Prevention of atypical accident scenarios through the use of resilience based early warning indicators

An “atypical” accident scenario is a scenario deviating from normal expectations and, thus, not deemed credible by common processes of risk assessment. Past experience shows that non identified accident scenarios as such represent a latent risk for industry and society and sometimes their occurrence can lead to consequences of unexpected extent. An evident example of an atypical accident was the major accident occurred at Buncefield on 11th December 2005. A detailed analysis of this and other cases in literature has shed some light on the complexity of their causal factors, demonstrating that an atypical major accident is not the consequence of a single uncommon event, but rather the result of a series of failures at different levels of risk management. Thus, it has been a major challenge to foresee combinations of such failures and corresponding unidentified accident scenarios. Two complementary approaches to deal with this challenge are: i) improved identification of atypical scenarios, to reduce the occurrence of unforeseen events; ii) improved early detection, to reduce the possibility of remaining unforeseen events leading to an accident. For this reason the Resilience based Early Warning Indicator (REWI) method has been considered in this contribution. The main aim of this work is to show the preliminary results of the application of this method to the site at Buncefield, obtained by adapting the candidate set of REWI indicators to the oil depot characteristics and defining new indicators on the basis of the accident causes. In this way it has been also possible to understand the relevance of these resilience based indicators as early warnings of the atypical scenario and to demonstrate, by the correspondence of the defined indicators with the accident causes, that this major accident would have been likely prevented by the application of the REWI method. to an accident would be reduced. For this reason the Resilience based Early Warning Indicator (REWI) method has been considered in this contribution. In fact, the concept of resilience refers to the capability of recognizing, adapting to, and coping with the unexpected and one of its key characteristics is the interaction and interchange between different (organizational) system layers, levels, and focal points. The main aim of this work is to show the preliminary results of the application of this method to the site at Buncefield. A candidate set of resilience based early warning indicators are adapted taking into account characteristics of the oil depot. Then, the accident causes identified in the analysis are related to the indicators, in order to understand the relevance of these resilience based indicators as early warnings of the atypical accident scenario occurrence and to which extent this major accident could have been prevented.