Results of an experimental study of flame propagation in a 100mm by 100mm cross section and 1500mm long open channel with a single obstacle (BR=0.9) are presented. The gas mixture in the experiments were 30%vol H2 in air. Both perpendicular and angular light were used for schlieren photography. The study included how point and distributed ignition source affected the flame propagation and pressure buildup. The main objective was to investigate whether the flame propagation could be simplified with a two-dimensional assumption for CFD simulation purposes. Flame front inversion was seen in the experiments, and after inversion it never turned back to the original shape again. After the inversion the flame could not be considered two-dimensional. A visible boundary layer grew in front of the flame as it inverted.