Definition:
An Independent Protection Layer (IPL) is a device, system, or action that can lower the risk (probability or severity) of a hazardous event independently from the initiating event. Technically, a SIF is an IPL, but not every IPL is a SIF.
An IPL must have all four of the following characteristics: independent, specific, dependable, and auditable.
Key Points:
- Must be independent, auditable, and dependable.
- Key building block in the Layer of Protection Analysis (LOPA).
Example:
A PSV (pressure relief valve) relieving excess pressure is an IPL independent of the BPCS. It is an IPL as it is fully mechanical and does not rely on anything else.
Cited Source:
- IEC 61511-1:2016, Clause 3.2.57
- CCPS Guidelines for Initiating Events and IPLs
- University of Michigan Chemical Engineering – Layer of Protection Analysis