Semiconductor Safety Handbook

SEMICONDUCTOR SAFETY HANDBOOK Safety and Health in the Semiconductor Industry

Edited by

Richard A. Bolmen, Jr. Aon Risk Services San Francisco, California

np

NOYES PUBLICATIONS Westwood, New Jersey, U.S.A.

Copyright © 1998 by Noyes Publications 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: 97-24032 ISBN: 0-8155-1418-2 Printed in the United States Published in the United States of America by Noyes Publications 369 Fairview Avenue, Westwood, New Jersey 07675 10 9 8 7 6 5 4 3 2 1

Library of Congress Cataloging-in-Publication Data Semiconductor safety handbook : safety and health in the semiconductor industry / edited by Richard A. Bolmen, Jr. p. cm. Includes bibliographical references and index. ISBN 0-8155-1418-2 1. Semiconductor industry--United States--Safety measures. 2. Integrated circuits--Design and construction--Safety measures. I. Bolmen, Richard A. TK7836.S463 1997 636.11' 96213815--dc21 97-24032 CIP

About the Editor Richard A. Bolmen, Jr. is presently with Aon Risk Services. Prior to that, he was Senior Vice President of Minet Risk Services, Palo Alto, California, responsible for the development and delivery of Minet’s Workers' Compensation, Disability Management and Hazards Management consulting services nationwide. He was also with American RiskConsultants and Marsh & McLennan Protection Consultants. He has over a decade of experience developing and managing safety, environmental workers' compensation and risk management programs for semiconductor manufacturing companies. Mr. Bolmen has served as the Northern California Regional Director and was on the Board of Directors for the Semiconductor Safety Association. He also served as the Division Safety Director for Semiconductor Equipment and Materials International from 1986 to 1989.

NOYES PUBLICATIONS Westwood, New Jersey

SEMICONDUCTOR SAFETY SERIES Series Editor: Richard A. Bolmen, Jr. CODE COMPLIANCE FOR ADVANCED TECHNOLOGY FACILITIES: by William R. Acorn SEMICONDUCTOR INDUSTRIAL HYGIENE HANDBOOK: by Michael E. Williams and David G. Baldwin, and Paul C. Manz SEMICONDUCTOR SAFETY HANDBOOK: edited by Richard A. Bolmen, Jr.

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Contributors

William R. Acorn Acorn Engineering and Consulting Tucson, AZ

Thomas E. Hawkinson Rust Environmental & Infrastructure Minneapolis, MN

David G. Baldwin Hewlett-Packard Company Palo Alto, CA

Daryl B. Korpela Northwest Airlines, Inc. St. Paul, MN

Richard A. Bolmen, Jr. Aon Risk Services San Francisco, CA

Robert G. Kuykendall SRI Environmental Engineers & Consultants Concord, CA

Richard P. Brookman Ceco Group Conshohocken, PA Lisa Brooks AT&T Bell Laboratories Murray Hill, NJ Rollin C. Chew Apple Computer, Inc. Cupertino, CA

Donald V. Lassiter Consultant Environmental/Occupational Health San Jose, CA Paul C. Manz Consultant Matawan, NJ

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Contributors Clifford E. Oliver Los Alamos National Laboratory Los Alamos, NM Robert J. Pearce Industrial Risk Insurers San Francisco, CA David Rainer Environmental Health & Safety Center North Carolina State University Raleigh, NC

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James H. Stewart Environment, Health & Safety Harvard University Cambridge, MA Bruce Tibbott Matheson Semiconductor Systems & Materials Group East Rutherford, NJ Michael E. Williams Apple Computer, Inc. Cupertino, CA

NOTICE To the best of our knowledge the information in this publication is accurate; however the Publisher does not assume any responsibility or liability for the accuracy or completeness of, or consequences arising from, such information. This book is intended for informational purposes only. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the Publisher. Final determination of the suitability of any information or product for use contemplated by any user, and the manner of that use, is the sole responsibility of the user. We recommend that anyone intending to rely on any recommendation of materials or procedures mentioned in this publication should satisfy himself as to such suitability, and that he can meet all applicable safety and health standards.

Preface

It is hard to imagine that less than fifteen years ago building and fire codes specific to the construction of a wafer fabrication facility were just in the process of being developed. Detection and evaluation of leaking underground storage tanks and epidemiological health studies aimed at qualifying and quantifying our “cleanroom” image were in their infancy stages and CalOSHA had just completed the first in-depth study of the industry’s chemical processes and associated industrial hygiene exposures. From a technology perspective, 64 k RAM chips were the hot item for a newly developing computer game market and the 8088 microprocessor provided previously unavailable information processing and storage capabilities at an affordable price. “Silicon Valley,” stretching from Palo Alto to South San Jose, still retained much of its agricultural base and we were always amazed at the beauty and contrast of blooming mustard fields and plum orchards adjacent to wafer fabs, deionized water plants, and chemical storage areas. SEMI was developing a Safety Division, and the Semiconductor Safety Association’s (SSA) annual conference was in its third year attended by a handful of health and safety professionals. Fifteen years later, “Silicon Valley,” as we have known it, now exists in cities like Austin, Phoenix and Boston. Megafabs with property values exceeding $1 billion have become commonplace. We think in terms of gigabytes of hard disk storage for our home computers and the Internet has become a way of life. The Pentium is becoming passé as the next generation of microprocessor looms on the horizon and submicron technology continues to push the envelop of our processing capabilities.

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However great our technological advances have been over this period of time, they have not been exclusive to semiconductors and related high technology products. Interwoven within our semiconductor technology development has been the development of technologies aimed at identifying, evaluating and mitigating the environmental, health and safety (EH&S) risks and exposures associated with the manufacturing and packaging of integrated circuits. Driving and advancing these technologies have been international efforts by SEMI’s Safety Division, the Semiconductor Safety Association (SSA), and the Semiconductor Industry Association (SIA). The purpose of the Semiconductor Safety Handbook is to provide a current, single source reference for many of the primary semiconductor EH&S technologies and disciplines. To this end, we have assembled a comprehensive text written by some of the leading experts in EH&S in the semiconductor industry. This text has taken three years to complete and has involved tremendous effort and commitment by the text’s authors. We have attempted to construct a reference manual that is comprehensive in its coverage of the technical aspects of each individual subject, while at the same time addressing practical applications of each topic. The scope of this text, from its inception, was intended to address significantly more than what would typically be classified under the definition of “safety.” However, we felt that all of the chapters have a direct application to the protection and preservation of semiconductor employees, the surrounding communities and the environment. As such, “The Semiconductor Safety Handbook - Safety and Health in the Semiconductor Industry” seemed an appropriate title. The Semiconductor Safety Handbook opens with Chapter 1, “Injury and Illness of Semiconductor Workers: Experience and Epidemiological Studies,” by Donald Lassiter and James Stewart. Donald Lassiter has been a key figure in the development and maintenance of the semiconductor industry’s Occupational Health System (OHS) injury and illness data base. Development of the OHS system was sponsored by SIA in the early 1980’s and OHS has become the leading occupational illness and injury tracking database for the industry. The OHS system has been in place since 1983 and has participation from approximately one-quarter to one-third of the US semiconductor industry. Data from the OHS system as well as annual incidence rates for OSHA-recordable work injuries and illnesses are presented and compared for the time period 1983–1995. The co-author of this chapter, James Stewart, provides a comprehensive review of epidemiological health studies that have been conducted for the semiconductor industry.

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This overview chronicles initial health studies, beginning with the University of Massachusetts reproductive study for Digital Equipment Corporation in 1984, through the recently published University of California, Davis, Semiconductor Health Study, a multi-disciplinary investigation which targeted reproductive and other health outcomes in the semiconductor industry. In Chapter 2, “Environmental Compliance in the Semiconductor Industry: Detection, Correction and Prevention,” we change gears from protection of employees to protection of the environment. Local, state and federal environmental regulations have increased exponentially over the past decade in response to the plethora of hazardous chemicals used, stored, treated and disposed of (as hazardous waste) in US manufacturing. Few US industries have experienced the impact of the combined environmental regulatory and control technology requirements as the semiconductor industry. Our authors, Robert Kuykendall and Rollin Chew collectively have over fifty years experience in environmental technology and compliance and present one of the most comprehensive reviews of environmental regulation, control and mitigation technologies written on the semiconductor industry. Key to the understanding of environmental, health and safety issues in the semiconductor industry is an understanding of the chemicals used in the manufacture and packaging of semiconductors and semiconductor related technologies. Chapter 3, “Chemical Hazards in Semiconductor Operations,” co-authored by Tom Hawkinson and Daryl Korpela offers an overview of the types of chemicals used in the semiconductor industry as well as the related processes. The chemical hazards of semiconductor manufacturing processes as well as the assessment, monitoring and control of these hazards are given an in-depth treatment by two of the most senior members of the industry’s EH&S community: Michael Williams and David Baldwin. Involved with semiconductor safety and industrial hygiene from the time these issues were first recognized within the industry, they provide invaluable insight to both the science and practical application of industrial hygiene principles and practices in Chapter 4, “Industrial Hygiene.” While the majority of our efforts, as a health and safety community within the semiconductor industry, have been aimed at the control of hazardous materials, some of our most significant safety exposures continue to be those associated with electrical hazards. Historically, electrical accidents have been the leading cause of serious injuries and fatalities in the semiconductor industry. Ironically, electrical safety is an area where we have the least amount of technical and practical expertise available to us as an

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industry. This is what makes Clifford Oliver’s Chapter 5, “Electrical Hazards,” a key reference. Clifford’s two decades of experience in electrical safety combined with his extensive knowledge of semiconductor processing and equipment, offer a unique perspective and valuable insight into this pervasive hazard. Chapter 6, “Radiation Safety,” again teams up co-authors David Baldwin and Michael Williams. In this chapter, we are offered a comprehensive review of the various classifications and associated hazards of radiation as well as potential sources and specific radiation exposures in a cleanroom environment. Included in this chapter are industrial hygiene identification, monitoring and control practices specific to semiconductor processes and equipment. David Rainer and Lisa Brooks, co-authors of Chapter 7, “Recognition, Evaluation and Control of Some Plasma Processing Hazards,” provide an overview of the plasma process as well as the various physical and chemical hazards associated with plasma processing. As megafabs with building values exceeding $1 billion have become commonplace, so has the emphasis on protecting those facilities and their business viability from damage and business interruption as a result of a fire or smoke contamination of a Class I wafer fab. Integral to these efforts has been fire and property protection standards and compliance efforts of the major property insurers. To address these exposures, Robert Pearce has authored Chapter 8, “Fire Protection Technology for Semiconductor Operations.” This chapter begins with the history of fire protection in the semiconductor industry. The chronology discusses the time period when there were no specific building and fire codes for semiconductor fabs other than those written by major property insurers. The evolution and development of Highly Protective Risk (HPR) standards, specific to semiconductor operations, are also discussed in addition to present day property and fire protection issues for large Class I wafer fabrication facilities. This chapter is unique in its breadth and scope and offers fire and property protection methodologies and scenarios from the micro to the macro. Issues from site selection for a wafer fab to protection of individual pieces of processing equipment are addressed by one of the industry’s most experienced property protection practitioners. The construction of a wafer fabrication facility involves numerous complex building and fire codes. The application and enforcement of these codes, by multiple building and fire code officials, with varying levels of understanding and expertise, add an additional level of complexity in the

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construction process. The primary objective of the various codes are to ensure the safety of building occupants as well as provide for a high level of protection of the building, its contents and processes. Experience has demonstrated that an in-depth understanding of both the “letter” and “intent” of the codes is essential by those responsible for the building and operation of a semiconductor processing facility. To this end, William Acorn has authored Chapter 9, “Building and Fire Codes Impacting the Semiconductor Industry.” In addition to providing a critical review of the fire and building codes specific to the construction, operation and occupancy of semiconductor and related occupancies, we are also provided a key reference guide to understanding the intent and practical application of these codes by one of the industry’s leaders in this arena. Of all the chemicals utilized by the semiconductor industry, no one group is as varied in its chemical properties, storage and delivery, monitoring and criticality to the semiconductor manufacturing process as process gases. With a wide range of toxicity, corrosivity, flammability and health hazards, compressed gases represent perhaps the most challenging and enigmatic elements of chemical hazards and control technologies to the industry. As such, process gas handling and the systems designed to control the hazards and at the same time facilitate production, are essential to our discussion. Richard Brookman and Bruce Tibbott have co-authored Chapter 10, “Gases and Gas Equipment,” which provides one of the most extensive treatises to date on this subject. Additionally, the gas data sheet references provided on the various chemical classifications, chemical and physical characteristics, and hazard information for the process gases utilized by the industry are invaluable. A major control factor in the storage and dispensing of process gases within semiconductor manufacturing is the requirement for monitoring of specific categories of hazardous production gases. These monitoring requirements are mandated by fire and building codes as well as local city and state “model ordinances.” The monitoring systems must also integrate with process equipment, have alarm capabilities, detect gases at part per billion levels and at the same time function twenty-four hours per day, seven days per week. These are just a few of the nuances and complexities involved in hazardous gas monitoring. Paul Manz’s Chapter 11, “Toxic Gas Monitoring,” analyzes gas monitoring requirements and methodologies from a technology, installation and utilization perspective. This chapter provides an overview of the origin of the requirements for monitoring process gases through the present day “Toxic Gas Model Ordinance.” In addition to

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monitoring requirements, types of detection methodologies, system installations, and selection of a gas monitoring systems are all discussed in great detail. The purpose of the Semiconductor Safety Handbook has been to provide a comprehensive, hands-on reference to environmental, health and safety issues critical to the semiconductor industry. It was also our intent to produce a text that provides a practical user’s guide for semiconductor environmental, health and safety practitioners as well as those individuals responsible for operation, maintenance and production in wafer fabrication facilities. It is our belief that the contributions of these authors have achieved that goal and we hope that you find the Semiconductor Safety Handbook a useful addition to your library. San Francisco, California September, 1997

Richard A. Bolmen, Jr.

Contents

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Contents

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Injury and Illness of Semiconductor Workers: Experience and Epidemiologic Studies ..................................................... 25 Donald V. Lassiter and James H. Stewart 1.0 INTRODUCTION ................................................................................ 25 2.0 REVIEW AND DISCUSSION OF SEMICONDUCTOR INDUSTRY WORK INJURIES AND ILLNESSES ................................................... 28 2.1 Work Injury and Illness Statistical Program of U.S. BLS .............. 29 2.2 OSHA Recordkeeping System ..................................................... 29 2.3 Usefulness of BLS Survey to U.S. Semiconductor Industry ........ 31 2.4 Occupational Health System (OHS) ............................................. 32 2.5 Work Injury and Illness Experience of Semiconductor Workers .. 34 3.0 REVIEWANDDISCUSSIONOFEPIDEMIOLOGICINVESTIGATIONS 44 3.1 UMASS—Digital Equipment Corporation (DEC) Historical Cohort Study ................................................................................ 44 3.2 UC Davis-Semiconductor Industry Association Study ............... 46 3.3 Johns Hopkins University-IBM Study (JHU) ............................... 53 3.4 Discussion of Reproductive Epidemiology in the Semiconductor Industry ..................................................... 56 4.0 CONCLUSION ................................................................................ 56 REFERENCES ................................................................................ 57

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Environmental Compliance in the Semiconductor Industry: Detection, Correction and Prevention .................................. 59 Robert G. Kuykendall and Rollin C. Chew 1.0 INTRODUCTION ................................................................................ 59 2.0 EXTERNAL AND INTERNAL SOURCES AFFECTING COMPLIANCE ................................................................................ 61 2.1 External Factors Affecting Compliance ........................................ 63 2.2 Internal Factors Affecting Compliance......................................... 64 3.0 DETECTION OF ENVIRONMENTAL COMPLIANCE AND MANAGEMENT ISSUES .................................................................... 68 3.1 Development of Environmental Audit Programs .......................... 69 4.0 CORRECTIVE ACTION FOR ENVIRONMENTAL COMPLIANCE AND MANAGEMENT ISSUES ................................. 79 4.1 Use of Audit Program Results ...................................................... 82 5.0 MITIGATION AND PREVENTION OF ENVIRONMENTAL COMPLIANCE AND MANAGEMENT ISSUES ................................. 84 6.0 ADOPTING PROACTIVE ENVIRONMENTAL STRATEGIES ............ 85 7.0 GOING BEYOND COMPLIANCE—HOLISTIC CONSIDERATIONS ............................................................................ 86 7.1 The Green Advantage .................................................................. 87 7.2 Corporate Environmentalists ........................................................ 89 REFERENCES AND SOURCE MATERIALS .............................................. 92 APPENDIX A:EPA POLICY ON ENVIRONMENTAL AUDITING ............ 94 APPENDIX B:ENVIRONMENTAL COMPLIANCE AUDIT CHECKLIST .............................................................................. 102 I. GENERAL .............................................................................. 102 II. COMPLIANCE AUDIT ................................................................. 103 A.Air .............................................................................. 103 B. Water .............................................................................. 106 C. TSCA (Toxic Substance Control Act) .................................... 111 D. Asbestos .............................................................................. 114 E. Proposition 65 ........................................................................ 115 F. Solid Waste ........................................................................... 116 G. Hazardous Waste .................................................................. 118 H. Hazardous Materials Management ........................................ 124 I. Underground Storage Tanks ................................................. 129 J. Aboveground Storage Tanks ................................................ 131 K. CERCLA Notification ............................................................. 134 L. Pesticides .............................................................................. 135 III. ENVIRONMENTAL MANAGEMENT AUDIT .................................. 138 A. Environmental Policy and Procedures.......................................... 138 B. Management Support and Attention ........................................... 140 C. Capital Project Coordination ........................................................ 142 D. Chemical Purchasing, Receiving & Inventory Control ................. 142 E. Emergency Procedures & Spill History ........................................ 145 F. Housekeeping .............................................................................. 147

Contents G. Property Transfer ......................................................................... H. Communications........................................................................... I. Monitoring Regulatory Activity .................................................. J. Recordkeeping ............................................................................. STEP I: BASE FINE .............................................................................. STEP II: AGGRAVATING FACTORS IN SENTENCING .......................... STEP III: FACTORS FOR ENVIRONMENTAL COMPLIANCE ............... STEP IV: GENERAL LIMITATIONS ......................................................... STEP V: PROBATION — ORGANIZATIONS ..........................................

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148 148 151 152 154 162 172 177 179

Chemical Hazards in Semiconductor Operations ............... 187 Thomas E. Hawkinson and Daryl B. Korpela OVERVIEW .............................................................................. 1.0 PHOTOLITHOGRAPHY .................................................................... 2.0 WET ETCH .............................................................................. 3.0 DRYETCH .............................................................................. 4.0 IMPLANT/DIFFUSION ..................................................................... 5.0 CLEANING .............................................................................. 6.0 METALLIZATION ............................................................................ 7.0 MAINTENANCE ISSUES .................................................................. 8.0 USE OF GASES ..............................................................................

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187 189 192 193 195 197 197 198 199

Industrial Hygiene ............................................................... 204 David G. Baldwin and Michael E. Williams 1.0 INTRODUCTION .............................................................................. 2.0 INDUSTRIAL HYGIENE MONITORING ........................................... 2.1 Overview of IH Monitoring ........................................................ 2.2 Assessment Tools ..................................................................... 2.3 Biological Monitoring ................................................................ 2.4 Airborne Contamination by Process .......................................... 2.5 Continuous Gas Monitoring ...................................................... 2.6 Surface Contamination ............................................................... 2.7 Noise .............................................................................. 3.0 Personal Protective Equipment .......................................................... 3.1 Background .............................................................................. 3.2 Chemical Protective Gloves ........................................................ 3.3 Respiratory Protection ............................................................... 4.0 ODOR IDENTIFICATION ................................................................. 5.0 RECORDKEEPING ..................................................................... 5.1 General .............................................................................. 5.2 Continuous Monitor Records .................................................... 5.3 Ventilation Records .................................................................... 5.4 Employee Communication .......................................................... 5.5 Personnel Records ..................................................................... ACKNOWLEDGMENTS .......................................................................... REFERENCES ..............................................................................

204 204 204 209 218 219 238 240 241 242 242 243 251 256 259 259 261 261 261 262 262 262

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Electrical Hazards ................................................................ 269 Clifford E. Oliver 1.0 INTRODUCTION .............................................................................. 269 2.0 WHERE DO WE START? ................................................................. 270 2.1 How Do You Identify an Electrical Hazard Before Someone Gets Hurt? .............................................................................. 270 3.0 TERMINOLOGY .............................................................................. 272 4.0 HUMAN EFFECTS ............................................................................ 274 5.0 SCENARIO OF AN ELECTRICAL SHOCK ....................................... 278 6.0 WHAT REALLY HAPPENS? ............................................................ 279 7.0 REPORTING .............................................................................. 280 8.0 COMMON ELEMENTS OF ELECTRICAL ACCIDENTS/ACCIDENT INVESTIGATION .............................................................................. 282 9.0 ELECTRICAL HAZARD MANAGEMENT ....................................... 288 10.0 TYPICAL ELECTRICAL HAZARDS ................................................. 289 10.1 Housekeeping Considerations ................................................ 290 10.2 General .............................................................................. 290 10.3 Installation .............................................................................. 290 10.4 Guarding .............................................................................. 291 10.5 Safety Signs ............................................................................. 291 10.6 Labeling .............................................................................. 291 10.7 Clearance .............................................................................. 292 10.8 Switches .............................................................................. 292 10.9 Manuals .............................................................................. 292 10.10 Water, Electricity, and Ground ................................................ 293 10.11 Extension Cords and Power Strips ........................................... 293 10.12 Electrical Plugs: 2- vs. 3-Prong 120-Volt .................................. 294 10.13 Circuit Breakers and Breaker Panel Boxes ................................ 294 10.14 Interlocks .............................................................................. 295 10.15 Hazardous Locations ............................................................... 295 10.16 Fire Extinguishers .................................................................... 296 11.0 HAZARD-BASED, SAFETY PLANNING ......................................... 297 12.0 LOCKOUT/TAGOUT ........................................................................ 298 12.1 OSHA .............................................................................. 298 12.2 Procedures .............................................................................. 298 12.3 Basics .............................................................................. 298 13.0 ELECTRICAL SAFETY COOKBOOK–What can be done? What can I do? .............................................................................. 299 13.1 Understand .............................................................................. 299 13.2 Communicate .............................................................................. 300 13.3 Never Work Alone ..................................................................... 300 13.4 Inspect .............................................................................. 300 13.5 No Shortcuts .............................................................................. 301 13.6 Safety Design Reviews............................................................... 301 13.7 Caution .............................................................................. 301 13.8 Final Thoughts ........................................................................... 301 REFERENCES .............................................................................. 302

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6 Radiation Safety .................................................................. 304 David G. Baldwin and Michael E. Williams 1.0 INTRODUCTION .............................................................................. 2.0 EXTREMELY LOW FREQUENCY ELECTROMAGNETIC FIELDS (ELF/EMF) ............................................................................ 3.0 RADIOFREQUENCY/MICROWAVE RADIATION .......................... 4.0 LASERS .............................................................................. 5.0 ULTRAVIOLET RADIATION ........................................................... 6.0 IONIZING RADIATION .................................................................... 6.1 X-Ray Generating Machines ...................................................... 6.2 Radioactive Material .................................................................. ACKNOWLEDGMENTS .......................................................................... REFERENCES ..............................................................................

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304 305 313 315 317 318 319 321 324 324

Recognition, Evaluation and Control of Some Plasma Processing Hazards ............................................................. 327 David Rainer and Lisa Brooks CHEMICAL SAFETY MANAGEMENT IN A NUTSHELL ...................... 1.0 INTRODUCTION .............................................................................. 2.0 HAZARD EVALUATION ................................................................. 3.0 PROCESS HAZARD REVIEW ........................................................... 4.0 OTHER MECHANISMS TO ADDRESS EQUIPMENT SAFETY CONCERNS ........................................................................ 5.0 GAS CHEMICAL SAFETY ................................................................ 5.1 Compressed Gas Cylinder Safety ............................................... 5.2 Flow Restrictors ......................................................................... 5.3 Gas Flow through Limiting Orifices ............................................ 5.4 Sizing the Orifice ........................................................................ 5.5 Orifice Purging ........................................................................... 5.6 Gas Storage Locations and Gas Cabinets ................................... 5.7 A System Approach to Gas Safety ............................................. 5.8 917 Alarm Response Processor .................................................. 5.9 PFD 959 Gas Panel Controllers ................................................... 5.10 904A Wall Valves ....................................................................... 5.11 Loss of Essential House Services .............................................. 5.12 Action-Reaction ......................................................................... 6.0 TOXICOLOGY .............................................................................. 6.1 History and Development .......................................................... 6.2 Occupational Toxicology ........................................................... 6.3 Basic Concepts of Toxicology ................................................... 6.4 Classification of Toxic Effects .................................................... 6.5 Toxicology of Halogen-Containing Plasma Etching Gases ........ 6.6 Fluorine and Fluorine-Containing Gases .................................... 6.7 Chlorine and Chlorine-Containing Gases ................................... 6.8 Bromine and Bromine-Containing Gases ....................................

327 328 330 332 338 339 346 348 350 352 353 353 356 358 358 358 359 359 360 360 361 361 368 371 371 372 373

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Contents 7.0 SOURCES OF INFORMATION ......................................................... 374 REFERENCES .............................................................................. 375 ADDITIONAL REFERENCES ................................................................... 377

8 Fire Protection Technology for Semiconductor Operations ... 378 Robert J. Pearce 1.0 INTRODUCTION .............................................................................. 378 1.1 History .............................................................................. 378 1.2 Highly Protected Risk ................................................................. 379 1.3 Codes .............................................................................. 380 2.0 SITE SELECTION .............................................................................. 381 2.1 Introduction .............................................................................. 381 2.2 Climate .............................................................................. 382 2.3 Topography .............................................................................. 382 2.4 Exposure .............................................................................. 383 2.5 Utilities .............................................................................. 384 3.0 CONSTRUCTION .............................................................................. 387 3.1 Exterior Envelope........................................................................ 387 3.2 Cleanroom .............................................................................. 387 4.0 AIR HANDLING SYSTEMS .............................................................. 389 4.1 Introduction .............................................................................. 389 4.2 Construction Materials ............................................................... 390 4.3 High Efficiency Particulate Air Filters ........................................ 390 4.4 System Design ........................................................................... 391 4.5 Fume Exhaust System ................................................................. 393 5.0 SPRINKLER PROTECTION ............................................................... 396 5.1 Scope .............................................................................. 396 5.2 NFPA Codes .............................................................................. 396 5.3 Cleanroom Sprinkler Systems ..................................................... 396 5.4 Types of Sprinkler Systems ........................................................ 398 5.5 Room Protection ......................................................................... 400 5.6 Service Aisles/Floors ................................................................. 400 5.7 Duct Sprinklers ........................................................................... 401 5.8 Chemical Storage Areas ............................................................. 403 5.9 Added Reliability........................................................................ 404 6.0 WATER SUPPLIES ........................................................................... 405 6.1 Scope .............................................................................. 405 6.2 Primary Supply ........................................................................... 406 6.3 Booster Pumps ........................................................................... 406 6.4 Primary Fire Pumps ..................................................................... 406 6.5 Drivers .............................................................................. 407 7.0 SUPERVISION .............................................................................. 409 7.1 Scope .............................................................................. 409 7.2 Water Flow .............................................................................. 409 7.3 Valve Tamper.............................................................................. 410 7.4 Supervision of the Fire Pump ..................................................... 411

Contents 7.5 Other Alarms .............................................................................. 7.6 Smoke Detection ........................................................................ 7.7 Other Detectors .......................................................................... 7.8 Signalling Systems ..................................................................... 7.9 Proprietary Supervisory Service ................................................. 7.10 Watchman Service ..................................................................... 8.0 CHEMICAL HANDLING ................................................................... 8.1 Scope .............................................................................. 8.2 Gases .............................................................................. 8.3 Liquids and Solids ...................................................................... 9.0 EQUIPMENT .............................................................................. 9.1 Scope .............................................................................. 9.2 Electrics .............................................................................. 9.3 Materials of Construction .......................................................... 9.4 Heated Baths .............................................................................. 10.0 HUMANENGINEERING ................................................................... 10.1 Scope ..............................................................................

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Building and Fire Codes Impacting the Semiconductor Industry ................................................................................ 429 William R. Acorn 1.0 2.0 3.0 4.0

UNDERSTANDING THE NEED FOR CODE COMPLIANCE ............ OVERVIEW OF APPLICABLE CODES ............................................. OVERVIEW OF UNIFORM BUILDING AND FIRE CODES .............. OCCUPANCY CLASSIFICATIONS .................................................. 4.1 Control Area .............................................................................. 5.0 CLASSIFICATION OF HAZARDOUS MATERIALS ....................... 5.1 Physical Hazards ........................................................................ 5.2 Health Hazards ........................................................................... 6.0 ALLOWABLE AREA AND SEPARATIONS .................................... 7.0 LOCATION .............................................................................. 8.0 EXITING .............................................................................. 9.0 EXIT CORRIDORS ............................................................................ 10.0 SERVICECORRIDORS ...................................................................... 11.0 HAZARDOUS MATERIAL STORAGE AND DISPENSE ROOMS ........................................................................... 11.1 Separation of HPMs ................................................................... 11.2 Flammable and Combustible Liquids .......................................... 11.3 Toxic Gas Monitoring ................................................................. 11.4 Smoke Detection ........................................................................ 11.5 Pyrophoric Materials .................................................................. 12.0 MECHANICAL HEATING, VENTILATING AND AIR CONDITIONING SYSTEMS .............................................................. 12.1 General .............................................................................. 12.2 Recirculating Air Handling Systems .......................................... 12.3 Exhaust Ventilation.....................................................................

429 430 431 432 432 439 439 439 440 441 442 444 444 445 445 446 446 446 446 446 446 447 447

xxii Contents 12.4 HPM Storage Area Ventilation ................................................... 448 12.5 Makeup Air .............................................................................. 449 12.6 Emergency Ventilation and Operation ........................................ 449 12.7 Air Handling System Isolation ................................................... 449 13.0 FIRE SUPPRESSION .......................................................................... 450 13.1 H-6 Occupancies ........................................................................ 451 13.2 Cleanrooms .............................................................................. 451 13.3 Storage Occupancies.................................................................. 452 13.4 Exhaust Ducts Containing Flammable Vapors ............................ 453 13.5 Exhaust Ducts Containing Corrosive Vapors ............................. 453 13.6 Gas Cabinets .............................................................................. 453 13.7 Alternate Suppression Systems ................................................. 454 14.0 ELECTRICAL POWER SYSTEMS ..................................................... 454 14.1 Transfer Switches ....................................................................... 455 14.2 Emergency Shutoffs ................................................................... 455 14.3 Hazardous Area Electrical Requirements .................................... 457 15.0 LIFE SAFETY ALARM AND MONITORING SYSTEMS ................. 458 15.1 Emergency Control Station (ECS) ............................................... 458 15.2 Fire Alarm and Monitoring Systems .......................................... 459 15.3 Continuous Toxic Gas Monitoring ............................................. 460 15.4 Emergency Spill Alarm ............................................................... 463 15.5 Audible Alarm Evacuation ......................................................... 464 15.6 Visual Alarm Signaling ............................................................... 464 15.7 Fireman’s Command Station ....................................................... 464 16.0 RETROFIT AND RENOVATION OF HAZARDOUS FACILITIES TO COMPLY WITH “H” CODES ................................. 465 16.1 Renovation .............................................................................. 465 16.2 Code Agency Liaison ................................................................. 466 17.0 PRIORITIZING CODE COMPLIANCE ISSUES .......................... 468 18.0 PHASING OF PROJECT CONSTRUCTION ....................................... 469 18.1 Scheduling .............................................................................. 470 18.2 Project Manager ......................................................................... 470 18.3 Contractors .............................................................................. 471

10 Gases and Gas Equipment .................................................. 472 Richard P. Brookman and Bruce Tibbott 1.0 INTRODUCTION .............................................................................. 472 2.0 GAS DISTRIBUTION SYSTEMS IN PLANT PIPING ........................ 473 2.1 Materials of Construction .......................................................... 473 2.2 Compression Fittings ................................................................. 474 2.3 VCR Fittings .............................................................................. 475 2.4 Orbitally Welded Fittings ........................................................... 475 2.5 Routing Considerations ............................................................. 476 2.6 Secondary Containment ............................................................. 476 2.7 Dedicated Versus Branched Lines ............................................. 477 2.8 Pressure Testing ........................................................................ 478

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2.9 Leak Testing .............................................................................. 2.10 Particulate Testing ..................................................................... GAS CYLINDERS—SAFE USE AND HANDLING ........................... 3.1 Cylinder Types and Specifications ............................................. 3.2 Compressed Gas Cylinders......................................................... 3.3 Liquefied Gas Cylinders ............................................................. 3.4 Cryogenic Cylinders ................................................................... 3.5 Cylinder Valves and Safety Devices .......................................... 3.6 Cylinder Connections, Types and Uses ..................................... 3.7 Safety Devices (Reliefs, Fuse Plugs, RFO’s, Etc.) ...................... 3.8 Receiving and Identification of Cylinders .................................. 3.9 Leaking Cylinders ....................................................................... 3.10 Transportation and Storage ....................................................... 3.11 Safe Use of the Cylinder ............................................................. GENERAL GAS HANDLING EQUIPMENT ....................................... 4.1 Pressure Regulators ................................................................... 4.2 Valves .............................................................................. 4.3 Pressure Sensors ........................................................................ 4.4 Flow Meters .............................................................................. 4.5 Filters and Purifiers..................................................................... 4.6 Vacuum Generators .................................................................... CYLINDERGASDELIVERYSYSTEMS ............................................ 5.1 Enclosures (Gas Cabinets, Gas Storage Rooms, Etc.) ................. 5.2 Gas Panels .............................................................................. 5.3 System Monitoring..................................................................... 5.4 System Control ........................................................................... GAS CANDIDATES .......................................................................... 6.1 Ammonia .............................................................................. 6.2 Argon .............................................................................. 6.3 Arsenic Pentafluoride ................................................................. 6.4 Arsine .............................................................................. 6.5 Boron Trichloride ....................................................................... 6.6 Boron Trifluoride ........................................................................ 6.7 Bromotrifluoromethane............................................................... 6.8 Chlorine .............................................................................. 6.9 Chloropentafluoroethane ........................................................... 6.10 Chlorotrifluoromethane .............................................................. 6.11 Diborane .............................................................................. 6.12 Dichlorodifluoromethane............................................................ 6.13 Dichlorosilane ............................................................................ 6.14 Disilane .............................................................................. 6.15 Germane .............................................................................. 6.16 Helium .............................................................................. 6.17 Hexafluoroethane ....................................................................... 6.18 Hydrogen .............................................................................. 6.19 Hydrogen Bromide ..................................................................... 6.20 Hydrogen Chloride .....................................................................

478 479 479 479 480 481 482 483 484 487 489 490 491 493 494 494 497 500 501 502 503 503 503 505 508 510 512 512 514 515 517 518 520 522 524 526 527 529 531 533 535 536 538 539 541 543 545

xxiv Contents 6.21 Hydrogen Fluoride ..................................................................... 547 6.22 Hydrogen Selenide ..................................................................... 549 6.23 Methyl Fluoride .......................................................................... 551 6.24 Nitrogen .............................................................................. 553 6.25 Nitrogen Trifluoride .................................................................... 554 6.26 Nitrous Oxide .............................................................................. 556 6.27 Oxygen .............................................................................. 558 6.28 Perfluoropropane........................................................................ 560 6.29 Phosphine .............................................................................. 562 6.30 Phosphorous Pentafluoride ........................................................ 564 6.31 Selenium Hexafluoride ................................................................ 566 6.32 Silane .............................................................................. 567 6.33 Silicon Tetrachloride .................................................................. 568 6.34 Silicon Tetrafluoride ................................................................... 570 6.35 Sulfur Hexafluoride ..................................................................... 571 6.36 Tetrafluoromethane .................................................................... 573 6.37 Trichlorofluoromethane .............................................................. 575 6.38 Trichlorosilane ........................................................................... 577 6.39 Tungsten Hexafluoride ............................................................... 579 BIBLIOGRAPHY .............................................................................. 580

11 Toxic Gas Monitoring .......................................................... 581 Paul C. Manz 1.0 REQUIREMENT FOR CONTINUOUS TOXIC GAS MONITORING .......................................................................... 581 1.1 Introduction .............................................................................. 581 1.2 Brief History .............................................................................. 582 2.0 PURPOSE OF A TOXIC GAS MONITORING SYSTEM .................... 583 3.0 FUNCTIONAL MODEL OF A TOXIC GAS MONITORING SYSTEM .............................................................................. 587 3.1 Transport .............................................................................. 588 3.2 Analysis .............................................................................. 588 3.3 Identification .............................................................................. 594 3.4 Alarm .............................................................................. 597 3.5 Action .............................................................................. 598 4.0 SELECTION OF A TOXIC GAS MONITORING SYSTEM ................ 598 4.1 Single- or Multi-Point ................................................................. 599 4.2 Gas Detection Technology......................................................... 604 4.3 Gas Detector Integration ............................................................ 608 4.4 Role of Portable Gas Detectors................................................... 612 5.0 FUTURE TRENDS ............................................................................. 613 REFERENCES .............................................................................. 614

Index .......................................................................................... 616

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1 Injury and Illness of Semiconductor Workers: Experience and Epidemiologic Studies Donald V. Lassiter and James H. Stewart

1.0

INTRODUCTION

The U.S. semiconductor industry workplace presents an interesting departure from the classic view of the American working environment. As the very essence of what has become known as “High Technology” or the “High Tech” industry, the semiconductor industry is characterized by rapid changes, based on intense competition to place increasingly smaller microcircuits on increasingly smaller substrate surfaces, with no loss in final product “yield.” Layered on top of competitive production change is the necessity to perform the crucial elements of manufacturing in isolated, ultraclean wafer fabrication units. Workers themselves are further isolated from the product being produced by wearing special “gowns,” hair covers and facial masks. They are protected from harmful exposures to toxic chemicals and physical agents in ways that no large, manufacturing work force has ever been protected previously. Only the aerospace and nuclear weapons industries provide similar worker exposure controls. Yet, in all three of these industries, worker exposure controls were designed primarily to 25

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maintain product purity in a working environment free of harmful contamination. Practically speaking, concerns for product purity have resulted also in worker protection. The wearing of personal protective clothing in semiconductor wafer fabrication rooms has been coupled with sophisticated systems of ventilation and chemical/gas air monitoring and detection. Alarms can be set at parts per million (ppm), or even parts per billion (ppb), to ensure that semiconductor employees are protected from harmful exposures resulting from releases of monitored chemical and gaseous substances. From this perspective, it must be understood that such controls on monitoring workplace air are absolutely essential in the wafer “fab.” Extremely toxic gases, such as arsine, phosphine and diborane have been in use in wafer fabrication since the beginning of the industry. The history of the industry is replete with wafer fab evacuations based on real or suspected leaks of gases or of solvents. Such evacuation episodes have become much less frequent in today’s wafer fabs largely because of the lessons learned in design of ventilation systems, toxic gas/chemical handling and increasingly sophisticated air monitoring systems with continuous air sampling. From the standpoint of traditional workplace injury and illness statistics, the U.S. semiconductor industry has provided a model for worker safety and health protection. The frequency of work-related accidents and exposures resulting in injuries and illnesses has been among the lowest in the U.S. Figure 1 provides a graphic illustration of this experience compared with the private sector, all U.S. manufacturing, and durable goods manufacturing. However, the industry has not been free of work injuries and illnesses, even though the rate of occurrence of such conditions has been low. Nor has the industry been free of concern that more subtle health effects may be present.[1] In this chapter, we attempt to address both aspects of the U.S. semiconductor injury and illness experience. The chapter will skim over the past decade characterized by very low incidence rates of work injuries and illnesses among semiconductor workers to focus, instead, on stratification of work injuries and illnesses experienced by this work force during 1993 (provided by the U.S. Bureau of Labor Statistics and the Occupational Health System of the Semiconductor Industry Association).[2] Because of a major concern for the reproductive health of workers which surfaced in this industry during the middle 1980’s, a review of three, independent epidemiologic investigations is presented and the results discussed.

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Finally, it must be emphasized that the U.S. semiconductor industry has represented a unique modeling opportunity for public health research. Although major companies within the industry have always been highly competitive, these same companies have formed several organizations designed to facilitate information and data exchange of a noncompetitive nature which have relevance to the safety and health of the semiconductor work force. These organizations include SEMATECH, the Semiconductor Safety Association (SSA), and the Environmental Safety and Health Committee of the Semiconductor Industry Association (SIA). The geographic “compactness” of the industry in the “Silicon Valley” of Northern California in the 1980’s made possible the development of the Occupational Health System (OHS), which will be discussed later. Without the ability to maintain a close, ongoing relationship with key members of the industry’s safety and health community (often involving ad hoc meetings on short notice) a work injury and illness surveillance system such the OHS might not have been possible.

Figure 1. Comparative annual incidence rates for Occupational Health System, U.S. semiconductor industry, durable goods, and all manufacturing (1983-95).

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2.0

REVIEW AND DISCUSSION OF SEMICONDUCTOR INDUSTRY WORK INJURIES AND ILLNESSES

During the past several decades the primary indicator of the safety and health experience of the American work force has been the incidence of work-related injuries and illnesses as published annually by the U.S. Bureau of Labor Statistics (BLS).[3] These incidence rates (calculated as the average number of new injury or illness cases per 100 full-time equivalent employees per year) have provided a standardized annualized statistic for comparing the overall work injury and illness experience of workers in various industry sectors. Prior to 1972 (the initial BLS survey year), the only significant sources of data concerning semiconductor worker safety and health were individual states’ workers’ compensation records. Because of the dearth of data concerning worker health prior to 1972, the growth of the industry during the 1970’s and the many manufacturing process changes which have become a signature of the industry, historical data concerning injuries and illnesses among semiconductor workers prior to 1972 can be considered fairly irrelevant. Hence, the safety and health experience of the U.S. semiconductor industry work force has been closely tied to the annual incidence of work injuries and illnesses as calculated by the BLS rate for this industry. Figure 1 compares annual incidence rates for various industry sectors with the rates for the semiconductor industry during the period 1983–1995. Beginning in 1982, the primary trade association of the U.S. semiconductor industry (Semiconductor Industry Association—SIA) has sponsored the development and maintenance of the Occupational Health System (OHS). This system provides detailed data analyses of pertinent work injury and illness case variables on an annual basis for the semiconductor industry. Approximately one-quarter to one-third of the U.S. semiconductor industry participates in the OHS program on a year-to-year basis. Prior to 1982, the only significant data concerning the safety and health experience of the nation’s semiconductor work force were those published annually in the BLS surveys, as discussed above. Other indicators of the safety and health status of semiconductor workers have been reports of surveys (Health Hazard Evaluations) performed by the National Institute for Occupational Safety and Health (NIOSH), a sprinkling of papers published in the open scientific literature and proceedings of symposia associated with environmental and worker safety and

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health issues.[4][5] In addition, an annual meeting of semiconductor safety, health and environmental professionals sponsored by the Semiconductor Safety Association (SSA) has provided timely presentations concerning worker safety and health issues. Finally, as stated above, several epidemiologic studies have been performed during the past decade which focus on reproductive health consequences of employment in the semiconductor industry. These sources of data and information concerning semiconductor worker injuries and illnesses are discussed in the following sections of this chapter to present a contemporary review of the current status of the safety and health of this industry’s work force.

2.1 Work Injury and Illness Statistical Program of U.S. BLS Because of both the historic and contemporary importance of the BLS Annual Surveys of Work-Related Injuries and Illnesses, with respect to understanding the safety and health status of U.S. semiconductor workers, a summary discussion of this program is in order.

2.2 OSHA Recordkeeping System The Occupational Safety and Health Act of 1970 (OSH Act) created two new federal agencies: the Occupational Safety and Health Administration (OSHA) within the U.S. Department of Labor and the National Institute for Occupational Safety and Health (NIOSH) within the U.S. Department of Health and Human Services. The role of OSHA was to promulgate and enforce national workplace standards designed to protect the safety and health of the American worker, while the role of NIOSH was to sponsor research, train occupational safety and health professionals and recommend criteria for workplace standards to OSHA. The OSH Act mandated the Secretary of Labor with responsibility for developing and maintaining a national system for collection and analysis of work injury and illness statistics. In 1971 (the initial year that the OSH Act took effect), the Secretary of Labor delegated this responsibility to the Bureau of Labor Statistics (BLS), within the Department of Labor. Since that time BLS has performed a national Annual Survey of Occupational Injuries and Illnesses, while OSHA has retained responsibility for enforcing compliance with the recordkeeping provisions of the Part 1904 of the OSHA regulations.

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In 1971, OSHA promulgated the initial recordkeeping requirements at Title 29 CFR Part 1904. These recordkeeping regulations required employers with eleven or more employees to maintain an annual log of work injuries and illnesses, except for minor, first aid injuries. The log form is entitled “Log and Summary of Occupational Injuries and Illnesses,” (OSHA No. 200 form) and is required to be maintained by employers in all workplace establishments covered by the OSH Act. Only certain “low hazard” industries are specifically exempted from the annual recordkeeping requirements of the regulations. The exempted industries include certain retail industries, all finance, insurance, and real estate industries and certain service industries. However, some employers in each exempted industry are required to maintain the OSHA-200 log from time to time to provide a statistical sample for the Annual Surveys performed by BLS. In addition to the OSHA-200 log itself, the recordkeeping regulations require completion of a supplemental record for each work injury and illness case recorded on the log. The supplemental record contains more detail concerning the characteristics of the recorded case, included demographic variables. Employers are provided the choice of completing a separate Supplementary Record of Occupational Injuries and Illnesses (OSHA No. 101 form) or of substituting an alternate form (e.g., Workers’ Compensation reporting form) as long as the alternate form contains equivalent data and information. The Annual BLS Survey is performed by selecting a representative sample of employers from all industries according to Standard Industrial Classification (SIC) code and employment size (“establishment size”) and requiring the selected employers to copy annual totals of cases and days of lost and restricted work to a survey form. Beginning in 1992, the Annual Survey began to require detailed data from the supplementary data form (OSHA-101 or equivalent) for a sample of cases involving lost days away from work. The data collected by BLS during the Annual Survey are compiled into simple, summary statistics and published approximately two years following the year of occurrence. The published statistics include the average annual incidence of cases of work injuries and illnesses which have occurred per 100 full-time equivalent workers per year by major industry division and 4-digit SIC code. Also, incidence rates associated with lost and restricted workdays cases are published. Hence, the BLS Annual Surveys provide the U.S. public with annualized frequency statistics concerning cases and work loss time associated with employee injuries and illnesses. In 1992, the Annual Survey began

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providing more detailed data concerning case and demographic characteristics of cases involving lost days away from work.

2.3

Usefulness of BLS Survey to U.S. Semiconductor Industry

In evaluating the usefulness of the BLS recordkeeping system with respect to a particular industry, it is important to understand the limits of that system. Firstly, the system is sustained by the thousands of the nation’s employers who are required (by OSHA regulation) to maintain the OSHA200 log and OSHA-101 (or equivalent form) supplemental data form. Despite OSHA’s view that the records provide employers with a valuable resource for analyzing the work injury and illness experience of their work force, many employers view the system as an encumbrance or, worse, a required nuisance. This assessment of the system on the part of employers is unfortunate, but understandable. The reasons for this viewpoint by employers are many and are varied. It is sufficient in this context simply to understand that the system has been maintained over the past two decades by individuals who have little at stake in its success and who would care little if it completely failed. The fact that organized labor has, likewise, placed little importance on increasing the effectiveness of the OSHA/BLS recordkeeping system simply underscores this perspective. Hence, the roots of the present system provide little support other than what is mandatorily required by OSHA regulation. For this reason, only the required minimal effort is expended by employers to maintain the system’s required records. Even that minimal effort often falls short in maintaining the detailed supplemental case form (OSHA-101 or equivalent). Secondly, employers view the system as a regulatory enforcement tool. Because OSHA compliance inspections normally begin with a review of the OSHA-200 log, employers have long regarded their OSHA-200 log as a self-incriminating document. This viewpoint became entrenched when it was widely understood that the course of an OSHA inspection could hinge on whether the establishment’s lost workday experience was considered excessive, compared to similar companies in the same SIC (Standard Industrial Classification) code. This situation tends to place undue emphasis on maintaining a low company profile with respect lost workdays and lost workday cases. Hence, company recordkeeping policies and adequate employee recuperation associated with work loss can become clouded issues.

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Thirdly, OSHA recordkeeping mechanics tend to complicate what is, in essence, really a very simple procedure. Requirements for (i) recording distinctions between injuries and illnesses on the OSHA-200 log, (ii) for placing X’s in various columns on the log and (iii) for carrying forward individual sheet totals of cases and work loss days to annual totals are fraught with possibilities for errors. From this perspective, it may seem incongruous that these records could be of prime, practical significance to estimating the work injury and illness experience of the U.S. semiconductor industry, much less the nation’s work force. However, because the BLS recordkeeping system is considered credible by the federal and individual state governments, and because it is used both to target OSHA inspections and to determine the work injury and illness experience of employees in individual workplaces, it must be included in any employer’s plan of injury and illness surveillance.

2.4

Occupational Health System (OHS)

In 1991, the Board of Directors of the Semiconductor Industry Association (SIA) sponsored development of the Occupational Health System (OHS). The primary purpose of the OHS was to document the work injury and illness experience of the U.S. semiconductor industry work force on an annual basis. The OHS was supported by participating companies on an annual fee basis. The primary components of the OHS include: 1. Occupational Title Directory The Occupational Title Directory was designed to provide a system of uniform coding of cases from participating companies based on common jobs. The Directory contains approximately 65 occupations common to the U.S. semiconductor industry work force. Although the source for the Directory was the U.S. Bureau of the Census classification of occupations, the Directory was specifically tailored for use in the OHS and includes a disproportionate number of jobs for engineers and technicians, compared with the source document.

Injury and Illness of Semiconductor Workers 2. Case characteristic codes A series of codes was developed to classify case characteristics of worker injuries and illnesses according to: • Type of accident or exposure or event • Source of injury or illness • Nature of injury or illness • Part of body affected • (Cause of accident or exposure—optional) All work injury and illness cases submitted for inclusion in the OHS database are coded except for “cause of accident or exposure” code. This latter code is, presently, optional in the OHS. 3. Demographic variables The following demographic variables are coded for each case entered into the OHS database: • Gender • Job code (from Occupational Title Directory) • Date of birth • Date of hire 4. Administrative variables The following case administration data are entered for each case: • Date of injury or illness • (Time of injury or illness—optional) • Employee name • Employee SSN • Employee Number • Number of work loss days (away from work) • Number of restricted workdays • Company/facility ID Code • Department/work division • OSHA classification as to “injury” or “illness”

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Semiconductor Safety Handbook 5. Computerized management information system A computerized management information system was developed to manage the OHS database, and tailored versions of this program are made available for use by participating companies. Companies which have either purchased or developed their own computer programs to manage work injury and illness data, or which perform such analyses manually, are required to provide computer files of coded cases or hard copies of coded data. Data from the OHS have been included along with comparable data from the BLS 1993 Survey in Figs. 1–14.

2.5 Work Injury and Illness Experience of Semiconductor Workers Annual incidence rates for OSHA-recordable work injuries and illnesses for various U.S. industry sectors during the period 1983–1995 are presented in Fig. 1. These rates (average numbers of cases per 100 full-time equivalent workers per year) compare all manufacturing and durable goods manufacturing with semiconductor manufacturing and with the OHS database for the same time periods. The primary distinction in these rates is between the incidence of cases for all manufacturing and durable goods manufacturing compared with rates for both semiconductor manufacturing (BLS) and the OHS database. During this period, incidence rates for semiconductor manufacturing have been approximately one-third of the rates for durable goods manufacturing. In fact, during the past decade the semiconductor industry has experienced some of the lowest incidence rates of work injuries and illnesses in the durable goods manufacturing sector. However, the practical significance of these rate comparisons is seriously limited. As discussed in the section of this chapter dealing with the BLS recordkeeping system, these rates provide no information beyond the rate statistic, itself. Unfortunately, rate comparisons (based on published BLS rates) have been used widely during the past several decades as surrogates of the status of worker safety and health of entire industry sectors, individual companies, company divisions etc. Although such comparisons—in the broadest sense—are justified, they tend to mask possible underlying problems. Only the composite experience is documented in the BLS published annual rates, with no stratification of the data beyond the 4-digit SIC code. Of course, from a relative risk standpoint, it is possible to

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identify industry sectors, companies, divisions, etc., which differ, significantly, from calculated “norms.” Fortunately, beginning in 1992, the U.S. Bureau of Labor Statistics (BLS) began publication of a new series of data analyses based on detailed coding of OSHA-recordable cases involving days away from work. Data obtained directly from BLS2 have been used to produce a series of figures (Figs. 2–14) which present direct comparisons of these data as they pertain to the experience of employees in the U.S. semiconductor industry during 1993. Although these data cannot be thoroughly analyzed at present because of the limited access afforded by BLS, as a whole they provide much greater clarity concerning the work injury and illness experience of U.S. semiconductor workers than has been available previously. A discussion of these data is presented below. With the exception of Fig. 5 (associated with race/ethnic characteristics) each figure compares the lost workday* case experience for the private sector, all manufacturing, semiconductor manufacturing and the OHS database. The incidence of cases with days away from work in 1993 for the industry sectors being compared in these figures was: • Private sector 3.0 cases per 100 workers • All manufacturing 3.5 cases per 100 workers • Semiconductors 1.2 cases per 100 workers • OHS 1.1 cases per 100 workers Figure 2 compares the distribution of lost workday cases according to the primary, major occupation of the affected worker. In the absence of incidence rates, these data illustrate a similar pattern of cases for the industry sectors depicted. For all sectors, the greatest proportion of cases occurred among workers employed as operators, fabricators or laborers. The OHS has documented that the greatest number of cases during the past decade have involved wafer fabrication employees, although the incidence of cases for this group has been only slightly in excess of the rate for the semiconductor industry, as a whole (e.g., 4.0–5.0). The comparative distribution of lost workday cases stratified by employee age at time of accident or exposure is presented in Fig. 3. A related set of data is presented in Fig. 4, associated with the length of employee service with the employer. In both figures, semiconductor workers predominate in the older worker groups (Fig. 3) and in the groups with most service with the employer (Fig. 4). The reasons for greater proportions of semiconductor workers in the older/longer service groups are, probably, * The terms lost workdays and lost workday cases will apply only to cases with days away from work in this chapter

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more likely associated with greater proportions of employees (“at risk”) in these two categories in the semiconductor industry. That is, it is possible that the semiconductor industry has a relatively greater proportion of older employees, which would also indicate a greater number of workers with more experience. However, in the absence of incidence rates, it is not possible completely to rule out a greater risk of injury or illness for these workers.

Figure 2. Comparative distribution of lost workday cases (cases with days away from work) by employee occupation—1993.

Figure 3. Comparative distribution of lost workday cases by employee age group—1993.

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Figure 4. Comparative distribution of lost workday cases by length of service with employer —1993.

In Fig. 5, the proportional distribution of lost workday cases according to employee race/ethnic group is presented. (The OHS does not code cases according to this variable.) With respect to the U.S. semiconductor industry, greater proportions of injuries or illnesses occurred among Hispanic and Asian/Pacific Islander employees in comparison with other race/ ethnic groups of semiconductor workers. In the case of Asian/Pacific Islander employees, a near fourfold excess of lost workday cases was documented for this group of semiconductor workers in 1993, compared with the other race/ethnic groups. Again, an absence of incidence rates by race/ethnic group precludes definitive analyses of these differences. It is most probable that the excess of cases is more reflective of greater numbers of workers in these race/ethnic categories employed in the semiconductor industry. There is no reason to believe that race or ethnicity would be expected to place semiconductor workers at proportionately greater risk of injury or illness.

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Figure 5. Comparative distribution of lost workday cases by race or ethnic group—1993.

Figure 6 examines differences in the distribution of days away from work for these industry sectors. Compared with the private sector and all manufacturing, both the semiconductor industry and the OHS database reported greater proportions of cases involving only one or two days way from work. This experience tends to indicate that lost workday cases involving semiconductor workers are less severe than for workers in the other comparison industry sectors. Figures 7 and 8 compare the lost workday experience of semiconductor workers with the private sector and with all manufacturing with respect to event or exposure (also stated as “type for accident or exposure”). From the viewpoint of proportional lost workday case distribution (Fig. 7), the U.S. semiconductor industry and the OHS database documented greater proportions of cases associated with overexertions and harmful exposures than the private sector or all manufacturing. However, in Fig. 8, which illustrates the incidence of cases with days away from work, the incidence rate for most categories was much less for the two semiconductor groups than for the private sector or all manufacturing. Cases involving overexertions among semiconductor workers were less than one-half the rate for workers in the rest of the manufacturing sector. The harmful exposure category (primarily associated with exposures to chemical substances) was equivalent among all four groups.

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Figure 6. Comparative Distribution of lost workday cases by numbers of days away from work—1993.

SOURCE: Annual Survey, US DOL, 1993, & OHS Annual Survey, 1993

Figure 7. Comparative distribution of lost workday cases by event or exposure—1993.

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Figure 8. Comparative incidence of lost workday cases by event or exposure—1993.

Comparative distributions of lost workday cases according to source of injury or illness are presented in Figs. 9 and 10. In Fig. 9, the two semiconductor groups predominate in the source categories associated with chemicals. In addition, the U.S. semiconductor group had greater proportions of lost workday cases associated with containers and “worker motion/ position” (i.e., ergonomic cases). A large difference was observed between the two semiconductor groups with respect to “machinery” as a source category. The OHS database reported an almost threefold greater proportion of cases for this group than for the U.S. semiconductor industry, as a whole. It is possible that this difference was associated with better source definition available to the OHS than is available to the BLS state agencies which perform case coding. In Fig. 10, the influence of low overall incidence rates for the two semiconductor groups is once again observed. Lost workday case rates for both semiconductor groups are below those for the private sector and all manufacturing with the exception of a slightly higher rate for the OHS database with respect to the “chemicals” source category. Figures 11 and 12 compare proportions of cases and incidence rates, respectively, associated with the nature of injuries or illnesses among the four groups. In Fig. 11, both semiconductor groups projected higher proportions of cases associated with strains or sprains and with chemical

Injury and Illness of Semiconductor Workers

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burns compared with the other two groups. In addition, the U.S. semiconductor group exhibited a greater proportion of carpal tunnel syndrome (CTS) than the private sector. The higher proportion of lost workday cases associated with strains or sprains among semiconductor workers is resolved in Fig. 12. In this figure, the rates for the two semiconductor groups were less than one-half of the rates for both the private sector and for all manufacturing in 1992. The incidence of chemical burns was slightly higher for semiconductor workers, but was very low for all comparison groups. The incidence of CTS among U.S. semiconductor workers was less than one-half the rate for all manufacturing. In Figs. 13 and 14, respectively, the distribution and incidence of cases involving days away from work is illustrated according to part of body affected. Proportional distributions of cases were similar among all four groups (Fig. 13) with the exception of greater proportions of cases among the two semiconductor groups associated with body system(s). These cases were consistent with the observation of greater numbers and rates associated with “chemicals” as a source category in Figs. 9 and 10, respectively. In Fig. 14, although the incidence of cases involving body systems was low for all comparison groups, the rates for semiconductor workers remained slightly elevated. This slight difference may be related to greater control over accuracy of data coding afforded by the OHS.

Figure 9. Comparative distribution of lost workday cases by source of injury or illness— 1993.

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Figure 10. Comparative incidence of lost workday cases by source of injury or illness— 1993.

Figure 11. Comparative distribution of lost workday cases by nature of injury or illness— 1993.

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Figure 12. Comparative incidence of lost workday cases by nature of injury or illness— 1993.

Figure 13. Comparative distribution of lost workday cases by part of body affected—1993.

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Figure 14. Comparative incidence of lost workday cases by part of body affected—1993.

3.0

REVIEW AND DISCUSSION OF EPIDEMIOLOGIC INVESTIGATIONS

3.1

UMASS—Digital Equipment Corporation (DEC) Historical Cohort Study[6]

In September of 1983, a female employee at DEC’s (Digital Equipment Corporation’s) semiconductor plant in Hudson, Massachusetts, indicated that she felt that there was an excess of miscarriages occurring among employees in the fab clean rooms. As a result of this allegation and the absence of internal data, the University of Massachusetts School of Public Health (Amherst) was requested to conduct a health study that focused on reproductive outcomes but would produce incidence data on other diseases in the worker population, as well. The study was begun in May of 1984 and completed in 1985. Overview. The UMASS team conducted an historical cohort study of all employees of the Digital Equipment Corporation semiconductor manufacturing plant in Hudson, Massachusetts. Current employees were interviewed by trained female interviewers that were blind to the hypothesis

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of the study. Employees who terminated for any reason were identified. Only those who terminated voluntarily were included in the study population. All current fab employees who had worked more than one month in the semiconductor production “fab areas” were invited to participate in the health study. The exposed group was composed of the photolithographic workers. Two comparison groups were constructed: one composed of workers from the diffusion areas, ion implant, epitaxy, and other production areas (not including assembly) where glycol ethers were not used. The second group was composed of non-fab employees who had minimal or no known chemical exposures and who had never worked in a fab area. The non-exposed referent group was composed of a random sample of nonexposed employees who were group-matched (on age and sex). The diffusion group was also a referent group but composed of chemically exposed workers who had mainly acid and metal exposures with little if any solvent exposure. The exposed group was composed of workers with mainly solvent exposures including glycol ethers. A spontaneous abortion was defined as a fetal loss at less than 29 weeks gestational age. Data were collected in two phases: November and December 1984, and April and May 1986. Two phases of data collection were used because only two pregnancies were identified in the exposed group. The second phase was designed to increase the sample size. This was done in two ways: one, the non-exposed group was expanded to include all women at the plant who never worked in fab or chemically exposed jobs; and two, the inclusion of non-exposed pregnancies that occurred prior to employment at Digital. The experimental unit was the pregnancy, not the woman. Therefore one woman could contribute more than one observation to the study. The male employees were also interviewed and the spouses of male employees were also invited to participate via phone interview. The industrial hygiene data for the plant were reviewed to attempt to establish exposure groups. The data showed that, of the 1500+ air samples taken, 89% contained nothing detectable. The highest exposure was approximately 1 ppm (xylene). The data were not used to construct exposure rankings. Exposures were determined by employees reporting their activities: where they worked, how often they performed certain tasks etc. Health information collected was heavily weighted towards reproductive health endpoints. Other disease data collected included arthritis, nausea, rash, sore throats, and headaches. Sociodemographic data such as previous health history, education, tobacco and alcohol use, etc., were also collected.

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Results. The UMASS study results are presented in Table 1. An elevated risk of miscarriage was found in both the photo group and the diffusion group when compared to the non-exposed group. The relative risk of 1.75 was not statistically significant at 0.05 while the 2.18 relative risk observed in the diffusion areas was significant.

Table 1. Relative risk of miscarriages. Group

Total Pregnancies

% SAB

Relative Risk

16 18 398

31.3 38.9 17.8

1.75 2.18*

Photolithography Diffusion (non-Photo) Non-exposed *Statistically significant at p < 0.05

This elevated risk held when factors such as tobacco use, previous medical history, alcohol use, marital status, education, etc. were considered (through multiple logistic regression analysis). Additional analyses were conducted to estimate the effect of including pre-Digital pregnancies from the non-exposed group. The elevated risk (though not statistically significant) was still present when the results were adjusted for recall bias (in the non-exposed group) for spontaneous abortions/pregnancies that occurred many years ago. General health outcomes such as nausea, arthritis, headaches, rashes, and sore throats were reported more often by photolithography workers than others. These analyses were prevalence-based rather than incidence-based as used in the reproductive portion of the study.

3.2

UC Davis-Semiconductor Industry Association Study[7]

The University of California at Davis (UC Davis)-Semiconductor Industry Association (SIA) study was proposed in 1988 and implemented in 1989. The UC Davis study was designed to test the hypothesis that semiconductor manufacturing presents an increased risk of miscarriage to female workers. This was a hypothesis testing study rather than the

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previous hypothesis generating study by the University of Massachusetts (UMASS) study[6] at Digital Equipment Corporation’s Semiconductor Manufacturing site. The study population was drawn from of 14 companies representing 42 production sites in 17 states. The highest concentration of sites (representing almost half of the employees) was in California. The average number of employees per site was 3,600 with a range from 100 to over 6,000 employees. Thirty-seven percent of the fabrication employees were nonwhite; all but one company were nonunion. There were actually three different components to the study: a crosssectional component;[8][9] an historical cohort component;[10] and a prospective component.[11] Central to each of these studies was an exposure assessment.[12][13] This exposure assessment categorized the study subjects into related exposure groups and assigned them a relative ranking (i.e., high exposure, low exposure, etc.). Historical Cohort Component.[10] Overview. The historical cohort [10] study was designed to specifically determine if work in semiconductor fabs presented a risk from during the period 1986 to 1989. To be eligible for inclusion in the study, a woman must have been between the ages of 18 and 44, and have become pregnant while working full-time in the semiconductor industry between 1986 and 1989. One site was selected from each of the 14 participating companies. A miscarriage was defined as a pregnancy that terminated before 20 weeks gestation. A pregnancy that ended after 20 weeks gestation but did not produce a live birth was defined as a stillbirth. This definition was the same as the UMASS study but different than the Johns Hopkins University (JHU) study.[15] In the historical study, 7,269 women were selected from 14 companies for a telephone interview. After screening through the telephone interview and eliminating ineligible women, 6,088 women remained. The most common reason for exclusion was an invalid telephone number or address. Of the 6,088 women, 953 had eligible pregnancies. Nine hundred four (904) of the 953 women completed an indepth interview covering work history, reproductive history, and personal habits. If a woman had more than one pregnancy, one was selected at random for inclusion in the study. A total of 891 verified eligible pregnancies were identified. A verified pregnancy was one that was diagnosed medically or reported by a study participant and verified through a telephone interview with a designated physician on the study team. Data collection instruments were available in English and Spanish.

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Classification as fab or non-fab worker was made by the study industrial hygienists based on responses to questions during the interview on work history.[13] Assignment to a work group was based on both the responses on the questionnaire and the industrial hygiene assessments of the workplace. Fabrication workers (except for maintenance workers, supervisors and engineers) were split into two “supergroups:” masking, and dopefilm. The masking supergroup was composed of workers in the photo application and the etching operations. The dopefilm supergroup, as the name implies, included workers in thin films, ion implant, and furnace operations. The referent group was composed of non-fab workers from office and non-office settings. Results. The historical component of the study indicated that the relative risk for fabrication workers when compared to non-fabrication workers was 1.45 (95% CIE 1.02, 2.05) which was a 45% increase in risk relative to women who did not work in the fabrication area. Since the 95% confidence interval estimate (CIE) did not encompass the value 1.0 (equal risk), the observed difference was probably not due to random factors. The 95% CIE can be interpreted as representing reasonable ranges of relative risk for the population based on the sample drawn in the study. From another perspective, if additional samples were drawn from the population in same manner, 95% of the time the relative risk would lie between 1.02 and 2.05. Information was collected on a number of other risk factors during the interview process. These data were then used to adjust the relative risk estimate to remove the effect of these other factors. Adjusting the relative risk for another potential risk factor means that the effect of that risk factor is held constant across groups and not allowed to influence the outcome. “Adjusting” for a risk factor such as smoking can be thought of as asking the question: “What would the risk be if they didn’t smoke?” When the relative risk for miscarriage was adjusted for smoking (RR = 1.34), age (RR = 1.81) and having had a prior miscarriage (RR = 1.64), the effect of the workplace remained; in fact, it sometimes increased (e.g., age and prior miscarriage). In addition, women who reported a high level of stress in their work had a relative risk of 2.18. Adjusting for recognized confounding variables did not appreciably change the estimate of risk (RR = 1.43). However, the 95% confidence interval did include 1.0 indicating a lack of statistical significance at p < 0.05. The highest risk group identified in the historical component of the study was the masking supergroup with an adjusted relative risk of 1.78.

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These women worked in photolithography or etching operations. The strongest effect was seen for those women performing etching operations (RR = 2.15). Another important finding was that the risk of miscarriage for women who worked with any photoresist or developer displayed a dose response relationship (i.e., the more exposure, the higher the risk). Increased risk was also identified for exposure to fluoride, although such exposures did not demonstrate a clear dose response relationship. When the data were examined in greater detail, the dose response relationship was evident for EGE but not for PGE (propylene glycol ethers). These analyses must be viewed with a fair amount of caution because pure exposures to either EGE or PGE could not be identified, and the workers were in an atmosphere of mixtures of a number of chemicals. Also, the exposure categorization was not based directly on air measurements but rather on an exposure algorithm. Nonetheless, a demonstrated dose response relationship was observed from these data. Prospective Cohort Component.[11] Overview. The prospective study[11] was designed to assess whether there was an effect on women who currently worked in the semiconductor fabs. In this component of the study, women were selected who were at risk of becoming pregnant and who were willing to participate in the study. These women were then followed forward in time, and their exposures were assessed along with the outcome variables (e.g. pregnancy, miscarriage, and menstrual cycle changes). Daily urine samples were collected and analyzed for HcG (human chorionic gonadotropin), an hormonal indicator of pregnancy. Using HcG, pregnancies may be detected which would otherwise go unidentified. It was estimated that by using this approach, pregnancies could be diagnosed 8–9 days after conception. This was in contrast to other methods which often required 4–6 weeks, or more, following conception for recognition of pregnancy. To select women for inclusion in the prospective component of the study, 2,639 women completed a questionnaire to determine their eligibility. To be eligible a woman must have been at risk of becoming pregnant (i.e. not sterilized, etc). Four hundred fourteen (414) women were selected from California and Utah semiconductor fabs and followed. Daily urine samples were submitted, standardized interviews were conducted, and daily diaries were submitted by the study participants. Information on sexual activities, menstrual cycle length and variability, confounding exposures, work activities and exposures were collected. The urine samples were analyzed by the UC Davis Endocrine Laboratory.

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Results. An increased rate of miscarriage (although not statistically significant at p = 0.05) for fabrication workers was also observed in the prospective component (RR = 1.34 95% CIE 0.82, 2.20). The 414 women experienced only 57 pregnancies: 20 in fabrication workers, 37 in nonfabrication workers. Of the 20 fab pregnancies, 6 (30%) resulted in live births. This compares to 20 (54%) live births in the non-fab women. Overall, 60% of the pregnancies (both occult and clinical) resulted in miscarriage in the fab group and 43% in the non-fab group. In the masking supergroup, the risk ratio increased to 1.47 and for the dopefilm supergroup it rose slightly more to 1.57. None of these findings were statistically significant at p = 0.05. The small number of pregnancies significantly reduced the statistical power of the study. In fact, reduced fertility was one of the findings of the study. Women who worked in a fab were less likely to become pregnant than those who did not. The crude fecundity ratios (FR) (probability of becoming pregnant in one menstrual cycle for fab vs non-fab women) was not statistically significant at p = 0.05. However, when logistic regression was used to adjust the FR for potential confounders, the FR was statistically significantly reduced for fab workers (FR = 0.51 95% CIE 0.27, 0.95). Since the sample size was so small, other analyses had little statistical power to identify effects. Analysis by agent indicated an increased risk for those women who worked with EGE (ethylene glycol monoethyl ether) but was based on only three pregnancies. One important finding was the general support for, and no contradiction of, the findings of the historical component. Cross-Sectional Component.[8][9] Overview. The cross-sectional component[8][9] of the study was conducted at eight sites. Eight different companies were represented. The sites were randomly selected using a stratified random sampling plan. This sampling plan was developed to ensure a representative sample of company sizes. The main objective of the cross-sectional component was to assess fertility and 23 nonreproductive health effects . The cross-sectional component was considered hypothesis generating rather than hypothesis testing. Both male and female fab and non-fab workers were included. A total of 3,175 workers participated in the study; 51% were female, 53% were fabrication workers. Overall, the average participation rate was 78%. Participation rates at the eight sites ranged from 64% to 90%. Participation rates for men and women were 77% and 79%, respectively. Questionnaires were developed primarily

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from existing validated questionnaires (e.g., National Health and Nutrition Examination Study [NHANES]; the Neurobehavioral Evaluation System [NES]). Questions on fertility were adapted from Levine, 1980. Industrial hygiene and job exposure questions were developed especially for this study. The questions covered general health, demographic characteristics, job activities and exposures, income, personal habits, education, income, and medical history. A final section of the questionnaire covered fertility and was completed by males only. The objective of this section was to assess whether work in wafer fabrication affected males by decreasing fertility. Examples of the nonreproductive endpoints measured were headaches, nausea, upper respiratory symptoms, lower respiratory symptoms, persistent wheezing, carpal tunnel syndrome, elbow pain, back pain, neck pain, alopecia, dermatitis, and anxiety (measured using a somatization index). Results. Upper respiratory symptoms were elevated and demonstrated a dose response relationship (odds ratio (OR) = 1.29 95%; CIE 1.09, 153). This trend was also evident in the work group analysis, primarily in the furnace and thin film groups. Lower respiratory symptoms were elevated slightly among fab workers (OR = 1.18; 95% CIE 1.00,1.39) but did not display a dose response relationship. The furnace group as in the previous case demonstrated a higher risk (OR = 1.57; 95% CIE 1.10, 1.23). Overall, persistent wheezing was elevated in fab workers. The furnace and thin film groups demonstrated the highest risk (OR = 3.91; 95% CIE 1.36, 11.3), followed by the etch and photo groups (OR = 2.96; 95% CIE 1.12, 7.82). One of the factors known to be associated with respiratory symptoms is cigarette smoking. When smokers were compared to nonsmokers, the odds ratio for the chronic cough was 7.8, for chronic phlegm production the odds ratio was 4.4 and for persistent wheeze it was 3.2. An interesting finding, not mentioned by the UC Davis study team in their final report, was the identification of apparent protective effects of various engineering controls, e.g., footrests and adjustable chairs to reduce back injuries. Exposure Assessment Component.[12][13] Overview. The objective of exposure assessment in the context of an epidemiological study is to categorize the study subjects in groups representing different exposures. The challenge was substantial in the UC Davis study in that 14 companies were participating in many different locations with different products being produced. The exposure assessment team developed a three-tiered approach

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to exposure assessment.[12][13] At the most basic level, the subjects were categorized as fab or non-fab. Next, the subjects were placed in work groups where individuals in a work group had similar exposures. Lastly, an individual exposure profile was developed for selected chemical and physical agents. Individual exposure profiles (IEP’s) were developed for chemical agents, physical agents, ergonomic stressors, and VDT’s. The IEP’s were not developed for all agents in the fab but for selected target agents. Algorithms were developed to assign numbers indicating intensity of exposure (0–3), with 3 being the highest exposure category. A personal exposure score was then calculated (numerically) for each individual based on the operations they performed, the frequency with which they performed the operations, and the type of controls that were present. The information necessary to assign subjects to exposure groups came from several sources: • company notebooks • subject questionnaires • site visits by study industrial hygienists The final exposure groups were as follows: 1. Referent group (non-fab) a. office b. non-office 2. Exposed group (fab) a. operators and line technicians (i) masking supergroup (ii) photo and etch b. dopefilm supergroup (i) furnace (ii) thin film c. supervisors and engineers Results. The air measurements made in the fabs found that chemical exposures ranged from none detected to 11 ppm for acetone. Personal air samples were taken for fluorides, a number of solvents and ELF-MF (extremely low frequency magnetic fields).[14] For fluorides, 68 individuals were sampled in 35 fabs. The average concentration was 0.01 ppm with the

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highest sample being 0.4 ppm. This contrasts to the OSHA PEL of 3.0 ppm. For solvents, 66 individuals were sampled at 35 fabs. Since analytical techniques vary for certain solvents, 115 actual solvent samples were taken. The average concentration was 0.701 ppm. Solvent exposures were