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Suggested Citation:"Letter Report." National Research Council. 2002. Letter Report to the Department of the Air Force from the Committee to Assess Potential Health Effects from Exposure to PAVE PAWS Low-level Phased-array Radiofrequency Energy. Washington, DC: The National Academies Press. doi: 10.17226/10575.
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THE NATIONAL ACADEMIES

Advisers to the Nation on Science, Engineering, and Medicine

National Academy of Sciences

National Academy of Engineering

Institute of Medicine

National Research Council

DIVISION ON EARTH AND LIFE STUDIES

Board on Radiation Effects Research

November 15, 2002

Lt. Col. Richard Ashworth,

Chief

Bioenvironmental Engineering

Office of the Command Surgeon

Headquarters Air Force Space Command 150 Vandenberg Street, Suite 1105 Peterson AFB, CO 80914–4550

Dear Col. Ashworth,

The National Research Council has been asked to update its 1979 report on the analysis of exposures to and potential biologic effects of the PAVE PAWS radar system. This update will be completed at a later date after an extensive review of available data. The committee is to first determine whether available research data on continuous and pulsed radiofrequency (RF) energy are adequate for determining the biologic and potential health effects of the PAVE PAWS phased-array system (see Appendix, lines 1–3 of Statement of Task). The Air Force has asked that this determination be communicated as a letter report. The committee’s initial assessment is that the data on continuous and pulsed RF energy are not adequate for determining the biologic and potential health effects of the PAVE PAWS phased-array system at this time. This conclusion is based on two observations.

First, issues related to the rise and fall portions of the PAVE PAWS waveform have been raised, but cannot be addressed, because we have available only preliminary, but inadequate, measurements of the PAVE PAWS waveform. These measurements are important to characterize transient aspects of PAVE PAWS radiation and to answer a question raised by others about the comparability of the PAVE PAWS phased-array radiation with radiation emitted by non-phased array systems. Hopefully, the significance of the PAVE PAWS wave shape will be clarified by the Phase IV measurement data (NRC 2002).

Second, although more than 2 decades of exposure to PAVE PAWS phased-array radiation has been experienced by the Cape Cod population which should allow a direct evaluation of any adverse health effects, there are currently inadequate data about the distribution of population exposures in the Cape Cod region. Adequate exposure data would be necessary to carry out this direct evaluation of the effects of the PAVE PAWS waveform. The 1978 and 1986 PAVE PAWS power-density measurements are limited to 37 locations in proximity to the PAVE PAWS site. Apparently these measurements were not designed to cover a wide range of census tracts for epidemiologic purposes. Use of epidemiologic methods is considered by this committee to be important to the determination of possible health effects of the PAVE PAWS radar. Accordingly, adequate power-density measurements that discriminate the PAVE PAWS emissions and that cover relevant census tracts are deemed necessary to facilitate the determination of possible health effects. It is our understanding that power-density measurements will

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Suggested Citation:"Letter Report." National Research Council. 2002. Letter Report to the Department of the Air Force from the Committee to Assess Potential Health Effects from Exposure to PAVE PAWS Low-level Phased-array Radiofrequency Energy. Washington, DC: The National Academies Press. doi: 10.17226/10575.
×

be commissioned by the PAVE PAWS Steering Group for use in their epidemiology effort and that this information may be available to our committee as well. The committee considers access to these data to be important to items 2 and 3 of the committee’s Statement of Task (see Appendix, items 2 and 3 of the Statement of Task). After the phase IV data are evaluated and during the committee’s update of the 1979 National Research Council report, the committee will re-evaluate the adequacy of the existing RF energy literature for determining the potential biologic and health effects of the PAVE PAWS phased-array system. The committee further expects that the Phase IV measurement data, additional power density measurements, and computed exposure estimates that include a propagation model will be extremely useful in its attempts to evaluate the potential health effects of the PAVE PAWS radar on the Cape Cod population. The committee recognizes that much research has been conducted over the past 23 years that may provide insight into the possible biologic and health effects of PAVE PAWS radiation, and the committee will be reviewing the cellular, animal, and epidemiologic RF exposure and health effect data in detail. To this end the committee has constructed a set of potentially relevant RF field characteristics that will be used as guidelines in the identification of experiments in the literature that could be relevant to the update of the 1979 Research Council report (see Table).

Characterization of the PAVE PAWS Waveform and Identification of Waveform Characteristics Suitable for the Evaluation of Biologic and Potential Health Effects of PAVE PAWS radar.

Characteristic

PAVE PAWS

Relevant range of data to be considered by the committee

Comments

Frequency

420–450 MHz

10MHz-2GHza

There are common mechanisms of interaction in-the 10 MHz-2 GHz frequency range

Incident average power density

<280bµW/cm2

<1 mW/cm2 or SAR <1 mW/g (<1 W/Kg)

Specific Absorption Rate increases for a given incident power with increasing frequency

Modulation

Pulse

Pulse (CDMA, TDMA, IDEN, GSM, etc.)

To include all existing RF pulse-modulation technologies

Pulse Width

0.25–16 ms

0.001–100 ms

 

Pulse Repetition Rate

0.02–20 Hz

0.01 Hz-10 kHz

 

Pulse Rise Time (τR)

>20 ns

10 ns<τR< 10µs

τR should be less than the charge relaxation time (ε/σ) for biologic tissue, where ε is the dielectric permittivity of tissue, and a the conductivity. Max estimated relaxation time is 10 µs.

Exposure Duration

Continuous

Continuous-1 hr/day

 

a Upper limit is intended to include cell-phone-frequency research (which goes as high as 1.9 GHz). The 2.45 GHz research in the literature is continuous RF energy and would be excluded by the modulation criteria (pulsed exceptions will be considered).

b The MITRE report on PAVE PAWS (2000) indicates that at the perimeter fence line the energy level does not exceed the IEEE thirty-minute average limit for human exposure. The IEEE limit is 280 microwatts per square centimeter.

The ranges described are to indicate the focus of the committee’s review, though the committee may determine that certain data obtained under other exposure conditions are relevant to its task. It is beyond the scope of this letter report to list all possible sources of data that fall within the committee’s

Suggested Citation:"Letter Report." National Research Council. 2002. Letter Report to the Department of the Air Force from the Committee to Assess Potential Health Effects from Exposure to PAVE PAWS Low-level Phased-array Radiofrequency Energy. Washington, DC: The National Academies Press. doi: 10.17226/10575.
×

proposed criteria to be reviewed. The committee is using a database with more than 37,000 references in addition to the information that various members have acquired in working in the field of bioelectromagnetics for many years. It should be further noted that the extensive literature on power-frequency fields is not considered relevant to the evaluation of PAVE PAWS health effects in our study because the physical mechanisms of interaction between power-frequency fields and tissue, on the one hand, and RF energy and tissue at low field strengths, on the other, are expected to be different. Furthermore, studies of power-frequency fields tend to concentrate on the effects of magnetic fields whereas studies on the effects of RF energy focus on power-density measurements or SAR’s. In addition, the committee proposes to focus on pulsed modulated fields rather than continuous wave fields. Continuous wave RF exposure experiments do not involve the same broad spectrum of energy and also utilize far lower peak exposure levels to attain the same average exposure levels. As a result, inclusion of continuous wave studies in the literature review may unfairly bias the observed results against any potential effects of exposure.

References Cited

MITRE. 2000. Kramer, A.G., Nelson, B.P., and Wakefield, R.E. RF Power Density Exposure at ground Level for the PAVE PAWS Radar at Cape Cod—Questions and Answers. Bedford, MA.

NRC (National Research Council) 2002. Letter Report to the Department of the Air Force from the Committee to Assess Potential Health Effects from Exposure to PAVE PAWS Low-level Phased-array Radiofrequency Energy: Recommendations for Phase IV Measurements Washington, D.C. National Academy Press http://www.nap.edu/books/NI000468/html/

Sincerely,

Frank Barnes

Chairman

Committee to Assess Potential Health Effects from Exposures to PAVE PAWS Low-level Phased-array Radiofrequency Energy

Suggested Citation:"Letter Report." National Research Council. 2002. Letter Report to the Department of the Air Force from the Committee to Assess Potential Health Effects from Exposure to PAVE PAWS Low-level Phased-array Radiofrequency Energy. Washington, DC: The National Academies Press. doi: 10.17226/10575.
×
Page 1
Suggested Citation:"Letter Report." National Research Council. 2002. Letter Report to the Department of the Air Force from the Committee to Assess Potential Health Effects from Exposure to PAVE PAWS Low-level Phased-array Radiofrequency Energy. Washington, DC: The National Academies Press. doi: 10.17226/10575.
×
Page 2
Suggested Citation:"Letter Report." National Research Council. 2002. Letter Report to the Department of the Air Force from the Committee to Assess Potential Health Effects from Exposure to PAVE PAWS Low-level Phased-array Radiofrequency Energy. Washington, DC: The National Academies Press. doi: 10.17226/10575.
×
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