MANUAL FOR MEASURING OCCUPATIONAL ELECTRIC AND MAGNETIC FIELD EXPOSURES Joseph D. Bowman* Michael A. Kelsh** William T. Kaune*** * National Institute for Occupational Safety and Health ** EcoAnalysis, Inc., Ojai, CA *** EM Factors, Inc., Richland, WA U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Public Health Service Centers for Disease Control and Prevention National Institute for Occupational Safety and Health Division of Biomedical and Behavioral Sciences October 1998 DISCLAIMER Mention of any company or product does not constitute endorsement by the National Institute for Occupational Safety and Health. This document is in the public domain and may be freely copied or reprinted. Copies of this and other NIOSH documents are available from Publications Dissemination, EID National Institute for Occupational Safety and Health 4676 Columbia Parkway Cincinnati, OH 45226 Fax number: (513) 533-8536 To order NIOSH publications or to receive information about occupational safety and health problems, call 1-800-35-NIOSH (1-800-356-4674) DHHS (NIOSH) Publication No. 98-154 ii PREFACE The National Institute for Occupational Safety and Health (NIOSH) has been studying whether electric and magnetic fields (EMF) from electrical equipment could cause cancer and other diseases since its Scientific Workshop on the Health Effects of EMF on Workers in 1991. The workshop's conclusions emphasized the need for better exposure assessments, and called for the development of standardized EMF measurement protocols. This undertaking is natural for NIOSH which throughout its 25-year history has developed and evaluated methods for measuring worker exposures to hazardous gases, vapors, and aerosols. These methods are published in a standardized format in the NIOSH Manual of Analytical Methods. Even though the health risks of EMF are research questions, exposure assessment protocols are still needed for epidemiologic studies, surveillance, and Health Hazard Evaluations. Therefore, the first edition of this document was prepared in 1992 for use by NIOSH investigators. NIOSH has also been conducting exposure assessment research to develop new measurement methods based on biological mechanisms of interaction with EMF. To review this question, NIOSH and the Department of Energy sponsored a workshop on EMF Exposure Assessment and Epidemiology: Hypotheses, Metrics, and Measurements in 1994. The workshop's starting point was that the exposure assessment methods in previous epidemiologic studies did not measure all the EMF characteristics needed to predict the outcome of the most plausible biologic mechanisms. Although exposure assessments for health studies should clearly be guided by biology, there was no consensus on which EMF mechanisms were the most credible. The workshop concluded with many good ideas but no recommendations for the best way to do future EMF studies. This uncertainty over which EMF features to measure clearly raises difficulties for developing standardized measurement protocols. On one hand, refining and testing a standard exposure assessment protocol is a questionable undertaking if the biologic assumptions underlying the method could be wrong. On the other hand, EMF epidemiologic studies and other health hazard evaluations are still taking place, and the scientific enterprise would be more productive if the investigators have some guidance on how to take measurements. To address these contradictory concerns, this Manual for Measuring Occupational EMF Exposures has collected important assessment protocols from previous studies and printed them in a standard format, each with a summary of its important features and a critique of its strengths and limitations. Important parts of the manual are its system for summarizing the methods and its definitions of EMF measurement terminology. The manual's philosophy is that providing investigators with successful methods from past studies will assist them in synthesizing protocols for their own applications. Exposure assessments serve many purposes: epidemiology, source assessment, compliance with guidelines, etc. Protocols written for one purpose can be of great value for other studies iii with minor modifications. As EMF biology evolves, these existing protocols can be the basis for improved methods. By providing this service to exposure assessors, this manual can assist in research to determine whether EMF is a health hazard. Where disease risks are established, these methods can be used to measure workers' exposures and assess sources so that any EMF hazard can be reduced. iv ABSTRACT The purpose of this manual is to assist investigators in developing methods for occupational exposure assessments for electric and magnetic fields (EMF). Scientific reports that associate EMF with increased risks of various diseases have led to exposure assessments for the purposes of research, source assessment, and the surveillance of worker exposures. To provide guidance for these studies, methods that have been used successfully to measure EMF are summarized and presented in a standard format. The scope of the manual is methods for measuring occupational EMF with frequencies below 30 kHz. This covers most fields resulting directly from DC or 50/60 Hz AC electricity, as well as common electric and electronic equipment such as Video Display Terminals (VDT). In this manual, exposure assessment protocols are classified either as complete methods or partial methods. Complete methods are sets of instructions for the sampling strategy, calibration, measurement, data management and calculation of EMF exposure metrics. The exposure metric and other information about the method are contained in a summary table accompanied by a critique of the method’s strengths and weaknesses. Partial methods are essentially parts of a full method that emphasize important aspects of EMF exposure assessments: sampling strategies, spot measurement surveys, personal monitoring, area monitoring, measuring EMF characteristics, measuring EMFs from sources, walkthrough monitoring, quality control, calibration, data management, and calculating exposure metrics. By combining aspects of these complete and partial methods, industrial hygienists and other investigators can assemble protocols specifically tailored to assess EMF exposures for different purposes, applications, and work environments. v vi CONTENTS I. INTRODUCTION .................................................. I-1 Purpose and Scope................................................. I-1 How the Manual is Organized......................................... I-3 How the Methods are Organized....................................... I-3 Method Title................................................... I-5 Summary Table................................................. I-5 Description and Purpose.......................................... I-5 Sampling Strategy............................................... I-6 Instrument..................................................... I-7 Exposure Metric................................................ I-8 Critique....................................................... I-9 Protocol ...................................................... I-9 How to Use this Manual............................................. I-9 Locating Complete and Partial Methods .............................. I-9 How to Assemble a Method ...................................... I-10 II. COMPLETE METHODS ............................................II-1 #201. ELF-EMF and High-frequency Transients ......................... II-201-1 #202. Time-Weighted Average (TWA) ELF Magnetic Fields ................ II-202-1 #203. Occupation- and Task-Specific Measurements of ELF Magnetic Fields .... II-203-1 #301. Area Measurements of ELF Electric and Magnetic Fields .............. II-301-1 #401. EMF Survey and Magnetic Field Characterization in Manufacturing ...... II-401-1 #501. Measurement of Power-frequency EMF from AC Transmission Lines .... II-501-1 III. PARTIAL METHODS ............................................ III-1 #001. Initial Walkthrough Survey of ELF Magnetic Fields................. III-001-1 #002. Monitoring ELF-EMF Exposures by Work Environment with Subject Logbooks...................................... III-002-1 #204. Personal Monitoring of ELF Magnetic Fields for Health Hazard Evaluations ................................... III-204-1 #302. Static Magnetic Field ........................................ III-302-1 vii #402. Area Measurements of Magnetic Field Characteristics ................ III-402-1 #701. Precision of Area Measurements ................................ III-701-1 #901. Calculating Time-weighted Averages (TWA) from Positron Monitor Data III-901-1 #902. Calculating Alternative Exposure Metrics from Time-Series Data ....... III-902-1 #903. Calculating Exposure Metrics from Three-Axis EMF Waveform Data .... III-903-1 IV. DEFINITIONS ..................................................IV-1 A. Terminology ..................................................IV-1 B. Units ........................................................IV-9 V. INDEX......................................................... V-1 A. Authors...................................................... V-1 B. Instruments ................................................... V-1 C. Exposure metrics............................................... V-2 viii I. INTRODUCTION Purpose and Scope This manual is a collection of procedures for measuring occupational exposures to electric and magnetic fields (EMF). Some epidemiological studies