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Abstract

Risk graphs are one of the techniques used to determine safety integrity levels (SILs) for the safety instrumented functions (SIFs) that make up safety instrumented systems (SISs) for processes. The standard risk graph approach originated in a German standard published in 1994. The standard approach has a number of disadvantages that are delineated in this article. An improved risk graph approach has been developed to overcome these disadvantages. The improved method is described and an example of its application is provided. The improved method preserves the simplicity of risk graph methods while providing a theoretical foundation that facilitates moving into more refined methods such as layers of protection analysis (LOPA) or quantitative risk analysis (QRA), if needed. Furthermore, the improved risk graph method can be incorporated easily into process hazard analysis (PHA). © 2006 American Institute of Chemical Engineers Process Saf Prog, 2007