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Safety and SIS · Glossary

What is Risk Reduction Factor?

Symbol: RRF1 ÷ PFDavgSafety and SIS

Risk reduction factor is how many times a safety function reduces the frequency of a hazardous event; it is the inverse of PFDavg.

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Risk Reduction Factor Explained

If the unmitigated event frequency is too high, the SIF must reduce it by the RRF needed to reach the tolerable frequency.

RRF and PFDavg describe the same thing; RRF is easier to relate to risk targets.

Risk Reduction Factor Formula

RRF = 1 ÷ PFDavg
PFDavgaverage probability of failure on demand
Example: PFDavg = 5 × 10⁻³ gives RRF = 200, which is SIL 2.
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Calculators for Risk Reduction Factor

CalculatorRisk Reduction Factor CalculatorFree online calculator with formula and worked example.CalculatorLOPA SIL CalculatorFree online calculator with formula and worked example.

Free Downloads

Free downloadSIL PFDavg Calculation Excel SheetFree download in Excel and PDF.

Frequently Asked Questions

What is Risk Reduction Factor?

Risk reduction factor is how many times a safety function reduces the frequency of a hazardous event; it is the inverse of PFDavg.

How is the required RRF found?

Divide the mitigated event frequency without the SIF by the tolerable frequency.

Can RRF be very high?

Above 10,000 you are in SIL 4 territory; redesigning the process is usually better.

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What is SIL (safety integrity level)

A practical guide on instrumentationblog.in with more detail on risk reduction factor and how it is applied on real plants.

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