Selecting Accident Scenarios for Land Use Planning Purposes

Selecting credible accident scenarios is a critical issue in land use planning with respect to major accident hazards. Several previous benchmark studies have shown that this is an uncertainty factor that can influence heavily the final results of a hazard analysis or risk assessment. It is commonly agreed that the effectiveness in comparing hazard or risk figures to address land use planning issues is reduced when considering different sets of accident scenarios. Hence having a validation procedure that enables a systematic identification of a set of reference accident scenarios is of fundamental importance in ensuring a coherent approach to land use planning. In the present study a procedure is developed to identify and validate a set of reference accident scenarios for land use planning. This procedure is based on an improved version of the MIMAH methodology which was originally developed within the EC FP6 ARAMIS project. The proposed procedure was applied to the analysis of a matrix of five reference installations and 12 hazardous substances. The application of the proposed methodology evidenced on one hand the effectiveness of the procedure in selecting coherent sets of reference scenarios. On the other hand, the analysis of the case studies provided significant useful hints on the application of different land use planning criteria and also highlighted the sensitivity of the results to threshold values used for the consequence assessment.