Vented explosion experiments involving hydrogen-air mixtures are performed in a 2 m-long cylindrical tube under the influences of the hydrogen concentration and vent burst pressure. Photos of the external flame shot by a high-speed camera show that the jet flame was expelled outside the vessel, and the relation between the flame propagation and external overpressure is summarized. The internal peak overpressure increases and then decreases with increasing hydrogen concentration. In contrast, the external peak overpressure exhibits the opposite correlation in comparison with the internal peak overpressure. The variations in the pressure peaks of the internal pressure curves are also discussed. When the hydrogen concentration is lower than 40 vol %, the second pressure peak plays a more dominant role than the other pressure peaks. However, when the hydrogen concentration is higher than 40 vol %, the third pressure peak becomes more dominant. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.