The work developed in the context of this article stems from the thesis work in progress (done in RIADI labs. at the National School of Computer Sciences, Tunisia in collaboration with the Research Unit of Evaluation of Automated Transport Systems and Safety IFSTTAR, French). The works treat the problem of knowledge management of a critical area, that of security and in particular the railroad accidents. The goal is to provide methodological support and tools to support the capitalization and exploitation of produced knowledge and/or used by domain experts. We have proposed an approach based on domain ontology and Case-based Reasoning CBR. We will present as part of this article, the first realized works in our approach.