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`INTERNATIONAL COMMISSION ON NON-IONIZING RADIATION PROTECTION
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`ICNIRP GUIDELINES
`FOR LIMITING EXPOSURE TO TIME-VARYING
`ELECTRIC, MAGNETIC AND ELECTROMAGNETIC
`FIELDS (UP TO 300 GHZ)
`
`
`
`PUBLISHED IN: HEALTH PHYSICS 74 (4):494-522; 1998
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`Notes:
`
`Equation 11 was subsequently amended by the ICNIRP Commission in the 1999 reference book.
`The amended version is added here at the end of the document.
`
`In addition to the ICNIRP Guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic
`fields (up to 300 GHz) published in: health physics 74 (4):494-522; 1998) this PDF contains two excerpts from:
`Guidelines on Limiting Exposure to Non-Ionizing Radiation. A reference book based on guidelines on limiting
`exposure to non-ionizing radiation and statements on special applications. Munich: International Commission on
`Non-Ionizing Radiation Protection; 1999. ISBN 978-3-9804789-6-0: Use of the EMF Guidelines and Questions and
`Answers on the EMF Guidelines.
`
`
`ICNIRP PUBLICATION – 1998
`
`
`
`Momentum Dynamics Corporation
`Exhibit 1022
`Page 001
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`ICNIRP Guidelines
`
`GUIDELINES FOR LIMITING EXPOSURE TO TIME-VARYING
`ELECTRIC, MAGNETIC, AND ELECTROMAGNETIC FIELDS
`(UP TO 300 GHz)
`International Commission on Non-Ionizing Radiation Protection*†
`
`INTRODUCTION
`
`IN 1974, the International Radiation Protection Associa-
`tion (IRPA) formed a working group on non-ionizing
`radiation (NIR), which examined the problems arising in
`the field of protection against the various types of NIR.
`At the IRPA Congress in Paris in 1977, this working
`group became the International Non-Ionizing Radiation
`Committee (INIRC).
`In cooperation with the Environmental Health Divi-
`sion of the World Health Organization (WHO),
`the
`IRPA/INIRC developed a number of health criteria
`documents on NIR as part of WHO’s Environmental
`Health Criteria Programme, sponsored by the United
`Nations Environment Programme (UNEP). Each docu-
`ment includes an overview of the physical characteris-
`tics, measurement and instrumentation, sources, and
`applications of NIR, a thorough review of the literature
`on biological effects, and an evaluation of the health risks
`of exposure to NIR. These health criteria have provided
`the scientific database for the subsequent development of
`exposure limits and codes of practice relating to NIR.
`
`* ICNIRP Secretariat, c/o Dipl.-Ing. Ru¨diger Matthes, Bundesamt
`fu¨r Strahlenschutz, Institut fu¨r Strahlenhygiene, Ingolsta¨dter Land-
`strasse 1, D-85764 Oberschleissheim, Germany.
`† During the preparation of these guidelines, the composition of
`the Commission was as follows: A. Ahlbom (Sweden); U. Bergqvist
`(Sweden); J. H. Bernhardt, Chairman since May 1996 (Germany); J. P.
`Ce´sarini (France); L. A. Court, until May 1996 (France); M. Gran-
`dolfo, Vice-Chairman until April 1996 (Italy); M. Hietanen, since May
`1996 (Finland); A. F. McKinlay, Vice-Chairman since May 1996
`(UK); M. H. Repacholi, Chairman until April 1996, Chairman emer-
`itus since May 1996 (Australia); D. H. Sliney (USA); J. A. J. Stolwijk
`(USA); M. L. Swicord, until May 1996 (USA); L. D. Szabo (Hun-
`gary); M. Taki (Japan); T. S. Tenforde (USA); H. P. Jammet (Emeritus
`Member, deceased)
`(France); R. Matthes, Scientific Secretary
`(Germany).
`During the preparation of this document, ICNIRP was supported
`by the following external experts: S. Allen (UK), J. Brix (Germany),
`S. Eggert (Germany), H. Garn (Austria), K. Jokela (Finland), H.
`Korniewicz (Poland), G.F. Mariutti (Italy), R. Saunders (UK), S.
`Tofani (Italy), P. Vecchia (Italy), E. Vogel (Germany). Many valuable
`comments provided by additional international experts are gratefully
`acknowledged.
`(Manuscript received 2 October 1997; accepted 17 November 1997)
`0017-9078/98/$3.00/0
`Copyright © 1998 Health Physics Society
`
`At the Eighth International Congress of the IRPA
`(Montreal, 18 –22 May 1992), a new, independent scien-
`tific organization—the International Commission on
`Non-Ionizing Radiation Protection (ICNIRP)—was es-
`tablished as a successor to the IRPA/INIRC. The func-
`tions of the Commission are to investigate the hazards
`that may be associated with the different forms of NIR,
`develop international guidelines on NIR exposure limits,
`and deal with all aspects of NIR protection.
`Biological effects reported as resulting from expo-
`sure to static and extremely-low-frequency (ELF) elec-
`tric and magnetic fields have been reviewed by UNEP/
`WHO/IRPA (1984, 1987). Those publications and a
`number of others, including UNEP/WHO/IRPA (1993)
`and Allen et al. (1991), provided the scientific rationale
`for these guidelines.
`A glossary of terms appears in the Appendix.
`
`PURPOSE AND SCOPE
`
`The main objective of this publication is to establish
`guidelines for limiting EMF exposure that will provide
`protection against known adverse health effects. An
`adverse health effect causes detectable impairment of the
`health of the exposed individual or of his or her off-
`spring; a biological effect, on the other hand, may or may
`not result in an adverse health effect.
`Studies on both direct and indirect effects of EMF
`are described; direct effects result from direct interaction
`of fields with the body, indirect effects involve interactions
`with an object at a different electric potential from the body.
`Results of laboratory and epidemiological studies, basic
`exposure criteria, and reference levels for practical hazard
`assessment are discussed, and the guidelines presented
`apply to occupational and public exposure.
`Guidelines on high-frequency and 50/60 Hz electro-
`magnetic fields were issued by IRPA/INIRC in 1988 and
`1990, respectively, but are superseded by the present
`guidelines which cover the entire frequency range of
`time-varying EMF (up to 300 GHz). Static magnetic
`fields are covered in the ICNIRP guidelines issued in
`1994 (ICNIRP 1994).
`the Commission
`In establishing exposure limits,
`recognizes the need to reconcile a number of differing
`expert opinions. The validity of scientific reports has to
`be considered, and extrapolations from animal experi-
`
`494
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`Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields c ICNIRP GUIDELINES
`
`495
`
`ments to effects on humans have to be made. The
`restrictions in these guidelines were based on scientific
`data alone; currently available knowledge, however,
`indicates that these restrictions provide an adequate level
`of protection from exposure to time-varying EMF. Two
`classes of guidance are presented:
`
`c Basic restrictions: Restrictions on exposure to
`time-varying electric, magnetic, and electromag-
`netic fields that are based directly on established
`health effects are termed “basic restrictions.”
`Depending upon the frequency of the field, the
`physical quantities used to specify these restric-
`tions are current density (J), specific energy
`absorption rate (SAR), and power density (S).
`Only power density in air, outside the body, can
`be readily measured in exposed individuals.
`c Reference levels: These levels are provided for
`practical exposure assessment purposes to deter-
`mine whether the basic restrictions are likely to be
`exceeded. Some reference levels are derived from
`relevant basic restrictions using measurement
`and/or computational techniques, and some ad-
`dress perception and adverse indirect effects of
`exposure to EMF. The derived quantities are
`electric field strength (E), magnetic field strength
`(H), magnetic flux density (B), power density (S),
`and currents flowing through the limbs (IL).
`Quantities that address perception and other indi-
`rect effects are contact current (IC) and, for pulsed
`fields, specific energy absorption (SA). In any
`particular exposure situation, measured or calcu-
`lated values of any of these quantities can be
`compared with the appropriate reference level.
`Compliance with the reference level will ensure
`compliance with the relevant basic restriction. If
`the measured or calculated value exceeds the
`reference level, it does not necessarily follow that
`the basic restriction will be exceeded. However,
`whenever a reference level
`is exceeded it
`is
`necessary to test compliance with the relevant
`basic restriction and to determine whether addi-
`tional protective measures are necessary.
`
`These guidelines do not directly address product
`performance standards, which are intended to limit EMF
`emissions under specified test conditions, nor does the
`document deal with the techniques used to measure any
`of the physical quantities that characterize electric, mag-
`netic, and electromagnetic fields. Comprehensive de-
`scriptions of instrumentation and measurement
`tech-
`niques
`for
`accurately determining such physical
`quantities may be found elsewhere (NCRP 1981; IEEE
`1992; NCRP 1993; DIN VDE 1995).
`Compliance with the present guidelines may not
`necessarily preclude interference with, or effects on,
`medical devices such as metallic prostheses, cardiac
`pacemakers and defibrillators, and cochlear implants.
`Interference with pacemakers may occur at levels below
`
`the recommended reference levels. Advice on avoiding
`these problems is beyond the scope of the present
`document but is available elsewhere (UNEP/WHO/IRPA
`1993).
`These guidelines will be periodically revised and
`updated as advances are made in identifying the adverse
`health effects of time-varying electric, magnetic, and
`electromagnetic fields.
`
`QUANTITIES AND UNITS
`
`Whereas electric fields are associated only with the
`presence of electric charge, magnetic fields are the result
`of the physical movement of electric charge (electric
`current). An electric field, E, exerts forces on an electric
`charge and is expressed in volt per meter (V m21).
`Similarly, magnetic fields can exert physical forces on
`electric charges, but only when such charges are in
`motion. Electric and magnetic fields have both magni-
`tude and direction (i.e., they are vectors). A magnetic
`field can be specified in two ways—as magnetic flux
`density, B, expressed in tesla (T), or as magnetic field
`strength, H, expressed in ampere per meter (A m21). The
`two quantities are related by the expression:
`B 5 mH,
`(1)
`where m is the constant of proportionality (the magnetic
`permeability); in a vacuum and in air, as well as in
`non-magnetic (including biological) materials, m has the
`value 4p 3 1027 when expressed in henry per meter
`(H m21). Thus,
`in describing a magnetic field for
`protection purposes, only one of the quantities B or H
`needs to be specified.
`In the far-field region, the plane-wave model is a
`good approximation of the electromagnetic field propa-
`gation. The characteristics of a plane wave are:
`
`c The wave fronts have a planar geometry;
`c The E and H vectors and the direction of propa-
`gation are mutually perpendicular;
`c The phase of the E and H fields is the same, and
`the quotient of the amplitude of E/H is constant
`throughout space. In free space, the ratio of their
`amplitudes E/H 5 377 ohm, which is the charac-
`teristic impedance of free space;
`c Power density, S, i.e., the power per unit area
`normal to the direction of propagation, is related
`to the electric and magnetic fields by the expression:
`
`S 5 EH 5 E2/377 5 377H2.
`(2)
`The situation in the near-field region is rather more
`complicated because the maxima and minima of E and H
`fields do not occur at the same points along the direction
`of propagation as they do in the far field. In the near field,
`the electromagnetic field structure may be highly inho-
`mogeneous, and there may be substantial variations from
`the plane-wave impedance of 377 ohms; that is, there
`may be almost pure E fields in some regions and almost
`pure H fields in others. Exposures in the near field are
`
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`496
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`Health Physics
`
`April 1998, Volume 74, Number 4
`
`Table 1. Electric, magnetic, electromagnetic, and dosimetric
`quantities and corresponding SI units.
`Unit
`Quantity
`Symbol
`s siemens per meter (S m21)
`ampere (A)
`I
`ampere per square meter (A m22)
`J
`hertz (Hz)
`f
`volt per meter (V m21)
`E
`H ampere per meter (A m21)
`B
`tesla (T)
`m henry per meter (H m21)
`farad per meter (F m21)
`e
`watt per square meter (W m22)
`S
`SA joule per kilogram (J kg21)
`SAR watt per kilogram (W kg21)
`
`Conductivity
`Current
`Current density
`Frequency
`Electric field strength
`Magnetic field strength
`Magnetic flux density
`Magnetic permeability
`Permittivity
`Power density
`Specific energy absorption
`Specific energy absorption
`rate
`
`more difficult to specify, because both E and H fields
`must be measured and because the field patterns are
`morecomplicated; in this situation, power density is no
`longer an appropriate quantity to use in expressing
`exposure restrictions (as in the far field).
`Exposure to time-varying EMF results in internal
`body currents and energy absorption in tissues that
`depend on the coupling mechanisms and the frequency
`involved. The internal electric field and current density
`are related by Ohm’s Law:
`J 5 sE,
`
`(3)
`
`where sis the electrical conductivity of the medium. The
`dosimetric quantities used in these guidelines, taking into
`account different frequency ranges and waveforms, are
`as follows:
`c Current density, J, in the frequency range up to
`10 MHz;
`c Current, I, in the frequency range up to 110 MHz;
`c Specific energy absorption rate, SAR,
`in the
`frequency range 100 kHz–10 GHz;
`c Specific energy absorption, SA, for pulsed fields
`in the frequency range 300 MHz–10 GHz; and
`c Power density, S,
`in the frequency range
`10 –300 GHz.
`
`A general summary of EMF and dosimetric quanti-
`ties and units used in these guidelines is provided in
`Table 1.
`
`BASIS FOR LIMITING EXPOSURE
`
`These guidelines for limiting exposure have been
`developed following a thorough review of all published
`scientific literature. The criteria applied in the course of
`the review were designed to evaluate the credibility of
`the various reported findings (Repacholi and Stolwijk
`1991; Repacholi and Cardis 1997); only established
`effects were used as the basis for the proposed exposure
`restrictions. Induction of cancer from long-term EMF
`exposure was not considered to be established, and so
`
`immediate
`these guidelines are based on short-term,
`health effects such as stimulation of peripheral nerves
`and muscles, shocks and burns caused by touching
`conducting objects, and elevated tissue temperatures
`resulting from absorption of energy during exposure to
`EMF. In the case of potential
`long-term effects of
`exposure, such as an increased risk of cancer, ICNIRP
`concluded that available data are insufficient to provide a
`basis for setting exposure restrictions, although epidemi-
`ological research has provided suggestive, but uncon-
`vincing, evidence of an association between possible
`carcinogenic effects and exposure at levels of 50/60 Hz
`magnetic flux densities substantially lower than those
`recommended in these guidelines.
`In-vitro effects of short-term exposure to ELF or
`ELF amplitude-modulated EMF are summarized. Tran-
`sient cellular and tissue responses to EMF exposure have
`been observed, but with no clear exposure-response
`relationship. These studies are of limited value in the
`assessment of health effects because many of the re-
`sponses have not been demonstrated in vivo. Thus,
`in-vitro studies alone were not deemed to provide data
`that could serve as a primary basis for assessing possible
`health effects of EMF.
`
`COUPLING MECHANISMS BETWEEN FIELDS
`AND THE BODY
`
`There are three established basic coupling mecha-
`nisms through which time-varying electric and magnetic
`fields interact directly with living matter (UNEP/WHO/
`IRPA 1993):
`c coupling to low-frequency electric fields;
`c coupling to low-frequency magnetic fields; and
`c absorption of energy from electromagnetic fields.
`
`Coupling to low-frequency electric fields
`The interaction of time-varying electric fields with
`the human body results in the flow of electric charges
`(electric current), the polarization of bound charge (for-
`mation of electric dipoles), and the reorientation of
`electric dipoles already present in tissue. The relative
`magnitudes of these different effects depend on the
`electrical properties of the body—that is, electrical con-
`ductivity (governing the flow of electric current) and
`permittivity (governing the magnitude of polarization
`effects). Electrical conductivity and permittivity vary
`with the type of body tissue and also depend on the
`frequency of the applied field. Electric fields external to
`the body induce a surface charge on the body; this results
`in induced currents in the body, the distribution of which
`depends on exposure conditions, on the size and shape of
`the body, and on the body’s position in the field.
`
`Coupling to low-frequency magnetic fields
`The physical interaction of time-varying magnetic
`fields with the human body results in induced electric
`fields and circulating electric currents. The magnitudes
`of the induced field and the current density are propor-
`
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`Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields c ICNIRP GUIDELINES
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`497
`
`tional to the radius of the loop, the electrical conductivity
`of the tissue, and the rate of change and magnitude of the
`magnetic flux density. For a given magnitude and fre-
`quency of magnetic field, the strongest electric fields are
`induced where the loop dimensions are greatest. The
`exact path and magnitude of the resulting current induced
`in any part of the body will depend on the electrical
`conductivity of the tissue.
`The body is not electrically homogeneous; however,
`induced current densities can be calculated using ana-
`tomically and electrically realistic models of the body
`and computational methods, which have a high degree of
`anatomical resolution.
`
`Absorption of energy from electromagnetic fields
`Exposure to low-frequency electric and magnetic
`fields normally results in negligible energy absorption
`and no measurable temperature rise in the body. How-
`ever, exposure to electromagnetic fields at frequencies
`above about 100 kHz can lead to significant absorption
`of energy and temperature increases. In general, expo-
`sure to a uniform (plane-wave) electromagnetic field
`results in a highly non-uniform deposition and distribu-
`tion of energy within the body, which must be assessed
`by dosimetric measurement and calculation.
`As regards absorption of energy by the human body,
`electromagnetic fields can be divided into four ranges
`(Durney et al. 1985):
`
`c frequencies from about 100 kHz to less than about
`20 MHz, at which absorption in the trunk de-
`creases rapidly with decreasing frequency, and
`significant absorption may occur in the neck and
`legs;
`c frequencies in the range from about 20 MHz to
`300 MHz, at which relatively high absorption can
`occur in the whole body, and to even higher
`values if partial body (e.g., head) resonances are
`considered;
`c frequencies in the range from about 300 MHz to
`several GHz, at which significant
`local, non-
`uniform absorption occurs; and
`c frequencies above about 10 GHz, at which energy
`absorption occurs primarily at the body surface.
`
`In tissue, SAR is proportional to the square of the
`internal electric field strength. Average SAR and SAR
`distribution can be computed or estimated from labora-
`tory measurements. Values of SAR depend on the fol-
`lowing factors:
`
`c the incident field parameters, i.e., the frequency,
`intensity, polarization, and source– object config-
`uration (near- or far-field);
`c the characteristics of the exposed body, i.e., its
`size and internal and external geometry, and the
`dielectric properties of the various tissues; and
`c ground effects and reflector effects of other ob-
`jects in the field near the exposed body.
`
`When the long axis of the human body is parallel to
`the electric field vector, and under plane-wave exposure
`conditions (i.e., far-field exposure), whole-body SAR
`reaches maximal values. The amount of energy absorbed
`depends on a number of factors, including the size of the
`exposed body. “Standard Reference Man” (ICRP 1994),
`if not grounded, has a resonant absorption frequency
`close to 70 MHz. For taller individuals the resonant
`absorption frequency is somewhat lower, and for shorter
`adults, children, babies, and seated individuals it may
`exceed 100 MHz. The values of electric field reference
`levels are based on the frequency-dependence of human
`absorption; in grounded individuals, resonant frequencies
`are lower by a factor of about 2 (UNEP/WHO/IRPA
`1993).
`For some devices that operate at frequencies above
`10 MHz (e.g., dielectric heaters, mobile telephones),
`human exposure can occur under near-field conditions.
`The frequency-dependence of energy absorption under
`these conditions is very different from that described for
`far-field conditions. Magnetic fields may dominate for
`certain devices, such as mobile telephones, under certain
`exposure conditions.
`The usefulness of numerical modeling calculations,
`as well as measurements of induced body current and
`tissue field strength, for assessment of near-field expo-
`sures has been demonstrated for mobile telephones,
`walkie-talkies, broadcast towers, shipboard communica-
`tion sources, and dielectric heaters (Kuster and Balzano
`1992; Dimbylow and Mann 1994; Jokela et al. 1994;
`Gandhi 1995; Tofani et al. 1995). The importance of
`these studies lies in their having shown that near-field
`exposure can result in high local SAR (e.g., in the head,
`wrists, ankles) and that whole-body and local SAR are
`strongly dependent on the separation distance between
`the high-frequency source and the body. Finally, SAR
`data obtained by measurement are consistent with data
`obtained from numerical modeling calculations. Whole-
`body average SAR and local SAR are convenient quan-
`tities for comparing effects observed under various ex-
`posure conditions. A detailed discussion of SAR can be
`found elsewhere (UNEP/WHO/IRPA 1993).
`At frequencies greater than about 10 GHz, the depth
`of penetration of the field into tissues is small, and SAR
`is not a good measure for assessing absorbed energy; the
`incident power density of the field (in W m22) is a more
`appropriate dosimetric quantity.
`
`INDIRECT COUPLING MECHANISMS
`
`There are two indirect coupling mechanisms:
`
`c contact currents that result when the human body
`comes into contact with an object at a different
`electric potential (i.e., when either the body or the
`object is charged by an EMF); and
`c coupling of EMF to medical devices worn by, or
`implanted in, an individual (not considered in this
`document).
`
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`Health Physics
`
`April 1998, Volume 74, Number 4
`
`The charging of a conducting object by EMF causes
`electric currents to pass through the human body in
`contact with that object (Tenforde and Kaune 1987;
`UNEP/WHO/IRPA 1993). The magnitude and spatial
`distribution of such currents depend on frequency, the
`size of the object, the size of the person, and the area of
`contact; transient discharges—sparks— can occur when
`an individual and a conducting object exposed to a strong
`field come into close proximity.
`
`BIOLOGICAL BASIS FOR LIMITING
`EXPOSURE (UP TO 100 KHZ)
`
`The following paragraphs provide a general review
`of relevant literature on the biological and health effects
`of electric and magnetic fields with frequency ranges up
`to 100 kHz, in which the major mechanism of interaction
`is induction of currents in tissues. For the frequency
`range .0 to 1 Hz, the biological basis for the basic
`restrictions and reference levels are provided in ICNIRP
`(1994). More detailed reviews are available elsewhere
`(NRPB 1991, 1993; UNEP/WHO/IRPA 1993; Blank
`1995; NAS 1996; Polk and Postow 1996; Ueno 1996).
`
`Direct effects of electric and magnetic fields
`
`Epidemiological studies. There have been many
`reviews of epidemiological studies of cancer risk in
`relation to exposure to power-frequency fields (NRPB
`1992, 1993, 1994b; ORAU 1992; Savitz 1993; Heath
`1996; Stevens and Davis 1996; Tenforde 1996; NAS
`1996). Similar reviews have been published on the risk of
`adverse reproductive outcomes associated with exposure
`to EMF (Chernoff et al. 1992; Brent et al. 1993; Shaw
`and Croen 1993; NAS 1996; Tenforde 1996).
`
`Reproductive outcome. Epidemiological studies on
`pregnancy outcomes have provided no consistent evi-
`dence of adverse reproductive effects in women working
`with visual display units (VDUs) (Bergqvist 1993; Shaw
`and Croen 1993; NRPB 1994a; Tenforde 1996). For
`example, meta-analysis revealed no excess risk of spon-
`taneous abortion or malformation in combined studies
`comparing pregnant women using VDUs with women
`not using VDUs (Shaw and Croen 1993). Two other
`studies concentrated on actual measurements of the
`electric and magnetic fields emitted by VDUs; one
`reported a suggestion of an association between ELF
`magnetic fields and miscarriage (Lindbohm et al. 1992),
`while the other found no such association (Schnorr et al.
`1991). A prospective study that included large numbers
`of cases, had high participation rates, and detailed expo-
`sure assessment (Bracken et al. 1995) reported that
`neither birth weight nor intra-uterine growth rate was
`related to any ELF field exposure. Adverse outcomes
`were not associated with higher levels of exposure.
`Exposure measurements included current-carrying ca-
`pacity of power lines outside homes, 7-d personal expo-
`sure measurements, 24-h measurements in the home, and
`self-reported use of electric blankets, heated water beds,
`
`and VDUs. Most currently available information fails to
`support an association between occupational exposure to
`VDUs and harmful reproductive effects (NRPB 1994a;
`Tenforde 1996).
`
`Residential cancer studies. Considerable contro-
`versy surrounds the possibility of a link between expo-
`sure to ELF magnetic fields and an elevated risk of
`cancer. Several reports on this topic have appeared since
`Wertheimer and Leeper reported (1979) an association
`between childhood cancer mortality and proximity of
`homes to power distribution lines with what the research-
`ers classified as high current configuration. The basic
`hypothesis that emerged from the original study was that
`the contribution to the ambient residential 50/60 Hz
`magnetic fields from external sources such as power
`lines could be linked to an increased risk of cancer in
`childhood.
`To date there have been more than a dozen studies
`on childhood cancer and exposure to power-frequency
`magnetic fields in the home produced by nearby power
`lines. These studies estimated the magnetic field expo-
`sure from short term measurements or on the basis of
`distance between the home and power line and, in most
`cases, the configuration of the line; some studies also
`took the load of the line into account. The findings
`relating to leukemia are the most consistent. Out of 13
`studies (Wertheimer and Leeper 1979; Fulton et al. 1980;
`Myers et al. 1985; Tomenius 1986; Savitz et al. 1988;
`Coleman et al. 1989; London et al. 1991; Feychting and
`Ahlbom 1993; Olsen et al. 1993; Verkasalo et al. 1993;
`Michaelis et al. 1997; Linet et al. 1997; Tynes and
`Haldorsen 1997), all but five reported relative risk
`estimates of between 1.5 and 3.0.
`Both direct magnetic field measurements and esti-
`mates based on neighboring power lines are crude proxy
`measures for the exposure that took place at various
`times before cases of leukemia were diagnosed, and it is
`not clear which of the two methods provides the more
`valid estimate. Although results suggest that indeed the
`magnetic field may play a role in the association with
`leukemia risk,
`there is uncertainty because of small
`sample numbers and because of a correlation between the
`magnetic field and proximity to power lines (Feychting
`et al. 1996).
`Little is known about the etiology of most types of
`childhood cancer, but several attempts to control for
`potential confounders such as socioeconomic status and
`air pollution from motor vehicle exhaust fumes have had
`little effect on results. Studies that have examined the use
`of electrical appliances (primarily electric blankets) in
`relation to cancer and other health problems have re-
`ported generally negative results (Preston-Martin et al.
`1988; Verreault et al. 1990; Vena et al. 1991, 1994; Li et
`al. 1995). Only two case-control studies have evaluated
`use of appliances in relation to the risk of childhood
`leukemia. One was conducted in Denver (Savitz et al.
`1990) and suggested a link with prenatal use of electric
`blankets; the other, carried out in Los Angeles (London
`
`Momentum Dynamics Corporation
`Exhibit 1022
`Page 006
`
`

`

`Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields c ICNIRP GUIDELINES
`
`499
`
`et al. 1991), found an association between leukemia and
`children using hair dryers and watching monochrome
`television.
`The fact that results for leukemia based on proxim-
`ity of homes to power lines are relatively consistent led
`the U.S. National Academy of Sciences Committee to
`conclude that children living near power lines appear to
`be at increased risk of leukemia (NAS 1996). Because of
`small numbers, confidence intervals in the individual
`studies are wide; when taken together, however, the
`results are consistent, with a pooled relative risk of 1.5
`(NAS 1996). In contrast, short-term measurements of
`magnetic field in some of the studies provided no
`evidence of an association between exposure to 50/60 Hz
`fields and the risk of leukemia or any other form of
`cancer in children. The Committee was not convinced
`that this increase in risk was explained by exposure to
`magnetic fields, since there was no apparent association
`when exposure was estimated from magnetic field meter
`readings in the homes of both leukemia cases and
`controls. It was suggested that confounding by some
`unknown risk factor for childhood leukemia, associated
`with residence in the vicinity of power lines, might be the
`explanation, but no likely candidates were postulated.
`After the NAS committee completed its review, the
`results of a study performed in Norway were reported
`(Tynes and Haldorsen 1997). This study included 500
`cases of all types of childhood cancer. Each individual’s
`exposure was estimated by calculation of the magnetic
`field level produced in the residence by nearby transmis-
`sion lines, estimated by averaging over an entire year. No
`association between leukemia risk and magnetic fields
`for the residence at time of diagnosis was observed.
`Distance from the power line, exposure during the first
`year of life, mothers’ exposure at time of conception, and
`exposure higher than the median level of the controls
`showed no association with leukemia, brain cancer, or
`lymphoma. However, the number of exposed cases was
`small.
`Also, a study performed in Germany has been
`reported after
`the completion of
`the NAS review
`(Michaelis et al. 1997). This was a case-control study on
`childhood leukemia based on 129 cases and 328 controls.
`Exposure assessment comprised measurements of the
`magnetic field over 24 h in the child’s bedroom at the
`residence where the child had been living for the longest
`period before the date of diagnosis. An elevated relative
`risk of 3.2 was observed for .0.2 mT.
`A large U.S. case-control study (638 cases and 620
`controls) to test whether childhood acute lymphoblastic
`leukemia is associated with exposure to 60-Hz magnetic
`fields was published by Linet et al. (1997). Magnetic
`field exposures were determined using 24-h time-
`weighted average measurements in the bedroom and 30-s
`measurements in various other rooms. Measurements
`were taken in homes in which the child had lived for 70%
`of the 5 y prior to the year of diagnosis, or the
`corresponding period for the controls. Wire-codes were
`assessed for residentially stable case-control pairs in
`
`which both had not changed their residence during the
`years prior to diagnosis. The number of such pairs for
`which assessment could be made was 416. There was no
`indication of an association between wire-code category
`and leukemia. As for magnetic field measurements, the
`results are more intriguing. For the cut off point of 0.2
`mT the unmatched and matched analyses gave relative
`risks of 1.2 and 1.5, respectively. For a cut off point of
`0.3 mT, the unmatched relative risk estimate is 1.7 based
`on 45 exposed cases. Thus, the measurement results are
`suggestive of a positive association between magnetic
`fields and leukemia risk. This study is a major contribu-
`tion in terms of its size, the number of subjects in high
`exposure categories, timing of measurements relative to
`the occurrence of the leukemia (usually within 24 mo
`after diagnosis), other measures used to obtain exposure
`data, and quality of an