The required probability of failure is defined by the industry standard that is associated with each SIL. The following table contains the standard PFD Avg values for each SIL.
| SIL Value | Required Probability of Failure (PFD Avg) | Target Risk Reduction Factor |
|---|---|---|
| 4 | ≥ 10-5 to < 10-4 | > 10,000 to ≤ 100,000 |
| 3 | ≥ 10-4 to < 10-3 | > 1,000 to ≤ 10,000 |
| 2 | ≥ 10-3 to < 10-2 | > 100 to ≤ 1,000 |
| 1 | ≥ 10-2 to < 10-1 | > 10 to ≤ 100 |
If you use an internal SIL Assessment method, the Risk Reduction Factor field is disabled, and populated with the inverse of the value in the Required Probability of Failure field.
If you use an external SIL Assessment method, the Risk Reduction Factor field is enabled and populated with the inverse of the value in the Required Probability of Failure field. If you modify the value in the Risk Reduction Factor field, the Required Probability of Failure field is populated with the inverse of the value in the Risk Reduction Factor field.