This paper deals with the organization of simulation exercises to prepare organizations to face emergencies. The original objective of such simulations is to train people to emergency procedures and devices; we raise the question of training people to face potential crisis situations: are simulations fitted to that objective? Through the observation of a number of exercises organized by private companies and rescue services, we can answer that naïve interprettation of simulation results limits their benefits to the correction of gaps between rescribed and observed actions, without addressing complex organizational behaviour. We introduce a method to organize simulations that gives access to this complexity and to the resilience and robustness apacities of the organization by giving specific roles to observers. This method uses a model of the organization seen as a combination of three levels: structures, relations and meaning.