The characteristics of risks of major disasters

Abstract

The quantification of risk requires measures of consequences and of frequency. Serious personal consequences are expressed as a ‘disaster profile’ giving the numbers of early deaths, late deaths, serious incapacity, forced permanent evacuation and serious birth defects. Profiles from the disasters at Bhopal and Chernobyl are quite different. In addition, there is a financial measure of harm that can include the personal measure if a value is assigned to a human life or adverse health effect. Timescales of disasters from earthquakes to long-term pollution are discussed; if they are long enough, the risk can be transferred from one of death or injury to one of evacuation and cost. This applies to most nuclear risks, which are better quantified by cost measures rather than by the unobservable hypothetical number of late cancer deaths. Measured by evacuation or cost, nuclear risks increase more than linearly with the size of the radioactive source term. Factors leading to risks are examined, and that of knowledge and its transmission is emphasized. The causes of only a few disasters, e. g. hurricanes, are wholly stochastic in nature; for others, their frequency can be reduced, possibly at some expense. Statistics is inferior to probabilistic safety analysis as a predictor of risk where knowledge is involved. Several recent disasters are listed, together with some others that have a high probability of occurrence in the near future. Those from long-term large-scale pollution, e. g. climatic change induced by the greenhouse effect, may pose the largest risk.