Systematic Failures, Systematic Capability and Prior-Use.

This paper is a discussion of the nature of systematic failures in Safety Instrumented Systems and the way that they can be managed. It identifies the upper bound to the probability of failure due to systematic failures as a function of demand rate and a systematic test interval. It discusses how the functional safety standards address systematic failures through systematic capability defences and how these considerations may be addressed when identifying a ‘Prior-use’ case for assessing fitness-for-purpose of system elements. [ABSTRACT FROM AUTHOR]