In this work, we present current results of our research which goal is to develop a decision support system (DSS) as an extension of a Geographical Information System (GIS) to model evacuation plans. It is presented why an A-Prolog approach seems to be appropriated to explore in order to add planning operation as an extension of a GIS. In order to achieve our objective, first it is model the disaster scenario. The disaster scenario should be described as close as possible to the real problem. We define an action language to model and give solution to evacuation plans, named ALEP. Syntax and semantics of ALEP are presented. Finally, we plan to test the expressiveness of ALEP language defining a DSS to model evacuation plans.