Quantitative Risk Assessment of accidents induced by seismic events in industrial sites

Several accidents occurred in the last decades evidenced that the impact of seismic events in industrial plants may trigger accidental scenarios involving the release of relevant quantities of hazardous substances. Severe scenarios typical of the process industry, as fires, explosions, toxic releases, water pollution were reported as the consequence of seismic events in industrial areas. Although the severity of this kind of accidents, scarce attention was devoted to the assessment of risk due to major accidents triggered by seismic events and a comprehensive approach to risk assessment and emergency planning in industrial sites extended to include the possible external hazard factors is still needed. In the present study, a specific approach was developed for the assessment of local and societal risk indexes caused by accidental scenarios triggered by earthquakes. The approach allows the identification and the consequence assessment of all the possible scenarios that may follow the seismic events. The starting point of the procedure was the use of available historical data to assess the expected frequencies and the severity of seismic events. Simplified empirical vulnerability models (fragility curves) were used to assess the damage probability of equipment items due to a seismic event. The data on the frequency of the natural events have to be combined with the data of the equipment vulnerability, in order to calculate a release probability, indispensable to obtain the final risk value. The procedure was implemented in a GIS-based software tool in order to manage the high number of event sequences that are likely to be generated in large industrial facilities. The developed methodology requires a limited amount of additional data with respect to those used in a conventional QRA. The application of the procedure to a storage plant sited in the Emilia-Romagna region evidenced that the scenarios initiated by seismic events may be important in the comprehensive assessment of industrial risk.