standards and guidelines for communication sites - Radio And ...
standards and guidelines for communication sites - Radio And ... 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
STANDARDS AND GUIDELINES FOR COMMUNICATION SITES ENVIRONMENTAL EVALUATION A.2.2 COMPLIANCE ANALYSIS A.2.2.1 SPATIAL-PEAK The maximum RF energy across the area of the human body (about 1.8 m (6 ft.) high) that an individual can be exposed to, is considered the Whole Body Peak (WBP). This level should be considered as the highest level that is found in the area of interest. If, during the evaluation of an area for exposure, there are no WBP exposures above the MPE being considered, the area is considered below the limits and requires no additional evaluation. A.2.2.2 SPATIAL-AVERAGING If, during the evaluation of an area for potential exposure, it is determined that there are areas where peak levels (WBP) will exceed the MPE, then spatial-averaging is required. Spatialaveraging considers the whole area of the human body in the evaluation of exposure. If there is an area that has RF fields above the applicable MPE, additional vertical measurements should be taken to understand the levels between ground level and 1.8 m (6 ft.) high. 1 The average of these vertical measurements is the Spatial-averaged exposure, which is used to evaluate compliance with the MPE. AVERAGE OVER AREA FIGURE A-2 SPATIAL AVERAGING A.2.2.3 TIME-AVERAGING MPEs in the guidelines are in terms of a time-averaged exposure, typically either 6-minute for Occupational/Controlled MPE or 30-minutes for General Population/Uncontrolled MPE. The averaging times are used to regulate the energy absorption rate in an individual exposed to RF fields so that the total energy delivered over the averaging time does not exceed FCC guidelines. This permits short duration exposure to much higher level fields as long as the average value over the prescribed time remains within the MPE. 1. The ANSI/IEEE C95.1 - 1992 standard uses a height of 2.0 meters. 68P81089E50-B 9/1/05 A-5
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STANDARDS AND GUIDELINES FOR COMMUNICATION SITES ENVIRONMENTAL EVALUATION<br />
A.2.2 COMPLIANCE ANALYSIS<br />
A.2.2.1 SPATIAL-PEAK<br />
The maximum RF energy across the area of the human body (about 1.8 m (6 ft.) high) that an<br />
individual can be exposed to, is considered the Whole Body Peak (WBP). This level should be<br />
considered as the highest level that is found in the area of interest. If, during the evaluation of an<br />
area <strong>for</strong> exposure, there are no WBP exposures above the MPE being considered, the area is<br />
considered below the limits <strong>and</strong> requires no additional evaluation.<br />
A.2.2.2 SPATIAL-AVERAGING<br />
If, during the evaluation of an area <strong>for</strong> potential exposure, it is determined that there are areas<br />
where peak levels (WBP) will exceed the MPE, then spatial-averaging is required. Spatialaveraging<br />
considers the whole area of the human body in the evaluation of exposure. If there is<br />
an area that has RF fields above the applicable MPE, additional vertical measurements should be<br />
taken to underst<strong>and</strong> the levels between ground level <strong>and</strong> 1.8 m (6 ft.) high. 1 The average of these<br />
vertical measurements is the Spatial-averaged exposure, which is used to evaluate compliance<br />
with the MPE.<br />
AVERAGE<br />
OVER<br />
AREA<br />
FIGURE A-2 SPATIAL AVERAGING<br />
A.2.2.3 TIME-AVERAGING<br />
MPEs in the <strong>guidelines</strong> are in terms of a time-averaged exposure, typically either 6-minute <strong>for</strong><br />
Occupational/Controlled MPE or 30-minutes <strong>for</strong> General Population/Uncontrolled MPE. The<br />
averaging times are used to regulate the energy absorption rate in an individual exposed to RF<br />
fields so that the total energy delivered over the averaging time does not exceed FCC <strong>guidelines</strong>.<br />
This permits short duration exposure to much higher level fields as long as the average value<br />
over the prescribed time remains within the MPE.<br />
1. The ANSI/IEEE C95.1 - 1992 st<strong>and</strong>ard uses a height of 2.0 meters.<br />
68P81089E50-B 9/1/05 A-5
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