In the last few years the potential hazard of microwave radiation has become a major item of media and public conern in the US. The publication of “The Zapping of America” by Paul Brodeur, many other articles, Senate hearings, public meetings, and some litigation, all derive from the disparity between Soviet and US standards. The net result is a partial erosion of confidence in the safety margins of the 10 mW/cm2 standard, which is now under review. It would not be surprising if, for reasons other than scientific, this US review recommends a difference between public and occupational permitted exposure, or even a more restrictive occupational standard. The current Western standard of 10 mW/cm2 which has been operational for more than two decades, merits some defense. Body resonance colours the new approach to standard setting. With standard man resonant at 70 MHz, and on ground plane therefore at 35 MHz, and allowing for younger and smaller humans, you have the rationale behind the tightening of the standard between 30 MHz and 300 MHz. A fair question is how practical is it to have a standard so influenced by resonance. It is a very conservative approach. Such theoretical assessments tend to exaggerate the risk. In practice, the body does not present a perfectly tuned system producing resonance effects. It can be suggested that if levels are set on a basis of resonance, then standards should reflect relaxation at frequencies outside the resonance band, i.e., <30 MHz and >300 MHz. Minor behavioural changes in small mammals are often quoted as reasons for tightening microwave radiation exposure standards, even though such changes can often be produced by totally acceptable levels of noise, illumination, and temperature for example. Also, a standard is only as good as its measurement, and the difficulties in monitoring microwave radiation have been mentioned already. However, with Canada tightening its standard, with the US more than likely to follow suit, restriction of the Western standard to 1 mW/cm2 for the general public long-term appears most probable in the near future, and this should be borne in mind during considerations of solar power satellite systems. LIVING WITH THE RECTENNA Aspects are raised and suggestions are made to provide a basis for future discussion. Persons periodically exposed to power densities greater than 10 mW/cm2 are classified as microwave radiation workers in the Royal Air Force, and this classification would have to apply to rectenna maintenance personnel. Protection in the first instance is by limitation of exposure time in accordance with the NATO standard (based on 10 mW/cm2) using the formula T = 6000/W2 where T is the permitted exposure time in minutes during any one hour period, and W is the power density in mW/cm2, e.g., at a power density of 23 mW/cm2 the permitted exposure time is 11.3 min in any 1 h period. The application of the formula has a practical limitation at 50 mW/cm2, i.e., a stay time in the hour of 2.4 min, as any less time is considered unworkable. This equates to the stay time of 2.8 min allowed for a power density of 23 mW/cm2 if the occupational level is restricted to 5 mW/cm2, as with the current Canadian standard. An occupational standard of 1 mW/cm2 would preclude the time limitation to protection
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