Getting Realistic Failure Rates for SIS Verification

Performance based functional safety standards like IEC 61511 offer many advantages including the opportunity to optimize and upgrade Safety Instrumented System (SIS) designs. But performance calculation depends upon realistic failure data for instruments used. A predictive analysis technique called Failure Modes Effects and Diagnostic Analysis (FMEDA) has been developed along with a component failure rate database that can predict failure rates of instruments based on their design strength and the expected stress environment. This method has been calibrated with over 150 billion unit operating hours of field failure data over the last 15 years.