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• The consensus among Symposium participants in the limits of frequency and SAR specified by was that public exposures from base stations are previous ANSI standards,including ANSI 095.1- extremely low—hundreds or thousands of times 1982.In the promulgation of revised guidelines, below the more conservative,uncontrolled ANSI the responsibility of the current Subcommittee IV limit.Does this mean that base stations are safe? is adherence to the scientific base of data in the One Symposium participant expressed concern determination of exposure levels that will be safe about a lack of data on long-term(chronic) not only for personnel in the working environ- exposures.However,another pointed out that 11 of ment,but also to the public at large. the 121 studies that the IEEE standards-setting One participant described the FCC's position as committee reviewed involved long-term exposures. that the ANSI standard sets the threshold of safety, The 1992 ANSI standard,which stems from the and that normally base stations are not an envi- IEEE work,answers the safety question this way: ronmental problem. The members of Subcommittee IV[one of the The FDA has also spoken on low-level RF expo- IEEE's standards-setting subcommittees]believe sures. Specifically in connection with cordless that the recommended exposure levels should be telephones,19 which create RF fields comparable safe for all,and submit as support for this conclu- in strength CO those from base stations, the FDA sion the observation that no reliable scientific data observed,in its'Talk Paper T93-7" (February 4, exist indicating that: 1993),that (1)Certain subgroups of the population are more at risk than others; The safety of so-called"cordless phones," (2)Exposure duration at ANSI C95.1-1982 levels which have a base unit connected to the is a significant risk; telephone wiring in a house and which (3)Damage from exposure to electromagnetic operate at far lower power levels and ire- fields is cumulative;or quencies[than mobile or portable cellular phones]has not been questioned.[20] (4)Nonthermal[athermal] (other than shock)or modulation-specific sequelae[aftereffects]of In sum,for public exposu--es,base stations have a exposure may be meaningfully related to safety margin in the range of hundreds or thousands human health. of times,relative to standard limits. No verified reports of injury to human beings or of adverse effects on the health of human beings who have been exposed to electromagnetic fields with- HOW MUCH IS ONE MICROWAIT/CMZ? Participants at the Federal Focus National Symposium on Wireless Transmission Base MODULATION ISSUES Station Facilities agreed that typical public exposures from base stations is one micro watt or less per square centimeter.How much is that? Report No.86 by the NCRP suggests that low- This may provide some idea.A typical night light frequency modulated RF carriers may call for consumes four watts of power,of which 5% greater protection in occupational settings. (200,000 microwatts)emanates as visible light Accordingly,the NCRP Standard calls for use of Assume the light spreads evenly in all directions, general population exposure limits for workers if its power flux density decreasing with the square carrier strength varies 50%or more at frequencies of distance from the bulb.At just over four feet; between 3 and l09 Hz Certain digital transmission one micro watt of light power falls on one square formats such as TDMA may call for such addi- centimeter—about the area in a middle-aged tional precautions for mobile or portable digital • adult's wide-open pupil.So,neglecting reflec- This is not an issue for base stations, tions,a power flux density of one microwatt per however—digital or analog. square centimeter of visible light enters a viewer's eye at just over four feet from a night lighti8