Towards the inclusion of external factors in quantitative risk assessment: the analysis of NaTech accident scenarios

Threats deriving from external hazard factors as natural events and intentional acts of interference are perceived as important issues affecting the safety of chemical and process plants where relevant quantities of hazardous substances are present. The increasing frequency of some natural events having a particularly high severity also raised a growing concern for industrial asset integrity and for the consequences of accident scenarios that may be triggered by intense natural events. The specific features of technological accidents triggered by natural events were recently recognized, and these scenarios are now indicated as NaTech accidents. The screening of past accident databases points out that NaTech accidents are quite common in industrial facilities. However, these scenarios are seldom considered in the safety assessment of industrial facilities and a specific evaluation of the potential consequences of NaTech accidents is generally not carried out. In the present contribution, the framework for the analysis of NaTech scenarios is defined and the recent advances in the tools available for the assessment of NaTech events are revised.