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Electromagnetic Radiation at Home
In homes located far from power lines, the background EM fields may reach values of about 0.03 T in case of properly wired buildings, or higher values of 0.2 to 3 T in case of faulty wiring. However, just beneath the lines, the levels of electric fields may be as high as 10 kV/m with a severe decrease in magnitude as the distance increases. Thus, at 50 to 100 m distance, the fields have again background levels. In addition, house walls or just the roofs and trees decrease significantly the electric field levels, even those corresponding to the Earth. When power lines are buried into the ground, the fields at the surface are hardly detectable.
The electric appliances in the household function under the same principle, i.e. at a distance of 30 cm, the EM fields are more than 100 times lower than the accepted limits for the general public. Moreover, in contrast to the electric fields that exist in the plugged wires even when there is no current flowing, the magnetic fields are produced only at the switching on of the appliance. Magnetic fields are not blocked by walls or other common materials. These fields vary greatly in flux density (70 T for a hairdryer or 0.1 T for a tape player).
The TV sets and VDU-s emit a wide spectrum of EM radiation ranging from X-rays to low frequency radiation. The emissions are both from front and rear of the monitor involving that way more people than the users. In these cases, thermal effects of the emitted radiation are negligible. Modern screens with liquid crystal displays have the advantage of lowering the immediate levels of EM radiation generated.
Domestic microwave ovens (see Table I.3.3.) function at very high power levels. A good appliance has low levels of leakage into the exterior; however, any microwave leakage decreases very rapidly with the distance from the oven.
Electromagnetic Radiation Outdoors
Radars are used by airports and harbors for navigation, by weather stations, the military, etc. The emissions in this case are in the form of pulsed microwave signals. Many types of radar rotate or move up and down, diminishing this way the power density to which the public is exposed to.
Examples of security systems that involve the production of EM fields are the anti-theft systems, metal detectors or airport security systems. The most common technology uses in the first case pulsed fields with a specific frequency between 8-13 MHz to detect self-adhesive tags resonant to this frequency. The main magnetic fields exposures from such devices are directed mainly to the customers (short occupancy time), although some systems are installed near the exits. Metal detectors as well as the airport security systems set up strong magnetic fields of densities up to 100 T that are disturbed by the presence of a metal object. In the vicinity of the detectors, the field strengths are high, but not considered a health hazard.
The biggest exposure of public to EM fields on electrical transport comes from the on-board traction components rather than the overhead lines or the power rails. Intercity trains use 25 kV / 50 Hz overhead lines to supply power to the engines.
In these cases, the traction components are located in the separate power cars (up to 50 mT for workers), therefore passengers are exposed only to radiation from the on-train power supplies. Magnetic flux densities of several T are mostly common. In case of local and tube trains or trams, the motors are normally located underneath the floors of the passenger cars. Thus, passengers may receive at floor level magnetic fields of tens of T or more. However, the exposure of the upper body is much lower.
Mobile phones are low-power radio wave devices that transmit and receive signals from a network of fixed base stations. Their usage is at present extensively spread (only in the UK 72% of population have one and 10% of children 11-15 years old spend more than 45 minutes daily on calls). This communication system uses pulsed microwaves (see Table I.3.3.) to “carry” the voice information. Usual phones generate values of 25 V/m in the air close to the head, whereas at 1 to 5 m from it the fields will be less than 3 V/m. The use of a “hands free” set as a headphone device allows keeping the antenna at distance from the head, reducing this way the user’s exposure.
The action of EM fields from all man-made sources is cumulative.
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