With the recent development of nuclear energy in large-scale, the problem of the exposure of the public has become to be regarded as of major importance nowadays. In spite of all the possible efforts of safety operation of nuclear facilities, there may be still a potential hazard of the exposure of human beings to small doses of ionizing radiations over prolonged periods of time. The biological evaluation of risks from radiation must be made on the basis of the dose-effect relationship, but the difficulties of obtaining such a relationship at low dose and dose-rate are due mainly to the extremely low frequency with which effects might occur. Therefore, the estimates of the incidence of the effects at low levels in man have been found on the extrapolation to low level of a few available data observed at relatively high dose and dose-rate. The validity of such an approach is influenced many unknown and undefinite factors.
The present paper will give a general outline of the problems concerning the risk evaluation of radiation hazards, centred on BEIR report published in 1972.