Probabilistic assessment aimed at the evaluation of escalating scenarios in process facilities combining safety and security barriers

Over the last twenty years, physical security threats to chemical and process facilities became more and more relevant all around the world. Intentional attacks have the potential to trigger severe escalation scenarios. However, in literature there is not a comprehensive and consolidated approach to account for the effect of physical protection systems (PPSs) in the framework of conventional process safety analysis and to consider their contribution with the prevention and mitigation actions of safety barriers. Therefore, the aim of the present work is to develop a probabilistic study dedicated to chemical and process facilities accounting for the combined contribution of safety barriers and PPSs in the prevention of cascading events triggered by security attacks. The quantitative performance of PPSs was characterized in terms of availably and effectiveness, building a specific data repository. The performance data obtained were included into event trees, in which safety barriers were implemented. The analysis of an industrial case study demonstrated the potentially of the methodology in analysing complex escalation scenarios, identifying the critical PPS elements and, at the same time, showing the critical role of safety barriers in protecting against scenarios triggered by security attacks.