Category
Instrumentation & Control
Subcategory
Safety System
Applicable standards
4
Issuing bodies
1
Description
Safety Instrumented System for SIL-rated functional safety per IEC 61511.
Applicable Standards (4)
IEC — 4 standards
IEC 61511
Functional safety — Safety instrumented systems for the process industry sector
SIS lifecycle, SIL, application of IEC 61508 in process industries.
Key requirements (9)
- Safety Instrumented Systems for the process industry.
- Safety lifecycle: H&RA → SIL allocation → design → operate → modify → decommission.
- SIL levels (by PFDavg): SIL 1 (10⁻²–10⁻¹), SIL 2 (10⁻³–10⁻²), SIL 3 (10⁻⁴–10⁻³), SIL 4 (10⁻⁵–10⁻⁴).
- Risk reduction factor RRF = 1/PFDavg.
- SIL determination: LOPA, risk graph, risk matrix.
- Architectures: 1oo1, 1oo2, 2oo3, 2oo4 — voting + redundancy for SIL.
- Proof test interval (PTI) drives PFDavg: PFDavg ≈ λDU·PTI/2 for 1oo1.
- MooN voting requires hardware fault tolerance (HFT) per Tables 3/4.
- Cybersecurity: refer to IEC 62443 for SIS.
IEC 61508
Functional safety of electrical/electronic/programmable electronic safety-related systems
Generic functional safety standard; basis of SIL determination.
Key requirements (6)
- Functional safety of electrical/electronic/programmable electronic safety-related systems (parent of 61511).
- Safe Failure Fraction (SFF) = (λS + λDD) / (λS + λDD + λDU).
- PFH (high demand) ranges: SIL 1 (10⁻⁶–10⁻⁵), SIL 2 (10⁻⁷–10⁻⁶), SIL 3 (10⁻⁸–10⁻⁷), SIL 4 (10⁻⁹–10⁻⁸).
- Type A vs Type B components — different SFF requirements.
- Systematic capability (SC1–SC4) certified by independent assessor.
- Common-cause beta factor typical 5–10 % unless explicit measures taken.
IEC 61882
Hazard and operability studies (HAZOP studies) — Application guide
HAZOP study application — guide words, methodology, recording.
IEC 62682
Management of alarm systems for the process industries
International counterpart of ISA 18.2.