Some examples of research activities will be described that cover parts of a safety and risk analysis (PRA) for a hydrogen production plant combined with a high temperature gas-cooled reactor (HTGR). In the 1980s, the Julich Research Centre conducted safety analyses for two conceptual designs of an HTGR under the modified operating conditions of process heat applications. At the Karlsruhe Research Centre, an experimental programme has been started to investigate the combustion behaviour of H-2-CO air mixtures under different conditions. Both H-2 and CO gases are components of the product gas after the st-earn reforming of methane. An impact from the outside to an HTGR hydrogen production system could be given by the explosion of flammable gas clouds in the open atmosphere. The proceeding step would be, for example, the inadvertent spillage of the cryogenic liquid LNG. The results of a predictive study will be given, in which the behaviour of different cryogenic liquids, LH2, LN2, LOX and LNG, were compared.