A framework of sensitivity analysis for the performance assessment of safety barriers impacted by NaTech accidents
Résumé
Hazardous Natural events can cascade into Technological accidental scenarios (so called NaTech accidents). The occurrence of these accidents can degrade the performance of the preventive and mitigative safety barriers installed in the technological plants. Such performance degradation is typically assessed by expert judgement, without considering the effect of the magnitude of the natural hazard, nor its increasing frequency of occurrence in view of climate change. In this work, a novel sensitivity analysis framework is developed to identify the safety barriers whose performance degradation is most critical and thus needs careful modeling for realistic risk assessment. The framework is based on the calculation of a set of sensitivity measures, namely the Beta, the Conditional Value at Risk (CVaR) and the Value of Information (VoI), and their use to prioritize the safety barriers with respect to the need of: accounting for performance degradation during an accidental scenario; planning investments for further characterization of the safety barrier performance.
An application is shown with respect to a case study of literature that consists of a chemical facility equipped with five safety barriers (of three different types, active, passive and procedural). NaTech scenarios can occur, triggered by floods and earthquakes. The results obtained with the Beta measure indicate that two-out-of-five barriers (one active and one passive) deserve accurate modelling of the performance degradation due to natural events. An additional outcome is that in the case study considered, both CVaR and VoI rank the passive barrier as the most effective in mitigating the scenarios escalation: therefore, this barrier is the one for which the decision maker could decide to invest resources for improving the characterization of its performance to obtain a more realistic assessment of the risk.