Work out safety integrity level instantly with clear inputs, formula shown and shareable results.
The required safety integrity level follows from the gap between the unmitigated hazard frequency and the tolerable frequency, divided by the risk reduction the existing layers already provide. The required probability of failure on demand is the reciprocal of that factor, and the SIL bands are defined in decades: SIL 1 covers PFD from 0.1 to 0.01, SIL 2 to 0.001, SIL 3 to 0.0001.
Risk reduction required
RRF = unmitigated frequency / tolerable frequency / existing risk reduction
SIL bands
PFD 0.1 to 0.01 is SIL 1, 0.01 to 0.001 SIL 2, 0.001 to 0.0001 SIL 3
Preliminary estimate only. SIL determination and verification must be carried out to the applicable functional safety standard by competent practitioners.
RRF = unmitigated frequency / tolerable frequency / existing risk reduction. The required safety integrity level follows from the gap between the unmitigated hazard frequency and the tolerable frequency, divided by the risk reduction the existing layers already provide.
No. Each SIL step demands an order of magnitude more testing, redundancy and management effort, and SIL 4 is generally regarded as a sign the process design itself should be changed instead.
This calculator takes 3 inputs: Unmitigated hazard frequency, Tolerable hazard frequency, Risk reduction from existing layers. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.