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The effects of electromagnetic fields (EMFs) break down into low frequency and high frequency effects. At low frequencies, below 100 kHz, there are two primary hazards. A shock hazard can occur from charged objects. Sufficiently strong fields can induce currents that may exceed naturally occurring body currents. The current density caused by muscle action is 10 mA/m². At a field strength of 10 kV/m, the induced current would be in the region of 4 mA/m². Large magnetic field strengths are also required to produce noticeable effects. A 50 Hz magnetic field of 500 µT will cause current densities of around 1 mA/m² in the body, given optimum conditions. At 5000 µT, a flickering sensation in the eyes can be produced. Typical public or worker exposures are usually less than 0.5 µT.
At radio frequencies, a strong field can induce heating in the same way that a microwave oven works. Current radio frequency guidelines are based on limiting the rise in body temperature to below 1°C and preventing shock or burn hazards. Normal activity will cause a similar rise in body temperature and, for example, a footballer expending a lot of energy can experience a temperature rise of a few degrees. There has also been considerable speculation about more subtle effects of electromagnetic fields at non thermal levels. These effects occur at very high levels that are rarely encountered by any persons, either in public or in a work environment.
Article on "Electromagnetic Fields and Human Health" by John McAuley, in The Engineers Journal, vol. 59: May 4, 2005 (Journal of The Institution of Engineers of Ireland, Cumann na nInnealtóirí.)
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