LOPA - More Observations from the Originators

Layer of protection analysis (LOPA) has been around for 20 years, and in general use for 15 years, with the LOPA textbook from CCPS/AIChE being officially published in 2001.  Most recently, two companion books have been published on the topics of Enabling Events & Conditional Modifiers and on Initiating Events and Independent Protection Layers (IPLs).   Many papers have been published in the past 20 years on LOPA, including some papers by the authors on deficiencies noted in the broad use of LOPA.  This paper shares observations and lessons learned from the two originators of LOPA and provides further guidance on how to and how Not to use LOPA.  The paper provides specific examples of best practices, some of which are not covered well enough in the textbooks on the topic.