Summary of Oral Evidence presented to IEGMP by Dr S M Mann, National Radiological Protection Board (NRPB), on Friday 10 September 1999

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Dr Mann presented an overview of mobile phone technology. It was stressed that there are few published data available as the whole subject is considered commercially sensitive. An authoritative source of information is a paper by Pedersen and Andersen (Rad. Prot. Dosim., 83, 1–2, 131–8 (1999)). The maximum power of handsets is defined by standards, but in practice there are significant advantages to manufacturing units that operate to the lower end of the allowed tolerance band. In addition, handsets and base stations use adaptive power control and discontinuous transmission and in general radiated power is kept to a minimum to avoid interference with other parts of the network and to conserve battery life. The single most important factor limiting the number of subscribers is the number of base stations. Operators would regard information about base station capacity as extremely sensitive. Nevertheless, it is possible to estimate that each unit can probably handle forty-eight subscribers at any one time (based on six channels and eight subscribers per channel). The maximum distance for communication between a Global System for Mobiles (GSM) base station and a phone is 35 km.

The power will vary with each subscriber, but one of the eight time-slots in one carrier always operates at full power. In addition, there are micro base stations, which are installed in urban areas and cover small cells. Although these are usually more accessible, they are likely to operate at lower power.

The Group were interested to know how exposures from base stations are likely to compare with those from television and radio masts, or emergency services equipment. In general, walkie-talkie type radios operate at higher power, but as they are used differently exposures are probably similar. Exposure of any individual will depend upon their proximity to the different sources. NRPB has made measurements near base stations and, in general, exposures of members of the public are a small fraction of exposure guidelines. It was recognised that as the signals from other sources are at different frequencies it would be difficult to use epidemiological data relating to other sources of exposure.

There was discussion on recommendations for restricting exposure. The UK follows advice from NRPB. However, this differs from advice from the International Commission on Non-Ionizing Radiation Protection (ICNIRP), which has more restrictive values for members of the public. Values for workers are the same. ICNIRP values for the public have now been adopted as a Council Recommendation by the European Commission (EC) (1999/519/EC) and are likely to be applied by many European countries. US advice is also similar, though more restrictive, than that of ICNIRP. In all three cases, the basis is the avoidance of thermal effects. However, whilst NRPB advice is based solely on the interpretation of scientific data, ICNIRP has embraced a philosophy of providing additional protection for members of the public which includes infants and children who may be more sensitive than adults. Essentially this is a form of prudent avoidance. It was, however, noted that all advice contains arbitrary protection factors, the justification for which is rarely provided. It was recognised that the mobile phone industry comply with both NRPB and ICNIRP guidelines; the main problems for compliance lie in the power supply sector (50 hertz).

First issued 5 April 2000 | Last updated 9 May 2000