Magnetic field exposures

Safety considerations for magnetic resonance (mr) experiments have received Htde attention except for the problems associated with the use of electronic devices such as pacemakers in the magnetic field. However, in a 1990 study of reproductive health involving more than 1900 women working in clinical mr facihties in the United States no substantial differences were reported between the group of women directly involved with mr equipment (280 individuals) and other working women (894 individuals) (10). Conclusions are restricted to exposure to the static external field. 

Fig. 5. Long-term magnetic field exposure limits for general public exposures in uncontrolled environment, where A is the 50/60 Hz window, according to B, IRPA C, VDE (Germany) D, NRPB (U.K.) and E (IEEE C95.1, 1991). To convert T to G, multiply by 10/...

Very little is known about the short-term and longterm effects of exposure to high magnetic fields. 

Mevissen, M., M. Haussler, A. Lerchi, and W. Loscher. 1998. Acceleration of mammary tumorigenesis by exposure of 7, 12-dimethylbenz[a] anthracene-treated female rats in a 50-Hz, 100-pT magnetic field replication study. Jour. Toxicol. Environ. Health 53A 401-418. 

Magnetic equipment, 15 434—435 Magnetic field exposure limits, long-term, 16 527... 

Biological Effects and Exposure Criteria for Ultrasound Biological Effects of Magnetic Fields Microprocessors in Dosimetry Efficacy Studies... 

Feychting M, Floderus B, Ahlbom A (2000) Parental occupational exposure to magnetic fields and childhood cancer (Sweden). Cancer Causes Control 11 151-156. 

Figure I. ESR spectra of gamma-irradiated Mylar film after postirradiation exposure to air (3). Dose rate 3 X 10 J Mrad min. Dose 10 Mrad. Spectra in a and b obtained at mutually perpendicular orientations of sample in magnetic field...

Emergency In vivo Tooth Dosimeter Oral Dosimeter. Tooth enamel is only material that records the accumulated radiation exposure dose in the past in a human body. An equipment for rapid dosimetry of teeth without their extraction was fabricated upon demand by Chernobyl medical doctors to judge whether immediate medical care such as spinal transplantation is necessary.97 A portable test apparatus of in vivo human tooth dosimeter consists of a resonator cavity with an aperture and a permanent magnet of Nd-B-Fe alloy (Neomax). The sensitivity is not sufficient due to the low Q factor and non-uniform magnetic field at the tooth. 

Some experiments on rats and mice show that for continuous exposure at high levels of EMF (400 mG) some physiological changes occur. These EMF levels are well above what humans are normally exposed to at home or at work. One study that exposed humans to high levels of electrical and magnetic fields (greater than 100 times normal) for a short duration found a slowing of heart rate and inhibition of other human response systems. 

The studies done so far do not definitively admit or dismiss a correlation between low-frequency magnetic fields and human health. During a typical day, humans are exposed to varying levels of low-frequency electromagnetic fields. This exposure is a byproduct of living in a fast-paced environment. A typical office space will have an ambient low-frequency electromagnetic field ranging between 0.5 and 3 mG. 

Table 7.3 shows the EMFs produced by some common household electrical appliances. While the EMF levels can be considered high, the exposure duration is low in most cases. It is important to realize that the effects of exposure to low-frequency fields are not clearly known, thus it is prudent to exercise caution and avoid prolonged exposure to electrical and magnetic fields. One way to minimize exposure is to maintain sufficient distance between the EMF source and people in the environment. As we saw earlier, electrical and magnetic fields diminish as the square of the distance from the source. For example, instead of sitting 1 ft away from a table lamp, one can move 2 ft away and reduce EMF exposure to approximately one fourth the level found at 1 ft. It is expected that studies conducted in the future will reveal more about the effects, if any, of low-frequency electromagnetic fields. 

Now, in laboratory experiments with alternating magnetic fields produced by a Helmoltz coil, the fields induced are up to 10 1 V cm-1, and these have been proven to produce biological effects, some of which were described above. These results are important for humans, not only in respect to the effects of power lines, but also their exposure to numerous other sources of electromagnetic radiation, including the wiring... 

The ability of a substance to become permanently magnetized by exposure to an external magnetic field. 

In contrast to diamagnetism, where all valence electrons of each atom are spin paired, paramagnetism is found in solids where the constituent atoms contain an unpaired valence electron(s). In a simple paramagnetic substance, the unpaired electrons spins are randomly oriented within the solid. Upon exposure to an external magnetic field, the spins become collectively oriented in a parallel direction to the applied field. However, the dipoles re-randomize when the field is removed. 

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