The French legislation regulates the functioning of factories that may be dangerous towards their environment. This legislation imposes the creation of an Internal Operation Plan (P.O.I.) on the plant managers. Those plans describe the proceedings that have to be implemented in case of an accident. Within a framework involving our laboratory and a gas company we have designed a software to create, maintain and execute P.O.I.s . In this paper, in addition to the software functionalities, we present our design method, as well as the used tools. Both are related to the problems of computing the design process of a P.O.I. and its exploitation in crisis situations. The approach is structured around the UML and the MATLAB tool for both physical simulation and 3D environment management. The final software is developed in Java and uses the API Java-VRML EAI. This solution is currently in use at our partner's plants and it has completely revolutionized their way of managing P.O.I.s.