Scenario 3: 95% detection coverage

Calculation 1: No FGS present (i.e. detection failure = 1, FGS failure = 1, mitigation failure = 1)
Calculation 1

Calculation 2: SIL1 FGS is used
Calculation 2

Calculation 3: SIL2 FGS is used
Calculation 1

Calculation 4: SIL3 FGS is used
Calculation 4

Calculation 5: Summary of risk reduction achieved
Calculation 5

The calculations show that when detection coverage is reduced to 95% (i.e. detection coverage = 0.95), the risk reduction achievable by a SIL3 or SIL2 FGS will both be reduced to SIL1 (risk reduction < 100), and the difference in achievable risk reduction between SIL3 and SIL2 FGS is insignificant.