standards and guidelines for communication sites - Radio And ...

ENVIRONMENTAL EVALUATION APPENDIX A: ELECTROMAGNETIC ENERGY INFORMATION
Different limits apply to different circumstances (see Figure A-1), based on whether a person at or near
a specific site knows or is informed and has control of potential RF exposure. Occupational/Controlled
Environment limits apply to individuals who should know that there is a potential for exposure as a
requirement of employment, or as the incidental result of transient passage through areas that may
exceed exposure levels beyond the General Population/Uncontrolled environment MPEs. For example,
a maintenance technician who performs work on transmitters should be aware (due to training and the
nature of his work) that transmitters produce RF energy. Because of the knowledge and understanding
that exposure is possible, this individual would be evaluated against the Occupational/Controlled
environment limits. General Population/Uncontrolled Environment limits apply to individuals assumed
to have no knowledge of, or control over, their possible exposure to RF energy. If the technician in the
example above brought his family to the same area, the situation would change. Because the family
members would not be assumed to have knowledge or understanding of the RF environment, their
exposures would be judged against the limits for General Population/Uncontrolled environments. The
technician, however, would be evaluated against the Occupational/Controlled environment limits.
Simple understanding or precautions can assure that RF levels at or near an antenna site do not exceed
maximum permitted exposure levels. The MPE exposure levels for General Population/Uncontrolled
environments are five times lower than the MPE exposure levels for Occupational/Controlled
environments. The technician, in the above example, could be exposed to a power density of 3 mW/cm 2
from a 900 MHz transmitter while the family members could only be exposed to 600 µW/cm 2 .
FIGURE A-1 FCC ADOPTED MAXIMUM PERMISSIBLE EXPOSURE LIMITS
A-4 68P81089E50-B 9/1/05