Safety Metrics Independent

PFD average (PFDavg) is a term used to describe the average probability of failure on demand. PFD will vary as a function of the operating time interval of the equipment. It will not reach a steady state value if any periodic inspection, test, and repair is done. Therefore, the average value of PFD over a period of time can be a useful metric if it assumed that the potentially dangerous condition (also called hazard) is independent from equipment failures in the safety instrumented function. 

The assumption of independence between hazards and safety instrumented function failures seems very realistic. (NOTE If control functions and safety functions are performed by the same equipment, the assumption may not be valid Detailed analysis must be done to insure safety in such situations, and it is best to avoid such designs completely.) When hazards and equipment are independent, it is realized that a hazard may come at any time. Therefore, international standards have specified that PFDavg is an appropriate metric for measuring the effectiveness of a safety instrumented function. 

Safety Health Sustainability was formally launched at the conference. This new non-profit organization, independent of ASSE, ciims to provide much needed safety and health metrics to be incorporated by... 

Three missions were evalirated to determine the flexibility of the architecture and the indoor facihty to test a variety of concepts rapidly. A specific metric was used for each mission to qitantify performance. The first mission was non-collaborative and consisted of several vehicles repeatedly performing independent flight plans on conflicting trajectories. The metric was focused on evalirating flight safety and the performance of colhsion avoidance methodologies. 

---