Instrumented protective function (IPF) is a safety function designed to achieve a safe state for a specific hazardous event. An IPF loop is made up of initiators, logic solvers and final elements. IPF is classified with a specific safety integrity level (SIL), which must be met throughout its life-cycle. IPF failures can cause severe consequences on people, environment, asset and reputation, if there is no alternative independent layer of protection. 35% of control system failures are estimated to occur in the operation and maintenance phase, in spite of the assumed compliance with the target integrity requirements. This paper deliberates the issues of functional proof testing, data collection, IPF study review, as well as awareness and competency of manpower, with the objective of improving functional safety management in the operation and maintenance phase.

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