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How to read a SIL verification report

For reviewers and managers: what to look at first in a verification report and which questions to ask.

2 min read · First Out AI knowledge library

A verification report answers one question: does this function, as designed and maintained, achieve the risk reduction it was given? Read it in this order.

  1. The target. Which hazard analysis set it, and what is the required PFDavg (not just the SIL)?
  2. The verdict on all three checks. Probability (PFDavg or PFH), fault tolerance (HFT against IEC 61511) and systematic capability. A pass on one says nothing about the others.
  3. Where the PFDavg comes from. The share per subsystem shows what drives the result; usually the final element.
  4. The assumptions. Proof test interval and coverage, β, repair times, mission time. Are they what the plant actually does?
  5. The sources. Every failure rate should have a source that applies to the installed device.
  6. Margin. A result at the edge of the band with optimistic assumptions is weaker than it looks.
  7. Spurious trips. Is the expected trip rate acceptable, so the function will not be bypassed?

Questions worth asking

  • What happens to the result if the valve test coverage is 10 % lower?
  • Is the proof test interval achievable with the turnaround plan?
  • Who maintains the failure data, and when was the verification last reviewed?

In First Out AI

The printed report shows the function, inputs with sources, the three checks, the share per group, the engineer's reading, the what-if table and the PFD chart, with the method and disclaimer.

Written for First Out AI as engineering guidance. It supports engineering work and does not replace it; check every value against your standards, certificates and company rules with a competent functional safety engineer.