-Han Solo, Star Wars, Episode V: The Empire Strikes Back, 1980
I have enjoyed watching and reading about the actions of the fictional Star Wars character Han Solo over the years. I recall hearing the above quotation more than once. And as much as I enjoyed watching this character,…
How often have you been at conferences where the presenters refer to the “Swiss Cheese Model”? The intent of the model is to convey what happens to the protection layers in Safety Instrumented Systems (SIS) when they are poorly designed, implemented and maintained. In this case, when any of…
This is a question I’ve been asked many times, with some stating that as long as the PFDavg (or PFH) meets the target SIL then that’s fine. Whereas this statement is partially true, it is not the full answer. IEC61511 defines the criteria for meeting the requirements of an…
Oftentimes when this comes up during class it’s clear that there’s a misunderstanding as to how these three variables can impact the PFDavg calculations. Mission Time is defined as the period of time over which a set of Safety Instrumented Function (SIF) equipment is expected to operate without major…
IEC 61508 and IEC 61511 are known as “performance” based standards. Specific design rules, as found in “prescriptive” standards, are not included, allowing for innovation and new technology, as well as creativity and advancement. However, it does imply that a certain level of competency is required.
Others would strongly…