Environmental accidents such as extensive radioactive or chemical contamination can have more serious consequences for a population than any other kind of accidents known before. Owing to the serious consequences and the high number of people who may be affected, the selection of the best countermeasures to ameliorate the imminent impact is very difficult and the political responsibility is enormous. In particular, high quality decision making in a crisis situation, where several decision makers are involved and a quick response is required, is very ambitious and normally implies great difficulties. To help overcome such problems the National Emergency Operations Centre in Zurich (Switzerland) has developed a decision support system to evaluate acceptable countermeasures for reducing ingestion dose after an accidental release of radioactive material. The system involves all the necessary modules and techniques for efficient decision making, based on the most recent developments in decision theory as well as the necessary structuring of the decision-making process. The decision-making concept comprehends decision-making on two different levels, a technical and a political one. To guarantee decisions of high quality, as many alternatives or countermeasures as possible have to be presented to the decision makers. Owing to the difficulty of evaluating all the possible countermeasures the space of alternatives is automatically generated. To protect the decision makers from information overload, irrelevant data are filtered out. The countermeasures for reducing the ingestion dose mainly involve different processing techniques in the agriculture and food industries. After having passed the filtering system, the residual alternatives are judged by the technical experts, who evaluate reasonable countermeasures from a technical point of view. Finally, the political decision makers have to decide about the political acceptance and the final ranking. To support the comparison and ranking of the different alternatives a multicriteria approach is used. This method allows the consequences of different measures to be assessed easily in relation to different coherent criteria.