Layers of Protection Analysis Using Possibility Theory

Abstract

An important issue faced by risk analysts is how to deal with uncertainties associated with accident scenarios. In industry, one often uses single values de- rived from historical data or literature to estimate events probability or their frequency. However, both dynamic environments of systems and the need to consider rare component failures may make unrealistic this kind of data. In this paper, uncertainty encountered in Layers Of Protection Analysis (LOPA) is considered in the frame- work of possibility theory. Data provided by reliability databases and/or experts judgments are represented by fuzzy quantities (possibilit ies). The fuzzy outcome fre- quency is calculated by extended multiplicat ion using α- cuts method. The fuzzy outcome is compared to a sce- nario risk tolerance criteria and the required reduction is obtained by resolving a possibilistic decision-making problem under necessity constraint. In order to validate the proposed model, a case study concerning the protec- tion layers of an operational heater is carried out.