Human exposure to 2450 MHz CW energy at levels outside the IEEE C95.1 standard does not increase core temperature†

Abstract

Permission was received from the Brooks AFB Institutional Review Board and the AF Surgeon General's Office to exceed the peak power density (PD = 35 mW/cm(2)) we had previously studied during partial body exposure of human volunteers at 2450 MHz. Two additional peak PD were tested (50 and 70 mW/cm(2)). The higher of these PD (normalized peak local SAR = 15.4 W/kg) is well outside the IEEE C95.1 guidelines for partial body exposure, as is the estimated whole body SAR approximately 1.0 W/kg. Seven volunteers (four males, three females) were tested at each PD in three ambient temperatures (T(a) = 24, 28, and 31 degrees C) under our standard protocol (30 min baseline, 45 min RF exposure, 10 min baseline). The thermophysiological data (esophageal and six skin temperatures, metabolic heat production, local sweat rate, and local skin blood flow) were combined with comparable data at PD = 0, 27, and 35 mW/cm(2) from our 1999 study to generate response functions across PD. No change in esophageal temperature or metabolic heat production was recorded at any PD in any T(a). At PD = 70 mW/cm(2), skin temperature on the upper back (irradiated directly) increased 4.0 degrees C in T(a) = 24 degrees C, 2.6 degrees C in T(a) = 28 degrees C, and 1.8 degrees C in T(a) = 31 degrees C. These differences were primarily due to the increase in local sweat rate, which was greatest in T(a) = 31 degrees C. Also at PD = 70 mW/cm(2), local skin blood flow on the back increased 65% over baseline levels in T(a) = 31 degrees C, but only 40% in T(a) = 24 degrees C. Although T(a) becomes an important variable when RF exposure exceeds the C95.1 partial body exposure limits, vigorous heat loss responses of blood flow and sweating maintain thermal homeostasis efficiently. It is also clear that strong sensations of heat and thermal discomfort will motivate a timely retreat from a strong RF field, long before these physiological responses are exhausted. Published 2001 Wiley-Liss, Inc.

Exposure time-dependent thermal effects of radiofrequency electromagnetic field exposure on the whole body of rats

“…Under the exposure condition employed in the present study, when the ambient temperature in the reverberation chamber was 23°C, heat balance remained at approximately 38.5°C. In a human study using MRI measurement, RF-EMF exposure induced core temperature rise by 0.15°C in warm (31°C) ambient temperature but did not induce the same in two lower (24°C or 28°C) ambient temperatures (Adair et al 2001). Here the core temperature linearly increased from 37.5°C to 42°C in 1 hr when the ambient temperature was set at 38°C (Fig.…”

“…On the other hand, high-intensity RF-EMF exposure at WBA-SAR of ≥ 4 W/kg causes thermal effects and behavioral disruption in rats, such as sleeping and spreading saliva on rat's tail (ICNIRP Guideline, 1998). Whole-body high-intensity RF-EMF exposure caused increases in skin, brain, and rectal temperatures in several animals (Adair et al, 2001;Jauchem and Frei, 1997). However, biological effects of RF-EMF exposure at WBA-SAR of 4 W/kg on thermal stress remain controversial, particularly, in real-time analyses of the variation in body temperature of free-moving animals.…”

Thermal aspects of exposure to radiofrequency energy: Report of a workshop

“…At the two lower ambient temperatures (24 , 28 C) the subjects experienced 'minimal or no' increases in core temperature over the course of the 45-min exposures; during many of these exposures the core (oesophageal) temperature of the subjects actually decreased slightly. At the highest exposure level used in these studies (about 1 W/kg whole body exposure) in the warmest ambient temperature (31 C), the average core body temperature in the group of seven subjects increased by 0.15 C [19]. In one of these subjects, however, core body temperature had increased by 0.5 C and was still increasing at the end of the 45-min exposure.…”

Thermoregulatory responses to RF energy absorption

“…Humans have an extraordinary capacity to lose body heat by sweating [Wenger, 1983]. Human sweating during RF exposure at high PD can be so profuse that T co falls significantly [Adair et al, 2001b].…”