Optimum staggered testing strategy for 1- and 2-out-of-3 redundant safety instrumented systems

Abstract In redundant safety instrumented systems (SIS), staggered testing is effective in reducing the unavailability or average probability of failure on demand (PFD) of SIS than simultaneous or consecutive testing. In this Chapter, the existing models are reviewed, SIS with 1- and 2-out-of-3 structure is analyzed, and the optimal staggered testing schemes are found. As a practical case, the optimal staggered testing method is investigated for SIS in which two units among three units are formed as a testing group with equal testing time points. We investigate also the optimality of grouping method. Finally, we study also numerical examples.