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.

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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.

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