Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
CHAPTER 3 SUMMARY AND CONCLUSIONS On the basis of available information, the maximal instantaneous microwave-field intensities anticipated in areas of public access in the vicinity of PAVE PAWS during normal operation of the existing radar should be about 100yW/cm . The corresponding time-averaged intensities as measured under normal operating conditions have been found to be lower by at least two orders of magnitude. A comparison of these time-averaged potential exposures with exposures resulting from other commercial, private, and military sources of microwave and radiofrequency radiation does not indicate any substantial variation from power densities to which segments of the general public are routinely exposed in some localities. PAVE PAWS, therefore does not appear to present unique exposure conditions with re- spect to the anticipated time-averaged field intensities. Although no overt deleterious health effects have been documented to result from such low-intensity exposure of the public, statistically de- signed epidemiologic studies have not been conducted. It is therefore not possible to conclude, on the basis of a comparison of time-averaged exposure intensities, that effects will or will not be induced by exposure to the radiation from PAVE PAWS. A review of experimental and epidemiologic studies of occupationally exposed workers indicates that both humans and experimental animals have been reported to be sensitive to microwave exposure intensities of about 1 mW/cm or greater, the nature of the effects depending on a large number of physical and biologic factors, most of which are inadequately understood. Documented effects on morbidity or mortality, most of which have been ob- served in experimental animals, are generally associated with exposure intensities over 10 mW/cm and attributed to excessive thermal stress. Possible exceptions, however, are alterations in central-nervous-system function and immunologic status, in both experimental animals and humans, that have reportedly occurred at about 1 mW/cm . Alterations in CNS func- tion include objective findings, such as changes in EEG patterns that have been reported to occur from occupational exposure of humans for periods of years or from acute microwave exposure of experimental animals at intensities of 1 mW/cm or greater. Subjective alterations in mood and behavior have also been reported in occupationally exposed microwave workers, and specific behavioral end points in experimental animals have reportedly been affected by microwave exposure at intensities of 1 mW/cm or greater. The subtle and subjective nature of the reversible effects in humans makes it difficult to establish quantitative relationships to ex- posure conditions. In vitro and in vivo exposures of nervous tissue have provided additional evidence of sensitivity to low-intensity microwave fields. Effects have been reported to occur in specific ranges ("windows") of -79-
intensity and pulse repetition rate, whose existence suggests that alterations in nervous tissue may not depend solely on exposure intensity or duration; i.e., such effects do not follow monotonic dose-response relationships. Although the physiologic significance of in vitro findings has not been established, their existence, with the in vivo findings of sensitivity of the mammalian CNS to microwave and weak electric and magnetic fields, suggests altered CNS function as a subject of greatest potential concern with respect to low-intensity microwave exposure from PAVE PAWS. Owing to the limited scope and extent of studies of the biologic effects of chronic low-intensity microwave exposure, it is not possible to conclude that other types of physiologic effects will not be induced in humans. But there is no evidence to suggest that other types of physiologic alterations should be anticipated as a result of exposure to PAVE PAWS radiation in areas of public access. There are no data on the biologic effects of microwave radiation with the specific characteristics of the PAVE PAWS radar, which, because of its rather unusual function, differs from more commonly encountered sources of microwave and RF radiation. The inherent problems of inter- species, interfrequency extrapolation limit the extent to which existing data may be used to assess the effect of PAVE PAWS radiation. Data from both in vivo and in vitro studies suggest maximal sensitivity of neural systems to fields modulated at mammalian brainwave frequencies (i.e., 1-20 Hz), which include the predominant PAVE PAWS modulation frequency at 18.5 Hz. Because of the aforementioned possibility of field-intensity windows and the lack of adequate data on mammalian systems, it is not known whether such effects will be induced in humans under the anticipated exposure conditions. During normal operation of PAVE PAWS, the direction of the radar beam will be continuously varied in the scanning mode, so exposure at a given location will be intermittent and at low time-averaged intensities, relative to the intensities associated with irreversible biologic damage. The effects of such exposures of members of the public, if they occur, will, on the basis of available data and the known inter- action mechanisms with biologic systems, be reversible or transient. Thus, the possible exposure effects of PAVE PAWS should be restricted to transient, reversible functional alterations in the CNS that may or may not be perceived by the exposed persons. Whatever the effects of exposure on the human central nervous system are, it is not known whether the effects are deleterious to health. It has not been established, for example, that such effects involve impairment of judgment or alterations in mood that would impose psychologic or physio- logic burdens on those affected. The microwave radiation from PAVE PAWS may present interference problems with electronic devices in the vicinity of the radar site. The design characteristics of device like electromagnetically shielded cardiac pacemakers are such that their operation should not be adversely affected by PAVE PAWS exposure intensities, but some pacemakers currently in use may be affected by exposure. There should not be any important deleterious consequences due to exposure of persons with surgical implants -80-
or other prosthetic devices. Interference with other electronic devices, such as television and radio receivers, is beyond the scope of this report, but obviously must be taken into account. Special attention should be given to the evaluation of the effects of PAVE PAWS radiation on electronic devices used for medical monitoring or health evaluation, because there is evidence that such devices may be sensitive to such exposure. In conclusion, the PAVE PAWS radar may be anticipated to expose a limited number of members of the general public intermittently to low intensities of pulse-modulated microwave fields with maximal instantaneous intensities of 100 vW/cm or less and time-averaged intensities lower by two orders of magnitude. There are no known irreversible effects of such exposure on either morbidity or mortality in humans or other species. Thus, it is improbable that exposure will present any hazard to the public. In view of the known sensitivity of the mammalian CNS to electro- magnetic fields, especially those modulated at brainwave frequencies, the possibility cannot be ruled out that exposure to PAVE PAWS radiation may have some effects on exposed people. Because these effects are still hypothetical, it is not feasible to assess their health implications. Such assessment will requir% additional research and surveillance and must be addressed in future evaluations of the potential exposure effects of PAVE PAWS and other high-power-output radar systems. -81-
