Scenario 1: 100% (perfect) 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 perfect (i.e. detection coverage = 1), the risk reduction that can be achieved by each FGS is closely in line with the respective SIL rating.