Engineering Risk-Based Methodology for Stress Testing of Critical Non-Nuclear Infrastructures (Strest Project)

Abstract eng:
An engineering risk-based multi-level stress test, named ST@STREST, is proposed aimed at enhancing procedures for evaluation of the risk exposure of critical non-nuclear infrastructures against natural hazards in the context of the European project STREST (2013-2016, within the European Union's Seventh Framework Programme) presented in a companion paper. In order to account for diversity of types of critical infrastructures (CIs), the potential consequence of failure of the CIs, the types of hazards and the available human/financial resources for conducting the stress test, each Stress Test (ST) level is characterized by a different scope (component or system), and by a different complexity of the risk analysis. The ST@STREST workflow consists of four phases: Pre-Assessment, the Assessment, the Decision and the Report phase. The phases are performed in sequence. In the Pre-Assessment phase all the data available on the CI (risk context) and on the phenomena of interest (hazard context) are collected. Then, the goal (i.e. the risk measures and objectives), the time frame, the total costs of the stress test and the most appropriate Stress Test Level to apply to test the CI are defined. This process is crucial and requires interaction among different experts and a detailed technical evaluation of the available information. In the Assessment phase both component and system ST levels (selected in the Pre-assessment phase) are performed. At the component level, initial design demand levels for each component of the CI are compared with the best available information about their capacity at the time of the stress test. Then, the systemic probabilistic risk analysis of the entire CI (system level) is performed. This process requires interaction with experts, to review and finalize the result of the assessment. In the Decision phase, results of the Assessment phase are compared to the risk objectives defined in the PreAssessment phase. The outcome of the Decision phase is the global outcome of the stress test. In this paper, a system to grade the outcome of a stress test is proposed. It is foreseen that CI can pass, partly pass, or fail the stress test. The CI partly passes the stress test when the assessed risk is considered possibly unjustifiable with respect to the risk objective defined in the Pre-Assessment phase. In this case, the proposed grading system prescribes by how much the safety of the CI should be improved until the next periodical verification of the CI. Finally, in the Decision Phase, critical events that most likely cause the exceedance of a given level of loss value are identified through a disaggregation analysis. Risk mitigation strategies and guidelines are formulated based on the identified critical events. In the Report Phase, the experts present the stress test results to CI authorities and regulators. The presentation includes the outcome of stress test in terms of the grade, the critical trigger events, the guidelines for risk mitigation, and the level of “detail and sophistication” of the methods adopted in the stress test.

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