When MOC Meets LOPA: A Quantitative Assessment of the Impact of Errors in MOCs

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Layers of Protection Analysis, "LOPA", has become a popular tool for conducting semi-quantitative risk assessments, in the chemical process industries. A key concept is that of "Independent Protection Layers", whereby subsequent layers are intended to mitigate adverse events that were not mitigated by prior layers.

Interestingly, as a Management of Change instance goes through its lifecycle--Initiation > Scoping > Change Design > Impact Analysis > Approvals > Implementation > PSSR > Close-out--each subsequent state is somewhat analogous to an independent protection layer. For example the Impact Analysis activities are intended to catch deficiencies made during Change Design; the PSSR is intended to catch deficiencies made during Implementation, and so on.

While the LOPA to MOC analogy is not perfect, it is useful as a guide to permit the calculation of overall error rates caused by and occurring during MOCs. This paper assesses the overall MOC error rates, and discusses their impacts on MOC costs, duration and risk, and recommends where effort should be directed to minimize negative impacts.


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