This paper focuses on the collaboration among emergency managers in charge of planning, coordinating and controlling the course of actions necessary to face an emergency. Our experience in different projects has led us to define a novel collaboration model grounded on decision support, considered as the core function that motivates and sustains inter-personal collaboration. According to this approach, a general knowledge-based decision support system is proposed, along with suitable methods for its customization to a specific domain. A case study concerning the emergency situation generated by a pandemic flu is finally analyzed with the purpose of illustrating the application of the proposed approach and demonstrating its practical impact.