Towards a new approach for the identification of atypical accident scenarios

Proper hazard identification in safety reports has become progressively more difficult to achieve. Several major accidents in Europe in recent years, such as Buncefield and Toulouse, were not even considered by their site “Seveso-II” Safety Case. One of the reasons is that available hazard identification (HAZID) methodologies take no notice of apparently least likely events. Non-identified scenarios thus constitute a latent risk, whose management is extremely complex and open-ended. For this reason the EC project iNTeg-Risk, in one of its tasks, aimed to investigate the issue of atypical scenarios and explain how they could have been identified. This study wants to describe the approach used and its immediate results, paving the way towards a new method for the identification of atypical accident scenarios. An in-depth accident analysis of some of these accidents was performed, in order to outline general features of plants in which they occurred, their causes, consequences and lessons learned. This analysis followed a precise common scheme, which allowed a systematic approach to the problem by the experts involved. Based on the findings, failures connected to risk management and risk appraisal were identified. Three main basic issues in risk appraisal were identified: the low perception of emerging risks related to atypical accident scenarios, the lack of knowledge about related events, such as early warnings, and the incapability of current techniques in leading analysts to the identification of atypical scenarios.