Guidelines for Initiating Events and Independent Protection Layers in Layer of Protection Analysis

Book excerpt: The book is a guide for Layers of Protection Analysis (LOPA)practitioners. It explains the onion skin modeland in particular, how it relates to the use of LOPA and the needfor non-safety instrumented independent protection layers. Itprovides specific guidance on Independent Protection Layers (IPLs)that are not Safety Instrumented Systems (SIS). Using theLOPA methodology, companies typically take credit for riskreductions accomplished through non-SIS alternatives; i.e.administrative procedures, equipment design, etc. Itaddresses issues such as how to ensure the effectiveness andmaintain reliability for administrative controls or“inherently safer, passive” concepts. This book will address how the fields of Human ReliabilityAnalysis, Fault Tree Analysis, Inherent Safety, Audits andAssessments, Maintenance, and Emergency Response relate to LOPA andSIS. The book will separate IPL’s into categories such as thefollowing: Inherent Safety eliminates a scenario or fundamentally reduces a hazard Preventive/Proactive prevents initiating event from occurring such as enhancedmaintenance Preventive/Active stops chain of events after initiating event occurs but beforean incident has occurred such as high level in a tank shutting offthe pump. Mitigation (active or passive) minimizes impact once an incident has occurred such as closingblock valves once LEL is detected in the dike (active) or the dikepreventing contamination of groundwater (passive).