Since the rapid development of hydrogen stationary and vehicle fuel cells this last decade, it is of importance to improve the prediction of overpressure generated during an accidental explosion which could occurs in a confined part of the system. In this aim, small scale vented hydrogen-air explosions were performed in a transparent cubic enclosure with a volume of 3375 cm3. The flame propagation was followed with a high speed camera and the overpressure inside the enclosure was recorded using high frequency piezoelectric transmitters. The effects of vent area and ignition location on the amplitude of pressure peaks in the enclosed volume were investigated. Indeed, vented deflagration generates several pressures peaks according to the configuration and each peak can be the dominating pressure. The parametric study concerned three ignition locations and five square vent sizes. The maximal overpressures measured in the enclosure, due to the external and internal combustion, were compared to models of the literature.