Difference between SIF or a SIS?

The philosophy of the standards suggests that a SIS or SIF should be implemented only if there is no other non-instrumented way of adequately eliminating or mitigating process risk.

Specifically, the ANSI/ISA-84.00.01-2004 (IEC 61511 Mod) recommends a multi-disciplined team approach that follows the Safety Lifecycle, conducts a process hazard analysis, designs a variety of layers of protection (i.e., LOPA), and finally implements a SIS when a hazardous event cannot be prevented or mitigated with something other than instrumentation.


We call this the KISS principle. Which stands for Keep It Simple, Stupid.
Just don’t rely on the Functional safety without reducing the probability of failure by simple and traditional ways.