ABSTRACT
Introduction That safety is important needs little argumentation; this and many other books bear witness to that. Because safety is important, it is also essential to know how an organisation or a system can achieve an adequate level of safety. The universal agreement about the importance of safety has, however, not produced a similar agreement about what safety is, i.e., how it should be defined. For the present purpose I shall use a popular definition of safety as “the freedom from unacceptable risks”. This is a definition that most people, safety professionals and amateurs alike, will happily agree with. Yet although this definition may seem to be straightforward, its usefulness depends on a number of rather important assumptions. Indeed, even a cursory reflection of the three major terms of the definition – “freedom”, “unacceptable”, and “risk” – gives rise to a number of further questions.
