Within an emergency unit, the head manager is required to make difficult decisions based on experts' assessments of many criteria, including personal injuries, environmental impacts, economic and media consequences. Uncertainty in this collective assessment is related to multiplicity of experts' points of view and imprecise assessments. We are proposing a decision support system derived from a situation awareness model, generalized herein to the case of multiple actors. It is able of representing, merging and aggregating expert assessments. Imprecise criteria assessments are first represented by intervals and then merged in the form of a possibility distribution that keeps track of all information provided, i.e. without any loss of information. Next, a Choquet integral-based aggregation is carried out in order to consider the relative importance of criteria and interactions between criteria in the overall assessment of the foreseeable alternatives to get out of the crisis. Lastly, a determination of the contributions of each criterion assessment uncertainty to the overall assessment uncertainty provides useful information to the head manager in controlling the decision deliberation by reducing the inconsistent points in the experts' assessments. The proposals are applied to the emergency issues resulting from a traffic accident occurring at a grade crossing.