Which characteristics must a protection layer generally have to receive full independent protection layer credit in LOPA? (Select all that apply)

For a protection layer to be credited as an Independent Protection Layer (IPL) in a Layer of Protection Analysis (LOPA), it must meet several key criteria. It must be independent of the initiating event and other layers. It must be specific, meaning it is designed to prevent a particular consequence from a single event. It must be dependable, with a sufficiently low and quantifiable probability of failure on demand (PFD). Finally, it must be auditable, allowing its functionality and integrity to be verified through testing and maintenance throughout its lifecycle.

E. Reliance on the same failure that initiates the event: This directly violates the core principle of independence, which is fundamental to the definition of an IPL.

1. Center for Chemical Process Safety (CCPS). (2001). Layer of Protection Analysis: Simplified Process Risk Assessment. AIChE.

Section 4.2, "Definition of an IPL," pp. 47-49, details the four key attributes: specificity, independence, dependability, and auditability.

2. Gowland, R. (2006). A practitioner's view on LOPA. IChemE Symposium Series, 151, 290-301.

Page 293 states, "To qualify as an IPL a device, system or action must be effective, independent of the initiating event and auditable." This summarizes the core requirements.

3. Marszal, E. M., & Scharpf, E. W. (2002). Safety Integrity Level Selection: Systematic Methods Including Layer of Protection Analysis. ISA.

Chapter 6, "Layer of Protection Analysis," discusses the required characteristics of an IPL, consistently listing independence, effectiveness (dependability/specificity), and auditability as essential.