SIF and SIS are closely related functional safety terms, but they are not interchangeable. Confusing them can lead to unclear requirements, poor testing strategies and incorrect statements such as “the whole safety PLC is SIL 2.” In practice, functional safety…
Functional safety is not achieved by purchasing a safety PLC or specifying SIL-rated equipment. It is achieved by managing Safety Instrumented Functions through a lifecycle that begins with hazard identification and continues through design, installation, operation, maintenance, modification and decommissioning.…
A Safety Integrity Level should not be selected because a shutdown function “feels critical” or because similar equipment has historically used a particular SIL. The target must come from a defined hazardous scenario, a tolerable-risk basis and a structured assessment…