RFR's biological effects are measured in terms of specific absorption rate (SAR) -- how much energy is absorbed into human tissue -- which is expressed in Watts per kilogram (W/kg). A dangerous level (by U.S. standards) is considered to be anything above 0.08 W/kg. Thus far, RFR measurements for Wi-Fi, both at home and abroad, are a minute fraction of emissions that could amount to this level. Wi-Fi, in fact, emits less than other common sources of RFR like microwaves and mobile phones. Since mobile phones were recently cleared as a potential carcinogen by a comprehensive, long-term study conducted by the Danish Institute of Cancer Epidemiology in Copenhagen, it seems very unlikely that devices emitting a lower (and less frequent) level could be more dangerous.
"Wi-Fi cards are quite low power," says John Moulder, PhD, Professor of Radiation Oncology at Medical College of Wisconsin, and Director of the Center for Medical Countermeasures Against Radiological Terrorism. "Their peak power is comparable to, or somewhat below, that of mobile phone handsets. They also have very low duty cycles; they aren't transmitting most of the time. In most environments, the Wi-Fi signal is below (often far below) other RFR signals."
The Times of London quotes Dr. Michael Clark of the HPA (a UK health agency similar to the American CDC) as saying, When we have conducted measurements in schools, typical exposures from Wi-Fi are around 20 millionths of the international guideline levels of exposure to radiation. As a comparison, a child on a mobile phone receives up to 50 percent of guideline levels. So, a year sitting in a classroom near a wireless network is roughly equivalent to 20 minutes on a mobile. If Wi-Fi should be taken out of schools, then the mobile phone network should be shut down, too and FM radio and TV, as the strength of their signals is similar to that from Wi-Fi in classrooms.
"In virtually all the environments I surveyed, the RF signal from WLANs was a small fraction of the total RF fields in the environment," Foster says. "Other sources included mobile base stations, and broadcast radio and TV stations in the region."
While the study was not designed to assess health risks to humans, the measurements taken by Dr. Foster provide clear data on real world exposure levels (versus lab environments or estimates.) Based on the levels he consistently detected, Dr. Foster concludes that there is no cause for concern.
"No expert review of the literature (by WHO or national health agencies) have indicated any cause for concern, nor do I know of any scientific papers in standard peer-reviewed journals that offer any evidence that would lead to concern," says Foster.
The Wi-Fi Alliance, whose primary mission is promoting interoperability between Wi-Fi products, has given some attention to the issues of health and safety. Its official position is that "although questions have been raised, there is no scientific evidence that these low-power wireless communications devices pose any health threat to the user or the general public."
Moulder, who has been studying RFR biology for nearly 25 years, concurs. "I know of no confirmed epidemiological evidence or experimental evidence that RFR exposures this low are of concern, and I know of no theoretical basis for thinking that such exposures would cause biological effects," he says.
The EMR Network, a non-profit organization based in Charlotte, Vermont, is not convinced by research that indicates the danger is non-existent -- in fact, quite the contrary. A request for an interview did not receive a response, but the EMR Network's Web site states, "We are in the midst of potentially the most pervasive and important environmental struggle of the new millennium, the struggle to understand the effects of exposure to electromagnetic radiation. Wireless devices and broadcast antennas threaten the natural and human environments in ways that affect every one of us at home, school, places of worship, and at work."
While measuring RFR levels, as Foster has done, is valuable, the fact remains that many people are complaining of symptoms which they are convinced are the result of Wi-Fi. While it looks from a reasonable scientific perspective as though they are wrong about the source, the symptoms remain.
Rather than simply measuring emissions and comparing them to scientifically accepted levels, one group of researchers in London decided to "test whether people who report being sensitive to mobile phone signals have more symptoms when exposed to a pulsing mobile signal than when exposed to a sham signal or a non-pulsing signal."
Their results, which were published in the British Medical Journal in March 2006 (based on research conducted between 2003-2005) concluded, "No evidence was found to indicate that people with self-reported sensitivity to mobile phone signals are able to detect such signals, or that they react to them with increased symptom severity. As sham exposure was sufficient to trigger severe symptoms in some participants, psychological factors may have an important role in causing this condition."
120 subjects were included in the study, half of whom were "sensitive" people who reported frequently getting headaches within 20 minutes of using a mobile phone, and 60 "control" participants who did not report any such symptoms. The study showed that a virtually identical proportion of "sensitive" participants believed a signal was present during real exposure (60%) to GSM cellular signals, as did when no signal was present whatsoever (63%).
Since this study was relatively small and based on mobile phones, not on Wi-Fi, it can't be considered the final word. But since Wi-Fi equipment emits less intense radiation than do mobile phones, it does give a strong indication that the source of reported symptoms may lie somewhere other than the nearest WLAN.
This article was first published on WiFiPlanet.com.