at the exclusion boundary. If there were sixty rectennas in the continental United States spaced an average of 300 km apart, the tails of the power beam patterns would combine and the minimum power density at any point would be about 10"u mW/cm2. These values have been compared to standards and guidelines for exposure to radio frequency power. In the USSR, the official maximum permissible average power densities for people occupationally exposed to radio frequency power in the frequency range from 300 MHz to 300 GHz emitted from stationary antennas are 10~2 mW/cm2 for a full working day, 10"1 mW/cm2 for two hours, and 1 mW/cm2 for 20 minutes. The maximum value for continuous (24 hour) exposure of the general population is 10“3 mW/cm2. The United States has no official maximum permissible exposure limit for radio frequency power for the general population. The Occupational Safety and Health Administration (OSHA) has promulgated a protection guideline of 10 mW/cm2 for persons occupationally exposed for greater than six minutes to power in the frequency range from 10 MHz to 100 GHz based on the same guideline value of the American National Standards Institute, and this guideline has been adopted by a number of organizations, including the DOD. SPS power density levels can be indirectly compared with background or ambient radio-frequency power densities. The EPA is measuring environmental field intensities at selected locations within various U.S. cities to permit estimations of cumulative fractions of the total population being exposed at or below various power density levels. A recent report3 presents the results for 15 cities, a total of 486 sites. The report concludes that, of the population group studied representing 20 percent of the total U.S. population, a median exposure value of about 5 x 10“6 mW/cm2 time averaged power density exists and less than 1 percent of the population is potentially exposed at levels above 10 3 mW/cm2. It was observed that the FM radio broadcast service (88-108 MHz) is responsible for most of the continuous illumination of the general population. Direct comparison with SPS cannot be made because of the frequency difference. Nevertheless, these data provide us with a measure of the ambient nonionizing radiation. The SPS workers within the rectenna area would not need to be exposed to levels exceeding current U.S. guidelines if precautions are taken and protective clothing used in some areas. The public near a rectenna would be exposed to levels in excess of the USSR standard and nearly all of the general population would be exposed to levels greater than the current background. Before this is done, a quantitative assessment of the risk associated with this exposure must be developed. Currently, the data necessary to make a quantitative assessment is not available. Furthermore, controversy exists over whether or not adverse biological effects should be expected for low level (less than 0.1 mW/cm2) power densities. For these reasons, as well as the fact that there is only a limited amount of data applicable to the SPS, conclusions regarding the potential
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