Risk Assessment
What is LOPA? Layer of Protection Analysis Explained
Vinit Pandey · Published 14 November 2025 · Updated 28 June 2026
In short: LOPA (Layer of Protection Analysis) is a semi-quantitative risk assessment technique that evaluates whether the independent protection layers safeguarding a hazard scenario provide sufficient risk reduction.
- HAZOP Scenario
- Initiating Frequency
- Identify IPLs
- Credit PFDs
- Mitigated Frequency
- Compare to Tolerance
Key takeaways
- Sits between qualitative HAZOP ranking and fully quantitative QRA
- Only safeguards that qualify as Independent Protection Layers (IPLs) get risk credit
- Each IPL's Probability of Failure on Demand (PFD) reduces the scenario frequency
- Any remaining gap to the tolerance criterion is often closed by a new target SIL
LOPA was developed by the Center for Chemical Process Safety (CCPS) as a middle ground between fully qualitative HAZOP risk ranking and fully quantitative QRA.
The technique starts from a HAZOP-identified scenario, assigns an initiating event frequency from recognised data sources, then identifies which safeguards qualify as truly Independent Protection Layers (IPLs).
Each qualifying IPL reduces the scenario frequency by its credited Probability of Failure on Demand (PFD), and the resulting mitigated event frequency is compared against a risk tolerance criterion.
Where the mitigated frequency still exceeds tolerance, LOPA identifies the additional risk reduction needed — often expressed as a target SIL for a new or upgraded safety instrumented function.