Layer of Protection Analysis (LOPA) is a relatively new methodology for hazard evaluation and risk assessment, which has been developed in the Process Safety field, as a powerful analytical tool for assessing the adequacy of ‘protection layers’ used to mitigate process risk.
It involves identifying potential accident scenarios and then applying semi-quantitative measures to evaluate the frequency of potential incidents, the probability of failure of the protection layers, and the likely consequences, resulting in an order-of-magnitude estimate of risk.
LOPA builds upon existing Process Hazards Analysis (PHA) techniques and can be used during any stage in a processes’ life cycle. It is particularly cost effective to implement LOPA during initial stages when process flow diagrams are complete and Project Initiation Documents (PID’s) are under development. For existing processes, LOPA should be used during or after the HAZOP review or revalidation, which provides the LOPA team with a listing of hazard scenarios with associated consequence description and potential safeguards for consideration.