LAUSR

Layer of Protection Analysis (LOPA) has gained popularity as a semi‐quantitative risk assessment tool, but often unexpected difficulties are encountered when rolling out LOPA. This article discusses the practical aspects of LOPA implementation in Marathon Petroleum Company LP's Refining Organization (MPC Refining). Specifically, it shows how scenarios are selected from a Hazard and Operability Study (HAZOP) and how they are organized for conducting LOPA efficiently, and it discusses whether to conduct LOPA concurrently or after the HAZOP. The article also compares the [cause → consequence] or [consequence → cause] methodology and addresses the implications of combining multiple causes in a single scenario.