Industrial Engineer · phase 6 of 16

SIL

Safety Integrity Level, a discrete integrity target for safety functions under IEC 61508 and related sector standards.

The Explain card

Plain English
Safety Integrity Level is a number from 1 to 4 that says how much a safety function can be relied on to work when it is needed. Higher means a lower allowed probability of failure on demand.
Example
A process shutdown valve on a reactor is rated SIL 2. The sensors, the logic solver and the valve together have to meet that number, with the math to prove it.
Why it matters
SIL comes from IEC 61508 and its process industry child IEC 61511, and it is about the whole loop rather than any single part. Buying a SIL 3 controller does nothing for a loop with a single unproven sensor.
Hook
How much you are allowed to trust the safety function.

Word knowledge

How the word is built, where it came from, and what it sits beside in memory.

In a sentence

During commissioning, the engineer confirms that the safety PLC, dual-channel emergency-stop inputs, and contactor feedback meet the specified SIL for the conveyor shutdown function.

Letter by letter
  • S Safety marks the functional-safety domain
  • I Integrity refers to dependable performance under specified conditions
  • L Level signals a numbered classification
Where it came from
Origin
English standards terminology, formed from the initials of a three-word technical phrase
Entered the language
1980s
What changed
moved from specialist standards language into routine engineering shorthand used in specifications, assessments, and commissioning records
How it is spelled
Capitalisation
written SIL in uppercase, including mid-sentence; numbered forms use a space, as in SIL 2
Plural and possessive
plural SILs; singular possessive SIL's; plural possessive SILs'
Out loud
Spelled out letter by letter.

Same family

  • SIF
  • SIS
  • HFT
  • SFF
Broken into chunks
  • SIL
    • SIF
    • SIS
    • ASIL
What it sits beside

Same subject

  • safety PLC
  • proof-test interval
  • PFDavg
  • dangerous failure
  • risk reduction factor

Same shape

functional safety initialisms

  • SIL
  • SIF
  • SIS
  • HFT
  • SFF

safety classification labels

Where it sits in the deck

Phase 6: PLC Operating Modes, Safety, and Diagnostics

Run, program and fault: what a controller does when something goes wrong, and the safety functions that decide how much that costs.

Neighbours in this phase