Take a Fresh Look at Existing Hazard Analysis Data to Assess Safety Instrumented System Needs

Abstract

Many traditional methods for assessing Safety Instrumented Systems (SISs) focus on controlling individual hazards on a scenario-by-scenario basis. In these existing approaches, engineers use a hazard analysis, or other form of risk assessment, to evaluate each potential accident scenario to determine the need for a SIS. While comprehensive, such methods can result in more SISs being defined than are necessary. This paper describes an approach for SISs using existing hazard analysis data from a new perspective. The approach goes beyond traditional scenario-by-scenario methods by explicitly considering the process as a whole. A major benefit is the potential to optimize resources by identifying the minimum set of SISs required to address all the hazards present in the process. Hence, this method can reduce capital expenditures, as well as testing and inspection requirements. This paper discusses the practicalities of taking a global perspective of a process in defining SIS requirements. Additionally, the concept of Importance Measures, used for prioritizing efforts to control and reduce risk, is extended to prioritizing and optimizing SIS selection from a risk-based perspective.