Occupational exposure to radio-frequency electromagnetic fields

Occupational exposure to radio-frequency (RF) electro-magnetic (EM) fields occurs in various industrial processes. The exposure usually takes place in the near field, i.e., within one free space wavelength from the RF source. When a survey of a workplace is performed from a leakage radiation point of view, the near-field situation implies that the electric as well as the magnetic field strengths have to be monitored in order to assess the health hazard. This paper discusses the field strengths typically encountered in some of these occupational situations. Thin sheets of plastic materials can be joined or sealed by application of RF energy. The plastic welding machine, using for this purpose, usually does not have shielded electrodes and this may lead to high levels of RF fields in the immediate vicinity of the machines. The ANSI standard is exceeded in several cases near the plastic welding machines. In medicine, for instance, RF energy is used in shortwave therapy. Due to the construction of the apparatus (i.e. presence of electrodes and cables) the physiotherapist as well as the maintenance personnel may be exposed to very high levels of both E and H fields. The results of measurements of these fields in the vicinity of shortwave diathermy apparatus are discussed. The maintenance personnel working in FM/TV broadcast towers are another group of workers subject to occupational exposure of intense RF fields, and some recent studies of the exposure are presented.