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LOPA misapplied: Common errors can lead to incorrect conclusions


  • This paper was originally presented at the AIChE Global Congress on Process Safety, 10th Process Plant Safety Symposium, April 7-9, 2008 and is reprinted with permission of AIChE.

  • This information was developed solely for Rohm and Haas Company's internal use. We are making this information available without any guarantee that it is appropriate for your purposes as conditions and methods of use of the information are beyond our control. Rohm and Haas Company disclaims any liability for use of this information by persons outside of the Company.


Layer of Protection Analysis is a powerful tool for quantitative risk assessments. If applied correctly, it 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. A nonconservative calculation of risk could result in an under-protected system and unacceptable risk of an undesired consequence occurring.

This article describes several categories of common errors, some overly conservative and some nonconservative. Case studies of actual plant scenarios are used to illustrate. © 2009 American Institute of Chemical Engineers Process Saf Prog 2009