Safety Integrity Level (SIL)
Industrial/ICS 🏭
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Difficulty: premium
Definition
Safety Integrity Level (SIL) is a discrete measure of the risk-reduction performance required of a Safety Instrumented Function (SIF), derived from hazard/risk analysis and verified by design, calculation, and testing across the functional safety lifecycle.
Examples
- A high-pressure SIF in a refinery is specified to SIL 2 based on LOPA; designers select 1oo2 pressure transmitters, a safety PLC, and an ESD valve with partial-stroke testing to meet the target PFDavg.
- A burner management SIF in a power boiler requires SIL 3 for flame failure; a 2oo3 voting scheme with diverse sensors and stringent proof testing achieves the necessary risk reduction.
Discover 🔎
SIL expresses how much risk reduction a specific SIF must deliver to prevent hazardous events when the process demands it. It is assigned from formal risk analysis (e.g., LOPA) and then engineered and proven via architecture, component selection, diagnostics, and proof testing. SIL applies to a function, not to a standalone device.
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