(94b) Single Scenario Risk Criteria: Why would I want them and how do I get them?

Traditional criteria for risk evaluation have been based on individual risk and societal risk. Both types of risk criteria are useful in techniques such as Quantitative Risk Assessment. Individual and societal risk criteria are also values which have been specified by several governmental authorities outside the United States. In recent history, the Layer of Protection Analysis (LOPA) technique has gained prominence as a popular risk analysis method particularly for the development of Safety Integrity Levels (SILs) for Safety Instrumented Systems (SIS). Some companies are using this technique as a method to evaluate cumulative risk and comparing this calculated risk to individual or societal risk criteria. However, since LOPA is a method for evaluating a single cause ? consequence scenario, it lends itself to the application of risk criteria that are calibrated for addressing the risk from individual scenarios. This paper discusses reasons for the development of scenario based risk criteria and presents a methodology of developing risk criteria for a single cause ? consequence scenario starting with individual and societal risk criteria supported by one governmental authority.