Silane is widely used in some kinds of industries such as semiconductor manufacturing. However, this compound is pyrophoric and can present a high hazard of fire and explosion. In order to suppress the inconvenient of silane pyrophoric behaviour, SiH4-N2O mixtures are used. The decomposition of silane occurs readily compared to the one of N2O and involves the formation of H2. It follows that the H2-N2O system seems to constitute an important sub-system of the silane oxidation mechanism. The induction delay times of this system have been widely studied but limited to low pressures. Consequently, the aim of the present study is to investigate both experimentally and numerically the high pressure behaviour of H2-N2O-Ar via OH UV emission. Characteristic times of reaction behind reflected shock waves of H2-N2O-Ar mixtures have been measured in the 1300-1860 K temperature range, at pressure of 912 kPa for mixtures with equivalence ratio equal to 0.5, 1 and 2. It has been shown that the equivalence ratio varying between 0.5 and 2 has no effect on this over the whole studied temperature range. The modelling of characteristic times has been performed using two models, one including an OH* chemistry sub-mechanism. Finally, using the developed mechanism and available detonation cell size experiments, the cell size-induction distance ratio has been correlated with initial conditions. This correlation leads to a detonation cell size of H2-N2O-(N2) mixtures with a mean relative error of 20 %.