Risk assessment of chemical processes using Layer of Protection Analysis (LOPA) method: case study in a petrochemical unit's drum

The Layer of Protection Analysis (LOPA) is a semi-quantitative risk assessment method which builds upon process hazard analysis techniques like HAZOP. It applies Safety Integrity Level (SIL) approach towards process hazards which determine the total amount of risk reduction level required according to corporate risk acceptable level. LOPA also estimates the required Safety Integrity Level (SIL) for the Safety Instrumented Function (SIF) without more time-consuming techniques such as Fault Tree Analysis (FTA). Besides its ability to be self-documented, it is a powerful analytical tool for assessing the adequacy of process protection layers. Therefore, risk reduction efforts focus towards impact events with the highest risks and provide a rational basis to allocate risk reduction resources efficiently. This paper briefly describes the LOPA methodology, and applies it into a drum in a Methanol production process as a case study. At the end the required Independent Protection Layers (IPL) of the drum is suggested.