(T0C07) RF Burn

T0C07:  What could happen if a person accidentally touched your antenna while you were transmitting?

A. Touching the antenna could cause television interference
B. They might receive a painful RF burn
C. They might develop radiation poisoning
D. All of these choices are correct

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Touching an antenna while transmitting with it is never a good idea. Although the hazard with very low power levels such as that of a 5 watt HT transceiver is negligible, higher power levels can produce hazardous conditions for touching a radiating element. You should take precautions against the possibility of your antenna being accidentally touched by a person while you are transmitting.

Radio frequency radiation is non-ionizing radiation. This means that RF radiation does not strip electrons from atoms as can occur with ultraviolet, X-ray, and gamma ray radiation that has much higher frequencies than RF. Radio frequencies do not damage genetic material such as DNA by such molecular disruption. Thus, it is not possible to develop radiation poisoning from RF or by touching a transmitting antenna.

It is also not reasonable that touching a transmitting radio antenna could incite television interference of any kind.

However, RF radiation is absorbed by the tissues of our bodies and transformed into heat that the body must remove to avoid damage from overheating or burning – to avoid cooking, essentially. Human cells die at about 107 degrees Fahrenheit or above. When you come into contact with an RF transmitting element such as an antenna that is conducting RF electrical currents, those currents may seek a path to ground potential voltage through your tissues, quickly heating your tissues near the point of contact with the antenna. In some cases this can cause an RF burn.

It is also possible to receive an RF burn from other conductors that are resonating from nearby RF fields. For example, ground conductors, cables, or other metal components of your station may develop non-uniform “hot spots” when your station is radiating at high power or if a transmitting antenna is very close by, especially if these conductors have dimensions approaching a significant fraction of the transmitting frequency. Antennas are not the only hazardous element with RF burn potential!

The severity of an RF burn depends upon several factors:

  • The strength of the electric field. This is the power output at the antenna where the contact is made. As noted, low power levels do not usually impose burns as the blood flow through tissues can readily carry away the mild heating imposed by low power RF. Higher power levels with stronger electric fields will, of course, impose more severe heating of tissue. Compare touching a 5 watt light bulb with touching a 60 watt light bulb, or a 100 watt light bulb. Although that is infrared heat, the relative comparison with RF energy is similar.
  • The frequency. Our bodies are more efficient at absorbing frequencies in the VHF realm than others. So, an RF burn may be imposed at VHF frequencies with lower power levels than at other frequencies. Note that VHF includes the very popular 6-meter and 2-meter bands.
  • How well grounded you are. The RF currents will seek a path through your tissue to ground potential. If you are very well grounded, such as standing barefoot in a puddle of sea water, you’re going to provide a very nice path to ground and the currents will flow readily, burning your tissues at the contact point where currents are most concentrated.
  • How much of your body contacts the radiating element. If you touch the antenna with your fingertip, a high concentration of RF will flow through the small area of your fingertip, potentially causing a severe burn. If you grab the antenna in the palm of your hand, a much larger surface area is in contact with the radiating element, and the RF current will be dispersed through that larger tissue area. The concentration of current in this case is lower, so tissue heating is less severe, but it may still burn you depending upon the other factors listed above. If the antenna is coursing with a kilowatt, you’re definitely going to feel it in the palm of your hand (and beyond).

Radio frequency burns can be deep and very painful, much more so than a conventional infrared heat burn. First aid for RF burns is to apply cold water or ice to burned areas and seek immediate medical attention. Of course, prevention is the preferred course. Make sure it is not possible for humans to accidentally come into contact with your antenna, and if the antenna is within reach such as a mobile mounted element on a car, be sure no one is in contact with it before you push to talk.

The answer to Technician question T0C07, “What could happen if a person accidentally touched your antenna while you were transmitting?” is B: They might receive a painful RF burn.

Related Question: T0C01, T0C04, T0C05, T0C06, T0C08