(190d) Use of Layer of Protection Analysis (Lopa) to Determine Protective System Requirements

Risks to safety, health, and the environment cannot be totally eliminated from process industries. However, tools such as Layers of Protection Analysis (LOPA) can be used to better understand and manage risks related to process safety.

Properly designed and maintained Safety Instrumented Systems (SIS) are important safeguards for reducing process risks to company-tolerable levels when other safeguards (i.e., other layers of protection) or inherently safer designs are not feasible. Before these protective systems can be designed, the proper number and types of Safety Instrumented Functions (SIF) must be determined. Determining the appropriate Safety Integrity Level (SIL) of each SIF is important to avoid under-protection (i.e., inadequate risk reduction) or over-protection (i.e., excessive cost). LOPA is an effective tool for making these determinations.

This paper provides an overview of LOPA methodology and how it may be used to (i) evaluate various safeguards that reduce the likelihood and severity of process safety incidents, (ii) determine if SIFs are required, and (iii) determine what SILs are necessary to reduce risks to company-tolerable levels. This paper also addresses the major factors a company should consider when developing a LOPA procedure specific to its needs.