QRZ! Ham Radio 1/QRZ Ham Radio Callsign Database - December 1993.iso/arrl/bioeffe.cts

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Reprinted from The 1992 ARRL Handbook chapter 36

Copyright 1992 American Radio Relay League, Inc.
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RF Radiation Safety

Although Amateur Radio is basically a safe activity, in recent
years there has been considerable discussion and concern about
the possible hazards of electromagnetic radiation (EMR),
including both RF energy and power frequency (50-60 Hz)
electromagnetic fields. xtensive research on this topic is under
way in many countries. This section was prepared by members of
the ARRL Committee on the Biological Effects of RF Energy ("Bio
Effects" Committee) and coordinated by Wayne Overbeck, N6NB. It
summarizes what is now known and offers safety precautions based
on the research to date.

All life on earth has adapted to survive in an environment of
weak, natural low-frequency electromagnetic fields (in addition
to the earth's static geomagnetic field). Natural low-frequency
EM fields come from two main sources: the sun, and thunderstorm
activity. But in the last 100 years, manmade fields at much
higher intensities and with a very different spectral
distribution have altered this natural EM background in ways that
are not yet fully understood. Much more research is needed to
assess the biological effects of EMR.

Both RF and 60-Hz fields are classified as nonionizing radiation
because the frequency is too low for there to be enough photon
energy to ionize atoms. Still, at sufficiently high power
densities, EMR poses certain health hazards. It has been known
since the early days of radio that RF energy can cause injuries
by heating body tissue. In extreme cases, RF-induced heating can
cause blindness, sterility and other serious health problems.
These heat-related health hazards may be called thermal effects.
But now there is mounting evidence that even at energy levels too
low to cause body heating, EMR has observable biological effects,
some of which may be harmful. These are athermal effects.

In addition to the ongoing research, much else has been done to
address this issue. For example, the American National Standards
Institute, among others, has recommended voluntary guidelines to
limit human exposure to RF energy. And the ARRL has established
the Bio Effects Committee, a committee of concerned medical
doctors and scientists, serving voluntarily to monitor scientific
research in this field and to recommend safe practices for radio
amateurs.

Thermal Effects of RF Energy

Body tissues that are subjected to very high levels of RF energy
may suffer serious heat damage. These effects depend upon the
frequency of the energy, the power density of the RF field that
strikes the body, and even on factors such as the polarization of
the wave.

At frequencies near the body's natural resonant frequency, RF
energy is absorbed more efficiently, and maximum heating occurs.
In adults, this frequency usually is about 35 MHz if the person
is grounded, and about 70 MHz if the person's body is insulated
from ground. Also, body parts may be resonant; the adult head,
for example, is resonant around 400 MHz, while a baby's smaller
head resonates near 700 MHz. Body size thus determines the
frequency at which most RF energy is absorbed. As the frequency
is increased above resonance, less RF heating generally occurs.
However, additional longitudinal resonances occur at about 1 GHz
near the body surface.

Nevertheless, thermal effects of RF energy should not be a major
concern for most radio amateurs because of the relatively low RF
power we normally use and the intermittent nature of most amateur
transmissions. Amateurs spend more time listening than
transmitting, and many amateur transmissions such as CW and SSB
use low-duty-cycle modes. (With FM or RTTY, though, the RF is
present continuously at its maximum level during each
transmission.)  In any event, it is rare for radio amateurs to be
subjected to RF fields strong enough to produce thermal effects
unless they are fairly close to an energized antenna or
unshielded power amplifier. Specific suggestions for avoiding
excessive exposure are offered later.

Athermal Effects of EMR

Nonthermal effects of EMR, on the other hand, may be of greater
concern to most amateurs because they involve lower-level energy
fields. In recent years, there have been many studies of the
health effects of EMR, including a number that suggest there may
be health hazards of EMR even at levels too low to cause
significant heating of body tissue. The research has been of two
basic types: epidemiological research, and laboratory research
into biological mechanisms by which EMR may affect animals or
humans.

Epidemiologists look at the health patterns of large groups of
people using statistical methods. A series of epidemiological
studies has shown that persons likely to have been exposed to
higher levels of EMR than the general population (such as persons
living near power lines or employed in electrical and related
occupations) have higher than normal rates of certain types of
cancers. For example, several studies have found a higher
incidence of leukemia and lymphatic cancer in children living
near certain types of power transmission and distribution lines
and near transformer substations than in children not living in
such areas. These studies have found a risk ratio of about 2,
meaning the chance of contracting the disease is doubled. (The
bibliography at the end of this chapter lists some of these
studies. See Wertheimer and Leeper, 1979, 1982; Savitz et al,
1988).

Parental exposures may also increase the cancer risk of their
offspring. Fathers in electronic occupations who are also exposed
to electronic solvents have children with an increased risk of
brain cancer (Johnson and Spitz, 1989), and children of mothers
who slept under electric blankets while pregnant have a 2.5 risk
ratio for brain cancer (Savitz et al, 1990).

Adults whose occupations expose them to strong 60-Hz fields (for
example, telephone line splicers and electricians) have been
found to have about four times the normal rate of brain cancer
and male breast cancer (Matanoski et al, 1989). Another study
found that microwave workers with 20 years of exposure had about
10 times the normal rate of brain cancer if they were also
exposed to soldering fumes or electronic solvents (Thomas et al,
1987). Typically, these chemical factors alone have risk ratios
around 2.

Dr. Samuel Milham, a Washington state epidemiologist, conducted a
large study of the mortality rates of radio amateurs, and found
that they had statistically significant excess mortality from one
type of leukemia and lymphatic cancer. Milham suggested that this
could result from the tendency of hams to work in electrical
occupations or from their hobby.

However, epidemiological research by itself is rarely conclusive.
Epidemiology only identifies health patterns in groups--it does
not ordinarily determine their cause. And there are often
confounding factors: Most of us are exposed to many different
environmental hazards that may affect our health in various ways.
Moreover, not all studies of persons likely to be exposed to high
levels of EMR have yielded the same results.

There has also been considerable laboratory research about the
biological effects of EMR in recent years. For example, it has
been shown that even fairly low levels of EMR can alter the human
body's circadian rhythms, affect the manner in which cancer-
fighting T lymphocytes function in the immune system, and alter
the nature of the electrical and chemical signals communicated
through the cell membrane and between cells, among other things.
(For a summary of some of this research, see Adey, 1990.)

Much of this research has focused on low-frequency magnetic
fields, or on RF fields that are keyed, pulsed or modulated at a
low audio frequency (often below 100 Hz). Several studies
suggested that humans and animals can adapt to the presence of a
steady RF carrier more readily than to an intermittent, keyed or
modulated energy source. There is some evidence that while EMR
may not directly cause cancer, it may sometimes combine with
chemical agents to promote its growth or inhibit the work of the
body's immune system.

None of the research to date conclusively proves that low-level
EMR causes adverse health effects. Although there has been much
debate about the meaning and significance of this research, many
medical authorities now urge "prudent avoidance" of unnecessary
exposure to moderate or high-level electromagnetic energy until
more is known about this subject.

Safe Exposure Levels

How much EM energy is safe?  Scientists have devoted a great deal
of effort to deciding upon safe RF-exposure limits. This is a
very complex problem, involving difficult public health and
economic considerations. The recommended safe levels have been
revised downward several times in recent years--and not all
scientific bodies agree on this question even today. In early
1991, a new American National Standards Institute (ANSI)
guideline for recommended EM exposure limits is on the verge of
being approved (see bibliography). If the new standard is
approved by a committee of the Institute of Electrical and
Electronic Engineers (IEEE), it will replace a 1982 ANSI
guideline that permitted somewhat higher exposure levels. ANSI-
recommended exposure limits before 1982 were higher still.

This new ANSI guideline recommends frequency-dependent and time-
dependent maximum permissible exposure levels. Unlike earlier
versions of the standard, the 1991 draft recommends different RF
exposure limits in controlled environments (that is, where energy
levels can be accurately determined and everyone on the premises
is aware of the presence of EM fields) and in uncontrolled
environments (where energy levels are not known or where some
persons present may not be aware of the EM fields).

Fig. 20 is a graph depicting the new ANSI standard. It is
necessarily a complex graph because the standards differ not only
for controlled and uncontrolled environments but also for
electric fields (E fields) and magnetic fields (H fields).
Basically, the lowest E-field exposure limits occur at
frequencies between 30 and 300 MHz. The lowest H-field exposure
levels occur at 100-300 MHz. The ANSI standard sets the maximum
E-field limits between 30 and 300 MHz at a power density of 1
mW/cm\2/ (61.4 volts per meter) in controlled environments--but
at one-fifth that level (0.2 mW/cm\2/ or 27.5 volts per meter) in
uncontrolled environments. The H-field limit drops to 1 mW/cm\2/
(0.163 ampere per meter) at 100-300 MHz in controlled
environments and 0.2 mW/cm\2/ (0.0728 ampere per meter) in
uncontrolled environments. Higher power densities are permitted
at frequencies below 30 MHz (below 100 MHz for H fields) and
above 300 MHz, based on the concept that the body will not be
resonant at those frequencies and will therefore absorb less
energy.

In general, the proposed ANSI guideline requires averaging the
power level over time periods ranging from 6 to 30 minutes for
power-density calculations, depending on the frequency and other
variables. The ANSI exposure limits for uncontrolled environments
are lower than those for controlled environments, but to
compensate for that the guideline allows exposure levels in those
environments to be averaged over much longer time periods
(generally 30 minutes). This long averaging time means that an
intermittently operating RF source (such as an Amateur Radio
transmitter) will show a much lower power density than a
continuous-duty station for a given power level and antenna
configuration.

Time averaging is based on the concept that the human body can
withstand a greater rate of body heating (and thus, a higher
level of RF energy) for a short time than for a longer period.
However, time averaging may not be appropriate in considerations
of nonthermal effects of RF energy.

The ANSI guideline excludes any transmitter with an output below
7 watts because such low-power transmitters would not be able to
produce significant whole-body heating. (However, recent studies
show that handheld transceivers often produce power densities in
excess of the ANSI standard within the head).

There is disagreement within the scientific community about these
RF exposure guidelines. The ANSI guideline is still intended
primarily to deal with thermal effects, not exposure to energy at
lower levels. A growing number of researchers now believe
athermal effects should also be taken into consideration. Several
European countries and localities in the United States have
adopted stricter standards than the proposed ANSI guideline.

Another national body in the United States, the National Council
for Radiation Protection and Measurement (NCRP), has also adopted
recommended exposure guidelines. NCRP urges a limit of 0.2
mW/cm\2/ for nonoccupational exposure in the 30-300 MHz range.
The NCRP guideline differs from ANSI in two notable ways: It
takes into account the effects of modulation on an RF carrier,
and it does not exempt transmitters with outputs below 7 watts.

Low-Frequency Fields

Recently much concern about EMR has focused on low-frequency
energy, rather than RF. Amateur Radio equipment can be a
significant source of low-frequency magnetic fields, although
there are many other sources of this kind of energy in the
typical home. Magnetic fields can be measured relatively
accurately with inexpensive 60-Hz dosimeters that are made by
several manufacturers.

Table 3 shows typical magnetic field intensities of Amateur Radio
equipment and various household items. Because these fields
dissipate rapidly with distance, "prudent avoidance" would mean
staying perhaps 12 to 18 inches away from most Amateur Radio
equipment (and 24 inches from power supplies and 1-kW RF
amplifiers) whenever the ac power is turned on. The old custom of
leaning over a linear amplifier on a cold winter night to keep
warm may not be the best idea!

Table 3

Typical 60-Hz Magnetic Fields Near Amateur Radio Equipment and
AC-Powered Household Appliances

Values are in milligauss.

Item                      Field      Distance

Electric blanket         30-  90     Surface Microwave oven
                         10- 100     Surface
                          1-  10     12"
IBM personal computer     5-  10     Atop monitor
                          0-   1     15" from screen
Electric drill          500-2000     At handle
Hair dryer              200-2000     At handle
HF transceiver           10- 100     Atop cabinet
                          1-   5     15" from front
1-kW RF amplifier        80-1000     Atop cabinet
                          1-  25     15" from front

(Source: measurements made by members of the ARRL Bio Effects
Committee)

There are currently no national standards for exposure to low-
frequency fields. However, epidemiological evidence suggests that
when the general level of 60-Hz fields exceeds 2 milligauss,
there is an increased cancer risk in both domestic environments
(Savitz et al, 1988) and industrial environments (Matanoski et
al, 1989; Davis and Milham, 1990; Garland et al, 1990). Typical
home environments (not close to appliances or power lines) are in
the range of 0.1-0.5 milligauss.

DETERMINING RF POWER DENSITY

Unfortunately, determining the power density of the RF fields
generated by an amateur station is not as simple as measuring
low-frequency magnetic fields. Although sophisticated instruments
can be used to measure RF power densities quite accurately, they
are costly and require frequent recalibration. Most amateurs
don't have access to such equipment, and the inexpensive field-
strength meters that we do have are not suitable for measuring RF
power density. The best we can usually do is to estimate our own
RF power density based on measurements made by others or, given
sufficient computer programming skills, use computer modeling
techniques.

Table 4 shows a sampling of measurements made at Amateur Radio
stations by the Federal Communications Commission and the
Environmental Protection Agency in 1990. As this table indicates,
a good antenna well removed from inhabited areas poses no hazard
under any of the various exposure guidelines. However, the
FCC/EPA survey also indicates that amateurs must be careful about
using indoor or attic-mounted antennas, mobile antennas, low
directional arrays, or any other antenna that is close to
inhabited areas, especially when moderate to high power is used.

Table 4

Typical RF Field Strengths near Amateur Radio Antennas

A sampling of values as measured by the Federal Communications
Commission and Environmental Protection Agency, 1990.

                     Freq,    Power,    E Field, Antenna Type
MHz      Watts     V/m      Location

Dipole in attic       14.15    100     7-100     In home
Discone in attic     146.5     250    10- 27     In home
Half sloper           21.15   1000        50     1 m from base
Dipole at 7-13 ft      7.14    120     8-150     1-2 m from earth
Vertical               3.8     800       180     0.5 m from base
5-element Yagi at 60' 21.2    1000    10- 20     In shack
                                          14     12 m from base
3-element Yagi at 25' 28.5     425     8- 12     12 m from base
Inverted V at 22-46'   7.23   1400     5- 27     Below antenna
Vertical on roof      14.11    140     6-  9     In house
                                      35-100     At antenna tuner
Whip on auto roof    146.5     100    22- 75     2 m from antenna
                                      15- 30     In vehicle
                                          90     Rear seat
5-element Yagi at 20' 50.1     500    37- 50     10 m from antenna

Ideally, before using any antenna that is in close proximity to
an inhabited area, you should measure the RF power density. If
that is not feasible, the next best option is make the
installation as safe as possible by observing the safety
suggestions listed in Table 5.

It is also possible, of course, to calculate the probable power
density near an antenna using simple equations. However, such
calculations have many pitfalls. For one, most of the situations
in which the power density would be high enough to be of concern
are in the near field--an area roughly bounded by several
wavelengths of the antenna. In the near field, ground
interactions and other variables produce power densities that
cannot be determined by simple arithmetic.

Computer antenna-modeling programs such as MININEC or other codes
derived from NEC (Numerical Electromagnetics Code) are suitable
for estimating RF magnetic and electric fields around amateur
antenna systems. And yet, these too have limitations. Ground
interactions must be considered in estimating near-field power
densities. Also, computer modeling is not sophisticated enough to
predict "hot spots" in the near field--places where the field
intensity may be far higher than would be expected.

Intensely elevated but localized fields often can be detected by
professional measuring instruments. These "hot spots" are often
found near wiring in the shack and metal objects such as antenna
masts or equipment cabinets. But even with the best
instrumentation, these measurements may also be misleading in the
near field.

One need not make precise measurements or model the exact antenna
system, however, to develop some idea of the relative fields
around an antenna. Computer modeling using close approximations
of the geometry and power input of the antenna will generally
suffice. Those who are familiar with MININEC can estimate their
power densities by computer modeling, and those with access to
professional power-density meters can make useful measurements.

While our primary concern is ordinarily the intensity of the
signal radiated by an antenna, we should also remember that there
are other potential energy sources to be considered. You can also
be exposed to RF radiation directly from a power amplifier if it
is operated without proper shielding. Transmission lines may also
radiate a significant amount of energy under some conditions.

SOME FURTHER RF EXPOSURE SUGGESTIONS

Potential exposure situations should be taken seriously. Based on
the FCC/EPA measurements and other data, the "RF awareness"
guidelines of Table 5 were developed by the ARRL Bio Effects
Committee. A longer version of these guidelines appeared in a QST
article by Ivan Shulman, MD, WC2S (see bibliography).

QST carries information regarding the latest developments for RF
safety precautions and regulations at the local and federal
levels. You can find additional information about the biological
effects of RF radiation in the publications listed in the
bibliography.

Table 5

RF Awareness Guidelines

These guidelines were developed by the ARRL Bio Effects
Committee, based on the FCC/EPA measurements of Table 4 and other
data.

o Although antennas on towers (well away from people) pose no
exposure problem, make certain that the RF radiation is confined
to the antenna radiating elements themselves. Provide a single,
good station ground (earth), and eliminate radiation from
transmission lines. Use good coaxial cable, not open wire lines
or end-fed antennas that come directly into the transmitter area.

o No person should ever be near any transmitting antenna while it
is in use. This is especially true for mobile or ground-mounted
vertical antennas. Avoid transmitting with more than 25 watts in
a VHF mobile installation unless it is possible to first measure
the RF fields inside the vehicle. At the 1-kilowatt level, both
HF and VHF directional antennas should be at least 35 feet above
inhabited areas. Avoid using indoor and attic-mounted antennas if
at all possible.

o Don't operate RF power amplifiers with the covers removed,
especially at VHF/UHF.

o In the UHF/SHF region, never look into the open end of an
activated length of waveguide or point it toward anyone. Never
point a high-gain, narrow-beamwidth antenna (a paraboloid, for
instance) toward people. Use caution in aiming an EME
(moonbounce) array toward the horizon; EME arrays may deliver an
effective radiated power of 250,000 watts or more.

o With handheld transceivers, keep the antenna away from your
head and use the lowest power possible to maintain
communications. Use a separate microphone and hold the rig as far
away from you as possible.

o Don't work on antennas that have RF power applied.

o Don't stand or sit close to a power supply or linear amplifier
when the ac power is turned on. Stay at least 24 inches away from
power transformers, electrical fans and other sources of high-
level 60-Hz magnetic fields.

BIBLIOGRAPHY

Source material and more extended discussion of topics covered in
this chapter can be found in the references given below and in
the textbooks listed at the end of Chapter 2.

W. R. Adey, "Tissue Interactions with Nonionizing Electromagnetic
Fields," Physiology Review, 1981; 61:435-514.

W. R. Adey, "Cell Membranes: The Electromagnetic Environment and
Cancer Promotion," Neurochemical Research, 1988; 13:671-677.

W. R. Adey, "Electromagnetic Fields, Cell Membrane Amplification,
and Cancer Promotion," in B. W. Wilson, R. G. Stevens, and

L. E. Anderson, Extremely Low Frequency Electromagnetic Fields:
The Question of Cancer (Columbus, OH: Batelle Press, 1989), pp
211-249.

W. R. Adey, "Electromagnetic Fields and the Essence of Living
Systems," Plenary Lecture, 23rd General Assembly, Internat'l
Union of Radio Sciences (URSI), Prague, 1990; in J. Bach
Andersen, Ed., Modern Radio Science (Oxford: Oxford Univ Press),
pp 1-36.

Q. Balzano, O. Garay and K. Siwiak, "The Near Field of Dipole
Antennas, Part I: Theory," IEEE Transactions on Vehicular
Technology (VT) 30, p 161, Nov 1981. Also "Part II; Experimental
Results," same issue, p 175.

D. F. Cleveland and T. W. Athey, "Specific Absorption Rate (SAR)
in Models of the Human Head Exposed to Hand-Held UHF Portable
Radios," Bioelectromagnetics, 1989; 10:173-186.

D. F. Cleveland, E. D. Mantiply and T. L. West, "Measurements of
Environmental Electromagnetic Fields Created by Amateur Radio
Stations," presented at the 13th annual meeting of the
Bioelectromagnetics Society, Salt Lake City, Utah, Jun 1991.

R. L. Davis and S. Milham, "Altered Immune Status in Aluminum
Reduction Plant Workers," American J Industrial Medicine, 1990;
131:763-769.

F. C. Garland et al, "Incidence of Leukemia in Occupations with
Potential Electromagnetic Field Exposure in United States Navy
Personnel," American J Epidemiology, 1990; 132:293-303.

A. W. Guy and C. K. Chou, "Thermographic Determination of SAR in
Human Models Exposed to UHF Mobile Antenna Fields," Paper F-6,
Third Annual Conference, Bioelectromagnetics Society, Washington,
DC, Aug 9-12, 1981.

C. C. Johnson and M. R. Spitz, "Childhood Nervous System Tumours:
An Assessment of Risk Associated with Paternal Occupations
Involving Use, Repair or Manufacture of Electrical and Electronic
Equipment," Internat'l J Epidemiology, 1989; 18:756-762.

D. L. Lambdin, "An Investigation of Energy Densities in the
Vicinity of Vehicles with Mobile Communications Equipment and
Near a Hand-Held Walkie Talkie," EPA Report ORP/EAD 79-2, Mar,
1979.

D. B. Lyle, P. Schechter, W. R. Adey and R. L. Lundak,
"Suppression of T-Lymphocyte Cytotoxicity Following Exposure to
Sinusoidally Amplitude Modulated Fields," Bioelectromagnetics,
1983; 4:281-292.

G. M. Matanoski et al, "Cancer Incidence in New York Telephone
Workers," Proc Annual Review, Research on Biological Effects of
50/60 Hz Fields, U.S. Dept of Energy, Office of Energy Storage
and Distribution, Portland, OR, 1989.

S. Milham, "Mortality from Leukemia in Workers Exposed to
Electromagnetic Fields," New England J Medicine, 1982; 307:249.

S. Milham, "Increased Mortality in Amateur Radio Operators due to
Lymphatic and Hematopoietic Malignancies," American J
Epidemiology, 1988; 127:50-54.

W. W. Mumford, "Heat Stress Due to RF Radiation," Proc IEEE, 57,
1969, pp 171-178.

S. Preston-Martin et al, "Risk Factors for Gliomas and
Meningiomas in Males in Los Angeles County," Cancer Research,
1989; 49:6137-6143.

D. A. Savitz et al, "Case-Control Study of Childhood Cancer and
Exposure to 60-Hz Magnetic Fields, American J Epidemiology, 1988;
128:21-38.

D. A. Savitz et al, "Magnetic Field Exposure from Electric
Appliances and Childhood Cancer," American J Epidemiology, 1990;
131:763-773.

I. Shulman, "Is Amateur Radio Hazardous to Our Health?" QST, Oct
1989, pp 31-34.

R. J. Spiegel, "The Thermal Response of a Human in the Near-Zone
of a Resonant Thin-Wire Antenna," IEEE Transactions on Microwave
Theory and Technology (MTT) 30(2), pp 177-185, Feb 1982.

T. L. Thomas et al, "Brain Tumor Mortality Risk among Men with
Electrical and Electronic Jobs: A Case-Controlled Study," J
National Cancer Inst, 1987; 79:223-237.

N. Wertheimer and E. Leeper, "Electrical Wiring Configurations
and Childhood Cancer," American J Epidemiology, 1979; 109:273-
284.

N. Wertheimer and E. Leeper, "Adult Cancer Related to Electrical
Wires Near the Home," Internat'l J Epidemiology, 1982; 11:345-
355.

"Safety Levels with Respect to Human Exposure to Radio Frequency
Electromagnetic Fields (300 kHz to 100 GHz)," ANSI C95.1-1991
(New York: IEEE American National Standards Institute, 1990
draft).

"Biological Effects and Exposure Criteria for Radiofrequency
Electromagnetic Fields," NCRP Report No 86 (Bethesda, MD:
National Council on Radiation Protection and Measurements, 1986).

US Congress, Office of Technology Assessment, "Biological Effects
of Power Frequency Electric and Magnetic Fields--Background
Paper," OTA-BP-E-53 (Washington, DC: US Government Printing
Office), 1989.