Guide to Functional Safety
and Safety Instrumented Systems in the Process Industry
In this free IEC 61511 guide, we explain the key terminology around Safety Integrity Level (SIL), outline the safety life-cycle and give links to further learning resources.
In the early years of functional safety and attempts at SIL conformance, there was a definite over-emphasis on purchasing “SIL-certified” equipment.
The technical aspect of calculating the “probability of failure” is attractive for engineers to get to grips with. Still, sadly, it hides far more important, albeit less technically appealing, issues.
Although achieved failure probabilities are certainly part of the requirement for demonstrating integrity, achieving specific numerical failure targets is only a small part of the functional safety picture.
Background to IEC 61511
At the turn of this century, the International Electrotechnical Commission published the very first version of functional safety standard IEC 61508. For the first time, IEC 61508 provided an internationally accepted standard for employing electrical, electronic, and especially programmable electronic systems in safety-related applications.
A few years after the first publication of IEC 61508, sector standard IEC 61511 was issued; specifically designed for those applying functional safety and Safety Instrumented Systems (SIS) in the process industry sector.
The functional safety principles are broadly identical in both IEC 61508 and IEC 61511, albeit IEC 61511 distills the four normative parts of IEC 61508 into a single normative standard of around 80 pages, aimed at the application of SIS in chemical, oil & gas, non-nuclear power generation, pharmaceuticals, pulp and paper and food & beverage plants.