Frequently Asked Questions

We have a combined barrier, which is using both instrumented function and a human intervention. Is it possible to take into account the human factor in the calculation with a PFDavg of 0,1 ? How could this human factor be calculated in the loop calculati
Last Updated a year ago

There is an old argument that manually initiated SIFs are not SIFs as the human is not an instrument, i.e. typically operator initiated functions are considered separately in, for example, a LOPA and do not follow the detailed requirements of IEC 61511 as they are not SIFs.

The assumption is that the operator is an input into the SIF, another sensor. exSILentia does not have the ability to directly input probability of failure numbers in the overall calculation, i.e. the calculations are based on failure rates. In this case we would recommend the creation of a User Defined component, in a sensor group, and select the measurement type as Other. Next to the "add sensor" button you will see a button named "UD" for user defined. Click on this UD button. You will be able to specify the name etc. of the user defined device.
When it comes to the failure rates, you will see an option to base your data on PFD numbers. Select this option. For the PFD use 0.1 and for the time interval use the proof test interval that you will be using in your SIF. The tool will then calculate the failure rates to be used to get a PFD of 0.1 at the point of proof testing.

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