In our society the use of hydrogen is continually growing and there will be a widespread installation of plants with high capacity storages in our towns as automotive refueling stations. For this reason, it is necessary to make accurate studies on the safety of these kinds of plants to protect our town inhabitants Moreover, hydrogen is a highly flammable chemical that can be particularly dangerous in case of release since its mixing with air in the presence of an ignition source, could lead to fires or explosions. Generally most simulation models, whether or not concerned with fluid dynamics, used in safety and risk studies are not validated for hydrogen use. This aspect may imply that the results of studies on safety cannot be too accurate and realistic. This paper introduces an experimental activity which was performed by the Department of Energetics of Politecnico of Torino with the collaboration of the University of Pisa. Accidental hydrogen release and dispersion were studied in order to acquire a set of experimental data to validate simulation models for such studies. At the laboratories of the Department of Mechanical, Nuclear and Production Engineering of the University of Pisa a pilot plant called Hydrogen Pipe Break Test was built. The apparatus consisted of a 12 m3 tank which was fed by high pressure cylinders. A 50 m long pipe moved from the tank to an open space and at the far end of the pipe there was an automatic release system that could be operated by remote control. During the experimental activity, data was acquired regarding hydrogen concentration as a function of distance from the release hole, also lengthwise and vertically. In this paper some of the experimental data acquired during the activity have been compared with the integral models, Effects and Phast. In the future, experimental results will be used to calibrate a more sophisticated model to atmospheric dispersion studies.