Large-scale deflagration and detonation experiments of hydrogen and air mixtures provide fundamental data needed to address accident scenarios and to help in the evaluation and validation of numerical models such as the AutoReaGas code (used by Mitsubishi Heavy Industries, Ltd). Several different experiments of this type were performed. Measurements included flame-front time of arrival (TOA) using ionization probes, blast pressure, heat flux, high-speed video, standard video, and infrared video.