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Target Failure Measure of the SIF
Sensor
Final
Element
P E
Safety Instrumented Function (SIF)
The Proof Test is essential to maintain the Target
Failure Measure of the SIF…PFDavg
PFDavg
Risk
Target Risk
Risks arising
from dangerous
failures in the
process & in the
BPCS
Demands
F1
Risk reduction
achieved by
Other Risk
Reduction
Measures
F3
Risk reduction
achieved by
Conditional
Modifiers
F4
Risk Reduction
Risk Reduction
Risk Reduction
Risk Model Example: Low Demand Mode
F2
1
3
2
4
SILs
Proof Testing
maintains this
Risk Reduction
F1 to F2