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Engineers Electronic Engineers Electromagnetic radiation and health
| Electromagnetic radiation and health |
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| Written by Eng.Admin | |||||||||
| Thursday, 06 November 2008 18:12 | |||||||||
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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 associated with two major potential hazards: electrical and biological. Additionally, induced electric current caused by radiation can generate sparks and create a fire or explosive hazard. Electrical hazards The oscillating electric and magnetic fields in electromagnetic radiation will induce an electric current in any conductor through which it passes. Strong radiation can induce current capable of delivering an electric shock to persons or animals. It can also overload and destroy electrical equipment. Fire Hazards Extremely high power electromagnetic radiation can cause electric currents strong enough to create sparks. These sparks can then ignite flammable materials or gases, possibly leading to an explosion. This can be a particular hazard in the vicinity of explosives or pyrotechnics, since an electrical overload might ignite them. This risk is commonly referred to as RadHaz or HERO (Hazards of Electromagnetic Radiation to Ordnance). Biological hazards of EMF The best understood biological effect of electromagnetic fields is to cause dielectric 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[citation needed]. 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.[citation needed] 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. There is also a body of evidence which supports the existence of complex biological effects of weaker non-thermal electromagnetic fields (see Bioelectromagnetics), including weak ELF magnetic fields[1][2] and modulated RF and microwave fields.The theoretical mechanism of action of non-thermal electromagnetic fields is not fully understood, though there is now support for some theories[5]. Because the definite existance and possible extent of Non-thermal effects is not fully established, the effects are not known. Sir William Stewart (chairman of the UK Health Protection Agency), has commented that as there is evidence of a possible but undetermined risk (Stewart Report, 2000 and 2005), the public approach should follow the precautionary principle. The official stance of the Health Protection Agency is that there is currently no proven risk from RF communication devices. transfer
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