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 Health & Safety Executive (HSE) in formulating advice to local planning authorities on the sitting of new major accident hazard installations. In such cases the initial consideration is to be assured that the proposed installation would not be incompatible with existing land uses in the vicinity, as determined by the categorization of the existing populations and the estimated levels of individual risk which the proposed installation would impose upon them. An analysis of the consequences and likelihood of a single "worst case" event, coupled with MHAU's "Risk Integral," is then undertaken. This enables the 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 methodology and includes several case studies based on MHAU's day to day work which illustrate its use.