Work out layer of protection analysis instantly with clear inputs, formula shown and shareable results.
Layer of protection analysis multiplies the initiating event frequency by the probability of failure on demand of each independent protection layer. Comparing the mitigated frequency with the tolerable frequency shows the additional risk reduction needed, and that factor maps directly to the safety integrity level a new instrumented function would require.
Mitigated frequency
f mitigated = initiating frequency x PFD of each independent layer
SIL from risk reduction
RRF up to 10 is SIL 1, to 100 SIL 2, to 1000 SIL 3, beyond that SIL 4
Preliminary estimate only. Layer of protection analysis and SIL determination must be carried out by a competent process safety team to the applicable functional safety standard.
f mitigated = initiating frequency x PFD of each independent layer. Layer of protection analysis multiplies the initiating event frequency by the probability of failure on demand of each independent protection layer.
It must be separate in sensor, logic and final element from the initiating cause and from other layers, and be auditable and specifically designed to prevent the consequence. Shared instruments break independence.
This calculator takes 4 inputs: Initiating event frequency, Probability of failure of the first protection layer, Probability of failure of the second protection layer, Tolerable event frequency. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.