Na-Tech accidents induced by floods: an approach to hazard and risk assessment

Several accidental events that occurred in chemical and process plants in the last decades evidenced that floods may cause severe damages to process plants and storage sites, resulting in multiple and extended releases of hazardous substances. Moreover, besides conventional release scenarios (fires, explosions and toxic clouds), floods may cause two further critical events: significant environmental contamination due to water pollution, and release of toxic gases and flammable vapours generated by reactions of chemicals with water. In the present study a qualitative assessment procedure was defined to identify the possible modes of structural damage of equipment items, also considering different categories of floods. The procedure also allows the identification of the credible scenarios that may be associated to the different modes of structural damage and then the identification of critical equipment items. The methodology was applied to the analysis of some case-studies.