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RF and Microwave Radiation Safety Handbook RF and Microwave Radiation Safety Handbook RONALD KITCHEN OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEWDELHI Newnes An imprint of Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd A member of the Reed Elsevier group First published 1993 by Butterworth-Heinemann as RF Radiation Safety Handbook Reprinted 1995, 2000 Second edition 2001 © Ronald Kitchen 1993, 2001 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1P 0LP. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publishers British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN 0 7506 43552 Composition by Genesis Typesetting, Laser Quay, Rochester, Kent Printed and bound in Great Britain Contents Preface vii 1 Introduction to RF and microwave radiation 1 2 Sources of radio frequency radiation 21 3 Effects of radio frequency radiation 47 Part 1 The exposure of human beings to RF radiation 47 Part 2 Incidents and accidents relating to RF exposure 78 4 The development of standards for human safety 86 Part 1 Basic concepts of RF safety standards and guides for human exposure 86 Part 2 Typical current safety standards for human exposure 95 Part 3 Safety calculations for structures involving flammable vapours 119 5 The calculation of RF field quantities 129 Part 1 Microwave antenna calculations and safety with moving microwave beams 129 Part 2 Other antenna system calculations 158 Part 3 Simultaneous irradiations and peak pulse power limits 168 6 Mobile communications systems 172 7 RF radiation measuring instruments and methods 293 8 X-rays and X-ray measuring instruments 244 9 Planning surveys and measurements 278 v vi Contents 10 Conducting radiation measurements and surveys 317 Part 1 Leakage surveys 317 Part 2 Exposure measurements 332 11 Designing to reduce radiation hazards 366 12 Radio frequency radiation safety management and training 392 Appendix 1 Useful data and relationships 413 Appendix 2 Technical and organisation abbreviations 416 Appendix 3 Information sources including the Internet 419 References 422 Index 429 Preface Since the previous volume on this topic was written about eight years ago many things have changed, not least the various safety standards and these interact with most aspects of the subject. I have endeavoured to implement some of the suggestions made to me for this revision without seriously increasing the book size. To some extent the updating of this sort of book is like being on an endless belt since new material appears almost daily and there is the need to draw the line at some point. As the book is addressed to people responsible for or concerned with safety, it cannot be assumed that all those involved are radio engineers. Often people from other disciplines such as mechanical engineering, chemistry and medicine, may be involved. Consequently some attempt has been made to explain things which the radio engineer might consider everyday matters. The general introduction to the book covers some of these aspects as previously. It is followed by updated pictorial examples of the sort of RF radiation sources likely to be met in RF radiation work, including RF process machines. Chapter 3 on RF radiation effects has been revised and a new part introduced dealing with actual RF incidents and accidents. I am indebted for part of this to Dr Rene´ de Seze and to various colleagues. The chapter on standards (Chapter 4) has been completely updated and current standards compared. The FCC limits tables have been added as have the FCC and UK tables of assessment levels applicable to radio amateurs. A chapter on mobile radio has been added (Chapter 6) and other chapters revised appropriately. Chapters 7 and 8 dealing with measuring instruments have been re-written with the new generation of instruments in mind although there is still some coverage of analogue RF radiation instruments since many are in use around the world. Every chapter now has an explanatory heading describing the contents. I am indebted to the various organisations for permission to publish parts of their standards and to BSI for permission to use material from their vii viii Preface standards. The European Union is still in the course of doing something about occupational RF radiation safety. The expectation is that the ICNIRP98 limits will be adopted for occupational purposes. The EC Machines Directive also touches the subject of radiation and is mentioned in this revision. The best development since the last book was written is the Internet and the availability of a lot of material which can be downloaded from various sites. This means that readers of this book can easily update themselves when something new arises. I have given some Internet data in Appendix 3 and though website arrangements do change in structure from time to time, it is usually easy to use the site search facilities to unearth the desired material. In all this I am indebted to many people for help with finding reports, pictures and other material, reading drafts, etc. They include: Robert Johnson of Narda for help with technical documents; Mike Spalding, a colleague from our Marconi days who apart from reading drafts has taken over the task of running the RF radiation safety courses; Stephen Sharples, NATS; Eric Randall, Cable and Wireless Communications; Chris Jacob, BT; John Coleman, Consultant; Steve Phillipo, Bill Hartley, NTL; Peter Condron, Crown Castle Int.; David Wood, Stuart Allen and Phillip Chadwick, NRPB, for help in finding information, and all those who provided pictures of their instruments and equipment. I am sure that I have missed people in the above list but if so, they can rest assured that their help was appreciated. Needless to say these people and their organisations are not responsible for any use I have made of information or any opinions expressed. Lastly, and by no means least, I am grateful for the love and support of my wife, Gene, both in reading the whole manuscript more than once despite the unfamiliar content, putting up with my long periods spent at the computer and being philosophical about the idea that I retired ten years ago. As this book is used as the course book on the training course which I set up at TUV Fareham, the book is dedicated to the Royal Air Force and others attending the course. Ron Kitchen Chelmsford The Birthplace of Broadcasting 1 Introduction to RF and microwave radiation This chapter gives an outline of the essential aspects of transmission and the nature of electromagnetic waves particularly for those from other disciplines who may otherwise find the electronic content unfamiliar. It includes explanations of the terms relevant to this form of non-ionising radiation. Radio frequency (RF) radiation The previous book on this subject was entitled RF Radiation Safety Handbook, the term ‘RF’ covering all frequencies used for communications, radar, satellites, etc., up to the nominal ceiling of 300GHz. However, it was suggested that some people regard ‘RF’ as applying only to the lower part of this spectrum. Consequently the word ‘microwave’ has been added in this revision, although it is redundant in the context of the book. It would be tedious to use both terms throughout the book so ‘RF’ is used to include ‘microwaves’ here as is understood by radio engineers. The term microwave is only specifically used when the topic involves something to which the term normally attaches, e.g. microwave oven, microwave antenna, etc. The subject of RF radiation is still regarded as mysterious and something of a black art. This is no doubt due to the fact that it cannot be seen or touched. There was also an element of magic in some of the very early experimental work, particularly that of Tesla, who seems to have mixed science and showmanship. Perhaps because RF is unseen, it has also become confused with ionising radiation in the minds of many people. It is essential to distinguish the difference between the two since, with our present state of knowledge, the consequences of exposure to them can confidently be stated as being very different. 1 2 RF and Microwave Radiation Safety Handbook Although we cannot see radio waves, most people will, at school or college, have done the classical experiments with magnetic fields and iron filings to demonstrate the patterns of the fields and used an electroscope to demonstrate the presence of electrostatic charge and the force which causes the gold leaf to move. From these early and rudimentary experiments with static fields it should at least be possible to conceive that such fields are not magical and are very common in any electrical environment. History of radio transmission Radio transmission is, relatively speaking, a very new technology which had its beginnings in the theoretical work of Maxwell in the nineteenth century and the experimental work of Hertz, the German physicist, in the last two decades of the nineteenth century. Many others also made contributions, including the development of devices which could detect the presence of radio waves. Whilst the question of who first transmitted radio signals is not without controversy, the subsequent practical development of radio communications systems is attributed to Guglielmo Marconi who was born in Italy in 1874. His first British patent was taken out in 1896 and covered the use of a spark transmitter. There are many accounts written of the experimental work carried out at various locations on land and on ships during the course of which the range of such equipment was very much increased. By 1921, the thermionic transmitter tube became available and made it possible to design transmitters to operate on a range of frequencies. The power output available increased with the development of electronic tubes which could, increasingly, handle higher powers with the aid of air or liquid cooling systems. Over the years, and stimulated by the needs of the First and Second World Wars, radio transmission has become an established technology which is taken for granted and which, among other things, provides for the broadcasting to our homes of entertainment, news and information of every kind in both the radio and television spheres. The most recent development, resulting in the domestic satellite dish antenna, brings the quasi-optical nature of microwaves to the notice of the consumer. The use of semiconductor devices (transistors) has become common- place and as a result the mass and volume of electronic products for a given function is much less than that of their earlier counterparts which used electronic tubes. However, in the high power transmitter field electronic tubes are still the mainstay of transmitters. These use very high voltages, depending on power output. 40kV or more is not unusual for very high power equipments. High power systems such as MF and HF