Risk assessment of escalation scenarios triggered by extreme flooding events: The role of safety barriers

Past accident analysis demonstrated that industrial facilities are vulnerable to floods, leading to the possible development of major accidents in case structures and equipment are damaged during the natural disaster. This type of accidents is referred to as “natural-technological” (NaTech) event, and both their frequency and severity are expectedly growing due to climate change and industrial development. Therefore, including NaTech scenarios induced by flooding in the framework of Quantitative Risk Assessment (QRA) is a pivotal task. A critical aspect to be accounted for in QRA studies is that NaTech accidents are characterized by exacerbated consequences caused by numerous simultaneous failures and likely further escalation to nearby equipment through domino effect. Usually multiple safety barriers are implemented in chemical plants to prevent and mitigate domino scenarios, however, their performance may be seriously affected during floodwater impact on the installation. The aim of the present study is to include the role of safety barriers in assessing domino effect risk related to chemical and process plants affected by severe flooding. The study is based on a previously developed procedure for the analysis of domino effect implementing specific metric for including effective barrier performance in escalation sequence of events, which is improved for including the possibility that safety systems may be impacted by floods.