Accidents, 'Black Swans' and Risk

Abstract

Major accidents and natural disasters with severe consequences have occurred in all sectors of industrial activity with relatively high frequency. The severe consequences of concern involve either significant loss of life or major economic loss, or both loss of life and economic loss. Such events have in the last two years often been referred to as 'Black Swan' events following publication of a best-selling book. The events demonstrate limits to the application of Probabilistic Risk Assessment (PRA) that arise from the underlying unquantifiable uncertainty associated with the estimation of the frequency of occurrence of such events. An approach is proposed in this paper that, consistent with the concept of defense in depth employed by the nuclear industry, augments probabilistic risk assessment with a methodology based upon 'threat -risk assessment'. This approach shifts these very low frequency, high uncertainty, and high consequence 'Black Swan' events out of the probabilistic risk assessment domain and into a deterministic emergency response assessment domain.