Design of procedures for rare, new or complex processes: Part 2 – Comparative risk assessment and CEA of the case study

The paper provides the comparative risk assessment for the case in related paper Design of Procedures for Rare, New or Complex Processes: Part 1 - An Iterative Risk-Based Approach and case study (this issue), where the optimization of the pressure testing procedure for an LPG storage sphere is discussed. Both the ‘Original’ and the ‘Optimized’ procedure alternatives were the subject of a double comparative risk assessment using two different methods, namely, Bayesian Belief Networks using the HUGIN programme and Integrated Dynamic Decision Analysis (IDDA) using the SPACCO programme. Results suggest that the outputs from both methods/programmes were essentially the same, while the differences are mainly related to the results visualization and their subsequent use. In addition, the adoption of the methods has shown a reduction of the overall failure probabilities considering the ‘Original’ and ‘Optimized’ procedural alternatives respectively. The results of the comparative cost effectiveness analysis between both alternatives suggest that the initial investment on developing and optimizing the procedure is easily compensated by direct savings in implementation costs, as well as by the further savings in delay risks, occupational safety risks and process safety risks. Pertaining uncertainties in the analysis are also discussed. The results were found valuable for the site management on the “how and why” of developing a rare and potentially hazardous test procedure.