More LOPA Misapplied: Common Errors and How to Avoid Them

Layer of Protection Analysis (LOPA) continues to be more and more widely utilized in the Petrochemical and other industries. LOPA is a “simplified” tool, which is true relative to tools such as Quantitative Risk Assessment and Fault Tree Analysis. However, simplified does not mean simple on an absolute basis. There are many complicating factors and nuances involved in the proper application of LOPA, which can lead to misapplication of the technique.

This paper is a follow-up to the 2008 published paper by the same authors, entitled “LOPA Misapplied: Common Errors Can Lead To Incorrect Conclusions”. In that paper, the authors stated that LOPA “can provide quick and efficient guidance on what additional safeguards are needed, if any, to protect against a given scenario. If misapplied, an overly conservative calculation of risk may result in over-instrumentation, additional life-cycle costs and spurious trips. Even worse, a non-conservative calculation of risk could result in an under-protected system and unacceptable risk of an undesired consequence occurring.” A number of practical examples of misapplication of LOPA were presented in that paper.

In this paper, the authors will cover more real-life examples of misapplication and how to avoid those pitfalls. Subjects covered include misuse of the concept of double jeopardy, assuming something will never fail against the “fail-safe” condition, using protective systems to justify scenarios as non-credible, and what types of situations warrant moving beyond LOPA to more sophisticated tools