Prove the SIL claim, not just the PFDavg

One SIF thread from risk to verification

Process safety, SIS, I&C and EPC engineers keep required SIL, architecture, verification evidence and specification on the same Safety Instrumented Function record. SILProof is built for IEC 61508 hardware and systematic capability thinking and for the design phase of an IEC 61511 process-sector SIF — without turning the browser into a certificate authority. What is in and out of scope is listed clause by clause on the scope page.

1. Risk — Set required SIL and risk-reduction basis with Risk Analysis (Risk Graph, LOPA or company matrix).
2. Register — Keep every project function in the SIF Register.
3. SIF — Open the hub for identity, status, architecture summary and next steps.
4. SRS — Capture safe state, response time, proof testing and interfaces in the SRS Builder.
5. Verify — Design the sensor, logic solver and final elements and prove the claim in SIL Verification.

Three gates to a defensible SIL claim

Claimed SIL is the lowest of quantitative integrity (PFDavg for low demand, or PFH for high demand / continuous), architectural constraints, and systematic capability. A calculated PFDavg that sits in a SIL 2 band does not by itself make the SIF SIL 2. Architecture (Route 1H, Route 2H or IEC 61511 Table 6) and systematic capability still have to support the claim. That is the three-gate rule explained in The Three Gates to SIL.

SIL Verification supports algebraic and Markov low-demand engines, voting including diagnostic 1oo2D, beta-factor common cause, proof-test coverage and explicit final-element train topology. Screening tools stay separate on purpose: the PFD / PFH calculator is a 1oo1 low- or high-demand estimate; the SFF / HFT calculator screens architectural SIL only.

PFD / PFH calculator versus full SIL verification

Use the calculator for a fast 1oo1 PFDavg or PFH screening number. Use SIL Verification when the whole SIF must be assessed — sensor, logic solver and final elements together — with architecture and systematic capability on the same record. Keeping those paths separate avoids presenting a screening result as a finished SIL claim. Background on the average probability of failure on demand is in the PFDavg knowledge note.

Open tools and engineering references

• Risk Analysis — required SIL from Risk Graph, LOPA or C×W matrix
• SIF Register — register of your SIFs in design
• SIL Verification — complete SIF Design & Verify
• SRS Builder — IEC 61511 Clause 10 structure
• PFD / PFH calculator — low- and high-demand 1oo1 screening
• SFF HFT calculator — Route 1H / 2H / Table 6 architectural screen
• FSMS — functional safety management starting packs

Start with language, then open a tool: What is SIL?, Knowledge Hub notes on PFDavg, Route 1H and Route 2H / Table 6.

Worked example and who it is for

The built-in Example SIF (high-high separator level shutdown) shows a complete sensor–logic–final-element loop with transparent failure-rate, proof-test and architecture assumptions so engineers can see how the three gates interact before they create a project record.

SILProof is aimed at oil & gas, chemicals, power, pharma, water and EPC teams who need the PFDavg basis, route and proof-test interval frozen with the SIF — not re-keyed across three spreadsheets. Tools stay open in the browser. Free membership unlocks issued reports, SRS issue and packs. The engine is checked against IEC 61508-6 Annex B on the validation page. Independent engineering review remains required.