Route 1H is the IEC 61508 hardware route that uses published SFF × HFT tables. Type A (well-defined failure modes, good field experience) is less strict than Type B (complex / incomplete failure-mode knowledge).
What you enter
- Type A or B — from the device safety manual, not from preference.
- SFF — (λS + λDD) / (λS + λDD + λDU), as a percentage from the same failure-rate set used in the PFD.
- HFT — for m-out-of-n voting, HFT = n − m (1oo1 → 0, 1oo2 → 1, 2oo3 → 1).
Type A (SILProof table)
| SFF | HFT 0 | HFT 1 | HFT 2 |
|---|---|---|---|
| < 60% | SIL 1 | SIL 2 | SIL 3 |
| 60% to < 90% | SIL 2 | SIL 3 | SIL 4 |
| 90% to < 99% | SIL 3 | SIL 4 | SIL 4 |
| ≥ 99% | SIL 3 | SIL 4 | SIL 4 |
Type B (SILProof table)
| SFF | HFT 0 | HFT 1 | HFT 2 |
|---|---|---|---|
| < 60% | Not allowed | SIL 1 | SIL 2 |
| 60% to < 90% | SIL 1 | SIL 2 | SIL 3 |
| 90% to < 99% | SIL 2 | SIL 3 | SIL 4 |
| ≥ 99% | SIL 3 | SIL 4 | SIL 4 |
These cells match the SFF HFT calculator and SIL verification. Confirm the applicable edition of IEC 61508-2 on the project. SILProof is engineering support, not a certified table reprint.
How this meets a target
If the cell is below the target SIL, Route 1H does not support that target — even if PFDavg looks fine. Claimed SIL is the lowest of quantitative SIL, this architectural SIL, and systematic capability.
Route 1H does not use the Route 2H field-data / 90% confidence rules, and it is not IEC 61511 Table 6. Pick the route that matches the evidence you actually have.
Open the interactive tables: SFF HFT SIL calculator. Apply them on a SIF: SIL verification.