The Effect of Safety Barrier Degradation on the Severity of Primary Natech Scenarios

The impact of natural events on technological infrastructures may lead to severe accident scenarios involving hazardous materials, generating the so-called Natech events. This typology of accidents is particularly critical since, besides damaging process or storage equipment items, natural hazards might concurrently impair safety barriers implemented to prevent and mitigate technological scenarios, reducing the overall safety of the system and increasing the likelihood of unmitigated outcomes and domino effects. In this study, a novel methodology to perform the quantitative risk assessment of the primary Natech scenarios directly caused by the impact of natural hazards considering the presence of safety barriers with depleted performance is proposed. A multi-level approach is tailored to assess the performance modification of safety systems designed to mitigate the primary technological scenarios. An innovative procedure for the quantitative assessment of these scenarios is proposed to enable the characterization of the final outcomes considered in the quantitative risk assessment accounting for depleted barrier performance. A case study is developed to demonstrate the application of the methodology, evidencing a relevant increase in risk compared to that assessed considering the baseline performance of safety systems. The proposed methodology thus enables a more comprehensive assessment of the final outcomes of primary Natech events, fostering the development of a holistic framework for Natech quantitative risk assessment.