Using Unrealistically Optimistic Failure Data: Is It Ethical?

Performance based functional safety standards such as IEC 61508 and IEC 61511 offer many advantages, including the opportunity to optimize and upgrade Safety Instrumented System (SIS) designs. However, an instrument’s performance calculations depend on realistic failure data.  While realistic failure data is unsurpassed, unrealistically optimistic failure data can be extremely hazardous.  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 the failure rates of instruments based on their design strength and the expected stress environment.  This method has been calibrated with over 150 billion of unit operating hours of field failure data over the last 15 years enabling realistic data to become more attainable.  With the knowledge that such data is within a company’s reach, using data that is too optimistic is inexcusable (from an engineer’s or a purchaser’s perspective). This presentation will examine functional safety standards, explore a range of realistic failure data for a simple mechanical device, and discuss the role of engineering ethics in regards to the use of overly optimistic failure data.