Electromagnetic radiation and health

From Wikipedia, the free encyclopedia

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 when an induced voltage exceeds the breakdown voltage of the surrounding medium (e.g. air). 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 HERO (Hazards of Electromagnetic Radiation to Ordnance). MIL-STD-464A could be used to evaluate HERO, which states a maximum field intensity of 50V/m@30Mhz or 200V/m@2700Mhz (i.e. 49cm@30Mhz and 12cm@2700Mhz for a 40W emitter).

On the other hand, the risk related to fueling is known as HERF (Hazards of Electromagnetic Radiation to Fuel). NAVSEA OP 3565 Vol. 1 could be used to evaluate HERF, which states a maximum power density of 0.09W/m2 for frequencies under 225Mhz (i.e. 4.2 meters for a 40 W emitter).

Biological hazards of EMF

The best understood biological effect of electromagnetic fields is to cause dielectric heating. For example, touching or standing around an antenna while a high-power transmitter is in operation can cause severe burns.

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[1] and many national governments have established safety limits for exposure to various frequencies of electromagnetic energy based on SAR, mainly based on ICNIRP Guidelines[2]; which are only oriented to thermal, short-term exposures (6 minutes). Using these guidelines (i.e. SAR 0.08 W/kg), examples of minimum safety distances could be 90cm@30Mhz and 30cm@3Ghz for a 40W emitter.

There are publications which support the existence of complex biological effects of weaker non-thermal electromagnetic fields (see Bioelectromagnetics), including weak ELF magnetic fields[3][4] and modulated RF and microwave fields[5][6]. Fundamental mechanisms of the interaction between biological material and electromagnetic fields at non-thermal levels are not fully understood[7].

The definite existence and possible extent of non-thermal effects is not fully established. The chairman of the United Kingdom's Health Protection Agency (HPA), Sir William Stewart, has said that "evidence of potentially harmful effects of microwave radiation had become more persuasive over the past five years." His report said that while there was a lack of hard information of damage to health, the approach should be precautionary.[1] The HPA, however, disagrees with his assessment, and claims that there is no risk and no need for precaution. The official stance of the Health Protection Agency is that there is currently no proven risk from RF communication devices.

Health effects of electric power transmission

The preponderance of evidence shows that the low-power, low-frequency, electromagnetic radiation associated with household current is very safe, and whilst some biophysical mechanisms for the promotion of cancer have been proposed (such as the electric fields around powerlines attracting aerosol pollutants.[8][9]), none have been substantiated.[10][11][12][13][14][15] Nevertheless, some research has implicated exposure in a number of adverse health effects. These include, but are not limited to, childhood leukemia (references below), adult leukemia[16], neurodegenerative diseases (such as amyotrophic lateral sclerosis)[17][18][19], miscarriage[20][21][22], and clinical depression.

Leukemia and cancer

In 1996, the Stevens Report was released by the National Academy of Sciences. Based on the current research of EMF produced from power lines, the report concluded that there was no evidence that showed exposure to EMF from power lines presented a human health hazard. Another report was released on July 3, 1997 by the National Cancer Institute (NCI). The report published in the New England Journal of Medicine, "Residential Exposure to Magnetic Fields and Acute Lymphoblastic Leukemia in Children" [23] was a result of a seven year epidemiological investigation. The study investigated 638 children with acute lymphoblastic leukemia (ALL) and 620 controls and concluded that their study provides little evidence that living in homes characterized by high measured time-weighted average magnetic-field levels or by the highest wire-code category increases the risk of ALL in children.

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