LOPA Calculator
Screen process-safety scenarios with a CCPS-style Layers of Protection Analysis worksheet — initiating-event frequency, conditional modifiers and credited IPLs multiply into a mitigated event likelihood compared against a tolerable target. Screening aid, not SIL verification. Export CSV or PNG.
Open LOPA Calculator →What is a LOPA calculator?
A free Layers of Protection Analysis (LOPA) worksheet in the CCPS style, running entirely in your browser. For each process-safety scenario you set an initiating-event frequency, apply enabling conditions and conditional modifiers (such as probability of ignition or occupancy), and credit the Independent Protection Layers that stand between the cause and the consequence. The tool multiplies these into a mitigated event likelihood and compares it against a tolerable target frequency derived from the consequence severity, showing the remaining risk gap and, where a gap exists, the required additional risk-reduction factor with an indicative SIL band. Typical order-of-magnitude frequencies and PFDs are offered as editable suggestions. It is a screening and documentation aid — not SIL verification — and nothing is uploaded: every scenario stays on your device.
How to use LOPA Calculator
- Describe the scenario — Give the scenario a title, describe the consequence and pick its severity — the severity sets the tolerable target frequency (TMEL), or choose Custom to enter your own.
- Set the initiating event — Describe the cause and enter its frequency per year. The typical-value list fills in common CCPS-style figures, which you can then edit.
- Add enabling conditions and modifiers — Add probabilities between 0 and 1 — probability of ignition, occupancy, time at risk. Leaving the list empty keeps the factor at a conservative 1.
- Credit your IPLs — Add each protection layer, pick its type to suggest a PFD, and tick Credited only if it is independent, specific, dependable and auditable.
- Read the result — The waterfall shows the mitigated event likelihood against the target. A gap reports the required additional risk-reduction factor and an indicative SIL band; export the worksheet as CSV or PNG.
Frequently asked questions
How is the mitigated event likelihood calculated?
It is the initiating-event frequency multiplied by every enabling-condition and conditional-modifier probability and by the probability of failure on demand (PFD) of every credited IPL — the standard order-of-magnitude LOPA arithmetic.
What counts as an Independent Protection Layer?
A layer you can credit must be independent of the initiating event and of the other IPLs, specific to the scenario, dependable and auditable. Do not double-count the basic process control system as both the initiating event and an IPL.
Does this tool perform SIL verification?
No. It is a screening and documentation aid. The SIL band shown for a remaining gap is indicative only — SIL assignment and verification require a full study to IEC 61511 using your organisation's approved failure data and risk criteria.
Is my analysis uploaded anywhere?
No. The whole worksheet runs client-side and scenarios are saved only in your browser's local storage. It also works offline.
Tips
- Use your organisation's approved failure-rate data and risk criteria — the built-in typical values are generic industry figures for screening only.
- Credit roughly one order of magnitude per protection layer; if you find yourself needing fractional credits, the scenario probably needs a more detailed study.
- Keep one scenario per initiating-event / consequence pair — use the scenario tabs rather than mixing causes in a single worksheet.