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This new “IEEE Standard for
Safety Levels with Respect to Human Exposure to Radio
Frequency Electromagnetic Fields, 3 kHz to 300 GHz” published
on April 19, 2006 is a revision of C95.1-1991 (1999 edition) and
C95.1b-2004 “Amendment 2: Specific Absorption Rate (SAR) Limits for
the Pinna.” The revision is based on scientific and medical
literature published through December 2003, but several 2004 and 2005
papers are included. The document includes a comprehensive review of
about 1300 references, including studies that involve low level
exposures where increases in temperature could not be measured or were
not expected (i.e., “non-thermal” effects). The revised standard
reflects new insights gained from improved experimental and numerical
methods and a better understanding of acute and chronic radiofrequency
(RF) electromagnetic field exposure effects on animals and humans. The
standard includes the rationale for all revisions. Harmonization with
ICNIRP guidelines to the extent scientifically defensible was one of
the major revision criteria.
The standard presents two sets of
rules to limit human exposure to electric, magnetic, and
electromagnetic fields and induced and contact currents to avoid all
established adverse health effects. Specifically, from 3 kHz to 5
MHz, the rules protect against electrostimulation; from 100 kHz to 300
GHz, the rules protect against heating due to absorption of RF energy.
These limits are expressed in terms of practical measures of external
fields and induced and contact current (maximum permissible exposures
or MPEs), or internal fields, SAR, and current density (basic
restrictions or BRs) which are more difficult to obtain. The MPEs and
BRs incorporate safety factors that account for uncertainties and that
provide a margin of safety for all persons, including children. The
upper tier, which is protective for all with an acceptable margin of
safety, generally applies to exposure of persons in controlled
environments, e.g., the workplace. While the weight of scientific
evidence supports the conclusion that there is no measurable risk
associated with RF exposure below the upper tier of this standard, a
well-known fact is that it is impossible to scientifically prove
absolute safety (the null hypothesis) of any physical or chemical
agent. The lower tier, with an additional margin of safety,
recognizes public concern and supports harmonization with other
standards.
Major changes (compared with the
1991 standard) include the following.
1) MPE limits between 30 MHz
and 100 GHz for the lower tier were changed to harmonize with the
ICNIRP guidelines.
2) The upper frequency for the
BR on whole-body averaged SAR is reduced from 6 to 3 GHz.
3) BRs on peak SAR have been
changed from 1.6 and 8 W/kg for the lower and upper tiers to 2 and 10
W/kg, respectively, with corresponding averaging mass increased from 1
to 10 g. For extremities (including forearms and lower legs) and
pinnae, peak SARs are now 20 and 4 W/kg for the upper and lower tiers.
4) Averaging times and areas
for both tiers have been changed for frequencies above 3 GHz.
5) Exposures exceeding action
levels require implementation of an RF safety program as defined in
C95.7-2005.
6) The standard is
substantially longer (250 pages) because of the explanations for the
revisions, the comprehensive literature review, and the reference list
containing 1143 citations.
The major differences between
C95.1-2005 and the 1998 ICNIRP guidelines are as follows.
1) SAR limits in the C95.1
standard apply between 100 kHz - 3 GHz instead of 100 kHz - 10 GHz.
2) The peak spatial-average
SAR is averaged over 10 g tissue in the shape of a cube instead of in
contiguous tissue.
3) The SAR is averaged over 30
min for the general public and 6 min for controlled environments,
instead of 6 minutes for both tiers.
4) The pinnae have the same
SAR limits as the extremities, instead of the same limits as the head
or body.
5) The upper arms and upper
legs have the same limits as the body instead of the same limits as
for the limbs.
6) Below 100 kHz, differences
in the assumed transition frequency for adverse electrostimulation of
the central nervous system are responsible for lower BRs and MPEs in
ICNIRPs standard as compared with ICES, rather than differences in
safety factors.
7) The microwave auditory
effect, a benign biological sensation that occurs only under very
special conditions, whereas ICNIRP considered it to be adverse.
This revision resolves a major
harmonization issue with the ICNIRP guidelines on the peak SAR limits
that apply to mobile phones and other body worn telecommunication
devices. As demonstrated by the C95.1-2005 standard, scientific
endeavors are expected to continue to converge toward a worldwide
harmonized RF safety standard that would be most beneficial for
consumers, regulators and manufacturers.
C-K. Chou, Ph.D.
IEEE, International Committee on
Electromagnetic Safety Technical Committee 95,
Subcommittee 4
([email protected])
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Additional Information: Dr. Chou was one of the
speakers at the Workshop on the Technical and Regulatory
Aspects Related to the Effects of Electromagnetic Non-Ionizing
Emissions that CITEL organized in Lima
on June 19, 2006.
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