Concept · Safety & Security
Safety integrity level
One of four levels of risk reduction that a safety function must provide under IEC 61508 and the standards derived from it. Higher levels need lower rates of dangerous failure, more fault tolerance and diagnostics, and more rigorous development.
- Type
- Concept
- Domain
- Safety & Security, Safety lifecycle
Overview
The safety integrity level is how industrial functional safety states how much a safety function must reduce risk. It is set by the hazard and risk analysis of the equipment under control and then belongs to the safety function and every element that carries it.
How it works
The hazard and risk analysis compares the risk without the safety function with the tolerable risk, and the gap sets the target level. Each level has a target for the probability of dangerous failure, depending on whether the function is demanded rarely or runs continuously.
Hardware meets the level through its architecture and its failure data: hardware fault tolerance, the share of failures that are safe or detected by diagnostics, and the failure rates. Software and systematic capability meet it through the techniques and measures the standard asks for at that level.
A chip or module has no level on its own, but it can be developed and assessed as able to support functions up to a stated level, with a safety manual setting the conditions.
Examples
- An emergency shutdown function in a process plant with a target level.
- A safety relay assessed as able to support a stated level.
- A controller chip with diagnostics designed for a higher level.
- Process industry and machinery standards that apply the levels to their sectors.
Why it matters
Functional safety managers and architects work to it from the hazard analysis onwards, safety analysts show the hardware meets it, and assessors judge whether the product supports the claimed level. It decides much of the cost of an industrial safety product.
It matters most to: Functional Safety Architect (Silicon), Functional Safety Assessor, Functional Safety Manager, Safety Analysis Engineer
Common confusions
- Not the same as ASIL
- The automotive safety integrity level comes from ISO 26262 and is set from severity, exposure and controllability; the safety integrity level comes from IEC 61508 and is set from the risk reduction needed.
- Not the same as Performance level
- ISO 13849 rates machinery safety functions as performance levels; the two scales are related but not the same.
- Not the same as Software in the loop
- The same three-letter abbreviation is used for testing software against a simulated plant, which has nothing to do with safety integrity.
Related standards
- IEC 61508 (functional safety of electrical, electronic and programmable electronic safety-related systems)
- IEC 61511 (safety instrumented systems for the process industry sector)
- IEC 62061 (functional safety of safety-related control systems for machinery)
Sources
- IEC 61508-1:2010 Functional safety of electrical/electronic/programmable electronic safety-related systems, Part 1: General requirements (opens in a new tab), International Electrotechnical Commission, 2026-11-10
- IEC 61508-5:2010 Functional safety of electrical/electronic/programmable electronic safety-related systems, Part 5: Examples of methods for the determination of safety integrity levels (opens in a new tab), International Electrotechnical Commission, 2026-11-10
- Safety integrity levels: an overview of system-design risk analysis (opens in a new tab), Engineers Ireland, Engineers Journal, 2026-11-10
Related terms
Part of the Safety & Security glossary, with every term in the topic and the lifecycles, tools and standards that use them.
Where it appears on the Hub
Used on 2 pages of the Hub. In each group, the pages that mention it most come first.
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Last reviewed . Written by The Semiconductor Hub editorial team. The full glossary