INTERNATIONAL COMMISSION ON NON-IONIZING RADIATION PROTECTIONICNIRP GUIDELINESFOR LIMITING EXPOSURE TO TIME-VARYING

ELECTRIC, MAGNETIC AND ELECTROMAGNETIC
FIELDS (UP TO 300 GHZ)

PUBLISHED IN: HEALTH PHYSICS 74 (4):494-522; 1998

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 andAnswers on the EMF Guidelines.

ICNIRP PUBLICATION – 1998

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*†
At the Eighth International Congress of the IRPA(Montreal, 18 –22 May 1992), a new, independent scientific organization—the International Commission on
Non-Ionizing Radiation Protection (ICNIRP)—was established as a successor to the IRPA/INIRC. The functions 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 exposure to static and extremely-low-frequency (ELF) electric and magnetic fields have been reviewed by UNEP/
WHO/IRPA (1984, 1987). Those publications and anumber 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.

INTRODUCTION
IN 1974, the International Radiation Protection Association (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 Division of the World Health Organization (WHO), theIRPA/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 document includes an overview of the physical characteristics, measurement and instrumentation, sources, andapplications of NIR, a thorough review of the literature
on biological effects, and an evaluation of the health risksof 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.

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 thehealth of the exposed individual or of his or her offspring; 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 interactionof 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 electromagnetic fields were issued by IRPA/INIRC in 1988 and1990, respectively, but are superseded by the present
guidelines which cover the entire frequency range oftime-varying EMF (up to 300 GHz). Static magnetic
fields are covered in the ICNIRP guidelines issued in
1994 (ICNIRP 1994).
In establishing exposure limits, the Commission
recognizes the need to reconcile a number of differingexpert opinions. The validity of scientific reports has tobe considered, and extrapolations from animal experi-* ICNIRP Secretariat, c/o Dipl.-Ing. Rüdiger Matthes, Bundesamt
für Strahlenschutz, Institut für Strahlenhygiene, Ingolstädter Landstrasse 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.
Césarini (France); L. A. Court, until May 1996 (France); M. Grandolfo, 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 emeritus since May 1996 (Australia); D. H. Sliney (USA); J. A. J. Stolwijk(USA); M. L. Swicord, until May 1996 (USA); L. D. Szabo (Hungary); 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 supportedby 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 valuablecomments 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 Society494

Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields ● ICNIRP GUIDELINES

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 levelof protection from exposure to time-varying EMF. Twoclasses of guidance are presented:● Basic

restrictions: Restrictions on exposure totime-varying electric, magnetic, and electromagnetic fields that are based directly on establishedhealth effects are termed “basic restrictions.”
Depending upon the frequency of the field, thephysical quantities used to specify these restrictions are current density (J), specific energy
absorption rate (SAR), and power density (S).
Only power density in air, outside the body, canbe readily measured in exposed individuals.
● Reference levels: These levels are provided forpractical exposure assessment purposes to determine whether the basic restrictions are likely to be
exceeded. Some reference levels are derived fromrelevant basic restrictions using measurement
and/or computational techniques, and some address perception and adverse indirect effects of
exposure to EMF. The derived quantities areelectric 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 indirect effects are contact current (IC) and, for pulsed
fields, specific energy absorption (SA). In any
particular exposure situation, measured or calculated values of any of these quantities can becompared with the appropriate reference level.
Compliance with the reference level will ensurecompliance with the relevant basic restriction. If
the measured or calculated value exceeds thereference level, it does not necessarily follow thatthe basic restriction will be exceeded. However,whenever a reference level is exceeded it isnecessary to test compliance with the relevant
basic restriction and to determine whether additional protective measures are necessary.
These guidelines do not directly address productperformance standards, which are intended to limit EMF
emissions under specified test conditions, nor does the
document deal with the techniques used to measure anyof the physical quantities that characterize electric, magnetic, and electromagnetic fields. Comprehensive descriptions of instrumentation and measurement techniques for accurately determining such physicalquantities may be found elsewhere (NCRP 1981; IEEE
1992; NCRP 1993; DIN VDE 1995).
Compliance with the present guidelines may notnecessarily 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

495

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 andupdated as advances are made in identifying the adverse
health effects of time-varying electric, magnetic, andelectromagnetic fields.
QUANTITIES AND UNITS
Whereas electric fields are associated only with thepresence of electric charge, magnetic fields are the resultof the physical movement of electric charge (electric
current). An electric field, E, exerts forces on an electriccharge and is expressed in volt per meter (V m21).
Similarly, magnetic fields can exert physical forces onelectric charges, but only when such charges are inmotion. Electric and magnetic fields have both magnitude 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 fieldstrength, H, expressed in ampere per meter (A m21). The
two quantities are related by the expression:

B 5 m H,(1)

where m is the constant of proportionality (the magnetic
permeability); in a vacuum and in air, as well as innon-magnetic (including biological) materials, m has thevalue 4p 3 1027 when expressed in henry per meter(H m21). Thus, in describing a magnetic field forprotection purposes, only one of the quantities B or H
needs to be specified.
In the far-field region, the plane-wave model is agood approximation of the electromagnetic field propagation. The characteristics of a plane wave are:
● The wave fronts have a planar geometry;● The E and H vectors and the direction of propa-

gation are mutually perpendicular;● The phase of the E and H fields is the same, andthe quotient of the amplitude of E/H is constantthroughout space. In free space, the ratio of theiramplitudes E/H 5 377 ohm, which is the characteristic impedance of free space;● 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 directionof propagation as they do in the far field. In the near field,
the electromagnetic field structure may be highly inhomogeneous, and there may be substantial variations fromthe 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496

Health Physics

Table 1. Electric, magnetic, electromagnetic, and dosimetricquantities and corresponding SI units.
Quantity

SymbolUnit

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

s
I
J
f
E
H
B
m
e
S
SA
SAR

siemens per meter (S m21)
ampere (A)ampere per square meter (A m22)
hertz (Hz)volt per meter (V m21)
ampere per meter (A m21)
tesla (T)henry per meter (H m21)
farad per meter (F m21)
watt per square meter (W m22)
joule per kilogram (J kg21)
watt per kilogram (W kg21)

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 nolonger 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 s E,(3)

where s is the electrical conductivity of the medium. The
dosimetric quantities used in these guidelines, taking into
account different frequency ranges and waveforms, areas follows:● Current density, J, in the frequency range up to

April 1998, Volume 74, Number 4

these guidelines are based on short-term, immediate
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 abasis for setting exposure restrictions, although epidemiological research has provided suggestive, but unconvincing, evidence of an association between possible
carcinogenic effects and exposure at levels of 50/60 Hz
magnetic flux densities substantially lower than thoserecommended in these guidelines.
In-vitro effects of short-term exposure to ELF or
ELF amplitude-modulated EMF are summarized. Transient cellular and tissue responses to EMF exposure havebeen observed, but with no clear exposure-response
relationship. These studies are of limited value in theassessment of health effects because many of the responses have not been demonstrated in vivo. Thus,in-vitro studies alone were not deemed to provide datathat could serve as a primary basis for assessing possible
health effects of EMF.
COUPLING MECHANISMS BETWEEN FIELDSAND THE BODY
There are three established basic coupling mechanisms through which time-varying electric and magnetic
fields interact directly with living matter (UNEP/WHO/
IRPA 1993):● coupling to low-frequency electric fields;● coupling to low-frequency magnetic fields; and● absorption of energy from electromagnetic fields.

10 MHz;● Current, I, in the frequency range up to 110 MHz;● Specific energy absorption rate, SAR, in thefrequency range 100 kHz–10 GHz;
● Specific energy absorption, SA, for pulsed fields

in the frequency range 300 MHz–10 GHz; anddensity, S, in the frequency range
10 –300 GHz.

● Power

A general summary of EMF and dosimetric quantities and units used in these guidelines is provided inTable 1.
BASIS FOR LIMITING EXPOSURE
These guidelines for limiting exposure have beendeveloped following a thorough review of all publishedscientific literature. The criteria applied in the course of
the review were designed to evaluate the credibility ofthe various reported findings (Repacholi and Stolwijk
1991; Repacholi and Cardis 1997); only establishedeffects 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

Coupling to low-frequency electric fields
The interaction of time-varying electric fields withthe human body results in the flow of electric charges(electric current), the polarization of bound charge (formation of electric dipoles), and the reorientation ofelectric dipoles already present in tissue. The relative
magnitudes of these different effects depend on theelectrical properties of the body—that is, electrical conductivity (governing the flow of electric current) andpermittivity (governing the magnitude of polarization
effects). Electrical conductivity and permittivity varywith the type of body tissue and also depend on thefrequency of the applied field. Electric fields external tothe 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 ofthe 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 electricfields and circulating electric currents. The magnitudesof the induced field and the current density are propor-

Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields ● ICNIRP GUIDELINES

tional to the radius of the loop, the electrical conductivityof the tissue, and the rate of change and magnitude of themagnetic flux density. For a given magnitude and frequency 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 electricalconductivity of the tissue.
The body is not electrically homogeneous; however,induced current densities can be calculated using anatomically and electrically realistic models of the bodyand computational methods, which have a high degree ofanatomical 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. However, exposure to electromagnetic fields at frequencies
above about 100 kHz can lead to significant absorptionof energy and temperature increases. In general, exposure to a uniform (plane-wave) electromagnetic field
results in a highly non-uniform deposition and distribution of energy within the body, which must be assessedby 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):● frequencies from about 100 kHz to less than about

20 MHz, at which absorption in the trunk decreases rapidly with decreasing frequency, andsignificant absorption may occur in the neck andlegs;● frequencies in the range from about 20 MHz to300 MHz, at which relatively high absorption canoccur in the whole body, and to even higher
values if partial body (e.g., head) resonances are
considered;● frequencies in the range from about 300 MHz toseveral GHz, at which significant local, nonuniform absorption occurs; and● frequencies above about 10 GHz, at which energy
absorption occurs primarily at the body surface.
In tissue, SAR is proportional to the square of theinternal electric field strength. Average SAR and SAR
distribution can be computed or estimated from laboratory measurements. Values of SAR depend on the following factors:● the incident field parameters, i.e., the frequency,

intensity, polarization, and source– object configuration (near- or far-field);● the characteristics of the exposed body, i.e., its
size and internal and external geometry, and thedielectric properties of the various tissues; and● ground effects and reflector effects of other objects in the field near the exposed body.

497

When the long axis of the human body is parallel tothe 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 humanabsorption; 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 underthese conditions is very different from that described for
far-field conditions. Magnetic fields may dominate forcertain devices, such as mobile telephones, under certain
exposure conditions.
The usefulness of numerical modeling calculations,as well as measurements of induced body current andtissue field strength, for assessment of near-field exposures has been demonstrated for mobile telephones,
walkie-talkies, broadcast towers, shipboard communication 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 dataobtained from numerical modeling calculations. Wholebody average SAR and local SAR are convenient quantities for comparing effects observed under various exposure conditions. A detailed discussion of SAR can befound elsewhere (UNEP/WHO/IRPA 1993).
At frequencies greater than about 10 GHz, the depthof penetration of the field into tissues is small, and SAR
is not a good measure for assessing absorbed energy; theincident power density of the field (in W m22) is a more
appropriate dosimetric quantity.
INDIRECT COUPLING MECHANISMS
There are two indirect coupling mechanisms:● contact currents that result when the human bodycomes into contact with an object at a different
electric potential (i.e., when either the body or theobject is charged by an EMF); and● coupling of EMF to medical devices worn by, or
implanted in, an individual (not considered in thisdocument).

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The charging of a conducting object by EMF causes
electric currents to pass through the human body incontact with that object (Tenforde and Kaune 1987;
UNEP/WHO/IRPA 1993). The magnitude and spatial
distribution of such currents depend on frequency, thesize of the object, the size of the person, and the area ofcontact; transient discharges—sparks— can occur when
an individual and a conducting object exposed to a strong
field come into close proximity.
BIOLOGICAL BASIS FOR LIMITINGEXPOSURE (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 inrelation to exposure to power-frequency fields (NRPB
1992, 1993, 1994b; ORAU 1992; Savitz 1993; Heath
1996; Stevens and Davis 1996; Tenforde 1996; NAS1996). Similar reviews have been published on the risk ofadverse reproductive outcomes associated with exposure
to EMF (Chernoff et al. 1992; Brent et al. 1993; Shawand Croen 1993; NAS 1996; Tenforde 1996).
Reproductive outcome. Epidemiological studies on
pregnancy outcomes have provided no consistent evidence of adverse reproductive effects in women working
with visual display units (VDUs) (Bergqvist 1993; Shawand Croen 1993; NRPB 1994a; Tenforde 1996). For
example, meta-analysis revealed no excess risk of spontaneous abortion or malformation in combined studies
comparing pregnant women using VDUs with women
not using VDUs (Shaw and Croen 1993). Two otherstudies concentrated on actual measurements of theelectric 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 numbersof cases, had high participation rates, and detailed exposure assessment (Bracken et al. 1995) reported thatneither birth weight nor intra-uterine growth rate wasrelated to any ELF field exposure. Adverse outcomes
were not associated with higher levels of exposure.
Exposure measurements included current-carrying capacity of power lines outside homes, 7-d personal exposure measurements, 24-h measurements in the home, andself-reported use of electric blankets, heated water beds,

April 1998, Volume 74, Number 4

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 controversy surrounds the possibility of a link between exposure to ELF magnetic fields and an elevated risk ofcancer. Several reports on this topic have appeared since
Wertheimer and Leeper reported (1979) an association
between childhood cancer mortality and proximity ofhomes to power distribution lines with what the researchers classified as high current configuration. The basic
hypothesis that emerged from the original study was thatthe contribution to the ambient residential 50/60 Hz
magnetic fields from external sources such as powerlines could be linked to an increased risk of cancer inchildhood.
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 powerlines. These studies estimated the magnetic field exposure from short term measurements or on the basis of
distance between the home and power line and, in mostcases, 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 andAhlbom 1993; Olsen et al. 1993; Verkasalo et al. 1993;
Michaelis et al. 1997; Linet et al. 1997; Tynes andHaldorsen 1997), all but five reported relative risk
estimates of between 1.5 and 3.0.
Both direct magnetic field measurements and estimates based on neighboring power lines are crude proxymeasures 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 themagnetic field may play a role in the association withleukemia risk, there is uncertainty because of small
sample numbers and because of a correlation between themagnetic field and proximity to power lines (Feychting
et al. 1996).
Little is known about the etiology of most types ofchildhood cancer, but several attempts to control for
potential confounders such as socioeconomic status andair pollution from motor vehicle exhaust fumes have had
little effect on results. Studies that have examined the useof electrical appliances (primarily electric blankets) in
relation to cancer and other health problems have reported generally negative results (Preston-Martin et al.
1988; Verreault et al. 1990; Vena et al. 1991, 1994; Li etal. 1995). Only two case-control studies have evaluateduse 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 electricblankets; the other, carried out in Los Angeles (London

Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields ● ICNIRP GUIDELINESet al. 1991), found an association between leukemia andchildren using hair dryers and watching monochrome
television.
The fact that results for leukemia based on proximity of homes to power lines are relatively consistent led
the U.S. National Academy of Sciences Committee toconclude that children living near power lines appear to
be at increased risk of leukemia (NAS 1996). Because ofsmall numbers, confidence intervals in the individual
studies are wide; when taken together, however, theresults are consistent, with a pooled relative risk of 1.5(NAS 1996). In contrast, short-term measurements ofmagnetic field in some of the studies provided noevidence of an association between exposure to 50/60 Hz
fields and the risk of leukemia or any other form ofcancer in children. The Committee was not convincedthat this increase in risk was explained by exposure tomagnetic fields, since there was no apparent association
when exposure was estimated from magnetic field meterreadings in the homes of both leukemia cases andcontrols. It was suggested that confounding by some
unknown risk factor for childhood leukemia, associatedwith residence in the vicinity of power lines, might be theexplanation, but no likely candidates were postulated.
After the NAS committee completed its review, theresults 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 transmission 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 firstyear of life, mothers’ exposure at time of conception, andexposure 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 beenreported 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 themagnetic field over 24 h in the child’s bedroom at theresidence where the child had been living for the longest
period before the date of diagnosis. An elevated relativerisk 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 timeweighted 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 thecorresponding period for the controls. Wire-codes wereassessed for residentially stable case-control pairs in499

which both had not changed their residence during theyears prior to diagnosis. The number of such pairs forwhich assessment could be made was 416. There was no
indication of an association between wire-code category
and leukemia. As for magnetic field measurements, theresults 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 basedon 45 exposed cases. Thus, the measurement results aresuggestive of a positive association between magnetic
fields and leukemia risk. This study is a major contribution in terms of its size, the number of subjects in highexposure categories, timing of measurements relative tothe occurrence of the leukemia (usually within 24 moafter diagnosis), other measures used to obtain exposure
data, and quality of analysis allowing for multiple potential confounders. Potential weaknesses include the procedure for control selection, the participation rates, andthe methods used for statistical analysis of the data. The
instruments used for measurements took no account oftransient fields or higher order harmonics. The size of thisstudy is such that its results, combined with those of otherstudies, would significantly weaken (though not necessarily
invalidate) the previously observed association with wirecode results.
Over the years there also has been substantial
interest in whether there is an association between
magnetic field exposure and childhood brain cancer, thesecond most frequent type of cancer found in children.
Three recent studies completed after the NAS Committee’s review fail to provide support for an association
between brain cancer and children’s exposure to magnetic fields, whether the source was power lines orelectric blankets, or whether magnetic fields were estimated by calculations or by wire codes (Guénel et al.
1996; Preston-Martin et al. 1996a, b; Tynes and Haldorsen 1997).
Data on cancer in adults and residential magnetic
field exposure are sparse (NAS 1996). The few studies
published to date (Wertheimer and Leeper 1979; McDowall 1985; Seversen et al. 1988; Coleman et al. 1989;
Schreiber et al. 1993; Feychting and Ahlbom 1994; Li etal. 1996; Verkasalo 1996; Verkasalo et al. 1996) all
suffer to some extent from small numbers of exposedcases, and no conclusions can be drawn.
It is the view of the ICNIRP that the results from theepidemiological research on EMF field exposure andcancer, including childhood leukemia, are not strong
enough in the absence of support from experimental research to form a scientific basis for setting exposure
guidelines. This assessment is also in agreement with recent
reviews (NRPB 1992, 1994b; NAS 1996; CRP 1997).
Occupational studies. A large number of epidemiological studies have been carried out to assess possible
links between exposure to ELF fields and cancer risk
among workers in electrical occupations. The first studyof this type (Milham 1982) took advantage of a deathcertificate database that included both job titles and500

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information on cancer mortality. As a crude method ofassessing exposure, Milham classified job titles according to presumed magnetic field exposure and found an
excess risk for leukemia among electrical workers. Subsequent studies (Savitz and Ahlbom 1994) made use ofsimilar databases; the types of cancer for which elevatedrates were noted varied across studies, particularly whencancer subtypes were characterized. Increased risks ofvarious types of leukemia and nervous tissue tumors,and, in a few instances, of both male and female breast
cancer, were reported (Demers et al. 1991; Matanoski etal. 1991; Tynes et al. 1992; Loomis et al. 1994). As wellas producing somewhat inconsistent results, these studies
suffered from very crude exposure assessment and fromfailure to control for confounding factors such as exposure to benzene solvent in the workplace.
Three recent studies have attempted to overcome
some of the deficiencies in earlier work by measuring
ELF field exposure at the workplace and by taking
duration of work into consideration (Floderus et al. 1993;
Thériault et al. 1994; Savitz and Loomis 1995). An
elevated cancer risk among exposed individuals wasobserved, but the type of cancer of which this was truevaried from study to study. Floderus et al. (1993) founda significant association with leukemia; an association
was also noted by Thériault et al. (1994), but one that was
weak and not significant, and no link was observed by
Savitz and Loomis (1995). For subtypes of leukemia
there was even greater inconsistency, but numbers in theanalyses were small. For tumors of nervous tissue,
Floderus et al. (1993) found an excess for glioblastoma(astrocytoma III–IV), while both Thériault et al. (1994)
and Savitz and Loomis (1995) found only suggestive
evidence for an increase in glioma (astrocytoma I–II). If
there is truly a link between occupational exposure tomagnetic fields and cancer, greater consistency andstronger associations would be expected of these recent
studies based on more sophisticated exposure data.
Researchers have also investigated the possibility
that ELF electric fields could be linked to cancer. The
three utilities that participated in the Thériault et al.
(1994) study of magnetic fields analyzed electric fielddata as well. Workers with leukemia at one of the utilities
were reported to be more likely to have been exposed toelectric fields than were control workers. In addition, theassociation was stronger in a group that had been
exposed to high electric and magnetic fields combined(Miller et al. 1996). At the second utility, investigators
reported no association between leukemia and higher
cumulative exposure to workplace electric fields, butsome of the analyses showed an association with brain
cancer (Guénel et al. 1996). An association with coloncancer was also reported, yet in other studies of large
populations of electric utility workers this type of cancer
has not been found. At the third utility, no association
between high electric fields and brain cancer or leukemia
was observed, but this study was smaller and less likely
to have detected small changes, if present (Baris et al.
1996).

April 1998, Volume 74, Number 4

An association between Alzheimer’s disease andoccupational exposure to magnetic fields has recently
been suggested (Sobel and Davanipour 1996). However,this effect has not been confirmed.
Laboratory studies. The following paragraphs provide a summary and critical evaluation of laboratory
studies on the biological effects of electric and magnetic
fields with frequencies below 100 kHz. There are separate discussions on results obtained in studies of volunteers exposed under controlled conditions and in laboratory studies on cellular, tissue, and animal systems.
Volunteer studies. Exposure to a time-varying electric field can result in perception of the field as a result of
the alternating electric charge induced on the bodysurface, which causes the body hairs to vibrate. Several
studies have shown that the majority of people canperceive 50/60 Hz electric fields stronger than
20 kV m21, and that a small minority can perceive fields
below 5 kV m21 (UNEP/WHO/IRPA 1984; Tenforde1991).
Small changes in cardiac function occurred in human volunteers exposed to combined 60-Hz electric andmagnetic fields (9 kV m21, 20 mT) (Cook et al. 1992;
Graham et al. 1994). Resting heart rate was slightly, but
significantly, reduced (by 3–5 beats per minute) during
or immediately after exposure. This response was absent
on exposure to stronger (12 kV m21, 30 mT) or weaker(6 kV m21, 10 mT) fields and reduced if the subject wasmentally alert. None of the subjects in these studies wasable to detect the presence of the fields, and there wereno other consistent results in a wide battery of sensory
and perceptual tests.
No adverse physiological or psychological effects
were observed in laboratory studies of people exposed to
50-Hz fields in the range 2–5 mT (Sander et al. 1982;
Ruppe et al. 1995). There were no observed changes inblood chemistry, blood cell counts, blood gases, lactate
levels, electrocardiogram, electroencephalogram, skintemperature, or circulating hormone levels in studies bySander et al. (1982) and Graham et al. (1994). Recent
studies on volunteers have also failed to show any effectof exposure to 60-Hz magnetic fields on the nocturnal
melatonin level in blood (Graham et al. 1996, 1997;
Selmaoui et al. 1996).
Sufficiently intense ELF magnetic fields can elicit
peripheral nerve and muscle tissue stimulation directly,
and short magnetic field pulses have been used clinicallyto stimulate nerves in the limbs in order to check the
integrity of neural pathways. Peripheral nerve and muscle stimulation has also been reported in volunteers
exposed to 1-kHz gradient magnetic fields in experimental magnetic resonance imaging systems. Threshold magnetic flux densities were several millitesla, and corresponding induced current densities in the peripheral
tissues were about 1 A m22 from pulsed fields producedby rapidly switched gradients. Time-varying magnetic
fields that induce current densities above 1 A m22 inGuidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields ● ICNIRP GUIDELINES

tissue lead to neural excitation and are capable ofproducing irreversible biological effects such as cardiac
fibrillation (Tenforde and Kaune 1987; Reilly 1989). In a
study involving electromyographic recordings from thehuman arm (Polson et al. 1982), it was found that apulsed field with dB/dt greater than 104 T s21 wasneeded to stimulate the median nerve trunk. The durationof the magnetic stimulus has also been found to be an
important parameter in stimulation of excitable tissues.
Thresholds lower than 100 mA m22 can be derived
from studies of visual and mental functions in humanvolunteers. Changes in response latency for complex
reasoning tests have been reported in volunteers
subjected to weak power-frequency electric currents
passed through electrodes attached to the head andshoulders; current densities were estimated to lie between 10 and 40 mA m22 (Stollery 1986, 1987). Finally,
many studies have reported that volunteers experienced
faint flickering visual sensations, known as magnetic
phosphenes, during exposure to ELF magnetic fields
above 3–5 mT (Silny 1986). These visual effects can also
be induced by the direct application of weak electric
currents to the head. At 20 Hz, current densities of about
10 mA m22 in the retina have been estimated as thethreshold for induction of phosphenes, which is above
the typical endogenous current densities in electrically
excitable tissues. Higher thresholds have been observed
for both lower and higher frequencies (Lövsund et al.
1980; Tenforde 1990).
Studies have been conducted at 50 Hz on visually
evoked potentials that exhibited thresholds for effects atflux densities of 60 mT (Silny 1986). Consistent with thisresult, no effects on visually evoked potentials wereobtained by either Sander et al. (1982), using a 50-Hz,
5-mT field, or Graham et al. (1994), using combined
60-Hz electric and magnetic fields up to 12 kV m21 and30 mT, respectively.
Cellular and animal studies. Despite the large
number of studies undertaken to detect biological effectsof ELF electric and magnetic fields, few systematicstudies have defined the threshold field characteristics
that produce significant perturbations of biological functions. It is well established that induced electric current
can stimulate nerve and muscle tissue directly once theinduced current density exceeds threshold values(UNEP/WHO/IRPA 1987; Bernhardt 1992; Tenforde
1996). Current densities that are unable to stimulate
excitable tissues directly may nevertheless affect ongoing electrical activity and influence neuronal excitability.
The activity of the central nervous system is known to besensitive to the endogenous electric fields generated by
the action of adjacent nerve cells, at levels below thoserequired for direct stimulation.
Many studies have suggested that the transductionof weak electrical signals in the ELF range involves
interactions with the cell membrane, leading to cytoplasmic biochemical responses that in turn involve changes
in cellular functional and proliferative states. From sim-

501

ple models of the behavior of single cells in weak fields
it has been calculated that an electrical signal in theextracellular field must be greater than approximately
10 –100 mV m21 (corresponding to an induced current
density of about 2–20 mA m22) in order to exceed thelevel of endogenous physical and biological noise incellular membranes (Astumian et al. 1995). Existing
evidence also suggests that several structural and functional properties of membranes may be altered in response to induced ELF fields at or below 100 mV m21(Sienkiewicz et al. 1991; Tenforde 1993). Neuroendocrine alterations (e.g., suppression of nocturnal melatonin
synthesis) have been reported in response to induced
electrical fields of 10 mV m21 or less, corresponding to
induced current densities of approximately 2 mA m22 orless (Tenforde 1991, 1996). However, there is no clear
evidence that these biological interactions of lowfrequency fields lead to adverse health effects.
Induced electric fields and currents at levels exceeding those of endogenous bioelectric signals present intissue have been shown to cause a number of physiological effects that increase in severity as the induced current
density is increased (Bernhardt 1979; Tenforde 1996). In
the current density range 10 –100 mA m22, tissue effects
and changes in brain cognitive functions have beenreported (NRPB 1992; NAS 1996). When induced current density exceeds 100 to several hundred mA m22 forfrequencies between about 10 Hz and 1 kHz, thresholds
for neuronal and neuromuscular stimulation are exceeded. The threshold current densities increase progressively at frequencies below several hertz and above
1 kHz. Finally, at extremely high current densities,
exceeding 1 A m22, severe and potentially lifethreatening effects such as cardiac extrasystoles, ventricular fibrillation, muscular tetanus, and respiratory failure
may occur. The severity and the probability of irreversibility of tissue effects becomes greater with chronic
exposure to induced current densities above the level
10 to 100 mA m22. It therefore seems appropriate tolimit human exposure to fields that induce current densities no greater than 10 mA m22 in the head, neck, andtrunk at frequencies of a few hertz up to 1 kHz.
It has been postulated that oscillatory magnetomechanical forces and torques on biogenic magnetite particles in brain tissue could provide a mechanism forthe transduction of signals from ELF magnetic fields.
Kirschvink et al. (1992b) proposed a model in which
ELF magnetic forces on magnetite particles are visualized as producing the opening and closing of pressuresensitive ion channels in membranes. However, onedifficulty with this model is the sparsity of magnetite
particles relative to the number of cells in brain tissue.
For example, human brain tissue has been reported tocontain a few million magnetite particles per gram,
distributed in 105 discrete clusters of 5–10 particles(Kirschvink et al. 1992a). The number of cells in brain
tissue thus exceeds the number of magnetite particles by
a factor of about 100, and it is difficult to envisage how
oscillating magnetomechanical interactions of an ELF

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Health Physics

field with magnetite crystals could affect a significant
number of pressure-sensitive ion channels in the brain.
Further studies are clearly needed to reveal the biologicalrole of magnetite and the possible mechanisms throughwhich this mineral could play a role in the transduction of
ELF magnetic signals.
An important issue in assessing the effects of electromagnetic fields is the possibility of teratogenic anddevelopmental effects. On the basis of published scientific evidence, it is unlikely that low-frequency fields
have adverse effects on the embryonic and postnatal
development of mammalian species (Chernoff et al.
1992; Brent et al. 1993; Tenforde 1996). Moreover,currently available evidence indicates that somatic mutations and genetic effects are unlikely to result fromexposure to electric and magnetic fields with frequencies
below 100 kHz (Cridland 1993; Sienkiewicz et al. 1993).
There are numerous reports in the literature on thein-vitro effects of ELF fields on cell membrane properties (ion transport and interaction of mitogens with cellsurface receptors) and changes in cellular functions andgrowth properties (e.g., increased proliferation and alterations in metabolism, gene expression, protein biosynthesis, and enzyme activities) (Cridland 1993; Sienkiewicz et al. 1993; Tenforde 1991, 1992, 1993, 1996).
Considerable attention has focused on low-frequency
field effects on Ca11 transport across cell membranes
and the intracellular concentration of this ion (Walleczek
and Liburdy 1990; Liburdy 1992; Walleczek 1992),
messenger RNA and protein synthesis patterns (Goodman et al. 1983; Goodman and Henderson 1988, 1991;
Greene et al. 1991; Phillips et al. 1992), and the activityof enzymes such as ornithine decarboxylase (ODC) thatare related to cell proliferation and tumor promotion(Byus et al. 1987, 1988; Litovitz et al. 1991, 1993).
However, before these observations can be used for
defining exposure limits, it is essential to establish boththeir reproducibility and their relevance to cancer orother adverse health outcomes. This point is underscoredby the fact that there have been difficulties in replicatingsome of the key observations of field effects on gene
expression and protein synthesis (Lacy-Hulbert et al.
1995; Saffer and Thurston 1995). The authors of these
replication studies identified several deficiencies in theearlier studies, including poor temperature control, lackof appropriate internal control samples, and the use of
low-resolution techniques for analyzing the productionof messenger RNA transcripts. The transient increase in
ODC activity reported in response to field exposure issmall in magnitude and not associated with de novo
synthesis of the enzyme (unlike chemical tumor promoters such as phorbol esters) (Byus et al. 1988). Studies on
ODC have mostly involved cellular preparations; morestudies are needed to show whether there are effects on
ODC in vivo, although there is one report suggesting
effects on ODC in a rat mammary tumor promotion assay(Mevissen et al. 1995).
There is no evidence that ELF fields alter the
structure of DNA and chromatin, and no resultant muta-

April 1998, Volume 74, Number 4

tional and neoplastic transformation effects are expected.
This is supported by results of laboratory studies designed to detect DNA and chromosomal damage, mutational events, and increased transformation frequency inresponse to ELF field exposure (NRPB 1992; Murphy etal. 1993; McCann et al. 1993; Tenforde 1996). The lackof effects on chromosome structure suggests that ELF
fields, if they have any effect on the process of carcinogenesis, are more likely to act as promoters than initiators, enhancing the proliferation of genetically alteredcells rather than causing the initial lesion in DNA or
chromatin. An influence on tumor development could be
mediated through epigenetic effects of these fields, suchas alterations in cell signalling pathways or gene expression. The focus of recent studies has therefore been on
detecting possible effects of ELF fields on the promotion
and progression phases of tumor development following
initiation by a chemical carcinogen.
Studies on in-vitro tumor cell growth and the development of transplanted tumors in rodents have provided
no strong evidence for possible carcinogenic effects of
exposure to ELF fields (Tenforde 1996). Several studies
of more direct relevance to human cancer have involved
in-vivo tests for tumor-promoting activity of ELF magnetic fields on skin, liver, brain, and mammary tumors inrodents. Three studies of skin tumor promotion (McLean
et al. 1991; Rannug et al. 1993a, 1994) failed to show any
effect of either continuous or intermittent exposure to
power-frequency magnetic fields in promoting chemically induced tumors. At a 60-Hz field strength of 2 mT,
a co-promoting effect with a phorbol ester was reported
for mouse skin tumor development in the initial stages ofthe experiment, but the statistical significance of this waslost by completion of the study in week 23 (Stuchly et al.
1992). Previous studies by the same investigators had
shown that 60-Hz, 2-mT field exposure did not promote
the growth of DMBA-initiated skin cells (McLean et al.
1991).
Experiments on the development of transformed
liver foci initiated by a chemical carcinogen and promoted by phorbol ester in partially hepatectomized rats
revealed no promotion or co-promotion effect of exposure to 50-Hz fields ranging in strength from 0.5 to 50
mT (Rannug et al. 1993b, c).
Studies on mammary cancer development in rodents
treated with a chemical initiator have suggested a cancerpromoting effect of exposure to power-frequency magnetic fields in the range 0.01–30 mT (Beniashvili et al.
1991; Löscher et al. 1993; Mevissen et al. 1993, 1995;
Baum et al. 1995; Löscher and Mevissen 1995). Theseobservations of increased tumor incidence in rats exposed to magnetic fields have been hypothesized to berelated to field-induced suppression of pineal melatonin
and a resulting elevation in steroid hormone levels andbreast cancer risk (Stevens 1987; Stevens et al. 1992).
However, replication efforts by independent laboratories
are needed before conclusions can be drawn regarding
the implications of these findings for a promoting effectof ELF magnetic fields on mammary tumors. It should

Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields ● ICNIRP GUIDELINES

also be noted that recent studies have found no evidence
for a significant effect of exposure to ELF magnetic
fields on melatonin levels in humans (Graham et al.
1996, 1997; Selmaoui et al. 1996).
Indirect effects of electric and magnetic fields
Indirect effects of electromagnetic fields may result
from physical contact (e.g., touching or brushing against)
between a person and an object, such as a metallic
structure in the field, at a different electric potential. The
result of such contact is the flow of electric charge(contact current) that may have accumulated on theobject or on the body of the person. In the frequency
range up to approximately 100 kHz, the flow of electric
current from an object in the field to the body of theindividual may result in the stimulation of muscles
and/or peripheral nerves. With increasing levels of current this may be manifested as perception, pain fromelectric shock and/or burn, inability to release the object,difficulty in breathing and, at very high currents, cardiac
ventricular fibrillation (Tenforde and Kaune 1987).
Threshold values for these effects are frequencydependent, with the lowest threshold occurring at frequencies between 10 and 100 Hz. Thresholds for peripheral nerve responses remain low for frequencies up to
several kHz. Appropriate engineering and/or administrative controls, and even the wearing of personal protective
clothing, can prevent these problems from occurring.
Spark discharges can occur when an individual
comes into very close proximity with an object at adifferent electric potential, without actually touching it(Tenforde and Kaune 1987; UNEP/WHO/IRPA 1993).
When a group of volunteers, who were electricallyinsulated from the ground, each held a finger tip close toa grounded object, the threshold for perception of spark
discharges was as low as 0.6 –1.5 kV m21 in 10% ofcases. The threshold field level reported as causing
annoyance under these exposure conditions is about
2.0 –3.5 kV m21. Large contact currents can result inmuscle contraction. In male volunteers, the 50th percentile threshold for being unable to release a charged
conductor has been reported as 9 mA at 50/60 Hz, 16 mA
at 1 kHz, about 50 mA at 10 kHz, and about 130 mA at
100 kHz (UNEP/WHO/IRPA 1993).
The threshold currents for various indirect effects offields with frequencies up to 100 kHz are summarized inTable 2 (UNEP/WHO/IRPA 1993).

Table 2. Ranges of threshold currents for indirect effects, including children, women, and men.
Threshold current (mA) at
frequency:
Indirect effect

50/60 Hz

1 kHz

100 kHz

Touch perception
Pain on finger contact
Painful shock/let-go threshold
Severe shock/breathing difficulty

0.2–0.4
0.9–1.8
8–16
12–23

0.4–0.8
1.6–3.3
12–24
21–41

25–40
33–55
112–224
160–320

503

Summary of biological effects and epidemiologicalstudies (up to 100 kHz)With the possible exception of mammary tumors,
there is little evidence from laboratory studies thatpower-frequency magnetic fields have a tumorpromoting effect. Although further animal studies areneeded to clarify the possible effects of ELF fields on
signals produced in cells and on endocrine regulation—
both of which could influence the development of tumors
by promoting the proliferation of initiated cells—it can
only be concluded that there is currently no convincing
evidence for carcinogenic effects of these fields and thatthese data cannot be used as a basis for developing
exposure guidelines.
Laboratory studies on cellular and animal systems
have found no established effects of low-frequency fields
that are indicative of adverse health effects when induced
current density is at or below 10 mA m22. At higher
levels of induced current density (10 –100 mA m22),
more significant tissue effects have been consistently
observed, such as functional changes in the nervous
system and other tissue effects (Tenforde 1996).
Data on cancer risk associated with exposure to ELF
fields among individuals living close to power lines areapparently consistent in indicating a slightly higher riskof leukemia among children, although more recent studies question the previously observed weak association.
The studies do not, however, indicate a similarly elevatedrisk of any other type of childhood cancer or of any formof adult cancer. The basis for the hypothetical link
between childhood leukemia and residence in close
proximity to power lines is unknown; if the link is not
related to the ELF electric and magnetic fields generated
by the power lines, then unknown risk factors forleukemia would have to be linked to power lines in someundetermined manner. In the absence of support fromlaboratory studies, the epidemiological data are insufficient to allow an exposure guideline to be established.
There have been reports of an increased risk ofcertain types of cancer, such as leukemia, nervous tissue
tumors, and, to a limited extent, breast cancer, among
electrical workers. In most studies, job titles were used toclassify subjects according to presumed levels of magnetic field exposure. A few more recent studies, however,
have used more sophisticated methods of exposure assessment; overall, these studies suggested an increased risk ofleukemia or brain tumors but were largely inconsistent withregard to the type of cancer for which risk is increased. The
data are insufficient to provide a basis for ELF field
exposure guidelines. In a large number of epidemiologicalstudies, no consistent evidence of adverse reproductive
effects have been provided.
Measurement of biological responses in laboratory
studies and in volunteers has provided little indication ofadverse effects of low-frequency fields at levels to whichpeople are commonly exposed. A threshold current
density of 10 mA m22 at frequencies up to 1 kHz has
been estimated for minor effects on nervous system
functions. Among volunteers, the most consistent effects

504

Health Physics

of exposure are the appearance of visual phosphenes anda minor reduction in heart rate during or immediately
after exposure to ELF fields, but there is no evidence thatthese transient effects are associated with any long-term
health risk. A reduction in nocturnal pineal melatonin
synthesis has been observed in several rodent species
following exposure to weak ELF electric and magnetic
fields, but no consistent effect has been reported inhumans exposed to ELF fields under controlled conditions. Studies involving exposures to 60-Hz magnetic
fields up to 20 mT have not reported reliable effects on
melatonin levels in blood.
BIOLOGICAL BASIS FOR LIMITINGEXPOSURE (100 k H z –300 GHz)
The following paragraphs provide a general review
of relevant literature on the biological effects and potential health effects of electromagnetic fields with frequencies of 100 kHz to 300 GHz. More detailed reviews canbe found elsewhere (NRPB 1991; UNEP/WHO/IRPA
1993; McKinlay et al. 1996; Polk and Postow 1996;
Repacholi 1998).
Direct effects of electromagnetic fields
Epidemiological studies. Only a limited number ofstudies have been carried out on reproductive effects andcancer risk in individuals exposed to microwave radiation. A summary of the literature was published by
UNEP/WHO/IRPA (1993).
Reproductive outcomes. Two extensive studies on
women treated with microwave diathermy to relieve thepain of uterine contractions during labor found no evidence for adverse effects on the fetus (Daels 1973, 1976).
However, seven studies on pregnancy outcomes among
workers occupationally exposed to microwave radiationand on birth defects among their offspring produced both
positive and negative results. In some of the larger
epidemiological studies of female plastic welders andphysiotherapists working with shortwave diathermy devices, there were no statistically significant effects on
rates of abortion or fetal malformation (Källen et al.
1982). By contrast, other studies on similar populationsof female workers found an increased risk of miscarriage
and birth defects (Larsen et al. 1991; Ouellet-Hellstrom
and Stewart 1993). A study of male radar workers foundno association between microwave exposure and the riskof Down’s syndrome in their offspring (Cohen et al.
1977).
Overall, the studies on reproductive outcomes andmicrowave exposure suffer from very poor assessment of
exposure and, in many cases, small numbers of subjects.
Despite the generally negative results of these studies, itwill be difficult to draw firm conclusions on reproductive
risk without further epidemiological data on highly
exposed individuals and more precise exposure assessment.

April 1998, Volume 74, Number 4

Cancer studies. Studies on cancer risk and microwave exposure are few and generally lack quantitative
exposure assessment. Two epidemiological studies ofradar workers in the aircraft industry and in the U.S.
armed forces found no evidence of increased morbidity
or mortality from any cause (Barron and Baraff 1958;
Robinette et al. 1980; UNEP/WHO/IRPA 1993). Similar
results were obtained by Lillienfeld et al. (1978) in astudy of employees in the U.S. embassy in Moscow, whowere chronically exposed to low-level microwave radiation. Selvin et al. (1992) reported no increase in cancer
risk among children chronically exposed to radiationfrom a large microwave transmitter near their homes.
More recent studies have failed to show significant
increases in nervous tissue tumors among workers andmilitary personnel exposed to microwave fields (Beall etal. 1996; Grayson 1996). Moreover, no excess total
mortality was apparent among users of mobile telephones (Rothman et al. 1996a, b), but it is still too early
to observe an effect on cancer incidence or mortality.
There has been a report of increased cancer risk
among military personnel (Szmigielski et al. 1988), but
the results of the study are difficult to interpret because
neither the size of the population nor the exposure levels
are clearly stated. In a later study, Szmigielski (1996)
found increased rates of leukemia and lymphoma among
military personnel exposed to EMF fields, but the assessment of EMF exposure was not well defined. A few
recent studies of populations living near EMF transmitters have suggested a local increase in leukemia incidence (Hocking et al. 1996; Dolk et at. 1997a, b), but theresults are inconclusive. Overall, the results of the small
number of epidemiological studies published provide
only limited information on cancer risk.
Laboratory studies. The following paragraphs provide a summary and critical evaluation of laboratory
studies on the biological effects of electromagnetic fields
with frequencies in the range 100 kHz–300 GHz. There
are separate discussions on results of studies of volunteers exposed under controlled conditions and of laboratory studies on cellular, tissue, and animal systems.
Volunteer studies. Studies by Chatterjee et al.
(1986) demonstrated that, as the frequency increases
from approximately 100 kHz to 10 MHz, the dominant
effect of exposure to a high-intensity electromagnetic
field changes from nerve and muscle stimulation toheating. At 100 kHz the primary sensation was one of
nerve tingling, while at 10 MHz it was one of warmth on
the skin. In this frequency range, therefore, basic healthprotection criteria should be such as to avoid stimulationof excitable tissues and heating effects. At frequencies
from 10 MHz to 300 GHz, heating is the major effect ofabsorption of electromagnetic energy, and temperaturerises of more than 1–2 °C can have adverse health effects
such as heat exhaustion and heat stroke (ACGIH 1996).
Studies on workers in thermally stressful environments
have shown worsening performance of simple tasks as

Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields ● ICNIRP GUIDELINES

body temperature rises to a level approaching physiological heat stress (Ramsey and Kwon 1988).
A sensation of warmth has been reported by volunteers experiencing high-frequency current of about 100 –200 mA through a limb. The resulting SAR value isunlikely to produce a localized temperature increment of
more than 1°C in the limbs (Chatterjee et al. 1986; Chenand Gandhi 1988; Hoque and Gandhi 1988), which has
been suggested as the upper limit of temperature increasethat has no detrimental health effects (UNEP/WHO/
IRPA 1993). Data on volunteers reported by Gandhi et al.
(1986) for frequencies up to 50 MHz and by Tofani et al.
(1995) for frequencies up to 110 MHz (the upper limit of
the FM broadcast band) support a reference level for limb
current of 100 mA to avoid excessive heating effects(Dimbylow 1997).
There have been several studies of thermoregulatory
responses of resting volunteers exposed to EMF inmagnetic resonance imaging systems (Shellock andCrues 1987; Magin et al. 1992). In general, these havedemonstrated that exposure for up to 30 min, underconditions in which whole-body SAR was less than
4 W kg21, caused an increase in the body core temperature of less than 1°C.
Cellular and animal studies. There are numerous
reports on the behavioral and physiological responses oflaboratory animals, including rodents, dogs, and nonhuman primates, to thermal interactions of EMF atfrequencies above 10 MHz. Thermosensitivity and thermoregulatory responses are associated both with the
hypothalamus and with thermal receptors located in theskin and in internal parts of the body. Afferent signals
reflecting temperature change converge in the central
nervous system and modify the activity of the major
neuroendocrine control systems, triggering the physiological and behavioral responses necessary for the maintenance of homeostasis.
Exposure of laboratory animals to EMF producing
absorption in excess of approximately 4 W kg21 hasrevealed a characteristic pattern of thermoregulatory
response in which body temperature initially rises andthen stabilizes following the activation of thermoregulatory mechanisms (Michaelson 1983). The early phase ofthis response is accompanied by an increase in blood
volume due to movement of fluid from the extracellularspace into the circulation and by increases in heart rateand intraventricular blood pressure. These cardiodynamic changes reflect thermoregulatory responses thatfacilitate the conduction of heat to the body surface.
Prolonged exposure of animals to levels of microwave
radiation that raise the body temperature ultimately leadto failure of these thermoregulatory mechanisms.
Several studies with rodents and monkeys have also
demonstrated a behavioral component of thermoregulatory responses. Decreased task performance by rats andmonkeys has been observed at SAR values in the range
1–3 W kg21 (Stern et al. 1979; Adair and Adams 1980;de Lorge and Ezell 1980; D’Andrea et al. 1986). In

505

monkeys, altered thermoregulatory behavior starts when
the temperature in the hypothalamic region rises by aslittle as 0.2– 0.3°C (Adair et al. 1984). The hypothalamus
is considered to be the control center for normal thermoregulatory processes, and its activity can be modified bya small local temperature increase under conditions inwhich rectal temperature remains constant.
At levels of absorbed electromagnetic energy thatcause body temperature rises in excess of 1–2°C, a large
number of physiological effects have been characterized
in studies with cellular and animal systems (Michaelson
and Elson 1996). These effects include alterations inneural and neuromuscular functions; increased bloodbrain barrier permeability; ocular impairment (lens opacities and corneal abnormalities); stress-associatedchanges in the immune system; hematological changes;
reproductive changes (e.g., reduced sperm production);teratogenicity; and changes in cell morphology, waterand electrolyte content, and membrane functions.
Under conditions of partial-body exposure to intense
EMF, significant thermal damage can occur in sensitive
tissues such as the eye and the testis. Microwave exposure of 2–3 h duration has produced cataracts in rabbits’eyes at SAR values from 100 –140 W kg21, which
produced lenticular temperatures of 41– 43°C (Guy et al.
1975). No cataracts were observed in monkeys exposed
to microwave fields of similar or higher intensities,
possibly because of different energy absorption patterns
in the eyes of monkeys from those in rabbits. At very
high frequencies (10 –300 GHz), absorption of electromagnetic energy is confined largely to the epidermal
layers of the skin, subcutaneous tissues, and the outerpart of the eye. At the higher end of the frequency range,
absorption is increasingly superficial. Ocular damage atthese frequencies can be avoided if the microwave power
density is less than 50 W m22 (Sliney and Wolbarsht
1980; UNEP/WHO/IRPA 1993).
There has been considerable recent interest in thepossible carcinogenic effects of exposure to microwave
fields with frequencies in the range of widely usedcommunications systems, including hand-held mobile
telephones and base transmitters. Research findings inthis area have been summarized by ICNIRP (1996).
Briefly, there are many reports suggesting that microwave fields are not mutagenic, and exposure to thesefields is therefore unlikely to initiate carcinogenesis(NRPB 1992; Cridland 1993; UNEP/WHO/IRPA 1993).
By contrast, some recent reports suggest that exposure ofrodents to microwave fields at SAR levels of the order of
1 W kg21 may produce strand breaks in the DNA oftestis and brain tissues (Sarkar et al. 1994; Lai and Singh
1995, 1996), although both ICNIRP (1996) and Williams(1996) pointed out methodological deficiencies that
could have significantly influenced these results.
In a large study of rats exposed to microwaves for
up to 25 mo, an excess of primary malignancies wasnoted in exposed rats relative to controls (Chou et al.
1992). However, the incidence of benign tumors did not
differ between the groups, and no specific type of tumor

506

Health Physics

was more prevalent in the exposed group than in stockrats of the same strain maintained under similar specificpathogen-free conditions. Taken as a whole, the resultsof this study cannot be interpreted as indicating atumor-initiating effect of microwave fields.
Several studies have examined the effects of microwave exposure on the development of pre-initiated tumor
cells. Szmigielski et al. (1982) noted an enhanced growthrate of transplanted lung sarcoma cells in rats exposed tomicrowaves at high power densities. It is possible that
this resulted from a weakening of the host immune
defense in response to thermal stress from the microwave
exposure. Recent studies using athermal levels of microwave irradiation have found no effects on the development of melanoma in mice or of brain glioma in rats
(Santini et al. 1988; Salford et al. 1993).
Repacholi et al. (1997) have reported that exposureof 100 female, Em-pim1 transgenic mice to 900-MHz
fields, pulsed at 217 Hz with pulse widths of 0.6 ms for
up to 18 mo, produced a doubling in lymphoma incidence compared with 101 controls. Because the mice
were free to roam in their cages, the variation in SAR
was wide (0.01– 4.2 W kg21). Given that the resting
metabolic rate of these mice is 7–15 W kg21, only theupper end of the exposure range may have produced
some slight heating. Thus, it appears that this study
suggests a non-thermal mechanism may be acting, whichneeds to be investigated further. However, before any
assumptions can be made about health risk, a number ofquestions need to be addressed. The study needs to be
replicated, restraining the animals to decrease the SAR
exposure variation and to determine whether there is adose response. Further study is needed to determine
whether the results can be found in other animal models
in order to be able to generalize the results to humans. It
is also essential to assess whether results found intransgenic animals are applicable to humans.
Special considerations for pulsed andamplitude-modulated waveforms
Compared with continuous-wave (CW) radiation,pulsed microwave fields with the same average rate ofenergy deposition in tissues are generally more effective
in producing a biological response, especially when there
is a well-defined threshold that must be exceeded to elicit
the effect (ICNIRP 1996). The “microwave hearing”
effect is a well known example of this (Frey 1961; Frey
and Messenger 1973; Lin 1978): people with normal
hearing can perceive pulse-modulated fields with frequencies between about 200 MHz and 6.5 GHz. The
auditory sensation has been variously described as abuzzing, clicking, or popping sound, depending on themodulation characteristics of the field. The microwave
hearing effects have been attributed to a thermoelastic
interaction in the auditory cortex of the brain, with athreshold for perception of about 100 – 400 mJ m22 forpulses of duration less than 30 ms at 2.45 GHz (corresponding to an SA of 4 –16 mJ kg21). Repeated or
prolonged exposure to microwave auditory effects may
be stressful and potentially harmful.

April 1998, Volume 74, Number 4Some reports suggest that retina, iris, and corneal
endothelium of the primate eye are sensitive to low levelsof pulsed microwave radiation (Kues et al. 1985; UNEP/
WHO/IRPA 1993). Degenerative changes in lightsensitive cells of the retina were reported for absorbed
energy levels as low as 26 mJ kg21. After administrationof timolol maleate, which is used in the treatment ofglaucoma, the threshold for retinal damage by pulsed
fields dropped to 2.6 mJ kg21. However, an attempt in an
independent laboratory to partially replicate these findings for CW fields (i.e., not pulsed) was unsuccessful(Kamimura et al. 1994), and it is therefore impossible atpresent to assess the potential health implications of theinitial findings of Kues et al. (1985).
Exposure to intense pulsed microwave fields has
been reported to suppress the startle response in conscious mice and to evoke body movements (NRPB 1991;
Sienkiewicz et al. 1993; UNEP/WHO/IRPA 1993). The
threshold specific energy absorption level at midbrainthat evoked body movements was 200 J kg21 for 10 ms
pulses. The mechanism for these effects of pulsed microwaves remains to be determined but is believed to berelated to the microwave hearing phenomenon. The
auditory thresholds for rodents are about an order ofmagnitude lower than for humans, that is 1–2 mJ kg21
for pulses ,30 ms in duration. Pulses of this magnitude
have also been reported to affect neurotransmitter metabolism and the concentration of the neural receptors
involved in stress and anxiety responses in different
regions of the rat brain.
The issue of athermal interactions of high-frequency
EMF has centered largely on reports of biological effectsof amplitude modulated (AM) fields under in-vitro conditions at SAR values well below those that produce
measurable tissue heating. Initial studies in two independent laboratories led to reports that VHF fields withamplitude modulation at extremely low frequencies(6 –20 Hz) produced a small, but statistically significant,release of Ca11 from the surfaces of chick brain cells(Bawin et al. 1975; Blackman et al. 1979). A subsequentattempt to replicate these findings, using the same type of
AM field, was unsuccessful (Albert et al. 1987). A
number of other studies of the effects of AM fields on
Ca11 homeostasis have produced both positive andnegative results. For example, effects of AM fields on
Ca11 binding to cell surfaces have been observed withneuroblastoma cells, pancreatic cells, cardiac tissue, andcat brain cells, but not with cultured rat nerve cells, chickskeletal muscle, or rat brain cells (Postow and Swicord1996).
Amplitude-modulated fields have also been reported
to alter brain electrical activity (Bawin et al. 1974),
inhibit T-lymphocyte cytotoxic activity (Lyle et al.
1983), decrease the activities of non-cyclic-AMPdependent kinase in lymphocytes (Byus et al. 1984), andcause a transient increase in the cytoplasmic activity ofornithine decarboxylase, an essential enzyme for cellproliferation (Byus et al. 1988; Litovitz et al. 1992). In
contrast, no effects have been observed on a wide variety

Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields ● ICNIRP GUIDELINES

of other cellular systems and functional end-points,
including lymphocyte capping, neoplastic cell transformation, and various membrane electrical and enzymatic
properties (Postow and Swicord 1996). Of particular
relevance to the potential carcinogenic effects of pulsed
fields is the observation by Balcer-Kubiczek and Harrison (1991) that neoplastic transformation was accelerated in C3H/10T1/2 cells exposed to 2,450-MHz microwaves that were pulse-modulated at 120 Hz. The effectwas dependent on field strength but occurred only whena chemical tumor-promoter, TPA, was present in the cell
culture medium. This finding suggests that pulsed microwaves may exert co-carcinogenic effects in combination
with a chemical agent that increases the rate of proliferation of transformed cells. To date, there have been noattempts to replicate this finding, and its implication forhuman health effects is unclear.
Interpretation of several observed biological effectsof AM electromagnetic fields is further complicated by
the apparent existence of “windows” of response in boththe power density and frequency domains. There are no
accepted models that adequately explain this phenomenon, which challenges the traditional concept of a monotonic relationship between the field intensity and theseverity of the resulting biological effects.
Overall, the literature on athermal effects of AM
electromagnetic fields is so complex, the validity ofreported effects so poorly established, and the relevanceof the effects to human health is so uncertain, that it is
impossible to use this body of information as a basis forsetting limits on human exposure to these fields.

Indirect effects of electromagnetic fields
In the frequency range of about 100 kHz–110 MHz,shocks and burns can result either from an individual
touching an ungrounded metal object that has acquired acharge in a field or from contact between a charged
individual and a grounded metal object. It should be
noted that the upper frequency for contact current (110MHz) is imposed by a lack of data on higher frequencies
rather than by the absence of effects. However, 110 MHz
is the upper frequency limit of the FM broadcast band.
Threshold currents that result in biological effects ranging in severity from perception to pain have beenmeasured in controlled experiments on volunteers (Chatterjee et al. 1986; Tenforde and Kaune 1987; Bernhardt
1988); these are summarized in Table 3. In general, it has
been shown that the threshold currents that produce
perception and pain vary little over the frequency range
100 kHz–1 MHz and are unlikely to vary significantly
over the frequency range up to about 110 MHz. As noted
earlier for lower frequencies, significant variations between the sensitivities of men, women, and children also
exist for higher frequency fields. The data in Table 3
represent the range of 50th percentile values for people ofdifferent sizes and different levels of sensitivity tocontact currents.

507

Table 3. Ranges of threshold currents for indirect effects, including children, women, and men.
Threshold current (mA) at
frequency:
Indirect effect

100 kHz

1 MHz

Touch perception
Pain on finger contact
Painful shock/let-go threshold
Severe shock/breathing difficulty

25–40
33–55
112–224
160–320

25–40
28–50
Not determined
Not determined

Summary of biological effects and epidemiologicalstudies (100 kHz–300 GHz)
Available experimental evidence indicates that the
exposure of resting humans for approximately 30 min to
EMF producing a whole-body SAR of between
1 and 4 W kg21 results in a body temperature increase ofless than 1 °C. Animal data indicate a threshold for
behavioral responses in the same SAR range. Exposure
to more intense fields, producing SAR values in excess
of 4 W kg21, can overwhelm the thermoregulatory
capacity of the body and produce harmful levels of tissue
heating. Many laboratory studies with rodent and nonhuman primate models have demonstrated the broad
range of tissue damage resulting from either partial-bodyor whole-body heating producing temperature rises inexcess of 1–2°C. The sensitivity of various types oftissue to thermal damage varies widely, but the thresholdfor irreversible effects in even the most sensitive tissues
is greater than 4 W kg21 under normal environmental
conditions. These data form the basis for an occupational
exposure restriction of 0.4 W kg21, which provides alarge margin of safety for other limiting conditions suchas high ambient temperature, humidity, or level ofphysical activity.
Both laboratory data and the results of limited
human studies (Michaelson and Elson 1996) make it
clear that thermally stressful environments and the use ofdrugs or alcohol can compromise the thermoregulatory
capacity of the body. Under these conditions, safety
factors should be introduced to provide adequate protection for exposed individuals.
Data on human responses to high-frequency EMF
that produce detectable heating have been obtained fromcontrolled exposure of volunteers and from epidemiological studies on workers exposed to sources such as radar,
medical diathermy equipment, and heat sealers. They are
fully supportive of the conclusions drawn from laboratory work, that adverse biological effects can be causedby temperature rises in tissue that exceed 1°C. Epidemiological studies on exposed workers and the generalpublic have shown no major health effects associatedwith typical exposure environments. Although there are
deficiencies in the epidemiological work, such as poor
exposure assessment, the studies have yielded no convincing evidence that typical exposure levels lead toadverse reproductive outcomes or an increased cancer
risk in exposed individuals. This is consistent with theresults of laboratory research on cellular and animal

508

Health Physics

April 1998, Volume 74, Number 4models, which have demonstrated neither teratogenic nor
carcinogenic effects of exposure to athermal levels ofhigh-frequency EMF.
Exposure to pulsed EMF of sufficient intensity leads
to certain predictable effects such as the microwave
hearing phenomenon and various behavioral responses.
Epidemiological studies on exposed workers and thegeneral public have provided limited information andfailed to demonstrate any health effects. Reports ofsevere retinal damage have been challenged following
unsuccessful attempts to replicate the findings.
A large number of studies of the biological effects ofamplitude-modulated EMF, mostly conducted with lowlevels of exposure, have yielded both positive and negative results. Thorough analysis of these studies reveals
that the effects of AM fields vary widely with theexposure parameters, the types of cells and tissues
involved, and the biological end-points that are examined. In general, the effects of exposure of biologicalsystems to athermal levels of amplitude-modulated EMF
are small and very difficult to relate to potential healtheffects. There is no convincing evidence of frequency
and power density windows of response to these fields.
Shocks and burns can be the adverse indirect effects
of high-frequency EMF involving human contact withmetallic objects in the field. At frequencies of 100
kHz–110 MHz (the upper limit of the FM broadcastband), the threshold levels of contact current that produce
effects ranging from perception to severe pain do notvary significantly as a function of the field frequency.
The threshold for perception ranges from 25 to 40 mA in
individuals of different sizes, and that for pain fromapproximately 30 to 55 mA; above 50 mA there may be
severe burns at the site of tissue contact with a metallic
conductor in the field.

are current density, SAR, and power density. Protection
against adverse health effects requires that these basic
restrictions are not exceeded.
Reference levels of exposure are provided for comparison with measured values of physical quantities;
compliance with all reference levels given in these guidelines will ensure compliance with basic restrictions. If
measured values are higher than reference levels, it does notnecessarily follow that the basic restrictions have been
exceeded, but a more detailed analysis is necessary to assess
compliance with the basic restrictions.

GUIDELINES FOR LIMITING EMF EXPOSURE● differences in absorption of electromagnetic en-

Occupational and general public exposure
limitations
The occupationally exposed population consists ofadults who are generally exposed under known conditions and are trained to be aware of potential risk and to
take appropriate precautions. By contrast, the generalpublic comprises individuals of all ages and of varying
health status, and may include particularly susceptiblegroups or individuals. In many cases, members of the
public are unaware of their exposure to EMF. Moreover,individual members of the public cannot reasonably be
expected to take precautions to minimize or avoid exposure. It is these considerations that underlie the adoptionof more stringent exposure restrictions for the public thanfor the occupationally exposed population.

Basic restrictions
Different scientific bases were used in the development of basic exposure restrictions for various frequency
ranges:Basic restrictions and reference levels
Restrictions on the effects of exposure are based on
established health effects and are termed basic restrictions. Depending on frequency, the physical quantities
used to specify the basic restrictions on exposure to EMF

General statement on safety factors
There is insufficient information on the biologicaland health effects of EMF exposure of human populations and experimental animals to provide a rigorous
basis for establishing safety factors over the whole
frequency range and for all frequency modulations. In
addition, some of the uncertainty regarding the appropriate safety factor derives from a lack of knowledge
regarding the appropriate dosimetry (Repacholi 1998).
The following general variables were considered in thedevelopment of safety factors for high-frequency fields:● effects of EMF exposure under severe environ-mental conditions (high temperature, etc.) and/or
high activity levels; and● the potentially higher thermal sensitivity in certain population groups, such as the frail and/or
elderly, infants and young children, and people
with diseases or taking medications that compromise thermal tolerance.
The following additional factors were taken into account in deriving reference levels for high-frequency fields:
ergy by individuals of different sizes and different
orientations relative to the field; and● reflection, focusing, and scattering of the incident
field, which can result in enhanced localized
absorption of high-frequency energy.

● Between 1 Hz and 10 MHz, basic restrictions areprovided on current density to prevent effects on
nervous system functions;● Between 100 kHz and 10 GHz, basic restrictions
on SAR are provided to prevent whole-body heatstress and excessive localized tissue heating; inthe 100 kHz–10 MHz range, restrictions areprovided on both current density and SAR; and● Between 10 and 300 GHz, basic restrictions areprovided on power density to prevent excessive
heating in tissue at or near the body surface.

Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields ● ICNIRP GUIDELINESIn the frequency range from a few Hz to 1 kHz, forlevels of induced current density above 100 mA m22, thethresholds for acute changes in central nervous system
excitability and other acute effects such as reversal of thevisually evoked potential are exceeded. In view of thesafety considerations above, it was decided that, forfrequencies in the range 4 Hz to 1 kHz, occupational
exposure should be limited to fields that induce current
densities less than 10 mA m22, i.e., to use a safety factorof 10. For the general public an additional factor of 5 isapplied, giving a basic exposure restriction of 2 mA m22.
Below 4 Hz and above 1 kHz, the basic restriction on
induced current density increases progressively, corresponding to the increase in the threshold for nerve
stimulation for these frequency ranges.
Established biological and health effects in thefrequency range from 10 MHz to a few GHz are
consistent with responses to a body temperature rise of
more than 1°C. This level of temperature increase resultsfrom exposure of individuals under moderate environmental conditions to a whole-body SAR of approximately 4 W kg21 for about 30 min. A whole-body
average SAR of 0.4 W kg21 has therefore been chosen as
the restriction that provides adequate protection foroccupational exposure. An additional safety factor of 5 isintroduced for exposure of the public, giving an averagewhole-body SAR limit of 0.08 W kg21.
The lower basic restrictions for exposure of thegeneral public take into account the fact that their age andhealth status may differ from those of workers.

In the low-frequency range, there are currently few
data relating transient currents to health effects. The
ICNIRP therefore recommends that the restrictions on
current densities induced by transient or very short-term
peak fields be regarded as instantaneous values whichshould not be time-averaged.
The basic restrictions for current densities, wholebody average SAR, and localized SAR for frequencies
between 1 Hz and 10 GHz are presented in Table 4, andthose for power densities for frequencies of 10 –300 GHz
are presented in Table 5.
REFERENCE LEVELS
Where appropriate, the reference levels are obtained
from the basic restrictions by mathematical modeling andby extrapolation from the results of laboratory investigations at specific frequencies. They are given for the condition of maximum coupling of the field to the exposed
individual, thereby providing maximum protection. Tables
6 and 7 summarize the reference levels for occupational
exposure and exposure of the general public, respectively,
and the reference levels are illustrated in Figs. 1 and 2. The
reference levels are intended to be spatially averaged values
over the entire body of the exposed individual, but with theimportant proviso that the basic restrictions on localized
exposure are not exceeded.
For low-frequency fields, several computational andmeasurement methods have been developed for deriving
field-strength reference levels from the basic restrictions.

Table 4. Basic restrictions for time varying electric and magnetic fields for frequencies up to 10 GHz.a
Exposure
characteristics
Occupational
exposure

General public
exposurea509

Frequency range

Current density forhead and trunk(mA m22) (rms)

Whole-body
average SAR(W kg21)

Localized SAR(head and trunk)(W kg21)

Localized SAR(limbs) (W kg21)

up to 1 Hz
1–4 Hz
4 Hz–1 kHz
1–100 kHz
100 kHz–10 MHz
10 MHz–10 GHz
up to 1 Hz
1–4 Hz
4 Hz–1 kHz
1–100 kHz
100 kHz–10 MHz
10 MHz–10 GHz

40
40/f
10
f/100
f/100
—
8
8/f
2
f/500
f/500
—

—
—
—
—
0.4
0.4
—
—
—
—
0.08
0.08

—
—
—
—
10
10
—
—
—
—
2
2

—
—
—
—
20
20
—
—
—
—
4
4

Note:
1. f is the frequency in hertz.
2. Because of electrical inhomogeneity of the body, current densities should be averaged over a cross-section of 1 cm2 perpendicular
to the current direction.
3. For frequencies up to 100 kHz, peak current density values can be obtained by multiplying the rms value by u2 (;1.414). For pulsesof duration tp the equivalent frequency to apply in the basic restrictions should be calculated as f 5 1/(2t p).
4. For frequencies up to 100 kHz and for pulsed magnetic fields, the maximum current density associated with the pulses can becalculated from the rise/fall times and the maximum rate of change of magnetic flux density. The induced current density can thenbe compared with the appropriate basic restriction.
5. All SAR values are to be averaged over any 6-min period.
6. Localized SAR averaging mass is any 10 g of contiguous tissue; the maximum SAR so obtained should be the value used for theestimation of exposure.
7. For pulses of duration t p the equivalent frequency to apply in the basic restrictions should be calculated as f 5 1/(2t p). Additionally,for pulsed exposures in the frequency range 0.3 to 10 GHz and for localized exposure of the head, in order to limit or avoid auditory
effects caused by thermoelastic expansion, an additional basic restriction is recommended. This is that the SA should not exceed
10 mJ kg21 for workers and 2mJ kg21 for the general public, averaged over 10 g tissue.

510

Health Physics

Table 5. Basic restrictions for power density for frequencies
between 10 and 300 GHz.a
Exposure characteristics

Power density (W m22)

Occupational exposure
General public

50
10

a
Note:
1. Power densities are to be averaged over any 20 cm2 of exposed area andany 68/f 1.05-min period (where f is in GHz) to compensate forprogressively shorter penetration depth as the frequency increases.
2. Spatial maximum power densities, averaged over 1 cm2, should notexceed 20 times the values above.

The simplifications that have been used to date did notaccount for phenomena such as the inhomogeneous distribution and anisotropy of the electrical conductivity andother tissue factors of importance for these calculations.
The frequency dependence of the reference fieldlevels is consistent with data on both biological effects
and coupling of the field.
Magnetic field models assume that the body has ahomogeneous and isotropic conductivity and apply simple circular conductive loop models to estimate induced
currents in different organs and body regions, e.g., thehead, by using the following equation for a pure sinusoidal field at frequency f derived from Faraday’s law of
induction:

J 5 p R f s B,

(4)

where B is the magnetic flux density and R is the radiusof the loop for induction of the current. More complex
models use an ellipsoidal model to represent the trunk or
the whole body for estimating induced current densities
at the surface of the body (Reilly 1989, 1992).
If, for simplicity, a homogeneous conductivity of
0.2 S m21 is assumed, a 50-Hz magnetic flux density of
100 m T generates current densities between
0.2 and 2 mA m22 in the peripheral area of the body
(CRP 1997). According to another analysis (NAS 1996),
60-Hz exposure levels of 100 mT correspond to average
current densities of 0.28 mA m22 and to maximum
current densities of approximately 2 mA m22. Morerealistic calculations based on anatomically and electrically refined models (Xi and Stuchly 1994) resulted in
maximum current densities exceeding 2 mA m22 for a
100-mT field at 60 Hz. However, the presence of biological cells affects the spatial pattern of induced currents
and fields, resulting in significant differences in bothmagnitude (a factor of 2 greater) and patterns of flow of
the induced current compared with those predicted bysimplified analyses (Stuchly and Xi 1994).
Electric field models must take into account the fact
that, depending on the exposure conditions and the size,
shape, and position of the exposed body in the field, thesurface charge density can vary greatly, resulting in avariable and non-uniform distribution of currents inside
the body. For sinusoidal electric fields at frequencies
below about 10 MHz, the magnitude of the induced
current density inside the body increases with frequency.

April 1998, Volume 74, Number 4

The induced current density distribution varies inverselywith the body cross-section and may be relatively high inthe neck and ankles. The exposure level of 5 kV m21 for
exposure of the general public corresponds, under worstcase conditions, to an induced current density of about 2
mA m22 in the neck and trunk of the body if the E-field
vector is parallel to the body axis (ILO 1994; CRP 1997).
However, the current density induced by 5 kV m21 willcomply with the basic restrictions under realistic worstcase exposure conditions.
For purposes of demonstrating compliance with thebasic restrictions, the reference levels for the electric andmagnetic fields should be considered separately and not
additively. This is because, for protection purposes, thecurrents induced by electric and magnetic fields are notadditive.
For the specific case of occupational exposures atfrequencies up to 100 kHz, the derived electric fields canbe increased by a factor of 2 under conditions in which
adverse indirect effects from contact with electricallycharged conductors can be excluded.
At frequencies above 10 MHz, the derived electricand magnetic field strengths were obtained from thewhole-body SAR basic restriction using computationaland experimental data. In the worst case, the energy
coupling reaches a maximum between 20 MHz andseveral hundred MHz. In this frequency range, thederived reference levels have minimum values. The
derived magnetic field strengths were calculated from theelectric field strengths by using the far-field relationshipbetween E and H (E/H 5 377 ohms). In the near-field,
the SAR frequency dependence curves are no longer
valid; moreover, the contributions of the electric andmagnetic field components have to be considered separately. For a conservative approximation, field exposurelevels can be used for near-field assessment since thecoupling of energy from the electric or magnetic field
contribution cannot exceed the SAR restrictions. For aless conservative assessment, basic restrictions on thewhole-body average and local SAR should be used.
Reference levels for exposure of the general public
have been obtained from those for occupational exposureby using various factors over the entire frequency range.
These factors have been chosen on the basis of effects
that are recognized as specific and relevant for thevarious frequency ranges. Generally speaking, the factors
follow the basic restrictions over the entire frequency
range, and their values correspond to the mathematical
relation between the quantities of the basic restrictions
and the derived levels as described below:● In the frequency range up to 1 kHz, the generalpublic reference levels for electric fields are
one-half of the values set for occupational exposure. The value of 10 kV m21 for a 50-Hz or 8.3
kV m21 for a 60-Hz occupational exposure includes a sufficient safety margin to prevent stimulation effects from contact currents under all
possible conditions. Half of this value was chosen for the general public reference levels, i.e.,Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields ● ICNIRP GUIDELINES

511

Table 6. Reference levels for occupational exposure to time-varying electric and magnetic fields (unperturbed rms
values).a
Frequency range

E-field strength(V m21)

H-field strength(A m21)

B-field(mT)

Equivalent plane wave
power density Seq (W m22)

up to 1 Hz
1–8 Hz
8–25 Hz0.025–0.82 kHz
0.82–65 kHz
0.065–1 MHz
1–10 MHz
10–400 MHz
400–2,000 MHz
2–300 GHz—
20,00020,000
500/f
610
610
610/f
61
3f 1/2137

1.63 3 105
1.63 3 105/f 2
2 3 104/f
20/f
24.4
1.6/f
1.6/f
0.16
0.008f 1/2
0.36

2 3 105
2 3 105/f 2
2.5 3 104/f
25/f
30.7
2.0/f
2.0/f
0.2
0.01f 1/2
0.45

—
—
—
—
—
—
—
10
f/40
50

a

Note:
1. f as indicated in the frequency range column.
2. Provided that basic restrictions are met and adverse indirect effects can be excluded, field strength values can be exceeded.
3. For frequencies between 100 kHz and 10 GHz, Seq, E2, H2, and B2 are to be averaged over any 6-min period.
4. For peak values at frequencies up to 100 kHz see Table 4, note 3.
5. For peak values at frequencies exceeding 100 kHz see Figs. 1 and 2. Between 100 kHz and 10 MHz, peak values for the fieldstrengths are obtained by interpolation from the 1.5-fold peak at 100 kHz to the 32-fold peak at 10 MHz. For frequencies exceeding
10 MHz it is suggested that the peak equivalent plane wave power density, as averaged over the pulse width, does not exceed 1,000
times the Seq restrictions, or that the field strength does not exceed 32 times the field strength exposure levels given in the table.
6. For frequencies exceeding 10 GHz, Seq, E2, H2, and B2 are to be averaged over any 68/f 1.05-min period (f in GHz).
7. No E-field value is provided for frequencies ,1 Hz, which are effectively static electric fields. Electric shock from low impedancesources is prevented by established electrical safety procedures for such equipment.

Table 7. Reference levels for general public exposure to time-varying electric and magnetic fields (unperturbed rms
values).a
Frequency range

E-field strength(V m21)

H-field strength(A m21)

B-field(mT)

Equivalent plane wave
power density Seq (W m22)

up to 1 Hz
1–8 Hz
8–25 Hz0.025–0.8 kHz
0.8–3 kHz
3–150 kHz
0.15–1 MHz
1–10 MHz
10–400 MHz
400–2,000 MHz
2–300 GHz—
10,00010,000
250/f
250/f
87
87
87/f 1/2
28
1.375f 1/2
61

3.2 3 104
3.2 3 104/f 2
4,000/f
4/f
5
50.73/f0.73/f0.073
0.0037f 1/2
0.16

4 3 104
4 3 104/f 2
5,000/f
5/f
6.25
6.25
0.92/f0.92/f0.092
0.0046f 1/2
0.20

—
—
—
—
—
—
—
—
2
f/200
10

a

Note:
1. f as indicated in the frequency range column.
2. Provided that basic restrictions are met and adverse indirect effects can be excluded, field strength values can be exceeded.
3. For frequencies between 100 kHz and 10 GHz, Seq, E2, H2, and B2 are to averaged over any 6-min period.
4. For peak values at frequencies up to 100 kHz see Table 4, note 3.
5. For peak values at frequencies exceeding 100 kHz see Figs. 1 and 2. Between 100 kHz and 10 MHz, peak values for the fieldstrengths are obtained by interpolation from the 1.5-fold peak at 100 kHz to the 32-fold peak at 10 MHz. For frequencies exceeding
10 MHz it is suggested that the peak equivalent plane wave power density, as averaged over the pulse width does not exceed 1,000
times the Seq restrictions, or that the field strength does not exceed 32 times the field strength exposure levels given in the table.
6. For frequencies exceeding 10 GHz, Seq, E2, H2, and B2 are to be averaged over any 68/f 1.05-min period (f in GHz).
7. No E-field value is provided for frequencies ,1 Hz, which are effectively static electric fields. perception of surface electric charges
will not occur at field strengths less than 25 kVm21. Spark discharges causing stress or annoyance should be avoided.

5 kV m21 for 50 Hz or 4.2 kV m21 for 60 Hz, toprevent adverse indirect effects for more than
90% of exposed individuals;● In the low-frequency range up to 100 kHz, thegeneral public reference levels for magnetic fields
are set at a factor of 5 below the values set for
occupational exposure;● In the frequency range 100 kHz–10 MHz, thegeneral public reference levels for magnetic
fields have been increased compared with thelimits given in the 1988 IRPA guideline. In thatguideline, the magnetic field strength reference
levels were calculated from the electric fieldstrength reference levels by using the far-field

512

Health Physics

April 1998, Volume 74, Number 4

Fig. 1. Reference levels for exposure to time varying electric fields (compare Tables 6 and 7).

Fig. 2. Reference levels for exposure to time varying magnetic fields (compare Tables 6 and 7).

formula relating E and H. These reference
levels are too conservative, since the magnetic
field at frequencies below 10 MHz does notcontribute significantly to the risk of shocks,
burns, or surface charge effects that form amajor basis for limiting occupational exposure
to electric fields in that frequency range;● In the high-frequency range 10 MHz–10 GHz, thegeneral public reference levels for electric andmagnetic fields are lower by a factor of 2.2 thanthose set for occupational exposure. The factor of
2.2 corresponds to the square root of 5, which isthe safety factor between the basic restrictions foroccupational exposure and those for general public

Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields ● ICNIRP GUIDELINES

exposure. The square root is used to relate thequantities “field strength” and “power density;”● In the high-frequency range 10 –300 GHz, thegeneral public reference levels are defined by thepower density, as in the basic restrictions, and arelower by a factor of 5 than the occupational
exposure restrictions;● Although little information is available on therelation between biological effects and peak values of pulsed fields, it is suggested that, forfrequencies exceeding 10 MHz, Seq as averaged
over the pulse width should not exceed 1,000
times the reference levels or that field strengths
should not exceed 32 times the field strengthreference levels given in Tables 6 and 7 or shownin Figs. 1 and 2. For frequencies between about
0.3 GHz and several GHz, and for localized
exposure of the head, in order to limit or avoid
auditory effects caused by thermoelastic expansion the specific absorption from pulses must
limited. In this frequency range, the threshold SAof 4 –16 mJ kg21 for producing this effect corresponds, for 30-ms pulses, to peak SAR values of
130 –520 W kg21 in the brain. Between 100 kHz
and 10 MHz, peak values for the field strengths in
Figs. 1 and 2 are obtained by interpolation fromthe 1.5-fold peak at 100 kHz to the 32-fold peakat 10 MHz.
● In Tables 6 and 7, as well as in Figs. 1 and 2,
different frequency break-points occur for occupational and general public derived reference
levels. This is a consequence of the varying
factors used to derive the general public reference
levels, while generally keeping the frequency
dependence the same for both occupational andgeneral public levels.

513

threshold contact currents that elicit biological responses
in children and adult women are approximately one-halfand two-thirds, respectively, of those for adult men, thereference levels for contact current for the general public
are set lower by a factor of 2 than the values foroccupational exposure.
For the frequency range 10 –110 MHz, reference
levels are provided for limb currents that are below thebasic restrictions on localized SAR (see Table 9).
SIMULTANEOUS EXPOSURE TO MULTIPLE
FREQUENCY FIELDS
It is important to determine whether, in situations ofsimultaneous exposure to fields of different frequencies,
these exposures are additive in their effects. Additivity
should be examined separately for the effects of thermaland electrical stimulation, and the basic restrictions
below should be met. The formulae below apply to
relevant frequencies under practical exposure situations.
For electrical stimulation, relevant for frequencies
up to 10 MHz, induced current densities should be added
according to

O JJ # 1.

10 MHzii51 Hz(5)

L, i

For thermal effects, relevant above 100 kHz, SAR
and power density values should be added according to:O

10 GHzO

300 GHz
SAR i
Si
1
# 1,
SAR L i.10 GHz S L
i5100 kHz

(6)

where
Ji 5 the current density induced at frequency i;
JL, i 5 the induced current density restriction at
frequency i as given in Table 4;
SARi 5 the SAR caused by exposure at frequency i;
SARL 5 the SAR limit given in Table 4;
SL 5 the power density limit given in Table 5;andSi 5 the power density at frequency i.

REFERENCE LEVELS FOR CONTACT AND
INDUCED CURRENTS
Up to 110 MHz, which includes the FM radiotransmission frequency band, reference levels for contact
current are given above which caution must be exercised
to avoid shock and burn hazards. The point contact
reference levels are presented in Table 8. Since theFor practical application of the basic restrictions, thefollowing criteria regarding reference levels of fieldstrengths should be applied.

Table 8. Reference levels for time varying contact currents fromconductive objects.a

Table 9. Reference levels for current induced in any limb at
frequencies between 10 and 110 MHz.a

Exposure characteristics

Frequency range

Maximum contact
current (mA)

Occupational exposure

up to 2.5 kHz
2.5–100 kHz
100 kHz–110 MHz
up to 2.5 kHz
2.5–100 kHz
100 kHz–110 MHz

1.0
0.4f
40
0.5
0.2f
20

General public exposureaf is the frequency in kHz.

a

Exposure characteristics

Current (mA)

Occupational exposure
General public

100
45

Note:
1. The public reference level is equal to the occupational reference level
divided by u5.
2. For compliance with the basic restriction on localized SAR, the squareroot of the time-averaged value of the square of the induced current overany 6-min period forms the basis of the reference levels.

514

Health Physics

For induced current density and electrical stimulation effects, relevant up to 10 MHz, the following two
requirements should be applied to the field levels:

O

O

1 MHz

For limb current and contact current, respectively,
the following requirements should be applied:

O S D

110 MHz

10 MHz

Ei
Ei
1
# 1,
E L, i i.1 MHz ai51 Hz(7)

O HH 1 O Hb # 1,

65 kHz10 MHzjL, j

j51 Hzj(8)j.65 kHz

where
Ei 5 the electric field strength at frequency i;
EL, i 5 the electric field reference level from Tables
6 and 7;
Hj 5 the magnetic field strength at frequency j;
HL, j 5 the magnetic field reference level from Tables 6 and 7;
a 5 610 V m21 for occupational exposure and
87 V m21 for general public exposure; andb 5 24.4 A m21 (30.7 mT) for occupational exposure and 5 A m21 (6.25 mT) for general public
exposure.
The constant values a and b are used above 1 MHz
for the electric field and above 65 kHz for the magnetic
field because the summation is based on induced current
densities and should not be mixed with thermal considerations. The latter forms the basis for EL,i and HL,j above 1
MHz and 65 kHz, respectively, found in Tables 6 and 7.
For thermal considerations, relevant above 100 kHz,the following two requirements should be applied to thefield levels:

O S D

OS

1 MHz

D

E i 2 300 GHz E i 21# 1,
c
E L, i
i5100 kHzi.1 MHz(9)O S Hd D 1 O S HH D # 1,

(10)

and
1 MHz

2

300 GHzj2

jj.1 MHzk510 MHz

Ik 2#1
I L, kO II # 1,

110 MHznn51 Hz

(11)

C, n

where

and

j5100 kHz

April 1998, Volume 74, Number 4

L, j

where
Ei 5 the electric field strength at frequency i;
EL, i 5 the electric field reference level from Tables
6 and 7;
Hj 5 the magnetic field strength at frequency j;
HL, i 5 the magnetic field reference level from Tables 6 and 7;
c 5 610/f V m21 (f in MHz) for occupational
exposure and 87/f 1/2 V m21 for generalpublic exposure; andd 5 1.6/f A m21 (f in MHz) for occupational
exposure and 0.73/f for general public exposure.

Ik 5 the limb current component at frequency k;
IL, k 5 the reference level of limb current (see Table
9);
In 5 the contact current component at frequency
n; andIC, n 5 the reference level of contact current at
frequency n (see Table 8).
The above summation formulae assume worst-caseconditions among the fields from the multiple sources.
As a result, typical exposure situations may in practicerequire less restrictive exposure levels than indicated by
the above formulae for the reference levels.
PROTECTIVE MEASURESICNIRP notes that the industries causing exposure
to electric and magnetic fields are responsible for ensuring compliance with all aspects of the guidelines.
Measures for the protection of workers include
engineering and administrative controls, personal protection programs, and medical surveillance (ILO 1994).
Appropriate protective measures must be implemented
when exposure in the workplace results in the basic
restrictions being exceeded. As a first step, engineering
controls should be undertaken wherever possible toreduce device emissions of fields to acceptable levels.
Such controls include good safety design and, where
necessary, the use of interlocks or similar health protection mechanisms.
Administrative controls, such as limitations on access and the use of audible and visible warnings, should
be used in conjunction with engineering controls. Personal protection measures, such as protective clothing,though useful in certain circumstances, should be regarded as a last resort to ensure the safety of the worker;
priority should be given to engineering and administrative controls wherever possible. Furthermore, when suchitems as insulated gloves are used to protect individuals
from high-frequency shock and burns, the basic restrictions must not be exceeded, since the insulation protects
only against indirect effects of the fields.
With the exception of protective clothing and otherpersonal protection, the same measures can be applied to
the general public whenever there is a possibility that thegeneral public reference levels might be exceeded. It isalso essential to establish and implement rules that will
prevent:● interference with medical electronic equipment

and devices (including cardiac pacemakers);

Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields ● ICNIRP GUIDELINES● detonation of electro-explosive devices (detona-tors); and● fires and explosions resulting from ignition of
flammable materials by sparks caused by induced
fields, contact currents, or spark discharges.
Acknowledgments—The support received by ICNIRP from the International Radiation Protection Association, the World Health Organization,
the United Nations Environment Programme, the International Labour
Office, the European Commission, and the German Government is gratefully acknowledged.

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APPENDIX
Glossary
Absorption. In radio wave propagation, attenuationof a radio wave due to dissipation of its energy, i.e.,
conversion of its energy into another form, such as heat.
Athermal effect. Any effect of electromagnetic
energy on a body that is not a heat-related effect.
Blood-brain barrier. A functional concept developed to explain why many substances that are transported by blood readily enter other tissues but do notenter the brain; the “barrier” functions as if it were acontinuous membrane lining the vasculature of the brain.
These brain capillary endothelial cells form a nearlycontinuous barrier to entry of substances into the brain
from the vasculature.
Conductance. The reciprocal of resistance. Expressed in siemens (S).
Conductivity, electrical. The scalar or vector quantity which, when multiplied by the electric field strength,yields the conduction current density; it is the reciprocalof resistivity. Expressed in siemens per meter (S m21).
Continuous wave. A wave whose successive oscillations are identical under steady-state conditions.
Current density. A vector of which the integral
over a given surface is equal to the current flowing
through the surface; the mean density in a linear conductor is equal to the current divided by the cross-sectional
area of the conductor. Expressed in ampere per square
meter (A m22).
Depth of penetration. For a plane wave electromagnetic field (EMF), incident on the boundary of agood conductor, depth of penetration of the wave is thedepth at which the field strength of the wave has been
reduced to 1/e, or to approximately 37% of its originalvalue.

Dielectric constant. See permittivity.
Dosimetry. Measurement, or determination by calculation, of internal electric field strength or induced
current density, of the specific energy absorption, or
specific energy absorption rate distribution, in humans or
animals exposed to electromagnetic fields.
Electric field strength. The force (E) on a stationary unit positive charge at a point in an electric field;
measured in volt per meter (V m21).
Electromagnetic energy. The energy stored in anelectromagnetic field. Expressed in joule (J).
ELF. Extremely low frequency; frequency below
300 Hz.
EMF. Electric, magnetic, and electromagnetic
fields.
Far field. The region where the distance from aradiating antenna exceeds the wavelength of the radiated
EMF; in the far-field, field components (E and H) and the
direction of propagation are mutually perpendicular, andthe shape of the field pattern is independent of the
distance from the source at which it is taken.
Frequency. The number of sinusoidal cycles completed by electromagnetic waves in 1 s; usually expressed in hertz (Hz).
Impedance, wave. The ratio of the complex number(vector) representing the transverse electric field at apoint to that representing the transverse magnetic field atthat point. Expressed in ohm (V).
Magnetic field strength. An axial vector quantity,
H, which, together with magnetic flux density, specifies
a magnetic field at any point in space, and is expressed inampere per meter (A m21).

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Magnetic flux density. A vector field quantity, B,that results in a force that acts on a moving charge or
charges, and is expressed in tesla (T).
Magnetic permeability. The scalar or vector quantity which, when multiplied by the magnetic fieldstrength, yields magnetic flux density; expressed in henry
per meter (H m21). Note: For isotropic media, magnetic
permeability is a scalar; for anisotropic media, it is atensor quantity.
Microwaves. Electromagnetic radiation of sufficiently short wavelength for which practical use can bemade of waveguide and associated cavity techniques in
its transmission and reception. Note: The term is taken to
signify radiations or fields having a frequency range of
300 MHz–300 GHz.
Near field. The region where the distance from aradiating antenna is less than the wavelength of theradiated EMF. Note: The magnetic field strength (multiplied by the impedance of space) and the electric fieldstrength are unequal and, at distances less than one-tenthof a wavelength from an antenna, vary inversely as thesquare or cube of the distance if the antenna is small
compared with this distance.
Non-ionizing radiation (NIR). Includes all radiations and fields of the electromagnetic spectrum that do
not normally have sufficient energy to produce ionizationin matter; characterized by energy per photon less thanabout 12 eV, wavelengths greater than 100 nm, andfrequencies lower than 3 3 1015 Hz.

April 1998, Volume 74, Number 4magnetic field strength (multiplied by the impedance of
space) and the electric field strength are equal.
Power density. In radio wave propagation, thepower crossing a unit area normal to the direction ofwave propagation; expressed in watt per square meter(W m22).
Public exposure. All exposure to EMF experienced
by members of the general public, excluding occupational exposure and exposure during medical procedures.
Radiofrequency (RF). Any frequency at whichelectromagnetic radiation is useful for telecommunication. Note: In this publication, radiofrequency refers to
the frequency range 300 Hz –300 GHz.
Resonance. The change in amplitude occurring as
the frequency of the wave approaches or coincides witha natural frequency of the medium; whole-body absorption of electromagnetic waves presents its highest value,i.e., the resonance, for frequencies (in MHz) corresponding approximately to 114/L, where L is the height of theindividual in meters.
Root mean square (rms). Certain electrical effects
are proportional to the square root of the mean of thesquare of a periodic function (over one period). Thisvalue is known as the effective, or root-mean-square(rms) value, since it is derived by first squaring thefunction, determining the mean value of the squares
obtained, and taking the square root of that mean value.

Occupational exposure. All exposure to EMF experienced by individuals in the course of performing
their work.

Specific energy absorption. The energy absorbed
per unit mass of biological tissue, (SA) expressed in joule
per kilogram (J kg21); specific energy absorption is thetime integral of specific energy absorption rate.

Permittivity. A constant defining the influence ofan isotropic medium on the forces of attraction or
repulsion between electrified bodies, and expressed in
farad per metre (F m21); relative permittivity is thepermittivity of a material or medium divided by thepermittivity of vacuum.

Specific energy absorption rate (SAR). The rate at
which energy is absorbed in body tissues, in watt per
kilogram (W kg21); SAR is the dosimetric measure thathas been widely adopted at frequencies above about 100kHz.

Plane wave. An electromagnetic wave in which theelectric and magnetic field vectors lie in a plane perpendicular to the direction of wave propagation, and the

Wavelength. The distance between two successive
points of a periodic wave in the direction of propagation,
at which the oscillation has the same phase.
f f

Note
Equation 11 in this publication (Health Physics, 1998) was subsequently amended by the ICNIRP
Commission in the 1999 reference book "Guidelines on Limiting Exposure to Non-Ionizing
Radiation", a reference book based on guidelines on limiting exposure to non-ionizing radiationand statements on special applications. R. Matthes, J.H. Bernhardt, A.F. McKinlay (eds.)
International Commission on Non-Ionizing Radiation Protection 1999, ISBN 3-9804789-6-3. The
amended version is available below.

“cçê= äáãÄ= ÅìêêÉåí= ~åÇ= Åçåí~Åí= ÅìêêÉåíI= êÉëéÉÅíáîÉäóI= íÜÉ= ÑçääçïáåÖ= êÉèìáêÉãÉåíë=ëÜçìäÇ=ÄÉ=~ééäáÉÇW==2

 Ik 
 1
  I L, k 

110 MHzk =10 MHz

2

10MHz

 I
I

n 1HznC,n1 In 
 1
  I C, n 

110 MHz(11)n=100 kHzïÜÉêÉ=
fâ=áë=íÜÉ=äáãÄ=ÅìêêÉåí=ÅçãéçåÉåí=~í=ÑêÉèìÉåÅó=â=
fiI=â=áë=íÜÉ=êÉÑÉêÉåÅÉ=äÉîÉä=çÑ=äáãÄ=ÅìêêÉåí=EëÉÉ=q~ÄäÉ=VF=
få=áë=íÜÉ=Åçåí~Åí=ÅìêêÉåí=ÅçãéçåÉåí=~í=ÑêÉèìÉåÅó=å=f`I=å=áë=íÜÉ=êÉÑÉêÉåÅÉ=äÉîÉä=çÑ=Åçåí~Åí=ÅìêêÉåí=~í=ÑêÉèìÉåÅó=å=EëÉÉ=q~ÄäÉ=UFK==
qÜÉ= ~ÄçîÉ= ëìãã~íáçå= Ñçêãìä~É= ~ëëìãÉ= ïçêëíJÅ~ëÉ= ÅçåÇáíáçåë= ~ãçåÖ= íÜÉ= ÑáÉäÇë=Ñêçã= íÜÉ= ãìäíáéäÉ= ëçìêÅÉëK= ^ë= ~= êÉëìäíI= íóéáÅ~ä= ÉñéçëìêÉ= ëáíì~íáçåë= ã~ó= áå= éê~ÅíáÅÉ=êÉèìáêÉ= äÉëë= êÉëíêáÅíáîÉ= ÉñéçëìêÉ= äÉîÉäë= íÜ~å= áåÇáÅ~íÉÇ= Äó= íÜÉ= ~ÄçîÉ= Ñçêãìä~É= Ñçê= íÜÉ=êÉÑÉêÉåÅÉ=äÉîÉäëKÒ=Ref: Excerpt 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. R. Matthes, J.H. Bernhardt, A.F. McKinlay (eds.) International
Commission on Non-Ionizing Radiation Protection 1999, ISBN 3-9804789-6-3.

ICNIRP GUIDELINES ON LIMITING EXPOSURE TO NON-IONIZING RADIATIONRESPONSE TO QUESTIONS AND COMMENTS ON THE
GUIDELINES FOR LIMITING EXPOSURE
TO TIME-VARYING ELECTRIC, MAGNETIC, AND
ELECTROMAGNETIC FIELDS (up to 300 GHz)*
Question: What dosimetric models were used by ICNIRP to derive thereference levels from the basic restrictions?
Answer: To a limited extent, the ICNIRP guidelines provide a description of thedosimetric models that were used, and give references to the primary literaturedescribing these models in detail. However, for purposes of brevity, ICNIRP
decided not to include a detailed discussion of these dosimetric models in its
published guidelines.

1)

Question: On which specific data are the guidelines for magnetic fields
at frequencies less than 4 Hz based?
Answer: The guidelines for magnetic fields below 4 Hz are ramped in a mannerthat joins the ELF reference levels with the values previously recommended by
ICNIRP for static fields, i.e., at 0 Hz (ICNIRP. Guidelines on limits of exposure
to static magnetic fields. Health Physics 66:100-106; 1994), and they are notbased on specific biological studies.
2)

Question: Why was 10 g chosen as the averaging mass without defininga regular tissue geometry?
Answer: The 10 g of tissue is intended to be a mass of contiguous tissue withnearly homogeneous electrical properties. In specifying a contiguous mass oftissue, ICNIRP recognizes that this concept can be used in computational
dosimetry, but may present difficulties for direct physical measurements. A
simple geometry such as a cubic tissue mass can be used provided that thecalculated dosimetric quantities have conservative values relative to the exposure
guidelines.

3)

Question: Is the 10 g averaging mass appropriate for the limbs of thebody?
Answer: ICNIRP recognizes that, under certain exposure conditions, thelocalized SAR basic restrictions for occupational and general public exposures
may be exceeded in the wrist by a small amount. However, this condition is not

4)*This response was published in Health Physics 75 (4), 438-439; 1998

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ICNIRP GUIDELINES ON LIMITING EXPOSURE TO NON-IONIZING RADIATION

considered to present any significant health risk.
Question: Would exposure to RF fields at the reference levels
recommended for workers or members of the general public lead to anincrease in body temperature?
Answer: Adherence to the ICNIRP guidelines under either occupational or public
exposure conditions would prevent an increase in temperature to levels that lie
outside of the normal range of variation associated with body functions.

5)

Question: Under certain circumstances, the fields emanating fromappliances and machine tools can exceed the ICNIRP reference levels.
Is there a problem with adhering to the ICNIRP guidelines under thesecircumstances?
Answer: ICNIRP recognizes that a number of common devices emit localized
fields in excess of the reference levels. However, this generally occurs underconditions of exposure where the basic restrictions are not exceeded because of
weak coupling between the field and the body.

6)

Question: What is the rationale for recommending a public exposure
guideline of 5 kV m-1 at 50 Hz and 4.17 at 60 Hz?
Answer: The reference levels for electric fields at power frequencies were set tolimit indirect effects of contact with electrical conductors in the field. Provided
that adverse health impacts of indirect effects of exposure (such as microshocks)
can be avoided, ICNIRP recognizes that the general public reference levels at
power frequencies can be exceeded provided that the basic restriction of 2 mA
m-2 is not surpassed. In many practical exposure situations external power
frequency electric fields at the reference levels will induce current densities incentral nervous tissues that are well below the basic restrictions. Recent
dosimetry calculations indicate that the reference levels for power-frequency
magnetic fields are conservative guidelines relative to meeting the basic
restrictions on current density for both public and occupational exposures(Dimbylow, P.J. Induced current densities from low-frequency magnetic fields
in a 2 mm resolution, anatomically realistic model of the body. Phys. Med. Biol.
43:221-230; 1998).
7)

Question: Why did ICNIRP not recommend guidelines for pulsed and/ortransient fields at low frequencies?
Answer: ICNIRP has provided frequency-dependent basic restrictions andreference levels from which a hazard assessment and exposure guidelines on
8)172

ICNIRP GUIDELINES ON LIMITING EXPOSURE TO NON-IONIZING RADIATIONICNIRP GUIDELINES ON LIMITING EXPOSURE TO NON-IONIZING RADIATION

pulsed and/or transient sources can be derived. A conservative approach involves
representing a pulsed or transient EMF signal as a Fourier spectrum of its
components in each frequency range, which can then be compared with the
ICNIRP reference levels for those frequencies. The summation formulae forsimultaneous exposure to multiple frequency fields given in the ICNIRP
guidelines can also be applied for purposes of determining compliance with the
ICNIRP basic restrictions.

300 GHz relative to the exposure limits at this frequency in the recently
published laser radiation guidelines. This difficulty will be addressed by ICNIRP
as more experimental evidence becomes available upon which to base a revisionof the guidelines at this frequency. It should be noted that, at the present time,
there are no sources of radiation at this frequency to which workers or membersof the general public are exposed.
Question: What is the basis for the added safety factors used for basic
restrictions and reference levels for the general public relative toworkers?
Answer: The safety factors used by ICNIRP are conservative, and were selected
for reasons given in the published guidelines (p. 508).

13)
Question: Why does ICNIRP not recommend higher basic restrictions orreference levels on exposure to ELF fields when exposures are of shortduration?
Answer: The basic restrictions for ELF fields are based on established adverse
effects on the central nervous system with a safety factor included. Such acuteeffects are essentially instantaneous, and it is ICNIRP's view that there is no
scientific justification to modify the basic restrictions for exposures of shortduration.

9)

Question: Is the basic restriction of 10 mA m-2 based only on thethreshold for acute effects in the central nervous system, or does it apply
to other tissues in the trunk of the body?
Answer: The basic restriction of 10 mA m-2 is intended to protect against acuteexposure effects on central nervous system tissues in the head and trunk of thebody, with a safety factor of 10. ICNIRP recognizes that this basic restriction
may permit higher current densities in body tissues other than the central nervous
system under the same exposure conditions.

10)

Question: Why are there no averaging times for induced and contact
currents at low frequencies?
Answer: ICNIRP has not included time averaging or limitations on the time of
exposure to fields at low frequencies because the known effects of induced andcontact currents at those frequencies are acute phenomena involving a rapid
response of the nervous system.

11)

Question: Does ICNIRP intend to modify its guidelines at 300 GHz toremove the discontinuity that occurs at this frequency between the EMF
guidelines and the recently published laser guidelines (ICNIRP.
Guidelines on limits of exposure to laser radiation of wavelengths
between 180 nm and 1,000: m, Health Physics 71:804-819; 1997)?
Answer: ICNIRP recognizes that a discontinuity exists in the EMF guidelines at

12)

173

Question: Are there scientific data indicating a variation in sensitivity
to EMF among individual workers or members of the general public?
Answer: ICNIRP is aware of scientific data on variations among individuals inelectrical and thermal sensitivity, and in accord with conventional healthprotection principles, has applied safety factors that encompass a possible range
of individual sensitivities to EMF.

14)

Question: It is not clear how the EMF guidelines should be applied to
exposure of the fetus, especially when the mother is at work. Would themother be subject to the general public exposure guidelines, and incertain cases, have to cease work during pregnancy as a result?
Answer: ICNIRP recognizes that exposure of the fetus and pregnant mother may
require evaluation on a case-by-case basis. Exposure of the fetus and pregnant
mother is an issue that should be dealt with on the basis of either national policy
or administrative rules established by individual employers.

15)

Question: For devices utilized in both occupational and public settings,
how is the user of the ICNIRP guidelines to decide which set of basic
restrictions apply?
Answer: This decision is to be made on the basis of administrative policies
established by the specific organization using the ICNIRP guidelines.

16)

Question: Are farm workers in fields under powerlines expected toadhere to occupational or general public exposure guidelines?
Answer: ICNIRP recognizes that differences exist in national policies on
occupational versus public exposures under this (and similar) conditions. In its

17)

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ICNIRP GUIDELINES ON LIMITING EXPOSURE TO NON-IONIZING RADIATION

guidelines ICNIRP has defined occupational and public exposures in generalterms. However, for exposure situations such as the above, it is ICNIRP`sopinion that authorities in each country should decide on whether occupationalor general public guidelines are to be applied in accord with existing policies.

175

USE OF THE ICNIRP EMF GUIDELINESUSE OF THE ICNIRP EMF GUIDELINESUSE OF THE ICNIRP EMF GUIDELINES *from both epidemiological and experimental studies, as well as the plausibility
that biological systems exposed to EMF fields could likely manifest biologicaleffects. It is also necessary to identify which EMF-induced biological effects areto be considered a hazard to human health.

Introduction and Purpose
Since the publication of the ICNIRP guidelines for limiting EMF
exposure up to 300 GHz (ICNIRP 1998a) (see page 101) several institutions havecriticized the guidelines as lacking clear interpretation on exposure safety or
direct application to equipment in existence. Concerns have also been expressed
about the use of safety factors, precautionary aspects and long term exposure aswell as points not included in the ICNIRP guidelines. This statement From
ICNIRP addresses these concerns and clarifies points such as the criteria used forevaluating scientific studies, the development and practical application of theguidelines, the need for special technical advice, how to consider social andeconomic aspects and how to handle current research. This statement clarifies theway in which the guidelines should be used in a regulatory and legislative
context. Some questions have already been addressed by publications in Health
Physics (ICNIRP 1998b) (see page 166)
Quality Criteria for evaluating scientific studies
Development of guidelines on exposure limits requires a critical, in depth
evaluation of the established scientific literature using internationally accepted
quality criteria. Experimental results can only be accepted for health risk
assessment if a complete description of the experimental technique and dosimetry
are provided, all data are fully analysed and completely objective, results showa high level of statistical significance, are quantifiable and susceptible toindependent confirmation, and the same effects can be reproduced byindependent laboratories (Repacholi and Cardis 1997). When evaluating
epidemiological studies, quality criteria are based on the need to evaluate, reduceor adjust for the influence of chance, bias and confounding. Cases of disease
should be assessed in a way not related to disease status. The influence of othervariables should be handled in the design or in the analysis of the study. Any dataon which the conclusions are based should be reported (IARC 1995). The final
overall evaluation of the evidence should include the assessment of the strengthand consistency of the association between EMF exposure and biological effects*

International Commission on Non-Ionizing Radiation Protection (1999). Use of the ICNIRPEMF guidelines, http://www.icnirp.de

293

The role of ICNIRPInternational recommendations on health-based guidance to limit
exposure requires an assessment of possible adverse health effects using
established scientific and medical knowledge. This must be based mainly on thescience and should be free of vested interest. ICNIRP, as an independentscientific body comprising all essential scientific disciplines, is qualified to carryout the task of assessing possible adverse health effects, together with WHO.
ICNIRP is the formally recognized non-governmental organization in NIR
protection for the WHO, the International Labour Organization (ILO), and theEuropean Union (EU) and maintains a close liaison and working relationshipwith these international bodies as well as IEC and CIE for the optical region andwith other bodies engaged in NIR protection. ICNIRP's review process includes
Standing Committees and additional experts. The consultation process is
extensive and includes IRPA national bodies and other independent scientists andorganisations world wide. ICNIRP works in conjunction with the WHO to assess
health effects of exposure to NIR, which are published in the WHO
Environmental Health Criteria monographs, and uses the results of thisassessment to draft health-based exposure guidelines.
Developing of exposure guidelines
Recently ICNIRP adopted guidelines on limits of EMF exposure forfrequencies up to 300 GHz (ICNIRP 1998a) (see page 101). While all thescientific literature was reviewed, the only adverse effects on humans that were
fully verified by a stringent evaluation were short term, immediate healthconsequences such as stimulation of peripheral nerves and muscles, functionalchanges in the nervous system and other tissues, shocks and burns caused bytouching conducting objects, and changes in behaviour caused by elevated tissue
temperatures. There are also data for chronic low level exposure that indicate that
there may also be other health effects. It is, however, ICNIRP's view that in theabsence of support from laboratory studies the epidemiological data are
insufficient to allow an exposure guideline to be established.
Limiting values are given as basic restrictions and reference levels. Basic
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USE OF THE ICNIRP EMF GUIDELINES

restrictions directly relate to established health effects. Appropriate safety factors
are included. Reference levels are derived from the basic restrictions for worstcase exposure situations and are in quantities that can be easily measured. They
provide levels that can be used to determine compliance with the basic
restrictions. By using the system of basic restrictions and derived reference
levels, the new ICNIRP guidelines offer flexibility for many exposure situations.
The use of safety factors
It is ICNIRP' s view that safety factors in the ICNIRP EMF guidelines
should relate to the precision of science, reflecting the amount of establishedinformation on biological and health effects of EMF exposure. Numericallyuncertain relationships between established effects and exposure levels resultsin higher safety factors and vice versa. As with the assessment of adverse healtheffects, setting safety factors should be free from vested interests. There is no
rigorous basis for determining precise safety factors. Safety factors are based ona conservative value judgement by experts. In the new ICNIRP guidelines thesafety factors vary from approximately 2 to >10 (see next section) depending
upon the extent of uncertainty in knowledge of thresholds for health effects for
direct and indirect field interaction at various frequencies. For the purpose ofdefining guidelines for protection, a simplified and conservative approximationof the frequency dependence of biological effects was chosen. In general,
threshold field levels for indirect effects (e.g., response to contact currents) are
better defined than for direct effects, and hence less conservative safety factors
are required.
Public guidelines include additional safety factors of 2 to 5 relative tooccupational guidelines (depending upon the frequency and the relevant
dosimetric parameters). Occupational health standards are aimed at protecting
healthy adults exposed as a necessary part of their work, who are aware of theoccupational risk and who are likely to be subject to medical surveillance.
General population guidelines must be based on broader considerations,
including health status, special sensitivities, possible effects on the course ofvarious diseases, as well as limitations in adaptation to environmental conditions
and responses to any kind of stress in old age. In most cases these considerations
will have been insufficiently explored, so guidelines for the general populationmust involve adequate safety factors.
Special concern about safety factors for the ELF basic restrictions

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USE OF THE ICNIRP EMF GUIDELINES

Basic restrictions for the ELF range roughly follow the frequency
dependence of thresholds of peripheral nerve and muscle tissue stimulation.
These are well known between several Hz and about 100 kHz. Field-induced
current densities that are unable to stimulate excitable tissues directly may
nevertheless affect tissue electrical activity and influence neuronalcommunication. It has been suggested that time-varying peri-cellular electricfields of 10-100 mV m-1 (about 2-20 mA m-2 , which can be induced by power
frequency optimally oriented magnetic fields above 100-1000 : T at a few
locations in the body) can affect biological signals. Furthermore, the electricalinhomogeneity of living tissue can enhance electric field intensities, and hence
induce higher currents at some points in the body. However, there is a lack of
microscopic dosimetric data.
Within a limited frequency range, between about 15 and 60 Hz, thesafety factor between the basic restriction of 10 mA m-2 and the threshold ofsome nervous system effects (i.e., magnetophosphenes or visual evoked
potentials) are even lower (safety factors between 2 and 5). While there are somebiological effects that have been reported from cellular and animal studies (seep. 115), there is no clear evidence that these biological interactions fromexposure to low frequency fields lead to adverse health effects. However, theseverity and the probability of irreversibility of tissue effects becomes greaterwith chronic exposure to induced current densities above 10 to 100 mA m-2.
Thus, summarizing the evidence for health effects for current densities greaterthan 10 mA m-2 , ICNIRP decided to limit human exposure to fields that induce
current densities not greater than 10 mA m -2 in the head, neck, and trunk at
frequencies of a few hertz up to 1 kHz. As a consequence, the safety factor
around 1 kHz may be unnecessarily conservative, but this is the result of
insufficient knowledge, and ICNIRP will reconsider this as soon as morescientific data are available.
With regard to severe and potentially life-threatening effects such as
cardiac extrasystoles, ventricular fibrillation, muscular tetanus, and respiratory
failure, the safety factor between these effects and the basic restriction is about
100 or greater. This is the same order of magnitude as safety margins limiting
exposure to dangerous toxicologic substances.
Practical application of the guidelines
Reference levels are provided for practical exposure assessment
purposes, to determine whether the basic restrictions are likely to be exceeded.
The reference levels are derived from the basic restrictions by mathematical
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USE OF THE ICNIRP EMF GUIDELINES

modelling and extrapolation from the results of laboratory investigations at
specific frequencies. They apply for maximum coupling conditions of the field
to the exposed person, thereby providing maximum protection. Restrictions aredifferent for workers and the general public. The frequency dependence of thereference field levels is consistent with data on both biological effects andcoupling of the fields. ICNIRP recommends the use of the reference levels as
general guidance for EMF limits for workers and the general public.
Safety factors and reference levels for ELF fields
There is special concern about the ICNIRP reference levels for magnetic
fields below several MHz which are low, relative to some other guidelines orstandards. Since one of the objectives of the new ICNIRP guidelines is to avoid
stimulation of peripheral nerves and muscles, it is reasonable to use models
describing worst-case coupling. An ellipsoidal model for magnetic fields, torepresent the trunk for estimating induced current densities will produce
approximate results. There is evidence, however, that a small fraction of suchconductive loop currents run through areas of the central nervous system.
There exist several investigations, resulting in current densities of
10 mA m-2 in peripheral areas of the body for a 500-: T field at power frequencies(see p. 115). These come from microdosimetric predictions, including
conductivities of sub-cellular organelles, the presence of biological cells andinter-cellular junctional arrangements. These may result in significant differencesin the patterns of flow of induced currents compared to those predicted bysimplified analysis. In summarizing the available dosimetric data it is ICNIRP'sview that the dosimetric models used for magnetic field coupling are defensible.
Need for technical standards
ICNIRP recognizes that the reference levels are given for the conditionof maximum coupling of the field to the exposed individual, thereby providing
maximum protection. However, when reference levels are exceeded this does notnecessarily mean that the basic restrictions will be exceeded. These need to be
determined by further investigations which may cause difficulties in some special
exposure situations.
Near-field exposure situations, localized and non-uniform field exposure
are of special interest. Examples of typical EM sources with near-field exposure
are hand-held mobile telephones, inductive or capacitive heating equipment, antitheft devices or electric appliances in homes and workplaces. Such devices can297

USE OF THE ICNIRP EMF GUIDELINES

emit localized fields in excess of the reference levels. In such situations, while
the reference levels may be exceeded, there may be compliance with the basic
restrictions due to the weak coupling of the field with the human body.
ICNIRP recognizes the need for technical advice on the translation of
biologically justified restrictions on human exposure into practical exposure
limitations for such special exposure situations. This requires physics andengineering expertise to develop practical measures that lead to compliance withthese guidelines. This includes guidance on the principles and practice ofmeasurements, design of equipment and/or shielding to reduce exposure. For
these reasons the ICNIRP EMF guidelines do not address product performancestandards or guidance concerning computational methods or measuring
techniques.
The organizations best qualified to carry out such tasks are theinternational, national and regional technical standardization organizations.
These include the International Electrotechnical Commission (IEC), theInternational Standards Organization (ISO), the International Commission on
Illumination (CIE), the Institute of Electric and Electronics Engineers Standards
Committee (IEEE) and the European Committee on ElectrotechnicalStandardisation (CENELEC).
ICNIRP considers that international bodies for technical standardization(e.g., IEC, CENELEC) should develop product standards for special types ofdevices to determine compliance with the basic restrictions.
Assessment of social and economic impact of compliance
Assessment of adverse health effects of EMF exposure and ICNIRP's
health-based guidance limiting EMF exposure are based on established scientific
data and are free of vested interest. They do not take into account political, socialand economic considerations. It is ICNIRP's view that political, social andeconomic considerations of higher or lower margins of safety in the exposure
limits is the responsibility of national authorities.
How to handle current research?
Development of EMF standards is an ongoing process. WHO's
International EMF Project includes encouragement of focussed, high quality
research and incorporation of research results into WHO 's Environmental HealthCriteria monographs where formal health risk assessments will be made of EMF
exposure. ICNIRP as the scientific arm of WHO 's NIR activities will use the298

USE OF THE ICNIRP EMF GUIDELINES

results of these assessments together with assessments carried out by its own
Scientific Committees to revise the present health based exposure guidelines.
REFERENCES
International Commission on Non-Ionizing Radiation Protection, Guidelines forlimiting exposure in time-varying electric, magnetic, andelectromagnetic fields (up to 300 GHz). Health Phys. 74, 494-522; 1998.
International Commission on Non-Ionizing Protection, Response to questions
and comments on ICNIRP Guidelines. Health Phys. 75, 438-439; 1998
Repacholi, M. H. and Cardis, E., Criteria for EMF health risk assessment. Radiat.
Prot. Dosim. 72, 305 - 312; 1997.
IARC: Monographs on the Evaluation of Carcinogenic Risks of Humans:
Preamble. Lyon: International Agency of Research of Cancer; 1995.

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300