[en] The possibility of repository overpressurization was considered in Nirex 97. The calculated overpressures are assessed to be too low to give rise to significant deleterious effects on the repository system in terms of cracking. Although a number of toxic gases, such as hydrogen sulphide may be generated in the repository, it is considered that they will react with the materials in the repository, and therefore no toxic hazards will arise in the biosphere. The possibility that flammable mixtures will form in surface engineered structures has been considered. It is assessed that flammable mixtures of gases are extremely unlikely to form in engineered structures at the surface, above a repository, even in the event of a highly focused discharge. (author)