(190c) Using Layer of Protection Analysis to Define Safety Integrity Level Requirements

The publication of ISA standard S84.01 ? 2004 defines the life safety cycle for the design and installation of safety instrumented functions (SIFs) using safety instrumented systems (SISs). However, the determination of the required safety integrity level (SIL) is an activity that the process designers need to complete prior to detailed design. This paper outlines an approach for the determination of the required SIL using the layer of protection analysis (LOPA) method. An example is presented along with a suggested format for documenting the LOPA, SIL, and SIF requirements in a manner that can be transferred to the detailed design team for implementation.