Methods and devices for removing inflammable gases produced by radiolysis in a closed chamber containing radioactive matters comprising organic compounds and possibly water, or radioactive matters in the presence of organic compounds and possibly water. Inside the chamber there may be placed a catalyst of at least one reaction for oxidizing the inflammable gases by oxygen contained in the chamber atmosphere, supported by an inert solid support; a catalyst of at least the reaction for oxidizing CO to CO.sub.2; possibly an oxygen source; and possibly a hygroscopic microporous inert solid support. Also, chambers for radioactive matters containing such devices.