For your immediate review, please download the latest free resource paper from PII, titled LOPA: Performed When and by Whom, co-written by Arthur M. Dowell, III, P.E. – PII Principal Engineer & Instructor, and William G. Bridges, PII President, and being presented at the 14th Global Congress on Process Safety in Orlando, Florida.

From the Abstract:

Layer of protection analysis (LOPA) was introduced in the mid-1990s by Art Dowell at Rohm and Haas Chemical Company (became Dow Chemical, now DowDuPont, Inc.) and by William Bridges at ARCO Chemical (now Lyondell-Basel) and JBF Associates. The first book was published in 2001 by CCPS. Since then, the method has swiftly grown in popularity for use in making risk judgments and in deciding on the SIL rating for an SIF. But, many users of LOPA do not know when to use LOPA and so they overuse this tool; and they do not know who should be doing LOPA, so they many times use a team, similar to or the same as a PHA/HAZOP team. This paper explains what the originators of LOPA intended and why, and also brings the industry up-to-date on the lessons learned from different approaches to using LOPA, related to when to do LOPA and who should do LOPA.

For other valuable free resource papers available from Process Improvement Institute, please visit the Free Resources section of the PII website at