Abstract: A system for decontaminating a clean-room has an H2O2 supply device for supplying the clean-room with H2O2 and an H2O2 breakdown device for effecting a chemical breakdown of H2O2 without catalyst in the clean-room. The H2O2 breakdown device comprises a supply vessel filled with gaseous agent which can be introduced via a gas line into the clean-room where it reacts with the H2O2. A valve is placed in the gas line with which the amount of the gaseous agent introduced into the clean-room can be introduced under open-loop or closed-loop control. Owing to the fact that the excess H2O2, that is to say the H2O2 which has not reacted with other materials in the clean-room during the decontamination is broken down in the clean-room itself, it need not be flushed out completely from the clean-room first and broken down afterwards.