ARE mobile phones and base stations capable of "frying" heads"? No, says informed scientific opinion, which dismisses such emotive terms with a batch of international standards.
Yet there are no mandatory regulations, and a dearth of research on health risks. Earlier this year, the World Health Organisation initiated an international project to assess the effects of electric and magnetic fields. But results are not expected for at least five years.
Given that mobile phones and their supporting base stations ore masts, have only existed for a decade, research is still at an early stage. Recently, scientific studies have claimed that microwave electromagnetic radiation, similar to that emitted by this technology, can damage DNA in rats and mice, and affect levels of a substance associated with the growth of tumours. But the International Committee on Non-Ionising Radiation Protection, which has set the relevant standards, says there is no proof of such adverse effects.
The British National Radiological Protection Board takes a similar view, stating that scientific data relating to cancer and exposure to electromagnetic radiation at the microwave frequencies used by hand held telephones is scant and inconsistent. Still, it acknowledges the need for further research.
In short, it is up to mobile phone manufacturers and transmission companies to ensure that consumers, and people living near base stations, are free from risk. Some companies have taken up the gauntlet. Siemens, one of the largest manufacturers, has said there are no serious dangers. While the phones expose the user to electromagnetic fields, exposure limits were laid down internationally at a very early stage, it says.
These standards are based on an awareness of the thermal effect of high frequency electromagnetic fields. Researchers have found that tissues exposed to the radiation from mobile phones can absorb the radiant energy, in the process causing hot spots, places, where the tissues warm up.
Calculations for this are based on the specific absorption rate. The SAR is the radiant power absorbed by the tissue in watts per kilogram of body weight. Tests have shown, Siemens says, that with a "whole body" SAR of 4 watts per kilogram, the temperature of the tissue increases by 1 Celsius after about 20 minutes. Such a thermal effect is compensated for by the body's own thermo regulation process, with no injury to health. It is similar to a person's metabolic rate during sports activities, when it can rise from 1.2 watts per kilogram to several times this level.
Those who believe harm can be caused by this equipment argue that while a whole body value is relatively low, the small volume of tissue adjacent to the source of the radiant energy can receive a more "concentrated" dose, causing a higher change in temperature.
The guidelines set by the ICNIRP are well below this range, it says, at 0.4 watts per kilogram for occupationally exposed persons, and 0.08 watts per kilogram for the general public. The latter value takes into account special cases such as pregnant women, children, and persons with a disturbed thermal regulation, and the low value corresponds to the energy absorbed within an hour by a person drinking a hot cup of coffee.
Ireland, which recommends ICNIRP guidelines, has charged, Forbairt, the State research body, with measuring levels of emissions from base stations. At ground level, such emissions are said to be negligible. Studies carried outs with the co operation of both Eircell and Esat Digifone have found emission levels to be less than 1,000 times below the international safe limits.
However, the only "mandatory" regulation has related to planning applications for masts. Some of the earlier base stations constructed in Dublin and around the country were given a planning exemption granted by the Department of the Environment, which permitted erection of 15 metre masts provided work began during the period May 6th to November 16th, 1994.
In a briefing issued in July of this year, the Department of Transport, Energy and Communications said that mobile telephones had a very low power output. The signal reaching the base station tower is quite weak, it said. To increase the power of the received signal, the base station employs two separate receivers on each radio channel and combines their outputs to provide a signal of adequate strength.
Fundamental to GMS networks is the balancing of received signal strengths - that is, the strength of signal picked up by the base station must equal the strength of the signal received by the phone. Hence, says the Department, a sector transmitter on a base stations would output about 3 watts per radio channel when all voice channels were occupied - and a mobile phone a few centimetres from the head would generate a exposures than that emanating from a 1 metre high tower.
Exposure standards for mobile" phones set in the US and Europe, vary from an energy absorption threshold of below 1.6 milliwatts per gram in the US to below 2.0 milliwatts per gram in Europe, it says. In almost all cases, mobile phone users do not experience such levels," it says, but adds that there are exceptions - such as using the phone with the aerial touching the head.
"In contrast," the Department says, the general public, even in the immediate vicinity of a blase station tower, are exposed to field strengths some 3,000 to 200,000 times less.
