Fact Sheet N°226
June 1999

ELECTROMAGNETIC FIELDS AND
PUBLIC HEALTH RADARS AND
HUMAN HEALTH
Radar systems detect the presence, direction or range ofaircraft, ships or other, usually moving objects. This isachieved 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. Theirprimary objective is individual and collective safety andprotection.
People who live or routinely work around radars haveexpressed concerns about long-term adverse effects ofthese systems on health, including cancer, reproductive
malfunction, cataracts and changes in behaviour ordevelopment of children. A recent example has been thealleged 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 therational behind existing international standards andprotective 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 tointeract 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 thefield 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 measurethe "dose" of RF fields between about 1 MHz and 10 GHz.

lAn SAR of at least 4 W/kg is needed to produce known
adverse health effects in people exposed to RF fields inthis 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 inmilliwatts per square metre (mW/m2) or microwatts persquare metre (µW/m2).
lExposure to RF fields above 10 GHz at power densities
over 1000 W/m2 are known to produce adverse healtheffects, 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, anumber of factors significantly reduce human exposure to
RF generated by radar systems, often by a factor of at least
100:
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 andresemble the beam of a spotlight. RF levels away fromthe main beam fall off rapidly. In most cases, theselevels are thousands of times lower than in the mainbeam.
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.
lRadar Sources: Some of the common types of radars
encountered in daily life include:
Air traffic control radars are used to track the location ofaircraft 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 peakpowers. As with air traffic control radars, under normalconditions, 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) andaverage 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, thepower densities associated with these systems vary
between 10 and 100 W/m 2 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 toground personnel. These units have relatively high average
powers (kW) and small area antennas, making it possible tohave power densities up to 10 kW/m 2. Members of thegeneral public would not be exposed to these emissions
because during ground testing of radars access to theseareas 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 tolarge 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 theantenna rotating, the average power density of the higher
power systems within a metre of the antenna is usually lessthan 10 W/m 2. In accessible areas on most watercraft, theselevels 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 tohealth, even when used in very close proximity to the body.

Possible Health Effects: Most studies conducted todate examined health effects other than cancer. They
probed into physiological and thermoregulatory responses,
behavioural changes and effects such as the induction oflens opacities (cataracts) and adverse reproductive outcomefollowing acute exposure to relatively high levels of RF

fields. There are also a number of studies that report nonthermal effects, where no appreciable rise in temperature
can be measured.
Cancer-related studies: Many epidemiological studies
have addressed possible links between exposure to RF andexcess risk of cancer. However, because of differences inthe design and execution of these studies, their results aredifficult 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 ofcancer. 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 ofcancer. However, further studies are necessary.
Thermal effects: RF fields have been studied in animals,including primates. The earliest signs of an adverse healthconsequence, found in animals as the level of RF fields
increased, include reduced endurance, aversion of the fieldand decreased ability to perform mental tasks. Thesestudies 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 wellestablished 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 byseveral groups to alter calcium ion mobility, which is
responsible for transmitting information in tissue cells.
However, these effects are not sufficiently established toprovide a basis for restricting human exposure.
Pulsed RF fields: Exposure to very intense pulsed RF
fields, similar to those used by radar systems, has beenreported to suppress the startle response and evoke body
movements in conscious mice. In addition, people withnormal hearing have perceived pulse RF fields withfrequencies between about 200 MHz and 6.5 GHz. This iscalled the microwave hearing effect. The sound has beenvariously described as a buzzing, clicking, hissing orpopping 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 inareas of their bodies with small cross sectional areas, suchas 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 verysmall.
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 theirproducts to RF interference.

Ignition of flammable liquids and explosives: RF fields
can ignite flammable liquids and explosives through theinduction of currents. This is a rare occurrence, andnormally 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 theInternational Commission on Non-Ionizing Radiation
Protection (ICNIRP). ICNIRP is a non-governmentalorganization formally recognised by WHO. The Commission
uses health risk assessments developed in conjunction withWHO to draft their guidelines on exposure limits. The
ICNIRP guidelines protect against all established RF healtheffects and are developed following reviews of all the peerreviewed scientific literature, including reports on cancer
and non-thermal effects. Environmental RF levels fromradars, 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, and25,000 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 beconstructed.
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 publicareas 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 andadministrative controls are used.
Engineering controls include interlocks, electronicmeans to exclude the radar pointing in certain areas,and shielding.
l Administrative controls include audible and visible
alarms, warning signs, and restriction of accessthrough barriers, locked doors, or limiting access timeto radar.
lWhen engineering and administrative controls do not
suffice, workers should use personal protective equipment
to ensure compliance with exposure standards. Conductivesuits, gloves, safety shoes and other types of personal
protective equipment for RF fields are now commerciallyavailable.
They should be used with great care, since theattenuation properties of the material used to make thisprotective equipment can vary dramatically withfrequency. Only when the attenuation properties of theequipment is known at the frequency in question canthey be used reliably.
l Special care should be exercised with RF safety
glasses since any metal may enhance local fields byacting 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 haveappeared on the consumer market claiming to have RFshielding properties, and directing their claims tol

"sensitive" members of the general population, such aspregnant women. The use of these types of products is
unnecessary and should be discouraged. They offer noeffective RF shielding, and there is no need for thesedevices.
Human exposure to EMF emitted by radar systems islimited by international standards and protective measures,
which were adopted on the basis the currently available
scientific evidence. In summary:RF fields cause molecules in tissue to vibrate andgenerate heat. Heating effects could be expected iftime 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 increasetissue temperature by at least 1o C. The very low RF
environmental field levels from radar systems cannot
cause any significant temperature rise.
l To date, researchers have not found evidence thatmultiple exposures to RF fields below threshold levels
cause any adverse health effects. No accumulation ofdamage occurs to tissues from repeated low level RF
exposure.
l At present, there is no substantive evidence thatadverse health effects, including cancer, can occur inpeople exposed to RF levels at or below the limits set
by international standards. However, more research isneeded to fill certain gaps in knowledgelFor more information, see http://www.who.int/emf/

For further information, journalists can contact :WHO Press Spokesperson and Coordinator, Spokesperson'sOffice,
WHO HQ, Geneva, Switzerland / Tel +41 22 791 4458/2599 / Fax +41
22 791 4858 / e-Mail: inf@who.int

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