Countries had established health protection standards for RF. These were based on the Specific Absorption Rate, which indicates the amount of energy from RFR absorbed by the body when a wireless phone is used. These standards weres based on substantial research from experiments with animals and cells. They generally were based on the whole-body average SAR, and only to a limited extent on the SAR in local tissues of the body. Use of the SAR enabled experimental data for various animals at different frequencies to be integrated, and extrapolated to human exposures. The IEEE relied on these animal experiments when it established its standards. Adverse biological effects had been found at SAR levels above 4 W/kg, and it was decided that for the general population a safety factor of 50 would be used. As a result the standard limited the exposure of the general population to 0.08 W/kg in one gram of tissue, averaged over the entire body, for periods of 15-30 minutes.
In the case of mobile phones, the effects of partial body exposure (e.g. the head) may be the most important consideration. A partial body limit of 20 times this value was accepted i.e. 1.6 W/kg in any 1 gram of tissue. Foster and Glaser (2007) have reviewed thermal mechanisms of interaction of RF energy with biological sytems.
Thermal effects: : In other jurisdictions, the limits of exposure are based on the prevention of an excessive rise in body temperature, or in local temperature increase in the case of partial body exposure. This is based on the observation that an excessive increase in body temperature can cause adverse effects. It is also assumed that when there is partial body exposure the effects may be modified by heat removal from unexposed parts of the body. Ziskin (2002) has reviewed medical aspects of RF radiation overexposure.
The biological basis for limiting RF exposure can be found in detailed scientific documents produced by various national and international scientific review panels. The standards employed by Canada are set out in Safety Code 6, which was issued in 1991and revised in 1999. The code specifies the limits of exposure to RF fields at frequencies 10 kHz – 300 GHz. M. Stuchly (1987) reviewed the scientific data on which the code was based, and the rationale for the specific clauses. These can be briefly summarized as follows:
• the limits of the electric field, magnetic field and power density are specified to protect against the direct effects due to RF field exposures, and are based on SARs; they are set at one tenth of the lowest level of exposure that could cause harm for people who are exposed to RF fields in their daily work environment.
• additional limits at frequencies 10 kHz – 30 MHz are set for contact currents to prevent shocks and burns; these limits are based on experimental data for humans;
• more restrictive limits, by a factor of five, for the general population are due to the exposure duration and potential for greater susceptibility to RF of some people compared to healthy workers;
• thresholds for adverse effects for far field exposures are estimated as SAR of 1 to 4 W/kg for the whole-body average. This results in the whole-body average SAR benchmarks for the limits of 0.08 W/kg for the general population, and of 0.4 W/kg for occupational workers. The preceding benchmarks are applied only above 3 MHz;
• below 100 kHz, SARs are much lower, and the ratios of the maximum induced current densities and current densities causing tissue stimulation are used as limits; this approach resulted in the limits for the electric and magnetic fields not being related by the uniform plane wave impedance;
• between 100 kHz and 3 MHz is the transition region to match the limits at two ranges in which specific rationales are used;
• the SAR limits for partial body exposures are based mostly on estimates or “scientific guesses” from the whole-body average SARs, and in the case of the eye on one experimental report.
United Arab Emirates, Abu Dhabi
Costa Mesa, California
Salt Lake City, Utah
Birmingham, Alabama, USA
Nedlands, Victoria, Australia
Maryborough, Queensland, Australia
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