An experimental study of flame propagation, acceleration and transition to detonation in hydrogen-air mixture in 2-m-long rectangular cross-section channel filled with obstacles located at the bottom wall was performed. The initial conditions of the hydrogen-air mixture were 0. 1 MPa and 293 K and stoichiometric composition (29.6% H-2 in air). The channel width was 0. 11 m and blockage ratio was 0.5 in all experiments. The effect of channel geometrical scale on flame propagation was studied by using four channel heights H of 0.0 1, 0.02, 0.04, and 0.08 in. In each case, the obstacle height was equal to H/2 and the obstacle spacing was 2H. The propagation of flame and pressure waves was monitored by four pressure transducers and four ion probes. The pairs of transducers and probes were placed at various locations along the channel in order to get information about the progress of the phenomena along the channel. As a result of the experiments, the deflagration and detonation regimes and velocities of flame propagation in the obstructed channel were established. (C) 2007 Elsevier Ltd. All rights reserved.