Having taught our FSE100 Functional Safety Lifecycle Course for the past five years, I am still amazed that some end users are maintaining a run-to-fail policy for their Safety Instrumented System (SIS) equipment. This webinar highlights why this is not a sound practice to follow and why it negates all the work performed during the analysis and design phases of the IEC61511 Safety Lifecycle for the SIS.
By maintaining a run-to-fail policy, end users are violating the performance aspects of IEC61511 for its SIS, because the premise of calculating a Probability of Failure on Demand (PFD) is based upon the assumption of a constant failure rate during Useful Life of the devices. Once a device has exceeded the manufacturer’s Useful Life, and it’s not replaced, then it’s into the “wear-out” portion of the “bathtub” curve, whereby constant failure rate can no longer be applied and relied upon. Therefore, this portion is not predictable and so the Safety Integrity of the Safety Instrumented Function and its associated equipment cannot be relied upon.
So if you have a run-to-fail policy, then perhaps it’s time to rethink this approach.
