I. Definition of an electro magnetic field by the WHO
1. The result of natural phenomena
"Electric and magnetic fields are generated by phenomena such as the Earth’s magnetic field, thunderstorms, and the use of electricity. When such fields do not vary with time they are referred to as static and have a frequency of 0 Hz."
1.1 Application in technologies
"Recent technological innovations have led to the use of magnetic fields up to 100 000 times stronger than the Earth’s magnetic field. They are used in research and in medical applications such as MRI that provides three-dimensional images of the brain and other soft tissues. For static magnetic fields, acute effects are only likely to occur when there is movement in the field, such as motion of a person or internal body movement, such as blood flow or heart beat. A person moving within a field above 2 T can experience sensations of vertigo and nausea, and sometimes a metallic taste in the mouth and perceptions of light flashes. Although only temporary, such effects may have a safety impact for workers executing delicate procedures (such as surgeons performing operations within MRI units)."
1.2 Recommendations of the WHO
“The WHO recommends that the authorities:
Adopt international norms based on scientific studies seen to limit human exposure;
Adopt protective measure during industrial and scientific utilization of magnetic fields presenting a risk in holding them at a distance by encasing generators or by using administrative means, such as awareness programs for personnel;
Envisage an agreement for magnetic resonance imagery (MRI) to guarantee that protective measures are applied when the power of the field exceeds 2 T;
Back up financing of research destined to fill in the gaps of important reports relative to public security;
Back up financing of MRI services and foundations so as to collect health information on the exposure of operators and sick people.”
For more information : http://www.who.int/mediacentre/factsheets/fs299/fr/index.html
Fact sheets - click to download (french pdf file)