In this study, the flame propagation behavior and the intensity of the blast wave by an accidental explosion of a hydrogen-air mixture in an open space were measured simultaneously using the soap bubble method. The results show that the flame in lean hydrogen-air mixtures propagated by spontaneous flame instabilities. The flame in rich hydrogen-air mixtures propagated smoothly in the early stage, and was intensively wrinkled and accelerated in the later stage by different type of instabilities. The flame wrinkling in the later stage of rich hydrogen flame is generated when the flame approaches the non-uniformity transition region of concentration distribution. The intensity of the blast wave of hydrogen/air mixtures is strongly affected by the acceleration of the flame propagation by these spontaneous flame disturbances. Copyright (c) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.