Major accidents due to the impact of natural events on technological systems

A high number of severe accidental events in process plants was caused by the impact of natural events. These so-called NaTech disasters deserve particular attention as they can result in multiple and simultaneous releases of hazardous materials due to the extended damage of process and storage units. NaTech scenarios have caused damage to population and workers as well as extended environmental contamination. However, due to the different features of the natural events that may trigger such scenarios, only limited data are available on the damage states, on the release intensities and on the final consequences of such events. The present contribution will focus on the characteristics of different categories of NaTech accidental events. Available data past accidents caused by the impact of natural events on process plants and storage sites were retrieved from several industrial accident databases. The analysis of past accident data allowed gathering data on the expected damage of process equipment caused by the impact of natural events. Failure modes and damage states caused by different natural events were identified. Information was obtained on the expected intensity of loss of containment (LOC). The scenarios caused by the release of the hazardous substance were related to substance hazard and to the intensity of LOCs. The presence and the role of safety barriers was investigated as well. The results allowed the identification of the more frequent failure modes of critical equipment items due to the impact of different natural events. Reference accidental scenarios likely to be triggered by natural events in industrial plants were also defined on the basis of substance hazard and of the expected intensity of loss of containment following equipment damage.