We present in this paper researches focussed on training scenario specification. These researches are conducted in the context of a collaboration with Giat-Industries (a French military manufacturer) in order to introduce Virtual Reality(VR) in maintenance training. The use of VR environments for training is strongly stimulated by important needs of training on sensitive equipment, sometimes fragile, unavaiblable, costly or dangerous. Our project, named GVT, is developped in a research/Industry collaboration. A first version of GVT is already available as a final product, which allows maintenance virtual training on GIAT-Industries equipments. Internal models have been designed in order to achieve reusability and standardization for the efficient development of new virtual training environments. In particular, we defined a scenario language named LORA, which is both textual and graphical. This language lets non-computer scientists author various and complex tasks in a virtual scene.