The Probability of Failure on Demand (average) — PFDavg is the standard measure of dependability for safety-related systems operating in Low Demand Mode (less than once per year demand rate), as defined in IEC 61508-1.

This calculator returns the achieved SIL band and the equivalent Risk Reduction Factor (RRF = 1/PFD), which is often easier to interpret for non-FS specialists (e.g., RRF = 100 means the safety function reduces the risk by a factor of 100).

For a full IEC 61511 lifecycle implementation including architectural constraints, common cause failures, proof test coverage and lifecycle reports, see fs.industryhub.cloud.