SAFEST: The Static and Dynamic Fault Tree Analysis Tool

We present S afest, the Static And dynamic Fault trEe analySis Tool. While standard (or static) fault trees (SFT) appeal as a relatively simple tool, they are limited in their modeling capabilities. Dynamic fault trees (DFT) extend SFT by support for faithfully modeling spare management, order-dependent failures and functional dependencies. While various analysis approaches for DFTs exist in the literature, tool support is scarce.

During the last years, we developed S afest, a modern, state-of-the-art tool for modeling and analysing (SFTs and) DFTs. S afest's web-based interface offers a drag-and-drop editor for creating fault trees. A step-by-step simulator visualizes how failures - given by the user - affect the state of DFT elements. S afest employs a plethora of analysis approaches. SFTs are best analyzed using binary decision diagrams (BDD) and S afest performs comparable to existing SFT tools. DFTs are analyzed via state-based techniques by translation into a Markov model. S afest can analyze these models via probabilistic model checking, yielding exact results efficiently. It also provides an approximation approach that builds only the most "important" parts of the DFT's behaviour. This enables the analysis of gigantic DFTs at the expense of exactness of results. This approximation provides upper and lower bounds on the reliability measure of interest. The precision can be tuned according to the user's needs.

The modeling and analysis capabilities of DFTs as well as the performance of our tool has been demonstrated in several practical and industrial case studies. DFTs with up to several hundreds of elements have been successfully analyzed with S afest.

Keywords: Fault tree analysis, Dynamic fault trees, Model checking, Formal methods, Risk management, Tool.

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