QRA of chemical reaction systems: The state of the practice

This paper discusses a quantitative risk assessment (QRA) of an exothermic chemical process. Fault tree/event tree techniques were used to estimate the frequency of runaway reactions that could result in over-pressure and vessel rupture. The paper focuses on the current methodology used in performing this type of study, emphasizing analytical techniques that help avoid potential time-consuming pitfalls. The challenging problem of predicting how rare sequences of events (e.g., involving failure of several engineered control and safety systems) will develop is systematically modeled using fault trees/event trees, which makes the QRA process a unique and powerful analytical tool. The results of this study provided the guidance for selecting the most appropriate action(s) to implement from a set of various design options for improving the safety of this system. Use of QRA has enabled plant management to have confidence that they are selecting the most cost-effective safety improvement option.