The interaction between combustion and turbulence in hydrogen-air mixtures in the early flame development phase is reviewed from the safety point of view. Detailed knowledge about the acceleration of hydrogen-air flames in real physical environments is needed to avoid deflagration-to-detonation transition (DDT). Depending on the initial and boundary conditions, the burning velocity of the same hydrogen-air mixture can vary by an order of magnitude. A time-dependent two-dimensional flow algorithm, using a direct numerical simulation method (DNS) and including large-scale eddy simulation in complex channel areas, is presented to calculate flame folding in the early burning phase after ignition. Complex mapping functions to realize different obstacle areas in tubes are presented. The effects of combustion on the structure of turbulence in the how field, in front of the flame surface and effects of flow field instability on the flame development in tubes containing line or expanded obstacles are discussed.