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I 1-3The 1992 ANSI Standard also has limits for Specific Absorption Rate (SAR),which expresses how much power a given amount of body tissue absorbs from ambient RF fields.There are different permissible SARs for different parts of the body,and a maximum whole-body average SAR.SAR limits are expressed in watts of power per gram(or kilogram)of body tissue.For the general public,the SAR limits are 0.08 watt/kg,as averaged over the entire body,and 1.6 watts/kg,as averaged over any one gram of tissue (other than the hands,wrists,feet,and ankles,where higher limits apply). 14The five-fold increase in the safety margin for the general public sterns from the fact that worst-case continuous exposures of members of the public are about five times longer than occupational exposures— 168 hours per week vs.35 hours per week,respectively. 15-Monitors can be worn on the body or installed around the perimeter of a base station.The monitors generate alarm signals if exposures exceed ANSI-permissible levels. 160f course,as Symposium participants observed,any RF source adds to the overall ambient RF level— even if only infinitesimally. 1 7The base station in question had three sectors,and in each sector, 16 channels and 80 watts per channel of ERR.No specific attempt was made to measure exposures with all channels activated,but another participant observed that,from his experience,each channel contributed about 20 nanowatts(0.02 microwatts)per square centimeter to the overall exposure level. 180f course,visible light is much higher in frequency than signals from a base station,and the mechanisms by wh;ch visible-light power interacts with cells differ from those by which microwave-frequency power interacts.In general,at higher frequencies,power deposits much more superficially(closer to the surface). But the power flux densities would be comparable. 19"!he FDA was referring to the phones available for about$50 to$150,which people install for cord- • free conversations in their homes. 20Base stations operate at higher frequencies(about 850 MHz) than 49 MHz cordless phones,but the frequencies base stations employ do not inherently pose any greater risk- •