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.

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.