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Section 4: Safety Guidelines and Warranty Information
228 4A: Safety
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