Compensation Measures as per IEC 61511 standard

Let's see what the "compensation measures" indicated by the IEC 61511 standard are and how they can be individualized.

According to the standard, compensatory measures are “the temporary implementation of planned and documented methods for risk management during any period of maintenance or process operation when SIS performance is known to be degraded.”

It is therefore clear that to keep the system safe, activities or other solutions must be considered in the event that any component included in a SIF is damaged or undergoing maintenance.

The danger could arise from dangerous faults, i.e. faults which prevent the activation of the SIF when required by the process due to a deviation of the parameters and which, if not controlled, could generate dangerous, even dramatic, events.

A dangerous fault can be detected through diagnostic tests, proof tests or other means of warning of the fault.

If the compensatory measures depend on an activity of the operator who must respond to a given alarm such as closing or opening a valve, this alarm must be considered part of the SIS itself.

These compensation measures obviously depend on the risk that the SIF must reduce and therefore be defined already during the risk analysis and obviously reported both in the SRS and in the operating procedures.

To evaluate the compensation measure, obviously many factors must be evaluated.

For example, would you ever give the responsibility to an operator to avoid an explosion through a shutdown button, when this scenario has been defined as SIL3 and in the event of a dangerous failure of the SIF itself?