NS ORD-1996-033 Zoning Ordinance Text Amendments - Telecommunication Towers

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DENNY & ASSOCIATES, P.G. 46 CONSULTING ENGtNBERS WASHINGTON, DC Engineering Statement Page 3 KNKA293, Carrboro, North Carolina ANSI C95.1-1982 specifies maximum exposure in terms of frequency- dependent protection guides. The protection guides are concerned with total whole. body absorption of radio-frequency energy over any 0.1-hour period. All of the radio- frequency sources at the IOMM93 cellular site are in the 869 to 894 megahertz (MHz) frequency range. The protection guide level for this frequency range corresponds to an average equivalent plane wave power density that may be calculated using the formula S= f 300 where f is frequency in megahertz and S is power density in milliwatts per square centimeter(mW/cm). Given this relationship, the most restrictive exposure guide level would occur at 869 MHz, the lowest possible operating frequency for cellular base stations. Applying this frequency to the formula yields a protection guide level of 2.9 mW/cm2. The revised standard, C95.1-1992,also specifies maximum exposure in terms of a frequency-dependent maximum level, but, instead of a protection guide, this level is referred to as a maximum permissible exposure WE)level. The new standard also categorizes exposure environments as controlled or uncontrolled. The 1982 standard did not distinguish between exposure environments. Under C95.1-1992, controlled environments are locations where there is exposure that may be incurred by persons who are agars of the potential for exposure as a concomitant of employment, by other cognizant persons,or as the incidental result of transient passage through areas where analysis shows the exposure levels may be above the MPEs for uncontrolled environments but less than the MPEs for controlled environments. The MPE for controlled environments under the 1992 standard for emissions in the 300 to 3000 MHz