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The FCC guidelines for human exposure to RF electromagnetic fields are derived from the
recommendations of two expert organizations, the National Council on Radiation Protection
and Measurements (NCRP) and the Institute of Electrical and Electronics Engineers (IEEE). In
both cases, the recommendations were developed by scientific and engineering experts
drawn from industry, government, and academia after extensive reviews of the scientific
literature related to the biological effects of RF energy.
Many countries in Europe and elsewhere use exposure guidelines developed by the
International Commission on Non-Ionizing Radiation Protection (ICNIRP). The ICNIRP safety
limits are generally similar to those of the NCRP and IEEE, with a few exceptions. For
example, ICNIRP recommends different exposure levels in the lower and upper frequency
ranges and for localized exposure from certain products such as hand-held wireless
telephones. Currently, the World Health Organization is working to provide a framework for
international harmonization of RF safety standards.
The NCRP, IEEE, and ICNIRP all have identified a whole-body Specific Absorption Rate (SAR)
value of 4 watts per kilogram (4 W/kg) as a threshold level of exposure at which harmful
biological effects may occur. Exposure guidelines in terms of field strength, power density
and localized SAR were then derived from this threshold value. In addition, the NCRP, IEEE,
and ICNIRP guidelines vary depending on the frequency of the RF exposure. This is due to the
finding that whole-body human absorption of RF energy varies with the frequency of the RF
signal. The most restrictive limits on whole-body exposure are in the frequency range of 30-
300 MHz where the human body absorbs RF energy most efficiently. For products that only
expose part of the body, such as wireless phones, exposure limits in terms of SAR only are
specified.
The exposure limits used by the FCC are expressed in terms of SAR, electric and magnetic
field strength, and power density for transmitters operating at frequencies from 300 kHz to
100 GHz. The specific values can be found in two FCC bulletins, OET Bulletins 56 and 65:
http://www.fcc.gov/oet/info/documents/bulletins/#56; http://www.fcc.gov/oet/info/
documents/bulletins/#65.
Section 5A: Safety
307
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