Safety Standards for Human Exposure to Radio Frequency Radiation and Their Biological Rationale ■ James C. Lin 22 December 2003 C urrently, there is a backdrop of persistent, publicly expressed lack of confidence in radio-fre- quency (RF) exposure standards, per- taining to the maximum permissible exposure (MPE) level of humans exposed to RF electromagnetic radia- tion. Several national and international organizations are engaged in examining existing guidelines or MPEs for human exposure. Each of these efforts has con- vened groups of interested parties to deliberate on the reasons for, and to decide on guidelines, to deem exposure as safe and, hopefully, to make explicit the philosophy and procedure invoked in the decision-making process. Exposure guidelines for RF radiation have been promulgated for nearly half a century. However, our understanding of biological effects of exposure to RF radia- tion is still evolving and more so for cel- lular mobile telephones and wireless per- sonal communication devices. It is expected, and mandated by some of the standards setting bodies, that any expo- sure criteria set forth should be evaluated periodically, and possibly revised as new information becomes available from con- tinuing research on the subject. Likewise, rationales for the exposure criteria must be reassessed in view of new laboratory findings and human health studies. There are two different sets of guide- lines promulgated for limiting human exposure to RF radiation, worldwide. Much of the current effort is driven by the advent of cellular mobile telephony, which uses RF radiation in the range of 800–2,500 MHz. In response, a standard was adopted by the U.S. Federal Communications Commission (FCC) for protection against any effects of RF radiation in August 1996 [1]. Likewise, guidelines for limiting human exposure to RF radiation from cellular mobile telephone operations have been adopt- ed around the globe. For example, the maximum power deposition (measured in specific absorption rate of RF energy- SAR) allowed varies between 1.6 W/kg in 1 g and 2 W/kg in any 10 g of tissue in the head, from exposure to cellular telephone wireless radiation. However, the popularity and ubiquity of cellular mobile telephones have posed new questions on the adequacy of the exist- ing knowledge of biological effects of RF electromagnetic fields and of the protection afforded the public from any harmful effects of these fields. In fact, the numbers used for the guidelines are not new, in that they were derived from then existing (and current- ly promulgated) exposure guidelines for RF radiation. There is the sense that a cellular mobile telephone puts a radiat- ing RF source next to the user’s head. This is a new phenomenon that has no precedence. There has been palpable concern about the adequacy of existing scientific knowledge and uncertainties, even among the users. It is of interest to examine the scientific basis used for establishing these exposure guidelines. (For this discussion, we will not address the well-known differences of the RF guidelines promulgated for limiting human exposure in countries like Russia and the former Soviet Union.) The use of the dosimetric quantity SAR was initiated as a recommendation of the National Council of Radiation Protection and Measurements (NCRP) [2]. This unit mass, time-averaged rate of RF energy absorption was adopted by the American National Standards Institute (ANSI) in 1982 [3]. The limit for the 1.6 W/kg in 1 g of body tissue, for the general public or the uncontrolled environment, was recommended by the IEEE in 1992 [4]. (Note that, since 1990, the development and revision of the ANSI standards have come under the sponsorship of the IEEE Standards Association.). The latter had followed considerations by NCRP that, for James C. Lin is with the University of Illinois, 851 S. Morgan Street, M/C 154, Chicago, IL 60607-7053 USA, +1 312 413 1052. lin@uic.edu.