IEC 61511

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.