Risk assessment

Probabilistic or quantitative risk assessment (QRA) aims to identify, estimate and evaluate a variety of threats to human health and safety. These threats arise primarily from particular technologies (such as commercial nuclear fission) or from environmental impacts (such as deforestation). Defined in terms of the probability that some consequence will occur, ‘risk’ typically is expressed as the average annual probability of fatality that a particular activity imposes on one individual. For example, because of normal lifetime exposure to dichloromethane (DCM), a multipurpose solvent, the average member of the public has an annual probability of dying from cancer of 0.0000041 or ( $4.1\times {10}^{-6}$ ). Or, for every million persons exposed to DCM throughout their lifetimes, on average the chemical will cause four cancer deaths each year.

Although risks may be individual (such as those from consuming saturated fats) or societal (such as those from liquified natural gas facilities), government typically regulates only societal risks. By definition, they are largely involuntarily imposed, whereas individual risks affect only the persons voluntarily choosing them. Most QRAs address societal risks, either because a government seeks a scientific basis for particular risk regulations, because some industry wishes to determine possible liability for its processes or products, or because actual or potential victims want to protect themselves or to allocate risks by means other than market mechanisms.

Philosophical contributions to QRA are of three main types: assessments of particular risks, criticisms of existing assessments, and clarifications of important QRA concepts, methods or theories. Such contributions usually focus on either epistemology (including philosophy of science) or ethics. Epistemological analyses address, for example, the adequacy and appropriateness of some scientific, probabilistic or policy technique used in QRA; the status of a specific causal hypothesis about risk; or the rationality of alternative decision rules for evaluating risks. Ethical analyses investigate, for instance, the equity of the risk distributions presupposed in a specific QRA or by general QRA methodology; the degree to which a particular method of risk evaluation accounts for crucial social values, such as free informed consent and due process; and the extent to which a given QRA technique, such as discounting the future (see Parfit 1983), begs important ethical questions such as rights of future generations.