A joint research project was carried out in the EU Fourth Framework Programme with the goal to develop verified and commonly agreed physical and numerical models for the analysis of hydrogen distribution, turbulent combustion and mitigation, which are suited for the multi-dimensional CFD codes that exist at the institutions of the participating partners. The work programme and the activities of the partners are described. Significant progress has been made in the areas of experiments, model development, model verification and model application to nuclear power plants. Joint benchmark tests were defined and analysed. In addition to the regular partners meetings, topical workshops were conducted to harmonize the experimental and theoretical work. The paper presents major experimental results, gives examples for the achieved multi-dimensional modelling capabilities, describes implementation into and validation of codes, and presents results of plant analysis activities. (C) 2001 Elsevier Science B.V. All rights reserved.