Assessment of risk modification due to safety barrier performance degradation in Natech events

Natural hazards may cause severe technological accidents involving hazardous substances (Natech accidents). Along with process equipment also safety critical elements as safety barriers might be impacted by such events, thus reducing the protection provided and the possibility to prevent escalation and cascading effects. In the present study a comprehensive methodology is developed to address the quantitative assessment of the risk caused by the escalation of Natech accidents, specifically addressing the effect of the performance modification of safety barriers caused by the impact of the natural hazard. Barrier performance depletion is modelled through an innovative multi-level approach, and it is then introduced in the quantitative risk assessment procedure by a modified event tree analysis. A demonstrative application of the proposed methodology to a case study is provided, showing a relevant increase in risk figures deriving from the degradation of safety barrier performance caused by natural events. The proposed framework extends the systemic assessment of Natech scenarios to encompass the specific criticalities introduced by safety barrier performance modification induced by natural events, providing a more effective support to decision-making in the management and control of risk deriving from the interaction of natural hazards with technological installations.