Glossary · Functional safety
Safety Integrity Level (SIL)
Also known as: SIL
German: Sicherheits-Integritätslevel (SIL)
In functional safety, a Safety Integrity Level (SIL) is a discrete level for specifying the safety integrity requirements of a safety function. IEC 61508 defines SIL 1 to SIL 4, and IEC 62061 uses SIL 1 to SIL 3 for machinery.
- Functional safety
- Verification
In one sentence
A Safety Integrity Level (SIL) specifies how much integrity a safety function needs: SIL 1 to 4 in IEC 61508, up to SIL 3 in IEC 62061.
Example
A safety-rated speed monitoring function on a CNC machine is specified as SIL 2 under IEC 62061, and the chosen drive and safety PLC carry certificates up to SIL 3.
How it applies
- Functional safety: A SIL covers random hardware failures (quantified, for example as PFH) and systematic capability (development process, architecture constraints). Both must meet the level claimed.
- Standards: IEC 61508 is generic and goes up to SIL 4. IEC 62061 applies it to machinery control systems up to SIL 3.
- Technical documentation: State the SIL per safety function and name the standard. A component certificate "SIL 3 capable" only states what the component can support; the function needs its own verification.
- Evidence: Keep the safety manual conditions of each component, such as proof test intervals, because the SIL claim depends on them.
SIL vs. Performance Level
SIL and PL are different scales from different standards. Their probability ranges overlap, which allows an approximate comparison, but the methods for determining them differ.