Assessment of safety barrier performance in the mitigation of domino scenarios caused by Natech events

Technological accidents triggered by natural hazards (Natech accidents) are likely to escalate in cascading scenarios with severe consequences. Indeed, safety barriers implemented in process plants to prevent and mitigate accidents may be affected by natural hazards as well. The present study proposes a novel comprehensive method to assess safety barriers and protection systems performance modification during natural hazards, as well as the resulting modification in the expected frequency of secondary technological scenarios that may arise. In particular, the probability and frequency of domino scenarios initiated by Natech events are assessed considering the possible concurrent degradation of safety barrier performance in case of floods and earthquakes. An approach based on layer of protection analysis is adopted to quantify safety barrier performance degradation, accounting for the modification of barrier availability and effectiveness. A dedicated event tree analysis is applied to domino effect assessment and quantification of overall escalation scenarios. The results obtained allowed a detailed assessment of the expected frequency of secondary mitigated escalation scenarios, considering the possible effect of barriers degradation within Natech events.