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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. 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. 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 are publications which support the existence of complex biological effects of weaker non-thermal electromagnetic fields (see Bioelectromagnetics), including weak ELF magnetic fields and modulated RF and microwave fields.
Fundamental mechanisms of the interaction between biological material and electromagnetic fields at non-thermal levels are not fully understood. The definite existence and possible extent of non-thermal effects is not fully established. The chairman of the Health Protection Agency, 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."[http://www.timesonline.co.uk/article/0,,591-2461748,00.html] 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 Some research has found that exposure to elevated levels of ELF magnetic fields such as those originating from electric power transmission lines may be implicated in a number of adverse health effects. These include, but are not limited to, childhood leukemia (references below), adult leukemia, breast cancer, neurodegenerative diseases (such as amyotrophic lateral sclerosis), miscarriage, and clinical depression.
Leukemia and cancerIn 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" 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.The NCI study was corroborated by a 1999 Canadian epidemiological study of leukemia in children. As a result of the NCI's findings, the US Department of Energy disbanded the EMF Research and Public Information Dissemination (RAPID) Program citing that its services were no longer needed.In 2001, Ahlbom et al conducted a review into EMFs and Health, and found that there was a doubling in childhood leukemia for magnetic fields of over 0.4 µT, though importantly summarised that "This is difficult to interpret in the absence of a known mechanism or reproducible experimental support". In 2007, the UK Health Protection Agency produced a paper showing that 43% of homes with magnetic fields of over 0.4 µT are associated with overground or underground circuits of 132 kV and above.Ahlbom's findings were echoed by Draper et al in 2005 when a 70% increase was found in childhood leukaemia for those living within of an overhead transmission line, and a 23% increase for those living between and . Both of these results were statistically significant. The authors considered it unlikely that the increase between and is related to magnetic fields as they are well below 0.4 µT at this distance. Bristol University (UK) has published work on a theory that could account for this increase, and would also provide a potential mechanism, being that the electric fields around power lines attract aerosol pollutants. The World Health Organisation factsheet on ELF (Extremely low frequency) EMFs and cancer concludes that they are "possibly carcinogenic", based primarily on IARC's similar evaluation with respect to childhood leukemia. It also stated that there was "insufficient" data to draw any conclusions on other cancers.WHO Factsheet "Electromagnetic fields and public health: extremely low frequency fields and cancer" This factsheet was written in October 2001, and is now largely out of date due to the increase in the scientific literature since then. Although a doubled risk may sound dramatic, childhood leukemia is a rather rare disease, and even at a doubled risk it would still be rare. In the US, the chance that a person develops leukemia during childhood is about one in 1,300 (based on 3,000 cases per year).
Other health concernsThe California Department of Health produced a report in 2002 from their California EMF program, set up to review the health effects from electric and magnetic fields from powerlines, wiring, and appliances. They concluded that EMFs were responsible for an increase in childhood leukemia, adult brain cancer, Lou Gehrig's disease, and miscarriage."An Evaluation of the Possible Risks From Electric and Magnetic Fields (EMFs) From Power Lines, Internal Wiring, Electrical Occupations and Appliances", California EMF Program This differs to a review by the International Agency for Research on Cancer in 2001, and the National Radiological Protection Board (now part of the UK Health Protection Agency) review in the same year. The reasoning for the differing opinion of the California Department of Health panel was that "there were reasons why animal and test tube experiments might have failed to pick up a mechanism or a health problem; hence, the absence of much support from such animal and test tube studies did not reduce their confidence much or lead them to strongly distrust epidemiological evidence from statistical studies in human populations. They therefore had more faith in the quality of the epidemiological studies in human populations and hence gave more credence to them."However, the California report concluded that they did not find there was a strong enough association between EMFs and birth defects and low birth weight, and were divided on the evidence for suicide and adult leukemia.
UK SAGE reportThe Stakeholder Advisory Group on ELF EMFs (SAGE) has been set up by the UK Department of Health to explore the implications and to make practical recommendations for a precautionary approach to power frequency electric and magnetic fields as a result of the HPA recommendations in March 2004.The first interim assessment of this group was released in April 2007, and found that the link between proximity to power lines and Childhood Leukemia was sufficient to involve a precautionary recommendation, including an option to lay new power lines underground where possible and to prevent the building of new residential buildings within of existing power lines.The latter of these options was not an official recommendation to government as the cost-benefit analysis based on the increased risk for childhood leukemia alone was considered insufficient to warrant it. The option was considered necessary for inclusion as, if found to be real, the weaker association with other health effects would make it worth implementing. "SAGE first interim assessment: Power Lines and Property, Wiring in Homes, and Electrical Equipment in Homes"
U.S. military definition In Federal Standard 1037C, the United States government adopts the following definition::Electromagnetic radiation hazards (RADHAZ or EMR hazards): Hazards caused by a transmitter/antenna installation that generates electromagnetic radiation in the vicinity of ordnance, personnel, or fueling operations in excess of established safe levels or increases the existing levels to a hazardous level; or a personnel, fueling, or ordnance installation located in an area that is illuminated by electromagnetic radiation at a level that is hazardous to the planned operations or occupancy. These hazards will exist when an electromagnetic field of sufficient intensity is generated to: (a) induce or otherwise couple currents and/or voltages of magnitudes large enough to initiate electroexplosive devices or other sensitive explosive components of weapon systems, ordnance, or explosive devices; (b) cause harmful or injurious effects to humans and wildlife; (c) create sparks having sufficient magnitude to ignite flammable mixtures of materials that must be handled in the affected area. —Department of Defense Dictionary of Military and Associated Terms
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