Offshore QRA and the ALARP principle

A discussion is presented of the use of QRA within a requirement, of the UK offshore safety case regime, to demonstrate that risks from offshore major accidents are ALARP. General considerations are given to uncertainties in failure and incident data, assumptions and consequence methodologies within the analysis element of offshore QRA. The validity of risk results arising from the analysis element is discussed in the context of such results being viewed on the basis of a classical interpretation of probability (the interpretation most often used for offshore QRA), and comments are made about the nature of results in relation to a distinction between objective knowledge and subjective ignorance. Consideration is given to a Bayesian interpretation of probability (rarely used for offshore QRA), and to the role that QRA may have when this interpretation is adopted against a background of some basic principles of engineering safety.