(153a) Lopa Misapplied: Common Errors Can Lead to Incorrect Conclusions"

Layer Of Protection Analysis (LOPA) is a powerful tool for quantitative risk assessments. If applied correctly, it can provide quick and efficient guidance on what additional safeguards may be needed to protect against a given scenario. If misapplied, an overly conservative calculation of risk may cause over-instrumentation, resulting in 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 event occurring.

This paper describes several categories of common errors, some overly conservative and some non-conservative. Case studies of actual plant scenarios are used to illustrate.