INERIS has set up large-scale fully instrumented experiments to study the formation of flammableclouds resulting from a finite duration spillage of hydrogen in a quiescent room (80 m3 chamber).Concentration, temperature and mass flow measurements were monitored during the release periodand several hours after. Experiments were carried out for mass flow rates ranging from 0,2 g/s to 1 g/s.The instrumentation allowed the observation and quantification of rich hydrogen layers stratificationeffects. This paper presents both the experimental facility and the test results. These experimentalresults can be used to assess and benchmark CFD tools capabilities.