How do you conduct failure mode and effects analysis (FMEA) for a Safety Instrumented Function?

SIF FMEA methodology: define scope (complete SIF from sensor to final element), decompose into components (each field device, wiring, logic solver I/O, application program), identify failure modes for each component (stuck, drift, no output, wrong output, delayed response), classify as safe or dangerous (does failure prevent SIF operation?), determine detectability (diagnostic coverage), and assess effect on SIF function. For each dangerous undetected failure mode, ensure it is captured in reliability data. Use FMEA to validate manufacturer failure rate data applicability, identify additional diagnostics needed, and verify fail-safe design assumptions. FMEA complements but doesn't replace PFDavg calculations.