RF Safety and Amateur Radio
RF Safety
Why are we concerned with RF Safety? To
date, despite extensive scientific studies, the only confirmed biological
danger from radio frequency energy is the heating of tissue to temperature levels
that cause it to be damaged. Although there are those who believe that any
exposure to RF energy must be dangerous, the evidence does not support that
belief. Yet, people do get sick and we would like to make sure that we
avoid doing any damage.
Radiation
One thing that scares people is that RF
energy radiates, and some use the term RF Radiation (RFR). Since
the word, radiation, is more commonly associated with atomic bombs and
radioactive substances, which are quite dangerous to living organisms, RFR
simply sounds dangerous. All energy radiates and there are different types
of radiation, some dangerous and some not. For instance, a radiant heater
causes heat to radiate so that we can stay warm in the winter. Yet the radiated
heat is not inherently dangerous. Visible light radiates and, for the most
part, is not dangerous. Radiating energy can be divided into two groups:
Ionizing Radiation and Nonionizing Radiation. The division between
the two is based on frequency. Ionizing Radiation, by definition, is
capable of knocking electrons loose from chemical substances, or ionizing
them. Since this energy is capable of changing chemical structures, it can be
extremely dangerous to living tissue. One of the more onerous results of
exposure to ionizing radiation is that DNA molecules in cells are ionized and
change their form. In some cases, the change of DNA can lead to cancer. Nonionizing
Radiation is not capable of ionizing chemicals and cannot cause cancer
as described above. Ultraviolet light has been shown to be the energy with the
lowest frequency that can still ionize. Its frequency is in the range of 1015
Hz (1,000,000,000,000,000 Hz). The highest radio frequencies that the
population is exposed to are in the range of GHz (109 Hz, or
1,000,000,000 Hz). Radio waves that people are exposed to are a million
times lower in frequency than the lowest frequency that is classified
as ionizing radiation.
High Frequency RF is not ELF
People often lump their concerns about RF
energy under one category. There are two distinct groups of energy, at least
with respect to bioeffects. The energy that is emitted from power lines and
appliances is often categorized as Extra Low Frequency (ELF) and typically
interacts with biological tissue through its magnetic field. The RF energy used
mostly for communications has much higher frequencies and tends to affect
tissue through its electric field. This energy is categorized by its frequency
ranges: Medium Frequency (MF, 300 kHz to 3 MHz), High Frequency (HF, 3 MHz to
30 MHz), Very High Frequency (VHF, 30 MHz to 300 MHz), and Ultra High Frequency
(UHF, 300 MHz to 3 GHz).
RF Dangers
Yet, there is still the possibility of
danger from radio frequency energy, particularly at MF and above. When any
energy is absorbed in tissue, it is converted to heat. The most common example
of this is what happens to food in the microwave oven. Food usually tastes
better after being heated. Living tissue does not fare so well. We all have
experienced what it feels like to have a fever. The body controls its
temperature very precisely at 98.6°F (37°C). By the time our core body
temperature has risen just a couple of degrees, say to 101°F (38.3°C), we feel
bad. If our body core temperature rises above 105°F (40.6°C) our lives are in
danger. RF safety guidelines prevent us from being exposed to levels of
energy that can cause dangerous temperature increases in our tissues.
Other RF Bioffects
Other biological processes have been shown
to be affected by levels of RF energy that do not produce significant amounts
of heat in tissue. These are all reversible effects (they go away when the RF
energy is removed) and include change of operation of the calcium channels in
cells, stimulation of the retina and optical nervous system to produce false
perception of light, stimulation of the cochlea and auditory nervous system to
produce false perception of sound, stimulation of nerve ending to produce a
tingling sensation, and others. There has been no indication that these other
effects are harmful to people.
How RF Bioeffects
are Studied
We have learned about the effects of RF
energy on humans by two different methods, each with its own advantages and
limitations. Studies based on epidemiology try to determine how risky a given
exposure or activity is to the general population. Laboratory studies look as
the mechanisms of interaction. Whatever damaging effects exists from RF
exposure, they are relatively subtle and require very long term exposures,
which makes it difficult to study them in a laboratory setting. However, there
are enough other things that influence our biology that we encounter during our
lifetimes that it is difficult to isolate only the effects of RF energy.
Epidemiology
If exposure to a given substance or energy
causes people to get sick, we should be able to realize that if we look at
enough people. The difficulty with this premise is that many people will get
the same illnesses without having been exposed to that substance. Consider
cancer. It has been suggested that people who use cell phones are likely to get
brain tumors. However, lots of people who never used a cell phone have already
gotten brain tumors. In this case, epidemiology uses population statistics to
see if there is a difference in the likelihood of getting a brain tumor for
those who use cell phones as compared to those who do not. This is true for
just about every disease; people get sick without an apparent cause. How do we
distinguish between those who get sick naturally from those who get sick
because of exposure to something?
By looking at the percentage of the general
population that gets a particular disease and comparing this to the percentage
of people who are exposed to a particular stimulus (such are RF energy), an
indication that the stimulus may be causing the disease would be if the
percentage of people with the disease that are exposed to the stimulus is
significantly higher than the percentage from the general population.
Epidemiology is capable of showing this association but, by itself, is
not able to infer cause and effect. If an epidemiological study shows an
association between a given stimulus and a disease, the proof of cause and
effect must be obtained by much more detailed study, usually in a laboratory
setting. For more detail on Epidemiology, see "My Rude Introduction
to Epidemiology."
Laboratory Studies
The major weakness of an Epidemiological
study is its lack of specificity about the stimulus in question and the effects
of other stimuli on the subjects. In our day-to-day lives we are exposed to any
number of stimuli that may have an effect on a particular disease. For a
particular stimulus, each individual is typically exposed to different levels
for different duration. Thus, it is very difficult to perform a meaningful
population-based study.
In the laboratory, these variations can be
controlled so that a group of subjects is known to be exposed to exactly the
same levels of stimulus for a specified duration. This is crucial in order to
show that the stimulus under test causes the disease. To transition from
a mere association to a cause, it is necessary to show 1) that the association
is a strong one, 2) that the stimulus consistently is associated with the
disease, 3) that increasing levels of stimulus lead to an increased incidence
of the disease, 4) that the amount of time that it takes between the exposure
to a stimulus and the initiation of the disease is consistent, and, finally, 5)
that there be a reasonable theory about how, on the physical level, the
stimulus can cause the disease.
Thus, we can only depend on Epidemiology to
identify areas of possible concern. We then use laboratory studies to
show whether or not the association identified by the epidemiological study
actually has a cause-and-effect relationship. The importance of depending on
both of these steps, i.e. the discovery of an association and the
subsequent demonstration of cause, and not jumping to conclusions after
an alarming epidemiological study is reported, can be illustrated with the
following simple, albeit absurd, example: An eager epidemiologist notices that
there may be an association between eating and getting cancer. He performs a
study with 1000 cancer patients in the hospital and discovers that 100% of them
have been eating for their entire lives. Stating his results like this, he
concludes that there is a strong association between eating and getting cancer.
This study is published in a scientific journal and is noticed by a reporter
for a local newspaper. Anxious to get a big scoop on the other papers, the
reporter convinces his editor to publish the story on page one with the
headline: Eating Causes Cancer. People read this, become alarmed
and stop eating. Lawsuits are filed by a legion of lawyers for many millions of
dollars in damages against food production companies, grocery stores, farmers,
and restaurants. One man brings suit against his wife for preparing his meals
for him. Some of the lawsuits are settled out of court for undisclosed amounts.
A number of smaller food-related companies declare bankruptcy and go out of
business. After a year passes with outrageous sums spent on defense attorneys
and expert witnesses, a judge rules that there is no scientific merit to the
case and dismisses the charges. Other cases fall like dominos and eventually
the number of open lawsuits dwindles to a mere few. People resume eating and
life goes on.
Amateur Radio
Radio amateurs make up one of the most
interesting groups to study in the field of RF Safety. Of all groups in the
population, amateurs typically have the longest term exposure to a variety of
frequencies at many different power levels. For instance, a person using a
standard analog cellular telephone in the United States will be exposed to between
0.06 and 0.60 watts from about 800 to 900 MHz at a distance of inches the
entire time he or she is talking to someone. An amateur radio operator can be
exposed to up to 1500 watts of power over a frequency range of 1.6 MHz to
several GHz. In the MF and HF frequency ranges (1.6 MHz to 29.7 MHz), it is
customary for amateurs to keep logs of their on-the-air activities, which could
prove useful exposure studies. Many radio amateurs also perform their own
maintenance activities, further affecting their exposure to radio frequency
energy. There are currently about 640,000 licensed radio amateurs in the United
States and over 2.77 million worldwide.
The ARRL
The American
Radio Relay League (ARRL) is the
largest organization of radio amateurs in the world, with over 200,000 members.
It has formed an RF Safety Committee, made up of scientists and physicians with
a professional interest in RF bioeffects who are also radio amateurs. The
purpose of the RF Safety Committee is to "monitor and interpret ongoing
scientific studies in the field of RF bioeffects, assist in the generation and
editing of RF safety-related text for ARRL publications, and advise the ARRL
Board of Directors on RF safety issues."
FCC RF Safety Regulations
As of January 1, 1998, the Federal
Communications Commission (FCC), the
governing body for communications in the United States, put into effect new
regulations requiring all radio amateurs to be aware of the levels of human
exposure that their transmissions cause and, in cases of exposures that exceed
recommended safe limits, to take action to increase the RF safety of their
stations (47 CFR Ch. I, Sections 1.1307b, 1.1310, 2.1093, 97.13c, and 97.503).
Similar regulations went into effect earlier for commercial radio transmitters.
Lower power amateur radio stations are exempted from performing detailed
analyses on the assumption that human exposure will be low. Stations that
transmit higher power levels are required to calculate what the exposure to
nearby people will be, taking into account their output power at different
frequencies, their antennas’ locations and transmitting patterns, and the
typical amount of time that they transmit. Questions related to RF Safety have
been added to the Amateur Radio licensing examinations.
Related Links
Read N9GL’s RF Safety
Column on the ARRL Web Page
Updated: February 15, 2002
Copyright © 1998-2002 by Gregory D. Lapin