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What levels of RF energy are considered safe?
Various organizations and countries have developed standards for exposure to
radiofrequency energy. These standards recommend safe levels of exposure for
both the general public and for workers. In the United States, the FCC has used
safety guidelines for RF environmental exposure since 1985.
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.
Why has the FCC adopted guidelines for RF exposure?
The FCC authorizes and licenses products, transmitters, and facilities that
generate RF and microwave radiation. It has jurisdiction over all transmitting
services in the U.S. except those specifically operated by the Federal
Government. While the FCC does not have the expertise to determine radiation
exposure guidelines on its own, it does have the expertise and authority to
recognize and adopt technically sound standards promulgated by other expert
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