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Safety and SIS · Glossary

What is Safety Integrity Level?

Symbol: SILSIL 1 to SIL 4Safety and SIS

Safety integrity level is a target level of risk reduction for a safety instrumented function, from SIL 1 (lowest) to SIL 4.

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Safety Integrity Level Explained

SIL is set during hazard and risk analysis, for example with LOPA. The SIF must then meet the PFDavg range, the architectural constraints and the systematic requirements for that SIL.

Most process SIFs are SIL 1 or SIL 2; SIL 3 is less common and SIL 4 is rare in process plants.

Safety Integrity Level: Typical Values

SIL 1PFDavg 10⁻² to 10⁻¹, RRF 10 to 100
SIL 2PFDavg 10⁻³ to 10⁻², RRF 100 to 1000
SIL 3PFDavg 10⁻⁴ to 10⁻³, RRF 1000 to 10,000
SIL 4PFDavg 10⁻⁵ to 10⁻⁴
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Calculators for Safety Integrity Level

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

Free Downloads

Free downloadSIL PFDavg Calculation Excel SheetFree download in Excel and PDF.Free downloadSIL Proof Test Record Template in ExcelFree download in Excel and PDF.

Frequently Asked Questions

What is Safety Integrity Level?

Safety integrity level is a target level of risk reduction for a safety instrumented function, from SIL 1 (lowest) to SIL 4.

Is a SIL 2 transmitter enough for SIL 2?

No. The whole SIF, including logic and valve, must meet SIL 2; a certified device only helps.

What does SIL capable mean?

The device has been assessed as suitable for use up to that SIL within the stated limits.

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What is SIL (safety integrity level)

A practical guide on instrumentationblog.in with more detail on safety integrity level and how it is applied on real plants.

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Related Terms

Safety termPFDavgPFDavg is the average probability that a safety function fails to act when a demand occurs, over the…Safety termRisk Reduction FactorRisk reduction factor is how many times a safety function reduces the frequency of a hazardous event; it…Safety termHardware Fault ToleranceHardware fault tolerance is the number of hardware faults a subsystem can have while still performing its…

More Safety and SIS Terms

Safety termPFHPFH is the average frequency of dangerous failures per hour, used for safety functions in high demand or…Safety termFailure RateFailure rate is the number of failures per unit time of a device; in safety it is split into safe and…Safety termSafe Failure FractionSafe failure fraction is the share of all failures that are either safe or dangerous but detected.Safety termDiagnostic CoverageDiagnostic coverage is the fraction of dangerous failures that automatic diagnostics detect.Safety termVoting ArchitectureVoting architecture describes how many of N redundant channels must act to trip, such as 1oo2 or 2oo3.Safety termCommon Cause FailureCommon cause failure is a single cause that makes redundant channels fail together, such as a shared…

All safety and sis terms · Full glossary A to Z

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