Atypical accident scenarios: from identification to prevention of underlying causes

The actual scenarios of several major accidents that took place in Europe in recent years were not considered by the site safety case because they deviated from normal expectations of unwanted events or worst case reference scenarios, despite several similar past events were present in literature. They witnessed that proper hazard identification has become progressively more difficult to achieve, in particular when routine activities such as safety reporting for well known technologies are carried out. Moreover, the identification of atypical accident scenarios is complicated by the rapid development in the industrial technology, which has brought about the need to upgrade the methodologies used. In fact, accident scenarios of new and emerging technologies, which are not still properly identified, may remain undetected until they take place for the first time. The consideration of atypical scenarios is an extremely challenging issue and non-identified scenarios constitute an unknown risk. This study outlines an innovative approach to tackle atypical accident scenarios on several levels in order to obtain structured and complete basis for accident prevention. A new and advanced HAZID technique for the identification of atypical accident scenarios has been developed with the purpose to obtain comprehensive but concise overviews of potential hazards related to the system. Moreover, a comparative assessment study has identified a complementary methodology aiming to address underlying causes of atypical scenarios. The synergy of the two methods constitutes an effective strategy against atypical accident scenarios in which human, organizational, cultural and technical factors are addressed in an integrated manner.