Overview

In the previous chapter, an account was given of the process of identifying hazards, of the methods available and of the follow-up. For the great majority of hazards the action to be taken is clear once the hazard is known. There are, however, some hazards that require further assessment. Originally, such hazard assessment was undertaken in order to assist in making engineering decisions in the grey areas where further investigation is needed in order to decide on the most cost-effective measures. This is still the prime purpose of hazard assessment, but increasingly in recent years, this activity has been enlarged to deal with major hazards which are realized only very rarely but which present a threat to the public.

The aims and nature of these two activities are somewhat different. The terminology used to describe them also differs. In the United Kingdom, the practitioners of the first type of hazard assessment have tended to call it hazard analysis (HAZAN). The second type is often called probabilistic risk analysis (PRA), a term which came into use in the US nuclear industry, or simply risk analysis .

Hazard assessment is introduced here, therefore, with an account of how it has developed historically. The use of hazard analysis as an aid to engineering decision-making is then described. As this account shows, the methods used in hazard analysis are often relatively simple.

Risk assessment is a more complex undertaking, as the account given indicates. The starting point is the identification of the hazards and...