I’m not sure why so many people are so intent to try to pound the square peg of alarms, emergency isolation valves, and other non-SIS instrumented safeguards into the round hole of IEC 61511 compliance. The IEC 61511 standard is really written around complete SIF, and trying to apply that standard to other than complete SIF leads to problems. Putting SIL targets on incomplete loops is quite problematic, and can lead to nonsense designs (SIL 3 operator?!?!). Other instrumented safeguards have their own design specifications that should be designed to, such as API 553 for emergency isolation valves and ISA 18.00.02 for alarms. Please use those specifically written standard for the design of those systems instead of applying IEC 61511 when it is not appropriate.
