(54o) LOPA Exemptions: When and Where

Layer of Protection Analysis (LOPA) has become a staple hazard analysis tool in the Process Industry. LOPA allows for a quick determination of the adequacy of protection systems, while providing significantly more rigor than qualitative methods such as HAZOP. LOPA has seen widespread use as both a risk analysis tool, and to establish Safety Integrity Levels (SIL) for Safety Instrumented Functions (SIFs). While there are many advantages to the LOPA methodology, there are also some scenarios for which LOPA may not be the proper analysis tool. Scenarios which develop over a long period of time, or those which affect an entire facility simultaneously, are just a few examples of scenarios which stretch the ability of LOPA to provide meaningful results.

To combat these weaknesses, many facilities have developed internal policies on the types of scenarios to which LOPA “exemptions” can be applied. This paper aims to explore these potential weak points in the LOPA methodology, and provide detailed reasoning as to why LOPA is not the best tool for analyzing specific types of scenarios. Representative examples will be presented and discussed in depth to demonstrate some of the potential difficulties in performing LOPA on various scenarios.