We can get the 3rd degree when we start poking around a facility’s safety instrumented systems(s). It seems that there are those who believe they can build a SIS that no human can screw up and oh how wrong they are! Even OSHA was smart enough to require us to consider the consequences of the failure of engineering and administrative controls (1910.119(e)(3)(iv) in our PHA’s. Here is a PERFECT EXAMPLE of how reliance on a SIS that is not under strictly controlled access or set up properly can leave us with an unsafe degree of confidence that “all is well”. Emergency Shutdown (ESD) safety instrumented systems (SIS) are the LAST LINE of defense and SHOULD NEVER be relied upon without the proper LAYERS of PROTECTION in place before it. This means it is intended to be used ONLY when all else that comes before it has FAILED US! Here is a how a SIS can fail…
High Pressure Shutdown Switch Fails – Catastrophic Equipment Failure
