Electromagnetic radiation and health
Electromagnetic radiation and health
Very strong radiation can induce current capable of delivering an electric shock to persons or animals. It can also overload and destroy electrical equipment. The induction of currents by oscillating magnetic fields is also the way in which solar storms disrupt the operation of electrical and electronic systems, causing damage to and even the explosion of power distribution transformers, blackouts, and interference with electromagnetic signals (e.g. radio, TV, and telephone signals).
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. MIL-STD-464A mandates assessment of HERO in a system, but Navy document OD 30393 provides design principles and practices for controlling electromagnetic hazards to ordnance.
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. These are exactly the kind of burns that would be caused inside a microwave oven.
This heating effect varies with the power and the frequency of the electromagnetic energy. A measure of the heating effect is the specific absorption rate or SAR, which has units of watts per kilogram. The IEEE and many national governments have established safety limits for exposure to various frequencies of electromagnetic energy based on SAR, mainly based on ICNIRP Guidelines, which guard against thermal damage.
There are publications which support the existence of complex biological effects of weaker non-thermal electromagnetic fields, 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 aren’t fully understood.
In May 2011, the WHO’s International Agency for Research on Cancer published a review of the evidence on health risks of electromagnetic fields, concluding that there was limited evidence that cellphone users might be at increased risk of glioma and acoustic neuroma, and that there was inadequate evidence of any other health risks posed by EMF. This designation as “possibly carcinogenic” has often been misinterpreted as indicating that of some measure of risk has been observed; the designation indicates that the possibility could not be conclusively ruled out using the available data.
There is no conclusive evidence of any harm caused by exposures [to electric and magnetic fields] at levels found in Canadian homes and schools, including those located just outside the boundaries of power line corridors.”
The preponderance of evidence suggests that the low-power, low-frequency, electromagnetic radiation associated with household current does not constitute a short or long term health hazard, and although some biophysical mechanisms for the promotion of cancer have been proposed, none have been substantiated. Nevertheless, some research has reported correlation with a number of adverse health effects, although controversy can include whether observed correlation implies causation. These include, but aren’t limited to, childhood leukemia, adult leukemia, neurodegenerative diseases (such as amyotrophic lateral sclerosis), miscarriage, and Alzheimer’s disease. Some research has found no relationship with amyotrophic lateral sclerosis, Parkinson’s disease, or multiple sclerosis.
One response to the potential dangers of overhead power lines is to place them underground. The earth and enclosures surrounding underground cables prevent the electric field from radiating significantly beyond the power lines, and greatly reduce the magnetic field strength radiating from the power lines, into the surrounding area. However, the cost of burying and maintaining cables at transmission voltages is several times greater than overhead power lines.
In 1997 the National Cancer Institute released a report published in the New England Journal of Medicine, the 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 provided “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.” Following the report, the US Department of Energy disbanded the EMF Research and Public Information Dissemination (RAPID) Program, saying that its services were no longer needed.
In 2005, the Canadian Federal-Provincial-Territorial Radiation Protection Committee said, “The outcome of a recently conducted pooled analysis of several epidemiological studies shows a two-fold increase in the risk of leukemia in children living in homes, where the average magnetic field levels are greater than 0.4 microtesla. [However,] it is the opinion of [this committee] that the epidemiological evidence to date isn’t strong enough to justify a conclusion that EMFs in Canadian homes, regardless of locations from power lines, cause leukemia in children.”
In 2010, Maslanyj et al., applying the Bradford-Hill criteria to available evidence, considered the application of low-cost exposure reduction measures as appropriate precautionary responses to “small and uncertain public health risks”. Even after pooling all the data, they found it fell short of establishing “strength of association, dose-response relationship, biological plausibility and coherence, and analogy”. They recognised that controversy would continue so long as other interpretations of the data were possible.
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 xT, but said that it “… may be partly due to bias. This is difficult to interpret in the absence of a known mechanism or reproducible experimental support.”
In 2002 a study by Michelozzi et al. found a relationship between leukemia and proximity to the Vatican Radio station transmitters although “the study has limitations because of the small number of cases and the lack of exposure data.”
The World Health Organisation issued Factsheet No. 263 in October 2001 on ELF EMFs and cancer. It said that they were “possibly carcinogenic”, based primarily on IARC’s similar evaluation with respect to childhood leukemia. It also said that there was “insufficient” data to draw any conclusions on other cancers. The WHO later noted that result had been based on evidence which was “weakened by methodological problems” and that “on balance, the evidence related to childhood leukaemia isn’t strong enough to be considered causal.”
In 2007, the UK Health Protection Agency produced a paper showing that 43% of homes with magnetic fields of over 0.4 xT are associated with overground or underground circuits of 132 kV and above.
Mobile phone radiation and health concerns have been raised, especially following the enormous increase in the use of wireless mobile telephony throughout the world. Mobile phones use electromagnetic radiation in the microwave range, and some[unreliable medical source?] believe this may be harmful to human health. These concerns have induced a large body of research (both epidemiological and experimental, in non-human animals as well as in humans). Concerns about effects on health have also been raised regarding other digital wireless systems, such as data communication networks.
The World Health Organization, based upon the consensus view of the scientific and medical communities, states that health effects are unlikely to be caused by cellular phones or their base stations, and expects to make recommendations about mobile phones in the 3rd quarter of 2010 at the earliest, or the 1st quarter of 2011 at the latest[dated info].
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