Fact Sheet N°226
June 1999
ELECTROMAGNETIC FIELDS AND
PUBLIC HEALTH RADARS AND
HUMAN HEALTH
Radar systems detect the presence, direction or range of
aircraft, ships or other, usually moving objects. This is
achieved by sending pulses of high frequency
electromagnetic fields (EMF). Invented some 60 years ago,
radar systems have been widely used for navigation,
aviation, national defence and weather forecasting. Their
primary objective is individual and collective safety and
protection.
People who live or routinely work around radars have
expressed concerns about long-term adverse effects of
these systems on health, including cancer, reproductive
malfunction, cataracts and changes in behaviour or
development of children. A recent example has been the
alleged increase in testicular cancer in police using speed
control hand-held radar "guns".
It is important to distinguish between perceived and real
dangers that radars pose, as well as to understand the
rational behind existing international standards and
protective measures used today.
EMF Emissions: Radars usually operate at radio
frequencies (RF) between 300 MHz and 15 GHz. They
generate EMFs that are called RF fields. RF fields within
this part of the electromagnetic spectrum are known to
interact differently with human body.
RF fields below 10 GHz (to 1 MHz) penetrate exposed
tissues and produce heating due to energy absorption.
The depth of penetration depends on the frequency of the
field and is greater for lower frequencies. Absorption of RF
fields in tissues is measured as a specific absorption rate
(SAR) within a given tissue mass. The unit of SAR is watts
per kilogram (W/kg). SAR is the quantity used to measure
the "dose" of RF fields between about 1 MHz and 10 GHz.
l An SAR of at least 4 W/kg is needed to produce known
adverse health effects in people exposed to RF fields in
this frequency range.
RF fields above 10 GHz are absorbed at the skin surface,
with very little of the energy penetrating into the underlying
tissues. The basic dosimetric quantity for RF fields above 10
GHz is the intensity of the field measured as power density
in watts per square metre (W/m2) or for weak fields in
milliwatts per square metre (mW/m2) or microwatts per
square metre (μW/m2).
l Exposure to RF fields above 10 GHz at power densities
over 1000 W/m2 are known to produce adverse health
effects, such as eye cataracts and skin burns.
Human Exposure: The power that radar systems emit
varies from a few milliwatts (police traffic control radar) to
many kilowatts (large space tracking radars). However, a
number of factors significantly reduce human exposure to
RF generated by radar systems, often by a factor of at least100:l Radar systems send electromagnetic waves in pulses
and not continuously. This makes the average power
emitted much lower than the peak pulse power.
l Radars are directional and the RF energy they generate
is contained in beams that are very narrow and
resemble the beam of a spotlight. RF levels away from
the main beam fall off rapidly. In most cases, these
levels are thousands of times lower than in the main
beam.
l Many radars have antennas which are continuously
rotating or varying their elevation by a nodding motion,
thus constantly changing the direction of the beam.
l Areas, where dangerous human exposure may occur
are normally inaccessible to unauthorized personnel.
Radar Sources: Some of the common types of radars
encountered in daily life include:
Air traffic control radars are used to track the location of
aircraft and to control their landing at airports. They are
generally located at elevated positions where the beam is
inaccessible to persons on the ground. Typical air traffic
control radars can have peak powers of 100 kW or more, but
average powers of a few hundred watts. Under normal
operating conditions, these systems pose no hazard to the
general public.
Weather radars are often co-located with air traffic control
radars in remote areas at airports. They operate at higher
frequencies but generally have lower average and peak
powers. As with air traffic control radars, under normal
conditions, they pose no hazards to the general public.
Military radars are numerous and vary from very large
installations, which have large peak (1 MW or greater) and
average powers (kW), to small military fire control radars,
typically found on aircraft. Large size radars often evoke
concern in communities living around them. However,
because its power is radiated over a large surface area, the
power densities associated with these systems vary
between 10 and 100 W/m2 within the site boundary. Outside
the site boundary RF field levels are usually unmeasurable
without using sophisticated equipment. However, small
military fire control radars on aircraft can be hazardous to
ground personnel. These units have relatively high average
powers (kW) and small area antennas, making it possible to
have power densities up to 10 kW/m2. Members of the
general public would not be exposed to these emissions
because during ground testing of radars access to these
areas by all personnel is prohibited. The military also use
most other types of radars described below.
Marine radars can be found on small pleasure boats to
large ocean going vessels. Peak powers of these systems
can reach up to 30 kW, with average powers ranging from 1
to 25 W. Under normal operating conditions, with the
antenna rotating, the average power density of the higher
power systems within a metre of the antenna is usually less
than 10 W/m2. In accessible areas on most watercraft, these
levels would fall to a few percent of present public RF
exposure standards.
Speed Control Radars are hand-held by police in many
countries. The average output power is very low, a few
milliwatts, and so the units are not considered hazardous to
health, even when used in very close proximity to the body.
Possible Health Effects: Most studies conducted to
date examined health effects other than cancer. They
probed into physiological and thermoregulatory responses,
behavioural changes and effects such as the induction of
lens opacities (cataracts) and adverse reproductive outcome
following acute exposure to relatively high levels of RF
fields. There are also a number of studies that report non-
thermal effects, where no appreciable rise in temperature
can be measured.
Cancer-related studies: Many epidemiological studies
have addressed possible links between exposure to RF and
excess risk of cancer. However, because of differences in
the design and execution of these studies, their results are
difficult to interpret. A number of national and international
peer review groups have concluded that there is no clear
evidence of links between RF exposure and excess risk of
cancer. WHO has also concluded that there is no convincing
scientific evidence that exposure to RF shortens the life
span of humans, or that RF is an inducer or promoter of
cancer. However, further studies are necessary.
Thermal effects: RF fields have been studied in animals,
including primates. The earliest signs of an adverse health
consequence, found in animals as the level of RF fields
increased, include reduced endurance, aversion of the field
and decreased ability to perform mental tasks. These
studies also suggest adverse effects may occur in humans
subjected to whole body or localized exposure to RF fields
sufficient to increase tissue temperatures by greater than 1°
C. Possible effects include the induction of eye cataracts,
and various physiological and thermoregulatory responses
as body temperature increases. These effects are well
established and form the scientific basis for restricting
occupational and public exposure to RF fields.
Non-thermal effects: Exposure to RF levels too low to
involve heating, (i.e., very low SARs), has been reported by
several groups to alter calcium ion mobility, which is
responsible for transmitting information in tissue cells.
However, these effects are not sufficiently established to
provide a basis for restricting human exposure.
Pulsed RF fields: Exposure to very intense pulsed RF
fields, similar to those used by radar systems, has been
reported to suppress the startle response and evoke body
movements in conscious mice. In addition, people with
normal hearing have perceived pulse RF fields with
frequencies between about 200 MHz and 6.5 GHz. This is
called the microwave hearing effect. The sound has been
variously described as a buzzing, clicking, hissing or
popping sound, depending on the RF pulsing
characteristics. Prolonged or repeated exposure may be
stressful and should be avoided where possible.
RF shocks and burns: At frequencies less than 100 MHz,
RF burns or shock may result from charges induced on
metallic objects situated near radars. Persons standing in
RF fields can also have high local absorption of the fields in
areas of their bodies with small cross sectional areas, such
as the ankles. In general, because of the higher frequencies
that most modern radar systems operate, combined with
their small beam widths, the potential for such effects is very
small.
Electromagnetic interference: Radars can cause
electromagnetic interference in other electronic equipment.
The threshold for these effects are often well below
guidance levels for human exposure to RF fields.
Additionally, radars can also cause interference in certain
medical devices, such as cardiac pacemakers and hearing
aids. If individuals using such devices work in close
proximity to radar systems they should contact
manufacturers to determine the susceptibility of their
products to RF interference.
Ignition of flammable liquids and explosives: RF fields
can ignite flammable liquids and explosives through the
induction of currents. This is a rare occurrence, and
normally of most concern where there is a large
concentration of radars, such as on board a naval ship
where measures are taken to prevent such effects.
International Standards: Exposure limits for RF fields
are developed by international bodies such as the
International Commission on Non-Ionizing Radiation
Protection (ICNIRP). ICNIRP is a non-governmental
organization formally recognised by WHO. The Commission
uses health risk assessments developed in conjunction with
WHO to draft their guidelines on exposure limits. The
ICNIRP guidelines protect against all established RF health
effects and are developed following reviews of all the peer-
reviewed scientific literature, including reports on cancer
and non-thermal effects. Environmental RF levels from
radars, in areas normally accessible to the general public,
are at least 1,000 times below the limits for continuous
public exposure allowed by the ICNIRP guidelines, and
25,000 times below the level at which RF exposure has
been established to cause the earliest known health effects.
Protective Measures: The aim of protective measures is
to eliminate or reduce human exposure to RF fields below
acceptable limits. An extensive program of measurement
surveys, hazard communication, coupled with effective
protective measures, is required around all radar
installations. In most countries, comprehensive
documentation is prepared, including an environmental
impact statement, before a radar system can be
constructed.
Following construction of the radar facility, site surveys
should be performed to quantify RF field levels in the area.
While extremely high RF field levels can be measured
directly in front of a radar, in most cases levels in public
areas are not easily measurable. In order to prevent both
workers and the general public from entering areas where
the RF levels are above the limits, both engineering and
administrative controls are used.
l Engineering controls include interlocks, electronic
means to exclude the radar pointing in certain areas,
and shielding.
l Administrative controls include audible and visible
alarms, warning signs, and restriction of access
through barriers, locked doors, or limiting access time
to radar.
When engineering and administrative controls do not
suffice, workers should use personal protective equipment
to ensure compliance with exposure standards. Conductive
suits, gloves, safety shoes and other types of personal
protective equipment for RF fields are now commercially
available.
l They should be used with great care, since the
attenuation properties of the material used to make this
protective equipment can vary dramatically with
frequency. Only when the attenuation properties of the
equipment is known at the frequency in question can
they be used reliably.
l Special care should be exercised with RF safety
glasses since any metal may enhance local fields by
acting as a receiving antenna.
l There are no exposure situations where members of
the general public need to use protective equipment for
RF fields from radars.
l In recent years, clothing and other materials have
appeared on the consumer market claiming to have RF
shielding properties, and directing their claims to
"sensitive" members of the general population, such as
pregnant women. The use of these types of products is
unnecessary and should be discouraged. They offer no
effective RF shielding, and there is no need for these
devices.
For more information, see http://www.who.int/emf/
For further information, journalists can contact :
WHO Press Spokesperson and Coordinator, Spokesperson's
Office,
WHO HQ, Geneva, Switzerland / Tel +41 22 791 4458/2599 / Fax +41
22 791 4858 / e-Mail: inf@who.int
Human exposure to EMF emitted by radar systems is
limited by international standards and protective measures,
which were adopted on the basis the currently available
scientific evidence. In summary:
l RF fields cause molecules in tissue to vibrate and
generate heat. Heating effects could be expected if
time is spent directly in front of some radar antennas,
but are not possible at the environmental levels of RF
fields emanating from radar systems.
l To produce any adverse health effect, RF exposure
above a threshold level must occur. The known
threshold level is the exposure needed to increase
tissue temperature by at least 1oC. The very low RF
environmental field levels from radar systems cannot
cause any significant temperature rise.
l To date, researchers have not found evidence that
multiple exposures to RF fields below threshold levels
cause any adverse health effects. No accumulation of
damage occurs to tissues from repeated low level RF
exposure.
l At present, there is no substantive evidence that
adverse health effects, including cancer, can occur in
people exposed to RF levels at or below the limits set
by international standards. However, more research is
needed to fill certain gaps in knowledge
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