Probabilistic Multi-hazard Risk Assessment—Development of an Aggregation Model Based on the Algebra of Events

It is useful to examine the safety of a strategic facility based on a multi-hazard approach, considering the extreme events the facility in question could be subjected to during its lifetime. This paper introduces a probabilistic model, based on the algebra of events, for a multi-hazard risk associated with extreme events (e.g., natural, climatological, environmental, and biological, etc.). The probabilistic multi-hazard assessment (PMHA) of the risk is a key issue in structural and environmental safety. A basic characteristic of a probability-based multi-hazard model is that it does not generate a single point estimate, but it rather produces a hazard curve. In the present paper, the annual risk is calculated using a probability-based multi-hazard model totally constructed with the algebra of events and with the aggregation of the multi-hazard curves. The PMHA model is based on the total probability theorem. It grants a more reliable practice by allowing key stakeholders to make risk-informed choices rather than simply relying on traditional deterministic single hazard estimates of risk, with a brief description of uncertainty. Two illustrative applications were performed to demonstrate the feasibility of the PMHA approach: (1) a strategic structure subjected to three independent events: “flooding”, “earthquake”, and “blast”; (2) the earthquake risk of a nuclear site subjected to two dependent events: “long duration” and “high magnitude” earthquake loads. The hazards fragilities are computed for the two examples and implemented in the framework of a multi-hazard approach leading to the estimation of the annual risk of failure.