Scalable Analysis of Fault Trees with Dynamic Features

Fault trees constitute one of the essential formalisms for static safety analysis of various industrial systems. Dynamic fault trees (DFT) enrich the formalism by time-dependent behavior, e.g., repairs or functional dependencies. Analysis of DFT is so far limited to substantially smaller models than those required for, e.g., nuclear power plants. We propose a fault tree formalism that combines both static and dynamic features, called SD fault trees. It gives the user the freedom to express each equipment failure either statically, without modelling temporal information, or dynamically, allowing repairs and other timed interdependencies. We introduce an analysis algorithm for an important subclass of SD fault trees. The algorithm (1) scales similarly to static algorithms and (2) allows for a more realistic analysis compared to static algorithms as it takes into account temporal interdependencies. Finally, we demonstrate the applicability of the method by an experimental evaluation on fault trees of nuclear power plants.