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.
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.
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;
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
- 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.
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.
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.
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
for limiting far-field exposure to radiofrequencies apply to mobile
phone base station antenna siting (FCC, 1996; ICNIRP, 1996).
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.
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,
WHO. Electromagnetic fields and public health. Fact sheet # 193 June
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)