (From the Uniform Fire Code.)

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Autoignition Temperature. The temperature that a vapor-air mixture must be raised to in order to initiate flaming combustion. Ignition sources such as arcs, sparks, glowing cigarette ashes, lit matches, etc., provide sufficient localized heating of the gas-air mixture to raise the temperature of that portion of the mixture up to, or above, its autoignition temperature. Availability. The percentage of time over which a system is capable of performing its intended function. If a safety system fails due to a faulted component, the system is not available. System availability is a function of reliability. Bias. The application of a steady voltage or current to an active device, as a sensor cell, to produce a desired mode of operation. Slight positive or negative voltage. Bulk Autoignition. The simultaneous combustion of all particles involved in the reaction. When pyrophoric gases ignite in bulk autoignition, no combustion wave will occur and the material will be converted to products of combustion simultaneously at all points. Ceiling Limit. An OSHA term defined as the maximum concentration contaminant to which one may be exposed.

of an airborne

CE Mark. A self-certification by manufacturers which is required in order to sell products throughout the European Economic Area without the need for further regulatory compliance in member countries.

Challenge Gas. A gas used to test (challenge) a gas sensor to verify its performance or calibration. In some cases, a gas that the sensor has a cross-sensitivity to may be used to calibrate sensors. Continuous Gas-Detection System. A gas-detection system where the analytical instrument is maintained in continuous operation and sampling is performed without interruption. The interval time for continuous gas detection shall be determined by the AHJ. The 1988 UFC defined a 30-minute maximum time interval for hazardous gas monitoring. Newer editions of the UFC do not indicate time interval. (From the Santa Clara Uniform Fire Code Amendments.) The City of San Jose 1994 UFC Amendments state that "Analysis is allowed to be performed on a cyclical basis at intervals not to exceed 5 minutes."

Control Area. Space within a building which is enclosed and bounded by exterior walls, fire walls, fire separation assemblies and roofs, or a combination thereof, where quantities of hazardous not exceeding the maximum amounts per control area are stored, dispensed, used or handled. (From the International Fire Code.)

Deflagration. An exothermic reaction, such as extremely rapid oxidation of flammable dust or vapor in air, in which the reaction progresses through the unburned material at a rate less than the velocity of sound. The reaction causes a shock wave and creates a wind in the open. Often manifested as a fireball classified as rapid burning with intense heat and light. Detonation. An exothermic reaction characterized by the presence of a shock wave in material that establishes and maintains the reaction. The reaction zone progresses through the material at a rate greater than the velocity of sound.

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Diffusion Sampling. A gas monitoring method where the gas sensor is placed at the desired monitoring point. The target gas diffuses across the sensor element to stimulate a response. Doping. The addition of an impurity element to a semiconductor material, such as germanium or silicon, during the manufacturing process to form P-type or N-type material required for semiconductor or diodes and transistors. The process of placing impurities in the near-surface region of solids is accomplished by a procedure known as implanting.

Electrical/Electronic/Programmable Electronic (E/E/PE) Safety Related Systems (SRS). Electrical refers to logic functions performed by electromechanical techniques (e.g., electromechanical relay, motor-driven timers, etc.); electronic refers to logic functions performed by electronic techniques (e.g., solid-state logic, solid-state relay, etc.); and programmable electronic refers to logic performed by programmable or configurable devices (e.g., programmable logic controller, single loop digital controller, etc.). Electromagnetic Interference (EMI). Interference from energy in the form of waves which have both an electronic and a magnetic component. Electromagnetic radiation includes frequencies in all spectrums: radio, visible light, infrared, ultra violet, x-rays, etc. Emergency Alarm System. A system to provide indication and warning of emergency situations involving hazardous materials and summon appropriate aid. (From the International

Fire Code.) Equilibrium Vapor Concentration (EVC). The state of a regulated material at which vapor pressure has stabilized and is no longer rising or falling: EVC (ppm) = Vapor Pressure x 106 / Atmospheric Pressure 760 mm Hg Extractive Sampling. A gas monitoring method utilizing an air pump to draw air samples through tubing from the sampling location to a remote-mounted gas sensor. Fail Safe. When a component fails, if a system goes to a predefined safe state as opposed to going to a dangerous state, it is said to be fail safe. Faraday's laws of electrolysis. The amounts of different substances dissolved or deposited by the passage of the same electric charge are proportional to their equivalent weights. Fault Tolerance. The ability of the control hardware to sustain a failure in a single component and be able to maintain correct, continued operation of the system. The fault should be detectable by the system, correctable online, all without affecting or compromising the system operation in any manner before and after the repair. Filter Lag. The time added to T~o detection time as a result of placing a filter over a sensor cell or extractive sensing tube. Gas Room. A separately ventilated, fully-enclosed room in which only compressed gases and associated equipment and supplies are stored or used. (From the International Fire Code.)

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Halide Gases. A binary compound of a halogen (fluorine, chlorine, bromine, iodine and astatine) with a more electropositive element or radical. Includes hydrogen chloride, hydrogen bromide, silicon tetrafluoride and tungsten hexafluoride. Hazardous Materials. Those chemicals or substances which are physical hazards or health hazards as defined and classified in Article 80 whether the materials are in usable or waste condition. Hazardous Materials Business Plan (HMBP). A written plan containing at a minimum the information required pursuant to Section 25500 et. seq. of the State of California Health and Safety Code. (from the City of San Jose 1994 UFC Amendments.) Hazardous Production Material (HPM). A solid, liquid or gas associated with semiconductor manufacturing that has a degree-of-hazard rating in health, flammability or reactivity of Class 3 or 4 as ranked by UFC Standard 79-3 and which is used directly in research, laboratory or production processes which have as their end product materials which are not hazardous. Health Hazard. A classification of a chemical for which there is statistically significant evidence based on at least one study conducted in accordance with established scientific principles that acute or chronic health effects could occur in exposed persons. Highly Toxic Material. A chemical that has a median lethal concentration (LCso) in air of 200 parts per million by volume or less of gas or vapor, or 2 milligrams per liter or less of mist, fume or dust, when administered by continuous inhalation for one hour, or less if death occurs within one hour, to albino rats weighing between 200 and 300 grams each. HPM Room. A room used in conjunction with or serving a Use Group H-5 occupancy where hazardous production materials are stored or used and which is classified as a Use Group H-2, H-3 or H-4 occupancy. (From the International Fire Code.) Immediately Dangerous to Life and Health (IDLH). A concentration of airborne contaminants, normally expressed in parts per million or milligrams per cubic meter, which represents the maximum level from which one could escape within 30 minutes without any escape-impairing symptoms or irreversible health effects. This level is established by the National Institute of Occupational Safety and Health (NIOSH). Interferent. Any material or condition which can affect the true measurement of the actual target gas concentration. For some sensors, gases other than the target gas may generate a sensor response. Sensor manufacturers provide cross-sensitivity tables listing gases that each sensor will respond to and the response in a percentage with respect to the target gas. Irritant. A chemical which is not corrosive, but which causes a reversible inflammatory effect on living tissue by chemical action at the site of contact. (From the International Fire Code.) Laminar Air Flow. Air flow in unidirectional layers where flow velocities are maintained above 70 f t / m i n . As air flows from the supply side (usually the ceiling) to the return side (either a perforated floor or sidewall vent), particulate matter is "washed" away in a shower of air. The high air speed and lack of turbulence can keep gas leaks from dispersing and reaching a detector. Detector placement is critical in laminar air flow areas.

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LCso. Fifty percent lethal concentration level. The mean exposure concentration level expected to cause death in 50 percent of the exposed test animal population. For UFC purposes, use the LCso data for albino white rats.

Level of Concern (LOC). The maximum concentration of a substance in air that will not cause serious health effects in the majority of the population when exposed to the substance for a relatively short period. If the substance has an established IDLH value, the LOC is equal to 0.1 IDLH as defined in the UFC. If the substance does not have an established IDLH, an estimated IDLH value can be based on acute toxicity data of 0.1 LCso. Listed. Equipment or materials included in a list published by an organization acceptable to the authority having jurisdiction and concerned with product evaluation, that maintains periodic inspection of production of listed equipment or materials and whose listing states either that the equipment or material meets appropriate standards or has been tested and found suitable for use in a specified manner. Lower Detectable Limit (LDL). The lowest gas concentration that a sensor can reliably and repeatably detect. Material Hazard Index (MHI). A numeric value used for ranking of chemical substances in order to determine the level of controls necessary for regulated materials. MHI is determined by dividing the Equilibrium Vapor Concentration (EVC) of a material at 25~ by the Level of Concern (LOC) for the material: MHI = EVC (ppm) at 25~ / LOC (ppm) (From the Santa Clara County Toxic Gas Ordinance.)

Moderately Toxic Gas. A chemical or substance that has a median lethal concentration (LCso) in air more than 2,000 ppm, but not more than 7,500 ppm, by volume of gas or vapor when administered by continuous inhalation for an hour, or less if death occurs within one hour, to albino rats weighing between 200 and 300 grams each. (From San Jose 1994 California Fire Code Amendments.) Occupational Exposure Limit (OEL). A generalized term for the gas concentration considered safe for personnel. The exact definition and limit values of OELs vary between jurisdictions and countries. In the United States, the most widely used OEL is the permissible exposure limit. Odor Thresholds.

A concentration level detectable by the olfactory senses.

Permissible Exposure Limit (PEL). Concentration deemed safe for 8-hour time-weighted average. PEL is similar to TLV, but is designated by the Occupational Safety and Health Administration (OSHA) and published in OSHA General Industry Air Contaminants Standard 29 CFR 1910.1000. Poisoning. A gas sensor exposed to very high levels of target gas (more than 20 times the designed operating range) becomes saturated and made inoperative. Poisoning also occurs when compounds react and form strong bonds with a sensor's catalyst surface thereby tying up reaction sites for the target gas. This action diminishes the sensitivity of the sensor to the target gas.

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Process Hazard Analysis (PHA). An organized and systematic effort to identify and analyze the significance of potential hazards associated with the processing or handling of highly hazardous chemicals. A PHA provides information which will assist employers and employees in making decisions for improving safety and reducing the consequences of unwanted or unplanned releases of hazardous chemicals. The process is outlined in OSHA's 29 CFR 119 Appendix C. Pyrolyzer. A device that causes chemical change through the action of heat. Pyrophoric. A chemical that will spontaneously ignite in air at or below a temperature of 130~ (autoignition temperatures are below 130~ Radio Frequency Interference (RFI). Interference from high-frequency electromagnetic waves emanating from electronic devices.

Registry of Toxic Effects of Chemical Substances (RTECS). A NIOSH publication listing various chemical properties and exposure values (such as IDLH and LCso) for a variety of chemical substances. Regulated Material Class I. A regulated material which has an MHI value equal or greater than 500,000 or which is classified as a DOT Poison A.

Regulated Material Class II.

A regulated material which has an MHI equal to or greater than 10,000 but less than 500,000.

Regulated Material Class III. A regulated material which has an MHI equal to or greater than 4,900 but less than 10,000. Reliability. The probability that a component or system will perform its required function under stated conditions for a stated period of time. The ability of a system to perform its function upon demand. Safety Integrity Level (SlL). A discrete integrity level of a safety system defined in terms of the probability of a system failing to respond to a demand. A SIL defines the level of performance needed to achieve a safety objective. The higher the SIL, the more available the safety function of the safety related system. Performance is improved by the addition of redundancy, diagnostic fault detection, and the use of diverse sensors and final control elements. Safety Life Cycle. The sequence of activities involved in the implementation of a safety system from conception through decommissioning.

Safety Related Systems (SRS).

See Electrical/Electronic/Programmable Electronic (E/E/PE)

Safety Related Systems (SRS). Simple Asphyxiant Gas. A gas which does not provide sufficient oxygen to support life and has none of the other physical or health hazards specified in section 2701.2.2.1. (From the International Fire Code.)

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HAZARDOUS GAS MONITORING

Simplex. A non-redundant system. Span Drift. The percentage change in the value at which the gas sensor or gas detection system is calibrated with a known concentration of target gas over a specific period of time. Target Gas. The specific gas that is intended to be monitored. Tso. The time for a gas sensor output to reach 50 percent of the maximum response of the sensor to the target gas. Tso. The time for a gas sensor output to reach 90 percent of the maximum response of the sensor to the target gas. T~oo. The time for a gas sensor output to reach 100 percent of the maximum response of the sensor to the target gas. T~oo.~o. The time for a gas sensor to recover from 100 percent of available scale to 10 percent of scale. Typical Electrochemical

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Uberwachungs Verein (TUV). A technical inspection agency composed of approximately 14 independent laboratories in Germany. TUV does not write standards, but reviews equipment for compliance to standards. TUV issues a "GS" mark on compliant equipment similar to the Underwriters Laboratories label. For both TUV and UL, the approval for compliant equipment is for the specific configuration reviewed. When a change in configuration is made, the revised equipment must be submitted for review. Technische

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TLV-TWA (Threshold Limit Value-Time Weighted Average). The time-weighted average concentration of a substance for a normal 8-hour workday, 5 days per week for 40 years to which nearly all workers may be repeatedly exposed without adverse effect. An occupational exposure metric pertaining to a majority of the population. National codes now refer to PEL in lieu of TLV.

Toxic Material. A chemical or substance that has a median lethal concentration (LCso) in air more than 200 parts per million but not more than 2,000 parts per million by volume of gas or vapor, or more than 2 milligrams per liter but not more than 20 milligrams per liter of mist, fume or dust, when administered by continuous inhalation for one hour, or less if death occurs within one hour, to albino rats weighing between 200 and 3 0 0 grams each.

Vapor Density. The ratio of molecular weight of the gas to molecular weight of air (29 for dry air). If the vapor density is less than 1, the gas is lighter than air and tends to rise. If the vapor density is the same as air, the gas tends to mix and not stratify. For example, carbon monoxide has a vapor density of 0.96. Vapor density and gas stratification tendencies can have an affect on where a gas goes after it leaks and it thereby influences choice of detector location. VCE (Vapor Cloud Explosion). The explosion caused by the accumulation of vapor in the open air. The different types of VCEs are deflagration, detonation and bulk autoignition. Voting. Taking signals from multiple sensors or control devices and comparing them to execute logic or control.

Zero Drift. The percentage change in the zero point or baseline of a gas sensor or gas detection system over a specific period of time. Zero Gas. A gas used for sensor calibration that is known to not contain any target gas.

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REFERENCES BOOKS & JOURNAL ARTICLES

Chou, Jack. Hazardous Gas Monitors: A Practical Guide to Selection, Operation and Applications. New York: McGraw-Hill Book Co., 2000. Chowdhury, Naser M. "Bulk Silane Release and Vapor Cloud Explosion." Semiconductor International June (1996):155-160. Gruhn, Paul, and Harry L. Cheddie. Safety Shutdown Systems: Design, Analysis and Justification. Research Triangle Park: Instrument Society of America, 1998. Kugler, George C., and David A. Fardig. "Fluorine Gas Detection; F2 vs. HF Gas Sensors." Conference Proceedings of the Semiconductor Safety Association (April 1998). Urano, Youkiehi et al. Chemical Technology Research 84, No. 10 (1989):585-93.

REPORTS & DATABASES

Chelton, C.F., ed. Manual of Recommended Practice for Combustible Gas Indicators and Portable Direct Reading Hydrocarbon Detectors, Second Edition, No. 158-SI-93 (1993). American Industrial Hygiene Association 2700 Prosperity Ave Ste 250, Fairfax VA 22031 Telephone: 703.849.8888 Facsimile: 703.207.3561 Internet: www.aiha.org E-mail: [email protected] Ruth, Jon H. Odor Thresholds and Irritation Levels of Several Chemical Substances: A Review. Wausau Insurance Companies 425 Market St, San Francisco CA 94105-2406 Telephone: 415.541.01 44 Odor Thresholds for Chemicals with Established Occupational Health Standards, No. 108-EA-89 (1989). American Industrial Hygiene Association 2700 Prosperity Ave Ste 250, Fairfax VA 22031 Telephone: 703.849.8888 Facsimile: 703.207.3561 E-mail" [email protected] Internet: www.aiha.org Recommendations for Gas Sensor Placement in Ducts, Report No. 1089 (November 1992). Wolfson Unit for Marine Technology and Industrial Aerodynamics University of Southampton, Highfield, Southampton, England

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Chemical Referral Center Washington, D. C. Telephone: 800.262.8200 (8:00 AM - 9:00 PM ET) Registry of Toxic Effects of Chemical Substances. National Institute of Occupational Safety and Health (NIOSH) 4676 Columbia Parkway, Cincinnati OH 45226 Telephone: 800.247.8737 Facsimile: 513.533.8573 Internet: www.cdc, gov/niosh/rtecs, html

FEDERAL LAWS

(ADA) Americans with Disabilities Act, Public Law 101-336 (1992) U S Department of Justice, Washington DC 20530 Telephone: 202.514.0301 (EPA) 40 CFR 68. 115: Chemical Accident Prevention Provisions, Threshold Determination. (EPA) 40 CFR 68. 130: Chemical Accident Prevention Provisions, List of Substances. (EPA) 40 CFR 68. 170: Chemical Accident Prevention Provisions, Prevention Program. Environmental Protection Agency, Research Triangle Park NC 27709 internet: www.access.gpo.gov/nara.sfr/index.html (OSHA) 29 CFR 1910. 119 Subpart H: Process Safety Management of Highly Hazardous Chemicals, Hazardous Materials. (OSHA) Fact Sheet No. 93-45 (3-page summary of 29 CFR 1910. 119). (OSHA) 29 CFR 1910. 119 Appendix C: Compliance Guidelines and Recommendations for Process Safety Management (Nonmandatory). (OSHA) 29 CFR 1910. 7: Accreditation of Testing Laboratories. Occupational Safety & Health Administration The United States Department of Labor Gateway Building Ste 2100, 3535 Market St, Philadelphia PA 19104 Telephone: 215.596.1201 Facsimile: 215.596.4872 Internet: www.osha.gov

MODEL CODES

International Fire Code. International Code Council 5203 Leesburg Pike Ste 708, Falls Church VA 22041 Telephone: 703.931.4533 Facsimile: 703.379.1546 Internet: www.intlcode.org

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Standard Fire Prevention Code. Southern Building Code Congress International (SBCCI) 900 Montclair Rd, Birmingham AL 35213-1206 Telephone: 205.591.1853 Facsimile: 205.591.0775 Internet: www.sbcci.org Uniform Fire Code. Uniform Fire Code Amendments. Uniform Fire Code Standard 79-3: Identification of the Health, Flammability, and Reactivity of Hazardous Materials. Western Fire Chiefs Association 300 N Main St #25, Fallbrook CA 92028 Telephone: 760.723.6911 Facsimile: 760.723.6912 Internet: www.wfca.com Uniform Building Code. Uniform Mechanical Code. International Conference of Building Officials 5360 Workman Mill Rd, Whittier CA 90601-2298 Telephone: 800.284.4406 or 562.699.0541 Facsimile: 888.329.4226 or 562.692.3853 Internet: www.icbo.org/

JURISDICTIONAL CODES Palo Alto, California, Toxic Gas Ordinance 1999 Edition. Palo Alto Fire Department P O Box 10250, Palo Alto CA 94303 Telephone: 650.329.2347 Facsimile: 650.327.6591 Internet: www.city.palo-alto.ca.uslfire/business/index.html San Jose California Fire Code Amendments. 4 North 2nd St, Ste 1100, San Jose, CA 95113-1308 Telephone: 408.277.4444 Internet: SJFD.com Santa Clara Uniform Fire Code Amendments. Santa Clara Fire Department 777 Benton St, Santa Clara CA 95050 Telephone: 408.984.3059 Facsimile: 408.241.3006 Internet: www.alphais.com/santa clara/53733.html

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Santa Clara County Fire Chiefs Association Toxic Gas Ordinance Concensus Guidelines. Santa Clara County Fire Chiefs Association P O Box 3707, Sunnyvale CA 94088-3707 Telephone: 408.299.6930 Facsimile: 408.280.6479 Internet: www.unidocs.org Sunnyvale, California, Toxic Gas Ordinance City of Sunnyvale Fire Prevention Bureau P 0 Box 3707, Sunnyvale CA 94088-3707 Telephone: 408.730.7212 Internet: www.ci.sunnyvale.ca, us/public-safety/fire-enviro/enviro-svcs

STANDARDS

ANSl/ASHRAE Standard 15-1994: Safety Code for Mechanical Refrigeration. ANSl/ASHRAE Standard 34-1992: Number Designation and Safety Classification of Refrigerants. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 1 791 Tullie Circle NE, Atlanta GA 30329 Telephone: 800.527.4723 Facsimile: 404.321.5478 Internet: www.ashrae.org/ BS 6959:1989 Code of Practice for Selection, Installation, Use and Maintenance of Apparatus for the Detection and Measurement of Combustible Gas. British Standards Institution British Standards House 389 Chiswick High Road, London, W4 4AL, United Kingdom Telephone: 44.0.181.996.9001 Facsimile: 44.0.1 81.966.7001 E-mail: [email protected] Internet: http://www.bsi.org, uk/ IEC 60839-5-4 Ed. 1.Oh-1991: Alarm Systems, Part 5, Requirements for Alarm Transmission Systems. IEC 61508: Functional Safety - Safety Related Systems. IEC SC65A WG9 1990: Software for Computers in the Application of Industrial SafetyRelated Computer Systems. International Electrotechnicai Commission 3 Rue de Varembe', 1211 Geneva 20, Switzerland Internet: www.iec.ch/

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ISA-RP60. 1-1990: Recommended Practice - Control Center Facilities. ISA-RP60.2-1995: Recommended Practice - Control Center Design Guide and Terminology. ISA-RP60.3-1985: Recommended Practice - Human Engineering for Control Centers. ISA-RP60. 4-1990: Recommended Practice - Documentation for Control Centers. ISA-RP60.8-1978: Recommended Practice - Electrical Guide for Control Centers. ISA-RP92.04.02: Installation, Operation and Maintenance of Instruments Used to Detect Oxygen-Deficient~Oxygen-Enriched Atmospheres. ISA-S84. 01-1996: Application of Safety Instrumented Systems for the Process Industries. ISA-S92. 04. 01: Performance Requirement for Instruments Used to Detect OxygenDeficient~Oxygen-Enriched Atmospheres. International Society of Measurement and Control P O Box 12277, Research Triangle Park NC 27709 Telephone: 919.549.8411 Facsimile: 919.549.8288 Internet: www.isa.org ISO Standard 7731-1986: Danger Signals for Work Places--Auditory Danger Signals. ISO Standard 11429-1996: Ergonomics--System of Auditory and Visual Danger and Information Signals. International Organization of Standardization Case Postale 56, CH-1211 Geneva, Switzerland Telephone: 41.22.749.01.11 E-mail: [email protected] Internet: www.iso.ch/home-e, htm Mil-STD-882B (30 Mar 1984) System Safety Program Requirements. Department of Defense Washington DC 20301 Internet: www.airtime.co, uk/users/wysywig/882b, htm NFPA Standard 49: Hazardous Chemicals Data. NFPA Standard 55: Storage, Use and Handling of Compressed and Liquified Gases in Portable Cylinders. NFPA Standard 70: National Electric Code. NFPA Standard 72: National Fire Alarm Code. NFPA Standard 318: Protection of Cleanrooms. NFPA Standard 704: Standard System for the Identification of Fire Hazards of Materials. National Fire Protection Association P O Box 9101, Quincy MA 02269-9101 Telephone: 800.344.3555 Internet: www.nfpa.org SEMI Standard $2: Safety Guidelines for Semiconductor Manufacturing Equipment. Semiconductor Equipment and Materials International 3081 Zanker Rd, San Jose CA 95134 Telephone: 408.943.6900 Facsimile: 408.943.9600 E-mail: [email protected] Internet: www.semi.org

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UL 864: Control Unit for Fire Protective Signaling Systems. UL 991: Safety-Related Controls Employing Solid-state Devices. UL 1971: Signaling Devices for the Hearing Impaired. UL 1998: Safety-Related Software. UL 2075: Gas and Vapor Detectors and Sensors. Underwriters Laboratories 333 Pfingsten Rd, Northbrook IL 60062 Telephone: 847.272.8800 internet: www.ul.com/

ORGANIZATIONS American Industrial Hygiene Association (AIHA) 2700 Prosperity Ave Ste 250, Fairfax VA 22031 Telephone: 703.849.888 Facsimile: 703.207.3561 Internet" www.aiha.org International Society for Measurement and Control (ISA) P O Box 12277, Research Triangle Park NC 27709 Telephone: 919.549.8411 Facsimile: 91 9.549.8288 Internet: www.isa.org International Electrotechnical Commission (IEC) 3 Rue de Varembe, P O Box 131, 1211 Geneva 20, Switzerland Telephone: 41.22.919.02.11 Facsimile: 41.22.91 9.03.00 Internet: www.iec.ch/home-e.htm International Organization of Standardization (ISO) Case Postale 56, CH-1211 Geneva, Switzerland Telephone: 41.22.749.01.11 E-mail: [email protected] Internet: www.iso.chl National Institute of Occupational Safety and Health (NIOSH) 4676 Columbia Parkway, Cincinnati OH 45226 Telephone: 800.247.8737 Facsimile: 513.533.8573 E-mail: [email protected] Internet: www. ntis.gov/rtecsfac, htm

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Semiconductor Equipment and Materials International (SEMI) 3081 Zanker Rd, San Jose CA 95134 Telephone: 408.943.6900 Facsimile: 408.943.9600 Internet: www.semi.org Semiconductor Safety Association (SSA) 1313 Dolley Madison BIvd Ste 402, McLean VA 22101 Telephone: 703.790.1745 Facsimile: 703.790.2672 Internet: www.semiconductorsafety.org

THIRD-PARTY CERTIFICATION Factory Mutual (FM) P O Box 9102, Norwood MA 02062 Telephone: 781.255.4983 Facsimile: 781.762.9375 Internet: www.factorymutual.com

Third-party certification of safety systems. Nationally-recognized testing laboratory.

Underwriters Laboratories (UL) 333 Pfingsten Rd, Northbrook IL 60062 Telephone: 847.272.8800 Internet: www.ul.com/

Third-party certification of safety systems. Nationally-recognized testing laboratory.

TUV-Product Services (TUV-PS) 5 Cherry Hill Dr, Danvers MA 01923 Telephone: 978.777.7999 Facsimile: 978.777.8441 Internet: www.tuvps.com E-mail: [email protected]

Third-party certification of safety systems. Nationally-recognized testing laboratory.

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INDEX A c o u s t i c sensors ..... 9 9 A c r o n y m n s and a b b r e v i a t i o n s ..... 1 8 5 Air c o m p o s i t i o n m o n i t o r ( A C M ) ..... 97 A l a r m a n n u n c i a t i o n ..... 3 3 , 3 5 , 4 5 , 5 2 , 6 2 , 7 2 , 1 4 5 A l a r m set p o i n t s ..... 1 0 9 A l t e r n a t e m a t e r i a l s and m e t h o d s ..... 3, 3 0 , 1 5 2 A N S I / A S H R A E S t a n d a r d 15 ..... 72 A N S I / I S A S t a n d a r d 61 5 0 8 ..... 63 A r s i n e ...... 1 0 0 , 101 A v a i l a b i l i t y ..... 1 2 1 , 1 8 7 B r e a t h i n g zone ..... 1 4 3 Boron t r i f l u o r i d e ..... 101 C a t a l y t i c bead sensors ..... 75, 88 Ceiling limit ..... 1 2, 3 4 , 1 8 7 C e r t i f i c a t i o n (see Listed) Central s y s t e m s ..... 11 5 C h e m c a s s e t t e t a p e s ..... 9 4 C h e m i c a l d e l i v e r y corridor alarm ..... 148 Chlorine t r i f l u o r i d e ..... 1 0 2 Class i material ..... 4 8 , 191 Code i n t e n t ..... 2 C o m b i n a t i o n s y s t e m s ..... 9 8 C o m m u n i c a t i o n c o n f i g u r a t i o n s ..... 1 3 8 C o m p l i a n c e c h e c k l i s t s ..... 1 6 2 C o m p l i a n c e r e v i e w ..... 1 5 5 , 159 C o n c e n t r a t i o n s ..... 7, 15 C o n t r o l area ..... 3 8 , 1 8 7 C o r p o r a t e s a f e t y s t a n d a r d s ..... 5 Corridors ..... 2 0 , 3 3 , 1 4 8 C o s t of o w n e r s h i p (TCO) ..... 8 4 C o v e r t failure ..... 1 1 8 Data a c q u i s i t i o n ..... 1 25 D e f i n i t i o n s ..... 1 8 6 D i a g n o s t i c s ..... 6 5 , 8 4 , 1 2 2 , 129 Diluted m i x t u r e s ..... 7, 15, 4 6 D i s p e n s i n g , c h e m i c a l ..... 2 4 D i s t r i b u t e d s y s t e m s ..... 11 5 D o c u m e n t a t i o n , s y s t e m ..... 1 25 Draeger ..... 8 5 , 9 1 , 1 1 1 , 1 1 2 , 135, 1 8 0 Ecosys M S T (see M S T ) E c o s y s T e l o S e n s e (see TeloSense) EIT (see S c o t t / B a c h a r a c h ) Electrically h a z a r d o u s l o c a t i o n s ..... 1 1 4 E l e c t r o c h e m i c a l sensors ..... 8 5

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Emergency alarm s y s t e m s ..... 17, 39, 188 E m e r g e n c y control station (ECS) ..... 1 6, 3 2 , 4 2 , 51, 140 E m e r g e n c y p o w e r ..... 36, 51 E m e r g e n c y response ..... 6 1 , 148 E m e r g e n c y response t e a m (ERT) ..... 148 EPA r e q u i r e m e n t s ..... 58, 6 3 , 77, 151 Extractive sensors ..... 9 2 Fail safe controls ..... 24, 3 9 , 1 20, 188 Fail-to-danger ..... 118 Fault tolerance ..... 1 21 Fire alarm panel-based m o n i t o r i n g s y s t e m s ..... 1 3 3 Fireman's telephone ..... 18, 148 F l a m m a b i l i t y hazard rating ..... 9 Fluorine ..... 103 Galvanic cell ..... 87 Gas cabinets ..... 20, 2 1 , 3 4 , 35, 4 3 , 56, 1 0 6 , 1 4 0 , 1 4 3 , 1 4 5 Gas room ..... 17, 20, 33, 3 6 , 4 0 , 188 Gases, monitored ..... 1 6 3 Health hazard rating ..... 8 Highly t o x i c material ..... 9, 1 8 9 HPM room ..... 17, 20, 3 3 , 1 8 9 Hydrides ..... 85, 9 4 , 95 H y d r o g e n ..... 55, 104, 108 , 151 H y d r o g e n sensors ..... 8 8 , 1 0 0 Hydrolysis ..... 4 6 , 50, 9 7 , 1 0 5 , 112 IEC Standard 6 1 5 0 8 ..... 6 3 I m m e d i a t e l y dangerous to life or health (IDLH) ..... 1 2, 189 ISA Standard S 8 4 . 0 1 ..... 65 Integration, s y s t e m ..... 1 23 Interference ..... 8 3 , 86, 1 0 8 , 189 International Fire Code ..... 28 Ionization sensors ..... 9 2 Listed ..... 2 1 , 2 2 , 3 1 , 4 9 , 71, 155, 190 L o n W o r k s n e t w o r k - b a s e d m o n i t o r i n g s y s t e m s ..... 137 M a i n t e n a n c e ..... 22, 31, 62, 77, 115 Material hazard index (MHI) ..... 1 1 , 4 4 , 1 9 0 Material safety data sheets (MSDS) ..... 11, 5 8 , 141 Matrix, alarm s y s t e m ..... 1 4 4 , 160 M a x i m u m threshold q u a n t i t y ..... 47 Mineral acids ..... 9 4 M i n i m u m threshold q u a n t i t y ..... 4 9 Molecular emission s p e c t r o m e t r y sensors ..... 9 8 M o n i t o r i n g m e a s u r e m e n t s ..... 1 2 MST ..... 85, 86, 9 2 , 1 8 2 N e t w o r k - b a s e d m o n i t o r i n g s y s t e m s . . . . . . 1 3 5 , 1 37 NFPA Standard 55 ..... 53

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NFPA Standard 3 1 8 ..... 54 Normalization factor ..... 15, 177 Nitrogen trifluoride ..... 105 O c c u p a n c y classifications ..... 3, 26 O c c u p a t i o n a l exposure limit (OEL) ..... 1 2, 1 9 0 Odor threshold values (OTV) ..... 19, 190 O S H A requirements ..... 57, 60, 65, 68, 143, 1 4 5 , 155, 157 O x y g e n depletion monitoring ..... 68 Ozone monitoring sensors ..... 25, 40, 100 Palo A l t o CA TGO ..... 4 8 Paper tape sensors ..... 9 4 Performance codes ..... 3 Permissable exposure limit (PEL) ..... 1 2, 20, 1 0 9 , 1 90 Prescriptive codes ..... 3 PLC-based monitoring systems ..... 1 27 Physiological warning properties ... 19, 23, 3 2 , 3 4 , 42, 150 Poisoning, sensor ..... 83, 190 Portable sensors ..... 109 Problematic gases ..... 100 Process hazard analysis ..... 60, 191 P r o g r a m m e d alarm response ..... 143 Proprietary n e t w o r k - b a s e d monitoring s y s t e m s ..... 135 PureAire ..... 93, 105, 153, 183 Pyrolyzer ..... 86, 92, 105, 114, 191 Reaction b y p r o d u c t s ..... 112 Reactivity hazard rating ..... 10 Recalibration, sensor ..... 110 R e d u n d a n c y ..... 1 20 Refrigerant classifications ..... 11 Refrigerant vapor alarm ..... 47, 69 Refrigeration m a c h i n e r y rooms ..... 73 Refrigeration sensors ..... 74, 75 Registry of Toxic Effects (RTECS) ..... 9, 191 Reliability ..... 11 7, 1 20, 191 Renovations ..... 5 Research laboratories ..... 4 RFI/EMI interference ..... 84 Risk m a n a g e m e n t plan (RMP) ..... 59, 1 63 RKI I n s t r u m e n t s ..... 55, 86, 87, 89, 93, 137, 1 8 3 Safety i n s t r u m e n t e d s y s t e m (SIS) ..... 24, 63, 65, 77, 1 27, 1 57 S a f e t y integrity level (SlL) ..... 64, 65, 191 S a f e t y life cycle ..... 63, 65, 191 Santa Clara C o u n t y TGO ..... 46 S c o t t / B a c h a r a c h ..... 84, 85, 87, 102, 103, 1 5 3 , 1 8 3 Scrubber monitoring ..... 46, 53, 88, 151 S e c o n d a r y c o n t a i n m e n t ..... 44, 46, 50

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SEMI Standard $2 ..... 67, 101, 102, 108, 121, 199 Sensor selection criteria ..... 81 Sensor locations ..... 105 Shutdowns/shutoffs ..... 21, 22, 24, 25, 33, 35, 38, 4 1 , 4 4 , 46, 50, 51, 56, 71, 145 Silane ..... 29, 54, 114, 195 Simple asphyxiant gas ..... 68, 191 S o f t w a r e ..... 67 Solid state sensors ..... 89 Sophistication, system ..... 117 Span drift ..... 82, 192 Spectrophotometric analysis ..... 97 Standard Fire Prevention Code ..... 42 Storage ..... 17, 18, 22, 23, 30, 34, 38, 39, 42, 45, 52, 53, 106, 145 Strobe lights ..... 147, 148 Sunnyvale CA TGO ..... 44 Supervision ..... 24, 39, 71, 118, 1 23, 138, 145 Suppliers ..... 179 Technical opinion ..... 29, 160 TeloSense Ecosys ..... 85, 97, 98, 99, 184 TEOS ..... 105 Testing, protocol for detectors ..... 1 67 Testing, system ..... 3 1 , 4 6 , 74, 77, 161 Threshold limit value (TLV) ..... 1 2, 193 Token ring ..... 139 Toxic gas ordinance (TGO) ..... 44, 46, 48 Toxic material ..... 9, 193 T r e a t m e n t systems ..... 23, 25, 34, 40, 42, 44, 46, 149 Triple modular redundancy (TMR) ..... 122, 129 Underwriters Laboratories Standards ..... 67 Valve manifold box ..... 34, 36 Visual alarm ..... 20, 23, 33, 42, 51, 147 Voice alarm system ..... 78, 146 Voting ..... 65, 121, 129, 193 Zellweger Analytics ..... 31, 80, 92, 94, 11 2, 167, 184 Zero drift ..... 82, 193