A series of experiments in a thin layer geometry performed at the HYKA test site of the KIT. The experiments on different combustion regimes for lean and stoichiometric H2/air mixtures were performed in a rectangular chamber with dimensions of 20 x 90 x h cm3 , where h is the thickness of the layer (h = 1, 2, 4, 6, 8, 10 mm). Three different layer geometries: (1) a smooth channel without obstructions; (2) the channel with a metal grid filled 25% of length and (3) a metal grid filled 100% of length. Detail measurement of H2/air combustion behavior including flame acceleration (FA) and DDT in closed rectangular channel have been done. Five categories of flame propagation regimes were classified. Special attention was paid to the analysis of critical condition for different regimes of flame propagation as function of the layer thickness and roughness of the channel. It was found that thinner layer suppresses the detonation onset and even with a roughness, the flame is available to accelerate to speed of sound. The detonation may occur only in a channel thicker than 6 mm.