Calculating SIF Achieved PFD and Verifying Integrity

You need to verify that the Achieved PFD is less than the Target PFD. 

(The Target PFD is normally calculated during the LOPA Assessment, but if not connected to a LOPA it could also be a static value that you enter on the SIF Analysis General Tab.) 

When you click Calculate PFDin the Approval Area IMS calculates the (90% upper limit of the) Achieved PFD. And then compares this with the Target PFD. The design is deemed to be OK if the 90% upper limit of the Achieved PFD is less than the Target PFD. If this is true a green checkmark will show next to the Achieved PFD.The 90% upper limit of the Achieved PFD is less than the Target PFD, thus a green checkmark shows.

Take note that if you have selected Continuous (rather than Demand) mode in the Assessment Summary on the General Tab then you will be verifying the DFR (Dangerous Failure Rate), rather than the PFD.

DFR will show, when you selected Continuous in the Assessment Summary.

The Calculate PFD button also checks the hardware Fault Tolerance on the SIF Design. The result will be shown by the Subsystem's Fault Tolerance indicator. If there is a problem with the SIF hardware Fault Tolerance, concerning the SIL, the Subsystem Fault Tolerance indicator will turn red. From a methodology and design perspective, this may imply that, in such a case, additional hardware must be added to the SIF design, or the SIL of the SIF must be reduced.