Section 4A: Safety 149
FDA, EPA and other US government agencies responsible for public health and safety
have worked together and in connection with WHO to monitor developments and
identify research needs related to RF biological effects.
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:
h
ttp://www.fcc.gov/oet/info/documents/bulletins/#56;
h
ttp://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
