Comparison
LOPA vs QRA: What Is the Difference?
Vinit Pandey · Published 28 June 2026
In short: LOPA (Layer of Protection Analysis) is a scenario-based, order-of-magnitude technique typically applied per HAZOP finding to judge whether existing safeguards are adequate. QRA (Quantitative Risk Assessment) is fully quantitative, models consequences with specialist software across an entire facility, and produces individual risk contours and societal risk F-N curves used for land-use planning and ALARP demonstration.
| Aspect | LOPA | QRA |
|---|---|---|
| Scope | Single hazard scenario at a time | Aggregated across all major scenarios at a facility |
| Rigor | Semi-quantitative, order-of-magnitude | Fully quantitative, software-modelled consequences |
| Typical trigger | Per HAZOP finding requiring safeguard adequacy check | Land-use planning, MAH siting, insurer/regulatory requirement |
| Key output | SIL target / safeguard gap per scenario | Individual risk contours, societal risk F-N curves |
| Consequence modelling | Not performed (consequence severity is categorical) | Full dispersion/fire/explosion modelling per scenario |
| Typical effort | Hours per scenario | Weeks to months for a full facility |
LOPA and QRA both sit in the quantitative-to-semi-quantitative end of process risk assessment, but they are designed to answer different questions at different scales.
LOPA is scenario-by-scenario: it takes a single HAZOP-identified deviation, assigns an initiating event frequency, credits the Independent Protection Layers (IPLs) safeguarding it, and checks whether the resulting mitigated frequency meets a risk tolerance criterion. It is fast — typically minutes to a few hours per scenario — and is the standard bridge between HAZOP and SIL determination.
QRA is facility-wide: it selects representative loss-of-containment scenarios across an entire hazardous inventory, models the physical consequences of each (dispersion, jet fire, pool fire, flash fire, vapour cloud explosion) using validated software, and integrates frequency and consequence results into individual risk contours and societal risk F-N curves for the whole site.
A practical way to see the difference: LOPA asks 'are the safeguards on this specific deviation good enough?' QRA asks 'what is the total risk profile of this facility, and does it meet tolerability criteria like ALARP for land-use planning or insurance purposes?' Many facilities use both — LOPA to close individual HAZOP gaps, QRA to demonstrate facility-wide risk tolerability.
Frequently Asked Questions
Does QRA replace the need for LOPA?
No. QRA assesses facility-wide risk tolerability and is not a substitute for the scenario-by-scenario safeguard adequacy check that LOPA provides, which directly feeds SIL target-setting for individual safety instrumented functions.
Is LOPA less accurate than QRA?
LOPA is intentionally order-of-magnitude rather than precisely quantitative — it is designed for speed and consistency across many HAZOP scenarios, not for the detailed consequence modelling precision that QRA provides for a smaller set of representative facility-wide scenarios.
Can LOPA results be used as an input to QRA?
LOPA frequency and IPL credit logic can inform QRA's frequency analysis, but QRA additionally requires full consequence modelling (dispersion, fire, explosion) that LOPA does not perform.