RF Burns (T0C07)
The safety questions in the 2022-2026 Technician License question pool asks about touching an antenna during transmission:
T0C07: What hazard is created by touching an antenna during a transmission?
B. RF burn to skin
C. Radiation poisoning
D. All these choices are correct
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.
If a person touching a transmitting antenna, the radio frequency electrical currents can be conducted by the body in seeking a low-impedance path to ground voltage. Human cells die at about 107 degrees Fahrenheit or above, and when contact is made with a strong RF transmitting element the tissues near the point of contact rapidly heat well above this level. In severe 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 hazard is created by touching an antenna during a transmission?” is B: RF burn to skin.