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COMAR Technical Information Statement the IEEE exposure limits for radiofrequency andmicrowave energy

Marvin C. Ziskin

IEEE ENGINEERING IN MEDICINE AND BIOLOGY MAGAZINE MARCH/APRIL 2005

COMAR Reports

IntroductionExcessive exposure to radiofrequency(RF) or microwave energy producedby radio transmitters, some industrialequipment, and other sources can behazardous. For this reason, the IEEEhas developed limits for human expo-sure to RF energy, and these limitshave been widely influential aroundthe world.

The IEEE standard represents a con-sensus of scientific opinion about safelevels of exposure to RF energy, and itsscientific rationale is consistent withconclusions of numerous expert groupsand health agencies throughout theworld. Nevertheless, laypeople oftenhave questions about the adequacy ofthe standard or the process by which itwas developed. This TechnicalInformation Statement discusses thedevelopment and rationale for exposurelimits for RF energy.

The present focus is on the processthat led to the IEEE C95.1 standard[1] covering the frequency range 3 kHz–300 GHz, which includes theradiofrequency part of the spectrum.Other major exposure limits, in par-ticular the widely-referenced guide-lines of the International Commissionon Nonionizing Radiation Protection(ICNIRP) [2] have a similar rationalebut were developed using differentprocesses.

History of IEEE ExposureLimits for RF EnergyThe origin of the IEEE C95.1 standardtraces back to 1960 when the AmericanStandards Association (now ANSI, aclearing house for standards of all sorts)approved the Radiation HazardsStandards Project C95 and established acommittee charged with developing RFexposure standards [3]. The first C95standard, USASI C95.1-1966, was pub-lished in 1966, and major revisions

were published in 1974 and 1982. In1989, the IEEE assumed sponsorship ofthe committee, which became IEEEStandards Coordinating Committee 28(SCC-28). In 2001 SCC-28 adopted thename IEEE International Committee onElectromagnetic Safety (ICES).

Under both IEEE and ANSI bylaws,standards (of all sorts) must be periodi-cally updated and revised. The lateststandard, IEEE C95.1-1991 wasapproved by the IEEE Standards Boardin 1991 and by ANSI in 1992. Thisstandard was reaffirmed in 1997 and asupplement published in 1999. It ispresently undergoing another round ofrevision, with publication of the revisedstandard anticipated in 2004.

Thus, the present IEEE exposureguidelines have a lineage that extendsback for nearly half a century. Whilethe C95.1 standards are voluntary, theyhave had a major influence on govern-ment policy in the United States and inthe development of exposure limits inmany places around the world.

Scientific Basis ofIEEE/ANSI (ICES) Standard When considering possible hazards ofRF energy, it is important to distinguishbetween levels of fields outside thebody (the exposure), and field levels orabsorbed energy within body tissues(the dose). The exposure is measured interms of the electric or magnetic fieldstrength, or power density incident onthe body. The dose depends on theexposure, as well as on body geometry,size, its orientation with respect to theexternal field, and other factors.

Between approximately 100 kHz and10 GHz, the specific absorption rate(SAR) is the dosimetric quantity thatcorrelates best with reported biologicaleffects of RF energy. The whole-body-averaged SAR is the total powerabsorbed by the animal or human (in

watts) divided by the body mass (kilograms), and is expressed in units ofW/kg. The whole-body SAR is comput-ed or measured experimentally, fre-quently using “phantom” models whoseelectrical characteristics are similar tothose of tissue.

For localized exposures to parts ofthe body, for example the head of theuser of a mobile phone, a more usefulmeasure is often the partial body expo-sure, which is the power absorbed perunit mass in a localized region of tissue,also expressed in W/kg.

At frequencies below about 100 kHz,a more useful measure of dose is oftenthe electric field strength in tissue, inunits of volts per meter.

The IEEE standard is based on a limitto the SAR (called a basic restriction)set on the basis of biological data. Inaddition, it defines limits to the expo-sure, as measured by field strength out-side the body, which will ensure thatthe absorbed power within the bodymeets the basic restriction, which wereset on the basis of engineering studies.The ICNIRP guidelines are similar,both in their use of a basic restrictionand exposure limits, and in the numeri-cal values of the limits.

As with exposure limits to manypotentially hazardous substances,radiofrequency safety standards in mostcountries have two tiers, which vary indefinition but correspond approximatelyto limits for occupational groups andthe general public. For a number of rea-sons, exposure limits for many agentsare higher for occupational groups ascompared to the general public.

In the IEEE standard, two tiers aredefined as applying to exposures incontrolled and uncontrolled environ-ments. In a controlled environment, theexposure is limited to individuals whoare aware of the possibility of expo-sure. Uncontrolled environments are

IEEE ENGINEERING IN MEDICINE AND BIOLOGY MAGAZINE MARCH/APRIL 2005 115

accessible to individuals who may nothave this awareness, including the gen-eral public, which may limit their abili-ty to respond appropriately if they enterareas with excessive exposure. For thatreason, the standard provides lowerexposure limits in uncontrolled areas.

Identification of HazardThe IEEE C95.1-1991 standard wasbased on a comprehensive review ofthe scientific literature, covering allreliable studies that reported biologicaleffects of RF/microwave energy. Thistask, and the development of a draftstandard, was accomplished by a 125member subcommittee (Subcommittee 4)of IEEE Standards CoordinatingCommittee 28 (Table 1).

The scientific literature related tobiological effects of RF energy ishighly diverse, both in terms of sci-entific quality and in terms of rele-vance to possible health and safetyrisks to humans. Consequently, thereview process examined only studiesthat met selection criteria that includ-ed adequate dosimetry and experi-mental design, and independentconfirmation of reported effects.Studies that were not published in thepeer reviewed scientific literature,and those that were inadequatelydescribed to permit critical analysis,were excluded from consideration.

Based on its review, the subcommit-tee concluded that disruption of food-motivated learned behavior in labora-tory animals is the most sensitive bio-logical response that is both well con-firmed and predictive of hazard. Thiseffect, known as behavioral disruption,has been observed in laboratory ani-mals ranging from rodents to monkeysexposed to RF fields at frequenciesranging from 225 MHz to 5.8 GHz.Depending on the animal species andRF frequency, the exposure needed toproduce behavioral disruption variedwidely, from about 100 to 1400W/m2 . However, the whole-bodySAR in the animals varied over asmaller range, from 3.2 to 8 W/kg.The threshold for behavioral disrup-tion has been associated with an

increase in body temperature of theanimals of about 18 ◦C.

Setting Basic Restriction andExposure LimitsFrom its literature review, the subcom-mittee chose a value of 4 W/kg for thewhole-body-averaged SAR as thethreshold for behavioral disruption inanimals. It reduced this SAR by a fac-tor of 10 to establish the basic restric-tion for exposure in controlled

environments, and then added anotherfactor of 5 for exposure in uncontrolledenvironments. The resulting basicrestrictions on whole body SAR are 0.4W/kg for controlled environments, and0.08 W/kg for uncontrolled environ-ments. The basic restrictions are, as aresult, a factor of 10 to 50 belowwhole-body exposure levels shown toproduce behavioral disruption in ani-mals in exposures ranging from severalminutes to several hours in duration.

Table 1(a). Affiliations of the 125 members of Subcommittee 4 of IEEE Standards Coordinating Committee 28 at the time the 1991 standardwas approved. This Subcommittee drafted the standard.

Affiliation Number Percentage

Research University: 37 29.6

Nonprofit 8 6.4

Military 15 12.0

Government (FDA, EPA, etc.) 30 24.0

Industry 12 9.6

Industry—consulting 4 3.2

Government—administration 5 4.0

General public and independent 14 11.2consultants

Total 125 100.0

Table 1(b). The principal disciplines of the 125 members of Subcommittee 4 of IEEE Standards Coordinating Committee 28 at the time the 1991 C95.1 stan-dard was approved.

Principal Discipline Number Percentage

Physical sciences (physics, 41 32.8biophysics, engineering, etc.)

Life sciences (biology, 54 43.2genetics, etc.)

Medicine (physicians) 12 9.6

Radiology, pharmacology, 4 3.2toxicology

Others (law, medical 14 11.2history, safety, etc.)

Total 125 100.0

116 IEEE ENGINEERING IN MEDICINE AND BIOLOGY MAGAZINE MARCH/APRIL 2005

COMAR Reports (continued)

Based on engineering analysis, thecommittee then established limits to theexternal field (exposure) that wouldensure that the basic restrictions aremet. Because the absorption propertiesof the body depend on frequency, theresulting exposure limits do also. Otherlimits were developed for partial bodyexposure and for fields of unusual char-acteristics, such as very short pulses ofvery high intensity.

Also based on engineering considera-tions, the subcommittee established lim-its to partial body exposure. This wasbased on observations that the maxi-mum SAR in any part of the body isapproximately 20 times higher than thewhole-body average SAR under manyexposure conditions. Consequently, thesubcommittee (Subcommittee 4 of IEEEStandards Coordinating Committee 28)established a limit of 8 W/kg for partialbody exposure for controlled environ-ments, and 1.6 W/kg for uncontrolledenvironments. These exposures are to beaveraged over small volumes (corre-sponding to 1 gram) of tissue.

Approval of StandardThe draft 1991 IEEE standard under-went a long and rigorous processbefore being finally approved byIEEE. The first stage in this processwas balloting at the level ofSubcommittee 4. Consistent with IEEEprocedure, the voting was done in sev-eral stages. After each preliminaryround of balloting, all negative votesand comments were circulated to thesubcommittee, and members who hadoriginally submitted ballots weregiven the opportunity to comment orreaffirm or change their votes; finalapproval required 75% affirmativevotes of those submitting ballots.After being approved by Sub-committee 4, the draft standard wasmoved to the main committee (SCC-28) for approval using the same ballot-ing process, and then to the IEEEStandards Board for final approval.The final approved IEEE standard wasthen forwarded to the AmericanNational Standard Institute (ANSI)which required a period of public com-

ment and response by the originalIEEE standards committee. In 1992,ANSI adopted the standard as anAmerican National Standard.

Presently the standard is undergoingyet another revision, which is expectedto be completed in 2004. Workinggroups of Subcommittee 4 are evaluat-ing approximately 1300 scientificpapers related to biological effects ofRF fields. These were selected from thepeer-reviewed scientific literature, withinputs from federal agencies and otherorganizations. Another working groupis evaluating the literature to determinea threshold SAR for which potentiallydeleterious effects are likely to occur inhuman beings. As part of this review, anumber of “white papers” have beenprepared that review the extant litera-ture relevant to specific topic areas.Many of these papers will be publishedin a special issue of the journalBioelectromagnetics [4]. As with earli-er versions of the standard, an exten-sive approval process is required,which is designed to provide trans-parency and documentation of theprocess at every level [5, 6].

Concerns RaisedAbout the IEEE StandardSome laypeople have expressed con-cern about the adequacy of the standardor of the process by which it was devel-oped. Some of these concerns areaddressed below.

Concern 1. The IEEE standardssetting process for RF energy iscaptive of industry and representsonly industry viewpoints. The IEEE exposure limits are devel-oped through an open process, whichhelps to ensure a level of transparencyand documentation that is unique inRF exposure limits. The proceduresused by the IEEE Standards Assoc-iation Standards Board, which governICES, are explained in [5], and the par-ticular procedures used by ICES aredescribed in [6].

To illustrate the diversity of partici-pants in the IEEE standards develop-ment process, the 1991 standard was

drafted by a 125-member subcommitteeof the main committee, whose memberswere broadly distributed as to their placeof employment and specialty (Table 1).

This committee represented a verybroad range of expertise, including physi-cians, basic scientists, and engineers.Only a minority of its members werefrom industry; the largest group of mem-bers was from academia. The ICES com-mittee that is developing the latestrevision of the standard has a similarbroad representation as shown in Table2(a) and (b).

Concern 2. The standard ignoreseffects of long term exposureand “nonthermal” effects.The IEEE and other RF/microwaveexposure limits standards are based prin-cipally on laboratory studies of animalsusing short exposure durations (hours atmost). The limiting effect for wholebody exposures (behavioral disruption)is clearly a thermal phenomenon.

Some investigators have reportedeffects at much lower exposure levels,which are sometimes called “non-thermal” effects. Each version of theIEEE standard has acknowledged theexistence of such reports, while at thesame time indicating that they wereinsufficient to be considered a healthhazard or to be used as a basis to devel-op exposure guidelines. For example,the 1991 standard states that “researchon the effects of chronic exposure andspeculations on the biological signifi-cance of nonthermal interactions havenot yet resulted in any meaningful basisfor alteration of the standard. It remainsto be seen what future research mayproduce for consideration at the time ofthe next revision of this standard”.Other organizations have independentlyreached this same conclusion.

In summary, the IEEE and otherexposure limits are designed to protectagainst identified hazards of RF energy.During each revision of the standard,ICES and earlier committees failed tofind credible evidence of cumulativeeffects due to chronic exposure, includ-ing cancer, or other hazardous effectsfrom low-level exposure.

IEEE ENGINEERING IN MEDICINE AND BIOLOGY MAGAZINE MARCH/APRIL 2005 117

This judgment, while based on alarge body of research that extendsback to the 1950s and before, is alwaysopen to reevaluation in future revisionsof the standard. Other refinements inthe standard are being considered in thepresent revision cycle of the IEEE stan-dard. For example, discussion contin-ues over improving the internalconsistency of the standard and elabo-rating on the use of safety factors inderiving exposure limits.

Concern 3. Other countries havelower limits than the IEEE/ANSIstandards, and offer higherprotection to their citizens.The exposure limits for RF energy varywidely in different countries. However,the guidelines of the great majority ofcountries are similar to those of IEEE orthe closely similar guidelines ofICNIRP. A few countries have chosenmuch lower limits, in part due to differ-ences in philosophy in setting limits.IEEE and most other Western exposurelimits are designed on the basis of iden-tified thresholds for hazards of RFfields and thus are science-based. Thephilosophy behind other exposure limitsis very different [7].

For example, Switzerland, Italy, anda few other countries have adopted“precautionary” exposure limits for RFenergy. These are not based on identi-fied hazards, but reflect the desire to setexposure limits as low as economicallyand technically practical, to guardagainst the possibility of an as-yet-unidentified hazard of RF exposure atlow levels.

A quite different situation exists withRF exposure limits of Russia, otherstates from the former Soviet Union(FSU), and several Eastern Europeancountries, which have long been muchlower than those of the United Statesand Western Europe. This situation hasexisted since the 1960s or before, andhas long been a source of public contro-versy in the West. The scientific basisfor the Russian limits is not clearly stated in their guidelines, and the origi-nal research by scientists in the FSU hasbeen difficult to evaluate in detail by

Western scientists. While these limitsappear to reflect a conviction on thepart of FSU scientists that low expo-sures to RF energy produces healtheffects, Western health agencies havebeen uniformly unable to identify anyhealth hazard at exposure levels belowIEEE or ICNIRP exposure guidelines.

For both philosophical and practicalreasons, it is desirable to “harmonize”exposure limits around the world. Thisis the goal of a project begun in 1998 bythe EMF Project of the World HealthOrganization, which was motivated inpart by the desire to bring similar levelsof health protection to different popula-tions around the world [8]. Commercialconsiderations, related to the increasingglobalization of trade, will also encour-age countries to adopt uniform expo-sure limits for RF energy in the future.

COMAR believes that science-based guidelines, such as those of

IEEE or the generally similar guide-lines of ICNIRP, offer a high level ofprotection against all identified haz-ards of RF energy and should serve asmodels throughout the world. Thestandards are living documents andwill be revised as more scientific databecome available.

AcknowledgmentsThis statement was prepared by mem-bers of the subcommittee on exposurestandards of COMAR: J. Cohen, L.Erdreich, K.R. Foster, J. Osepchuk, R.Petersen (Chair), R. Tell, and M.C.Ziskin. It has been reviewed by themembers of COMAR, all of whomhave expertise in the general area of theinteractions of electromagnetic fieldswith humans. This final report wasapproved by vote of the full COMAR

Table 2(a). Affiliations of the 128 members of the current Subcommittee 4 of ICES.

Category Number Percentage

Academic 33 25.8

Consultant 28 21.9

Government 42 32.8

Industry 21 16.4

General Public 2 1.6

Other 2 1.6

Total 128 100.0

Table 2(b). Principle Disciplines of the 128 members of the current Subcommittee 4 of ICES.

Principle Discipline Number Percentage

Physical sciences (physics, 69 53.9biophysics, engineering, etc)

Life sciences (biology, 48 37.5medicine, genetics, etc)

Others (law, medical 11 8.6history, safety, etc)

Total 128 100.0

(continued on page 121)

IEEE ENGINEERING IN MEDICINE AND BIOLOGY MAGAZINE MARCH/APRIL 2005 121

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Address for Correspondence: HanliLiu, Joint Graduate Program inBiomedical Engineering, The Universityof Texas at Arlington and The Universityof Texas Southwestern Medical Center atDallas Arlington, TX 76019 USA.Phone: +1 817 272 2054. Fax: +1 817272 2251. E-mail: hanli@uta.edu.

membership and by the IEEE EMBSExecutive Committee.

Sources and Further Reading[1] IEEE C95.1-1991, Standard for Safety Levelswith Respect to Human Exposure to RadioFrequency Electromagnetic Fields, 3 kHz to 300GHz, (1999 edition).

[2] International Commission on Non-IonizingRadiation Protection, “Guidelines for limiting expo-sure to time-varying electric, magnetic and electro-

magnetic fields (up to 300 GHz),” Health Physics,vol. 74, no. 4, pp. 494–522, 1998.

[3] J. M. Osepchuk and R. C. Petersen, “Safetystandards for exposure to electromagnetic fields,”IEEE Microwave Magazine, vol. 2, no. 2, pp.57–69, June 2001.

[4] “Reviews of the Effects of RF Fields on VariousAspects of Human Health,” Bioelectromagnetics,vol. 24, no. S6, 2003.

[5] Welcome to IEEE standards development online[Online]. Available: http://standards.ieee.org/resources/development/index.html

[6] IEEE international committee on electromagneticsafety [Online]. Available: http://grouper.ieee.org/groups/scc28/

[7] K. R. Foster, “Limiting Technology: Issues inSetting Exposure Guidelines for RadiofrequencyEnergy,” in Ma Jian-Guo, Ed. 3rd GenerationMobile Communication Systems: FutureDevelopments and Advanced Topics, Springer,Sept. 2003.

[8] Framework for harmonization of standards[Online]. Available: http://www.who.int/peh-emf/standards/framework/en/

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