Assessment of the Possible Health Effects of Ground Wave Emergency Network (1993) / Chapter Skim
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Risk Analysis and Management
Risk Analysis and Management
Pages 143-166
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From page 143... ...
Exposure response evaluation involves gleaning from epidemiologic studies and experiments on laboratory animals a functional relation between the level of exposure and the magnitude of the induced health hazard. Risk characterization combines estimates of exposure and estimates of effect per unit of exposure from the two preceding stages to derive quantitative statements about human health risk.
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From page 144... ...
In the remainder of this chapter, we summarize information on population exposure to GWEN fields, compare GWEN exposures to existing standards and to exposures to nonionizing fields from other sources of nonion~zing fields, and draw on existing negative epideniiological evidence at or near GWEN frequencies to derive upper bounds on GWEN-related risks. We also discuss some important risk-management issues including likely public concerns regarding risks associated with GWEN emissions and ways to address those concerns.
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From page 145... ...
Thus, much of the population exposure of interest occurs in the near field of the EF antenna and in the far field of the UHF antenna. Population exposures to UHF fields can be completely specified by the UHF electric field, by the magnetic field, or by power density alone.
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From page 146... ...
For instance, UHF fields couple much more strongly to the body than do EF fields. A vertically polarized electric field at ultrahigh frequencies induces an internal electric field in an ungrounded standing adult that is 300 times that induced by an EF electric field of the same incident strength and polarization.6 In many areas outside the boundaries of GWEN sites, EF-field strengths at ground level can be expected to exceed UHF-field strengths by less than a factor of 300, so that the internal electric fields from a GWEN site watt be predominantly from the UHF component.
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From page 147... ...
Cumulative distribution of number of homes in six contiguous concentric regions around sample of 40 RN sites.
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From page 148... ...
4.06 1.37 1.28 1.49 1.57 1.81 FIGURE 11-2. Cumulative distribution of home density in six contiguous concentric regions around sample of 40 RN sites.
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From page 149... ...
The persons exposed to the strongest GWEN fields continuously are, of course, those who live closest to the sites. Someone living at a site boundary would be exposed to GWEN EF fields at ground level of up to 40 V/m and 0.7 mG.
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From page 150... ...
citiesi° enable comparisons of GWEN exposures to exposures from those broadcast sources. Figure 11-4 shows the numbers of people exposed above a given field level for both the 15-city urban population of the EPA study and populations near GWEN facilities.
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From page 151... ...
The situations include living next to a 500-kV transmission line .ct~n-Ain~, h`~ne.nth ~ n~iabhn~hr~f`A ~1:~4~_:1~ ~:~ 1 ·_ ~ 1 ·~ · _ _ 1 ~ 7 ~ ~ ~ ~ ~4 ~ ^~_~4V~4 AlVV~ Ul~LllUULlUll 1111U, 1lvmg in an urDan area served by FM radio, using a cordless telephone, and standing ~ m away from a microwave oven. Comparisons are based on four measures of exposure: time- and body-averaged magnetic flux density, time- and body-averaged power absorption, instantaneous peak power absorption in any tissue, and fraction of time exposed.
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From page 152... ...
Cumulative distributions of people exposed to GWEN and commercial broadcast fields above given electric-field strength. Broadcast exposures are derived by combining census data with EPA survey of RF-field exposures in urban areas.
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From page 153... ...
Situations include living on edge of 500-kV right-of-way, standing beneath neighborhood distribution line, being exposed to ambient FM-broadcast radiation in urban areas, using cordless phone, and using microwave oven. SAR, specific absorption rate.
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From page 154... ...
The upper bounds on GWEN risks derived below are based on indirect evidence and so represent the largest risk that cannot be ruled out by available evidence. The probability is small that GWEN risks could be as large as any of the bounds that fall out of these indirect arguments, as discussed in a later section of this chapter.
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From page 155... ...
A person living adjacent to a GWEN RN in an EF field of 40 V/m with a duty cycle of 0.014 and a coupling efficiency that is 22% of that at AM frequencies would be exposed to a time-averaged electric field that is about half (0.12 V/m) that induced by the median AM broadcast exposure in the United States (0.28 V/m)
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From page 156... ...
TABLE 11-4. 14-Year Trends in Age-Adjusted Incidence per 100,000 Population for Cancers Possibly Associated with Electromagnetic-Field Exposure.
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From page 157... ...
MEADOWLANDS SPORTS COMPLEX The Meadowlands Sports Complex in East Rutherford, NI, is very near a number of AM radio broadcast antennae.~4 A recent study by Kraut and colleagues of cancer incidence and cancer deaths in a population of almost 8,000 workers at the sports complex found no significant differences in cancer risk between worker and reference populations over the period 1978-1987.~s Electric fields measured at outdoor locations across the complex ranged from ~ to 16 V/m, with typical values of 3-10 V/m. Indoors, electric fields were much smaller, typically less than 0.3 V/m.
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From page 158... ...
BOUNDS ON EXCESS POPULATION RISK FROM GWEN FIELDS The upper bound on risk of excess cancer mortality associated with operation of GWEN EF and UHF transmitters can be estimated from four factors: (1) information on health surveillance of census tracts surrounding AM broadcast facilities; (2)
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From page 159... ...
In our approach, an upper bound estimate of the health risks associated with GWEN EF radiation is computed from information on the absence of public health effects associated with exposure to AM broadcast fields. Public health statistics are regularly reviewed at the level of the census tract, which can be smaller than a city block in urban areas and larger than a county in sparsely populated areas.
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From page 160... ...
(11-3) If p is the average population density in the region in persons/km2, then the upper bound on excess population risk for a single GWEN facility for those living between rat and r2 kilometers from the antenna is: r2 Cases per year < J 2 ~ p Rear)
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From page 161... ...
During a 70-yr lifetime, the upper bound risk estimate would be 2.5 x 104 cases per site. For the full complement of 125 GWEN sites, the total upper bound estimate on the number of possible excess cancer cases is 0.03 over a 70-yr lifetime.
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From page 162... ...
For a 70-yr lifetime and the full complement of 125 GWEN sites, the total upper bound estimate on the number of possible excess cancer cases is 0.5. Similar arguments can be made for the UHF emissions from the GWEN system.
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From page 163... ...
A number of actions might he taken to reduce population exposures to GWEN LF and UHF emissions. They include choosing sites for the RNs that avoid people, placing the UHF transmitting antenna in each site so as to minimize UHF exposures of those living nearby, placing the UHF transmitting antennae on higher poles, increasing the size of each GWEN RN site to reduce field strengths at the site boundary, and reducing the number of RNs in the final GWEN system.
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From page 164... ...
Additional federally supported RF-effects research would not only further our scientific understanding of the interactions of EMFs with biological systems, but also provide a basis on which the public could generate informed opinions concerning possible health risks associated with RF emitters.
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From page 165... ...
1976. Sensitivity of calcium binding in cerebral tissue to weak environmental electric fields oscillating at low frequency.
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From page 166... ...
1988. An investigation of radiofrequency field strengths in the vicinity of the meadowlands sports complex, East Rutherford, NJ.
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