A suggested limit for population exposure to radiofrequency radiation

Unlike a number of other nations, the U.S. does not currently have guidelines for the exposure of the public to radiofrequency (RF) radiation. In order to determine whether the current data base was sufficient to support an interim determination of a limit for population exposure to RF radiation (0.5 MHz-100 GHz), a critical and comprehensive review of the available literature on the biological effects of RF radiation was recently completed. In the analysis of this data, a number of simplifying assumptions had to be employed; among them was the use of the specific absorption rate (SAR) as the mass-normalized, frequency-independent measure of RF energy input into biological systems. The biological effects reported in acceptable studies were assessed in terms of their associations with (1) core temperature increases, (2) SAR, (3) SAR as a percentage increase over resting metabolic rate, and (4) direct evidence for human effects. Based on information now available and analyzed from these four perspectives, a conservative SAR threshold value of approx. 0.4 W/kg is apparent. Since the unknowns and uncertainties are potentially significant, one might consider, from the standpoint of prudence, the further application of a safety factor of 10. Given the present state of knowledge, the resultant SAR limit of 0.04 W/kg is, in the author's opinion, unlikely to be associated with the adverse health effects in the general population. This SAR translates into a power density of approximately 200 mu W/cm2 in the human resonant frequency range of 30-300 MHz.