When modeling fault-tolerant systems, state-based methods yield much more realistic results in comparison to traditional combinatorial methods. To avoid the difficult manual design of large state-based models, we advocate an approach, by which a high-level input model is used from which a semantically equivalent low-level model is automatically generated. This approach was implemented in the tool OpenSESAME (Simple but Extensive Structured Availability Modeling Environment). Its input uses reliability block diagrams as a wide-spread modeling technique favored by many reliability engineers. In addition, users can specify intercomponent dependencies of the system without having to create a state-based model. The main contributions of this paper are, first, a detailed description of the input model showing the application areas and limitations of OpenSESAME; second, a detailed explanation of the transformation process into the state-space domain; and third, it contains a realistic industrial example modeling a water supply system of a city.