Design of functional safety model for tail gas treating process

This paper addresses the design of functional safety model for process automation in accord with IEC 61508/61511 standard. Functional safety design of a tail gas treating unit has been conducted in this study. The quantitative fault tree analysis approach which has been proved to be acceptable and widely applied in many applications of modeling and methods supporting the designer and safety engineer not only to identify how subsystems and components could fail and what are the corresponding effects on the whole system, but also to quantify the reliability parameters for complex systems. The analytical evaluation of the probability failure on demand and the failure rate for the system, all these component are supposed to be not repairable and the probability distributions of time to failure random variables are assumed to be exponential function. The calculation result is used as the criterion for the safety instrumented function design in order to conform the required safety integrity level. The experimental show that the subsystem architecture of safety instrumented function has a significant impact on improving the average probability of failure on demand of the process.