Experimental data obtained for hydrogen mixtures in a room-size enclosure are presented and compared with data for propane and methane mixtures. This set of data was also used to develop a three-dimensional gasdynamic model for the simulation of gaseous combustion in vented enclosures. The experiments were performed in FM Global's 64 m3 chamber, a 4.6 x 4.6 x 3.0 m chamber with a vent opening on one side. Vent areas of either 2.7 or 5.4 m2 were used. Tests were performed with ignition either at the center of the chamber or at the center of the wall opposite the vent. Hydrogen-air mixtures with hydrogen concentrations close 18%2vol., stoichiometric propane-air and stoichiometric methane-air mixtures were used in these tests. Pressure data, as function of time, and flame time-of-arrival data were obtained both inside and outside the chamber near the vent. Modeling was based on a Large Eddy Simulation (LES) solver created using the OpenFOAM CFD toolbox using sub-grid turbulence and flame wrinkling models. A comparison of these simulations with experimental data is discussed.