SIL calculation Excel template.
The IEC 61511 register that sets each safety function's target SIL against the SIL its design achieves, with the PFDavg, voting and proof-test interval behind it.
- ASIF Tag
- BHazardous Event
- CDemand ModeLow demandHigh demandContinuous
- DTarget SILSIL 1SIL 2SIL 3SIL 4
- EAchieved SILSIL 1SIL 2SIL 3SIL 4
- FPFDavg
- GRRF
- HVoting Architecture1oo11oo22oo22oo32oo4
- ISensor Elements
- JLogic Solver
- KFinal Elements
- LMTTR
- MProof Test Interval
- NCommon-Cause β
Frozen header, auto-filter on every column, 48 blank rows ready to fill. No macros.
Every column, defined.
14 columns, in the order the sheet carries them. Demand Mode, Target SIL, Achieved SIL and Voting Architecture are dropdowns; the rest stay free text, so house notation fits.
| Col | Column | What goes in it |
|---|---|---|
| A | SIF Tag | Safety instrumented function identifier |
| B | Hazardous Event | Hazard the SIF protects against |
| C | Demand Mode | Low demand, High demand, Continuous |
| D | Target SIL | SIL 1, SIL 2, SIL 3, SIL 4 |
| E | Achieved SIL | SIL 1, SIL 2, SIL 3, SIL 4 |
| F | PFDavg | Average probability of failure on demand |
| G | RRF | Risk reduction factor, the inverse of PFDavg. |
| H | Voting Architecture | 1oo1, 1oo2, 2oo2, 2oo3 or 2oo4 |
| I | Sensor Elements | Sensor tag references |
| J | Logic Solver | Logic solver tag reference |
| K | Final Elements | Final element tag references |
| L | MTTR | Mean time to restore, hours. |
| M | Proof Test Interval | Months between proof tests |
| N | Common-Cause β | Common-cause beta factor fraction |
The SIL bands.
Target SIL comes out of the risk assessment. Achieved SIL is read off the result of the calculation: PFDavg for a low-demand function, PFH for a high-demand or continuous one. These are the bands IEC 61511 sets.
| SIL | PFDavg, low demand | Risk reduction factor | PFH per hour, high demand |
|---|---|---|---|
| SIL 4 | ≥ 10⁻⁵ to < 10⁻⁴ | > 10,000 to ≤ 100,000 | ≥ 10⁻⁹ to < 10⁻⁸ |
| SIL 3 | ≥ 10⁻⁴ to < 10⁻³ | > 1,000 to ≤ 10,000 | ≥ 10⁻⁸ to < 10⁻⁷ |
| SIL 2 | ≥ 10⁻³ to < 10⁻² | > 100 to ≤ 1,000 | ≥ 10⁻⁷ to < 10⁻⁶ |
| SIL 1 | ≥ 10⁻² to < 10⁻¹ | > 10 to ≤ 100 | ≥ 10⁻⁶ to < 10⁻⁵ |
What the voting architecture changes.
The Voting Architecture dropdown offers five arrangements. Each trades a missed trip against a false one differently, per subsystem.
| Voting | Trips when | One channel fails dangerously | One channel trips falsely |
|---|---|---|---|
| 1oo1 | The one channel demands it | The function is lost | The plant trips |
| 1oo2 | Either of two channels demands it | The other still trips | The plant trips |
| 2oo2 | Both channels demand it | The function is lost | Nothing happens |
| 2oo3 | Two of three channels demand it | The other two still trip | Nothing happens |
| 2oo4 | Two of four channels demand it | The other three still trip | Nothing happens |
Common questions
What columns are in this template.
Does this template do the SIL calculation.
Run it on your drawings.
The template is a manual starting point you fill yourself. Upload the source document instead and review the register Tagsight reads from it.