Radiation scientists reassure public about low-level waves from antennae and power lines

Press, 4 December 1985, Page 21

Radiation scientists reassure public about low-level waves from antennae and power lines

By

GARRY ARTHUR

The building of a new satellite earth station near Rangiora and the proliferation of microwave reception and transmission dishes on the Port Hills has raised the question of just how safe it is to be near microwaves and other electromagnetic radiation. Since the showing of an Australian documentaiy on the subject, on Television One’s “Close Up” programme, the National Radiation Laboratory has had numerous inquiries about whether there is any danger to health from such radiation. So many, in fact, that the laboratory surveyed the research data and issued a statement reassuring the public that it was satisfied that in the case of high voltage transmission lines there was no evidence of any adverse effects on health.

In the case of radiofrequency dielectric welders used to weld plastic, however, it said that its two-year study of 93 machines in 26 factories showed that more than a third of the machines were exceeding the amount of radiation allowed by the latest standards. Some exceeded the limits set by the old, lower standards. “Although there are some questions about the applicability of existing and proposed standards in these situations, advice on limiting operator exposure has been provided where levels have been found to be relatively high,” said the laboratory. It added that apart from some instances of radiofrequency bums, no adverse effects on health had been reported by equipment operators. Extremely low frequency electric fields around high voltage power lines cause electric currents to flow through the body, and at sufficiently high external levels the internal electric fields and body currents interfere directly with nerve activity and some biochemical reactions. Electric field strengths near the ground directly beneath high voltage power lines are often between one and two kilovolts per metre, but can reach four kilovolts per

metre. But the National Radiation Laboratory says that external field strengths of less than 10 kilovolts per metre appear not to present a hazard. “But at levels greater than three kilovolts per metre some individuals experience microshocks, due to almost microscopic discharges

from the skin, which can produce startle reactions. These appear not to be hazardous as such, but are uncomfortable and distressing, and can increase risk of accidents,” it says. Sensitive individuals are able to perceive field strengths down to two kilovolts per metre. The laboratory adds that claims of increased headaches, fatigue, insomnia, and of cancer, miscarriages, and birth deformities associated with long-term relatively low-level exposure, have not been substantiated. Extremely low frequency magnetic fields do not appear to react directly with tissues of humans or other mammals, it says, but some birds, insects, and micro-organisms respond to even weak levels. However, humans might be affected by the eddy currents generated by the alternating magnetic field which at certain levels can cause a disturbing effect on the optic nerve, perceived as light flashes or phosphenes. It notes, too, that the generation of body currents can actually be beneficial, and have been used in medical practice to promote the healing of diseased or fractured bone.

The laboratory says that surveys have been made of the medical histories of linemen and of people living close to pylons, and experiments have been performea on human volunteers and small animals, “but deficiencies in technique have often led to unrepeatable and sometimes contradictory results.” The Soviet Union, which has done considerable research in this area, has very stringent standards limiting the exposure of workers to extremely low frequency radiation — about four times as stringent as western recommendations. In a paper on the health effects of microwave and radiofrequency radiations, the laboratory says that these can be harmful because they can produce heat in body tissue. Areas with little blood circulation, such as the lens of the eye, and the testes, may be more susceptible to heat damage. Cataracts have been induced in rabbits’ eyes at high exposure rates. In some Eastern European countries, effects have been reported arising from exposure to low levels of microwave radiation, where significant heating was not expected. “There was considerable controversy about the validity and possible health significance of these

findings,” says the National Radiation Laboratory. “Some of the effects were largely non-specific, in that they can be produced by stresses other than microwaves, or the disturbances have been within clinical norms or tolerances and are reversible. Others have been attributed to localised heating arising from resonance or focusing effects. “However,” it adds, “behavioural and metabolic changes, and changes in bioelectrical activity of the brain, have been demonstrated in various animals at levels of ImW per square centimetre for certain frequencies.” Microwaves are prevented from leaking from microwave ovens by safety features such as door interlock switches, but excessive leakage can occur if the aoor is bent or does not close properly. Regulations control the power density level of microwave radiation on the external surface of the oven. The Consumer Council recently surveyed all ovens on the New Zealand market and found them all to be safe, with leakage levels within the small amount allowed. “This level is so 1 low that you would receive more radiation by standing under a clear blue sky,” the “Consumer” magazine added. “Consumer” did warn that it is not sensible to stand for any length of time peering into a microwave

oven, nor is it wise to allow children to “press their faces against the door while they watch a cake being cooked.” Dr Andrew McEwan, director of the National Radiation Laboratory, says the Post Office microwave tower on Cashmere Hills has four parabolic antennae which radiate power of about one watt, producing a power density of about 0.4 watts per square metre. “The total power emitted is fairly low,” says Dr McEwan. “For communications antennae the level is below that likely to cause any health effects. At ground level in front of the tower nothing is detectable at all. You would have to get up in front of the dish.” Dr McEwan says that when the antenna is on a tower on a hill, people cannot get into the beam, but even if they did the total power is so low that it would not matter. Very powerful airport radars and military surveillance systems could be a health danger, particularly overseas where very powerful radars are used. Microwave links to satellites are also of very high power, but the satellite earth station near Rangiora does not transmit to satellites — it is just a passive receiver. Microwave limits were originally set on the basis that energy from a strong beam would cause heating which the body’s regula-

tory biological response would not be able to cope with. The safe limit was set at 100 watts per square metre, a fraction of the rate at which the body could cope with such heating. Later, it was realised that at lower frequencies, and for certain body sizes, resonance effects might occur which might lead to unacceptably high rates of energy ab-

sorption in some parts of the body. “That is the reason there has been a modification to the proposed limits in the last five years,” Dr McEwan explains. He has not heard of anyone being harmed by microwaves in New Zealand, although he knows of an Australian case where a man’s hand was “cooked” by an industrial microwave oven.