| SIL | PFDavg (low demand) | RRF | PFH per hour (high demand) |
|---|---|---|---|
| 4 | 10⁻⁵ to below 10⁻⁴ | 10,000 to 100,000 | 10⁻⁹ to below 10⁻⁸ |
| 3 | 10⁻⁴ to below 10⁻³ | 1,000 to 10,000 | 10⁻⁸ to below 10⁻⁷ |
| 2 | 10⁻³ to below 10⁻² | 100 to 1,000 | 10⁻⁷ to below 10⁻⁶ |
| 1 | 10⁻² to below 10⁻¹ | 10 to 100 | 10⁻⁶ to below 10⁻⁵ |
Hand formulas (perfect proof test, small terms omitted)
| Case | Approximation |
|---|---|
| 1oo1 | λDU · T1 / 2 |
| 1oo2 | ((1−β)λDU·T1)² / 3 + β·λDU·T1 / 2 |
| 2oo3 | ((1−β)λDU·T1)² + β·λDU·T1 / 2 |
| Imperfect test, 1oo1 | PTC·λDU·T1/2 + (1−PTC)·λDU·MT/2 |
| Maximum test interval, 1oo1 | T1 ≈ 2 · PFD_required / λDU |
| LOPA | MEF = IEF × Π(factors); RRF = MEF / TMEL |
| SFF | (λSD + λSU + λDD) / λtotal |
Unit reminders: 8,760 hours per year; 1 FIT = 10⁻⁹ per hour.
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.