For Layers of Protection Analysis (LOPA) scenarios involving overpressure of equipment, pressure relief systems are often given significant Independent Protection Layer (IPL) credit, and in most cases this is appropriate. However, LOPA teams need to be aware of the many factors of design, installation, and maintenance of these systems that must be properly addressed in order for this IPL credit to be valid. These factors are represented in the context of generic IPL criteria of Independence, Functionality, Integrity, Reliability, Auditability, and Management of Change. Additionally, appropriate IPL credit for multiple relief devices and the use of rupture disks in combination with pressure relief valves is defined, and best practices are presented for developing recommendations that most effectively address identified LOPA gaps.
Keywords: Hazard Identification and Risk Analysis, Understand Hazard & Risk, Venting & Emergency Relief
