Electromagnetic radiation hazard
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Electromagnetic radiation can be classified into ionizing radiation and non-ionizing radiation, based on whether it is capable of ionizing atoms and breaking chemical bonds. Ultraviolet and higher frequencies, such as X-rays or gamma rays are ionizing. These pose their own special hazards: see radiation and radiation poisoning.
Non-ionizing radiation, discussed here, is not capable of having these effects on molecules. There are three major potential hazards associated with non-ionizing electromagnetic radiation: electrical, fire, and biological.
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Electrical hazards
Strong electromagnetic fields can generate an electric current in other metal objects by electromagnetic induction. The induced current can cause an electric shock to persons or animals. It can also overload and destroy electrical equipment. This can be a particular hazard in the vicinity of explosives, since an electrical overload might ignite it.
Fire hazards
Again by electromagnetic induction, a strong electromagnetic field can cause electric currents which may flow across an air gap to ground, causing sparks. These sparks can then ignite flammable materials or gases, possibly leading to an explosion or a fire.
Biological hazards
The main biological effect of electromagnetic fields is to cause heating. For example, touching an antenna while a transmitter is in operation can cause severe burns. Birds sitting on very high-power antennas when transmission begins can be instantly cooked by RF energy. In fact, that is the principle behind the operation of a microwave oven.
This heating effect varies with the frequency of the electromagnetic energy. The eyes are particularly vulnerable to RF energy in the microwave range, and prolonged exposure to microwaves can lead to cataracts. Each frequency in the electromagnetic spectrum is absorbed by living tissue at a different rate, called the specific absorption rate or SAR, which has units of watts per kilogram (W/kg). The IEEE and many national governments have established safety limits for exposure to various frequencies of electromagnetic energy based on SAR.
U.S. military definition
In Federal Standard 1037C, the United States government adopts the following definition:
- Electromagnetic radiation hazards (RADHAZ or EMR hazards): Hazards caused by a transmitter/antenna installation that generates electromagnetic radiation in the vicinity of ordnance, personnel, or fueling operations in excess of established safe levels or increases the existing levels to a hazardous level; or a personnel, fueling, or ordnance installation located in an area that is illuminated by electromagnetic radiation at a level that is hazardous to the planned operations or occupancy. These hazards will exist when an electromagnetic field of sufficient intensity is generated to: (a) induce or otherwise couple currents and/or voltages of magnitudes large enough to initiate electroexplosive devices or other sensitive explosive components of weapon systems, ordnance, or explosive devices; (b) cause harmful or injurious effects to humans and wildlife; (c) create sparks having sufficient magnitude to ignite flammable mixtures of materials that must be handled in the affected area.
—Department of Defense Dictionary of Military and Associated Terms