The report deals with the investigation of non-stationary combustion of hydrogen-air mixtures extremely relevant to the issues of safety. Considered are the conditions of its formation and development in the tubes, in the conic element and in the spherical 12-m diameter chamber. The report shows that at the formation of non-stationary combustion in the conic element, in its top the pressure can develop exceeding 100 MPa. It is also shown that in large closed volumes non-stationary combustion can develop from a small energy source, in contrast to detonation for its stimulation in large volumes of significant power influences are required. Simultaneously, in the large closed volume a pressure can be formed by far exceeding the Chapman-Jouguet pressure in the front of stationary detonation. (C) 2009 Published by Elsevier Ltd on behalf of International Association for Hydrogen Energy.