Is it safe? safety factor reasoning in policy-making under uncertainty

Abstract: This thesis examines the practice of using safety factors in decision-making under uncertainty, in particular in the areas of toxicology and civil engineering. The aim is to expose and clarify some of the philosophical issues surrounding the practice.Paper I (co-written with Sven Ove Hansson and Fred Nilsson) gives an historical background to the practice of formal safety factor and safety margin use. The notion of an uncertainty function is presented as a more general concept covering safety margins, safety factors and the related uncertainty factors. Three categories of uncertainty functions are identified: explicit, implicit and natural safety reserves. Finally, the problems of countervailing risks and distribution arbitrariness are discussed.Paper II (co-written with John Cantwell) discusses the relation between decision-making with safety factor rules and the ideal of formal normative decision theory. The role of safety factor rules in practical and theoretical reasoning is also examined and certain difficulties regarding normative evaluation of safety factor rules are pointed out.Paper III (co-written with Sven Ove Hansson) looks at two current regulatory systems under development: Eurocodes for construction and REACH for chemicals. The two regulations have many similarities but reactions to them have been highly divergent. The differences are discussed and some hypotheses as to their explanation are suggested.