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New exida Whitepaper: Accurate Modeling of Shared Components in High Reliability Applications

  June 14, 2010

This paper addresses how to model and evaluate the risk reduction factor (RRF) of safety instrumented systems (SIS) when one or more of the components in the SIS can cause the dangerous condition or hazard that the SIS is designed to protect against. Generally a failure that can cause a hazard is referred to as an initiating event (IE). International standards for SIS safety evaluation require that shared components either be prohibited or accurately modeled. Current practice generally falls into one of two extremes, ignoring any degradation of system reliability due to shared components or completely discounting any improvements in reliability as a result of redundancy created by the shared component.