The inclusion of natural hazards in QRA: the seismic event

Abstract

QRA procedures applied to industrial equipment require special attention when dealing with unconventional hazard scenarios. In this perspective, the role played by severe natural events on the functionality of an industrial system is surely of interest in any exhaustive risk assessment study.
The focus on earthquake initiating events is due to their severity and strong destructive potential that can lead to severe damages, domino effects and cross effects on residential and industrial sites.
In this work, a probability approach that includes unconventional initiating events in usual Fault Tree and Event Tree analysis procedures is proposed to ensure a reliable earthquake-related event management. Main relevant parameters are evaluated, in addition to the typical expected structural behaviour of the industrial structure. The comparison between the scenario without the seismic event and that aggravated by the earthquake shows that, depending on the both the seism and structural parameters, such an unconventional initiating event worsen the final outcomes. Variations are depending on the site-epicentre distance and the seism magnitude and peculiar effects on the final outcomes are observed both in the FTA and ETA initiating branches.