Using quantitative analysis to make risk-based decisions

Often the purpose of performing a qualitative hazard analysis is to judge the acceptability of, or offer improvements to, an engineered system. Many papers and techniques exist that describe the well-defined hazard analysis philosophy of (1) defining the hazards, (2) identifying the potential accident scenarios and causes, and (3) listing the preventive and mitigative safeguards. However, qualitative studies alone are sometimes inadequate for making specific decisions, such as comparing the relative risks and benefits of competing solutions. Therefore, risk and reliability professionals are occasionally asked to "sharpen their pencils" to provide quantitative support to these decisions. The goal of performing any type of analytical work is to achieve the correct level of detail, and that is especially true for quantitative risk analysis (QRA) techniques. The detail in these studies should be barely adequate to provide sufficient information to answer the risk-based decision. There are different levels of detail (i.e., phases) for the frequency/ consequence aspects of risk. This paper presents the technique used by ABSG Consulting Inc. (ABS Consulting) for performing QRAs in phases in order to produce only the information necessary for managers to answer their risk-based questions. Three real-life studies are provided as case studies that demonstrate the use of QRA techniques to make a trade-off decision. Often the decision involves competing risks that can only be appropriately analyzed by identifying the frequency/consequence pairings of the various accident scenarios. This paper describes a general procedure for performing a risk-based decision input study.