Because of hydrogen low volumetric energy content under its gaseous form, transport and storage of liquid hydrogen will certainly play a major role in any future hydrogen economy. One of the obstacles to the expected development of the use of hydrogen is the poor state of knowledge on explosion risks in the event of an extensive spillage. INERIS set up a large-scale experiment to study the mechanisms of the formation of the gas cloud resulting from such a spillage and the associated mixing process and turbulence effects. Dispersion tests have been performed with cryogenic helium presenting similar dispersion characteristics than liquid hydrogen (buoyancy). Flowrates up to 3 kg/s have been investigated and the instrumentation allowed the observation and quantification of buoyancy effects including internal turbulence. Those results constitute an original set of data which can be used as a basis for the development of dispersion software and reinterpretation of other existing databases ([10, 11]).