Widening the discussion on tolerability of risk

Assessments of the risks to an individual from ionising radiation currently compare the probability of the resulting harm, e.g. fatal cancer, with the probability of harm from other causes, e.g. fatal accident. However, many of the effects of exposure to radiation are expressed only after a latent period of many years, whereas the effect of an accident is usually more immediate. The difficulties inherent in such comparisons have been addressed by the International Commission on Radiological Protection who developed an 'Index of Harm' which uses loss of life expectancy as a common basis on which to compare different forms of risk. The author describes a graphical presentation of loss of life expectancy which illustrates these differences in approach to risk assessment. This type of presentation is particularly useful for broadening the perspective on the Health and Safety Executive discussions on the tolerability of risk.