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 98.6F (37C). By the time our core body temperature has risen just a couple of degrees, say to 101F (38.3C), we feel bad. If our body core temperature rises above 105F (40.6C) 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 N9GLs RF Safety Column on the ARRL Web Page

 

Return to Home Page

 

 Updated: February 15, 2002

Copyright 1998-2002 by Gregory D. Lapin