A "worst case" methodology for risk assessment of major accident installations

This paper considers the application of one of the weighted risk indicators used by the Major Hazards Assessment Unit (MHAU) of the United Kingdom's H ealth & Safety Executive (HSE) in formulating advice to local planning auth orities on the sitting of new major accident hazard installations. In such cases the initial consideration is to be assured that the proposed installa tion would not be incompatible with existing land uses in the vicinity, as determined by the categorization of the existing populations and the estima ted levels of individual risk which the proposed installation would impose upon them. An analysis of the consequences and likelihood of a single "worst case" eve nt, coupled with MHAU's "Risk Integral," is then undertaken. This enables t he societal risk aspects of the proposal to be considered at an early stage and, in many cases, allows a prompt response. The paper describes the meth odology and includes several case studies based on MHAU's day to day work w hich illustrate its use.