Large-scale deflagration and detonation experiments of hydrogen and air mixtures provide fundamental dataneeded to address accident scenarios and to help in the evaluation and validation of numerical models.Several different experiments of this type were performed. Measurements included flame front time ofarrival (TOA) using ionization probes, blast pressure, heat flux, high-speed video, standard video, andinfrared video. The large-scale open-space tests used a hemispherical 300-m3 facility that confined themixture within a thin plastic tent that was cut prior to initiating a deflagration. Initial homogeneous hydrogenconcentrations varied from 15%2to 30%2 An array of large cylindrical obstacles was placed within themixture for some experiments to explore turbulent enhancement of the combustion. All tests were ignited atthe bottom center of the facility using either a spark or, in one case, a small quantity of high explosive togenerate a detonation. Spark-initiated deflagration tests were performed within the tunnel usinghomogeneous hydrogen mixtures. Several experiments were performed in which 0.1 kg and 2.2 kg ofhydrogen were released into the tunnel with and without ventilation. For some tunnel tests, obstaclesrepresenting vehicles were used to investigate turbulent enhancement. A test was performed to investigateany enhancement of the deflagration due to partial confinement produced by a narrow gap betweenaluminium plates. The attenuation of a blast wave was investigated using a 4-m-tall protective blast wall.Finally a large-scale hydrogen jet experiment was performed in which 27 kg of hydrogen was releasedvertically into the open atmosphere in a period of about 30 seconds. The hydrogen plume spontaneouslyignited early in the release.