Exposure Limits

By the early 1990s, an international organization, the IEEE, and many individual 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.

Safety Code 6 applies to employees of the federal public service departments and agencies. This code was also adopted by Industry Canada and enforced in granting licenses to operate RF installations.

What Safety Code 6 measures.
Safety Code 6 requires the conduct of RF radiation safety surveys to determine whether a device or an installation complies with the recommended standards of performance and personnel exposure. Surveys need only be made when the new or modified installation is capable of exceeding the limits specified in the Code. Some installations and devices have sufficiently low radiated power and physical location to produce RF levels in areas accessible to people that are well below the Code limits. Base stations for cellular telephones, when located on towers or other structures preventing people from accessing the antenna, are a good example of an RF installation that produces levels of RF well below the limits.

Further information:
Health Canada. Safety Code 6 (2009): Limits of human exposure to radiofrequency electromagnetic fields in the frequency range from 3 kHz to 300 GHz. Ottawa: Health Canada, 1999. http://www.hc-sc.gc.ca/ewh-semt/pubs/radiation/radio_guide-lignes_direct-eng.php

Stuchly MA. Proposed revision of the Canadian recommendations on radiofrequency-exposure protection. Health Physics 1987;53:649-665.

Foster KR, Glaser R: Thermal mechanisms of interaction of radiofrequency energy with biological systems with relevance to exposure guidelines. Health Phys 2007;92:609-620.

Standards in other countries
Several other countries, e.g. USA, United Kingdom, other European Community countries, Australia and Japan, recommend very similar limits to those in the Canadian Safety Code 6.
Roy and Martin (2007) point out that Eastern European countries differ in their approach from those that follow the IEEE and ICNIRP standards, in that they aim to protect against non-thermal effects caused by chronic, low-level exposure.

Standards for limiting far-field exposure to radiofrequencies apply to mobile phone base station antenna siting (FCC, 1996; ICNIRP, 1996).

Standards for limiting near-field exposure to radiofrequencies (e.g., localized SAR limits) have also been established in recent years (FCC, 1996; ICNIRP, 1996, 1998). ICNIRP recommends a localized SAR limit of 10 W/kg averaged over any 10 gram mass of tissue in the head for occupational exposures, and 2 W/kg averaged over any 10 gram mass of tissue in the head for general public exposures. The localized SAR limits are not likely to be exceeded under normal use conditions. . For further information on SAR, see the separate section on this in the web site.

Further information:
Federal Communication Commission. OET Bulletin #56. www.fcc.gov/oet/info/documents/bulletins

International Commission on Non-Ionizing Radiation Protection (ICNIRP).
Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz). www.icnirp.de/documents/Emfgdl.PDF

International Electrical and Electronic Engineering Organization (IEEE). IEEE Standard for safety levels with respect to human exposure to radio frequency electromagnetic fields, 3kHz to 300 GHz, sponsored by IEEE Standards Coordinating Committee 28 on Non-Ionizing Radiation Hazards, IEEE C95.1-1991.

WHO. Electromagnetic fields and public health. Fact sheet # 193 June 2000. www.who.int/peh-emf/publications/facts

Lin JC (2004): Current standards and their bases for safe human exposure to radio-frequency radiation. Radio Science Bulletin 309:50-52. (This is available at www.ursi.org)

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