Safety aspects will become essential for the introduction and acceptance of gaseous and liquid hydrogen as an energy carrier and fuel in energy supply systems. Prevention and control of accidental formation and ignition of large volumes of fuel-air mixtures are of primary importance when safety aspects of released gaseous hydrogen are discussed. Detailed knowledge of the overpressure in an accidental situation is essential for the protection of the public as well as for the corresponding plants and safety installations. Considerable progress has been made in the last few years concerning the understanding of the complex phenomena involved in combustion processes of gaseous mixtures. This holds in particular for flame acceleration and maximum turbulent flame speeds in unconfined and confined geometries. Fast turbulent deflagrations often transit spontaneously to detonations if flame speeds are high enough, depending on the combustible and boundary conditions. This paper discusses the potential hazards of hydrogen in the energy market as compared with other and already familiar energy carriers like natural gas and propane.