About Safety Integrity Level (SIL) Assessment Using a Hazards Analysis

If you have already performed risk assessments for a Hazards Analysis via the Hazards Analysis module, you can use one of those risk assessments to assess the Safety Integrity Level (SIL) for an instrumented function.

To determine SIL using a PHA Internal assessment, you must:

Specify the SIL Threshold values. An SIL Threshold record stores the upper and lower boundary values for each SIL.
Select the Hazards Analysis and the Cause-Consequence pair that you want to use to assess the SIL value.

The category that has been assigned with the highest risk rank in the risk assessment is called the Driving Risk, and the corresponding risk rank is called the Driving Risk Rank.

The system determines which risk rank values to use based on the following criteria:

If the risk from the Hazards Analysis has not been mitigated, the Driving Risk Rank of the unmitigated risk assessment is used to calculate SIL.
If the risk from the Hazards Analysis has been mitigated, then the Driving Risk Rank of the mitigated risk assessment is used to calculate SIL.

Depending on the range in which the driving risk rank value falls, GE Digital APM determines the SIL, and then populates the Selected SIL Level field with this value.

Note: If the driving risk rank value falls on the boundary value of two SIL thresholds, GE Digital APM populates the Selected SIL Level field with the higher SIL value. For example, suppose that the SIL Threshold contains SIL value 1 for the risk range 0 through 10, and SIL value 2 for the risk range 10 through 100. If the driving risk in the risk assessment is 10, the Selected SIL Level field is populated with the SIL value 2.