Abstract: A breathing apparatus provides a closed circuit which is capable of delivering substantially pure oxygen and removing carbon dioxide exhaled by a subject. The apparatus has low breathing resistance, the ability to provide intermittent positive pressure breathing and can be completely and efficiently purged of inert gases and other fluid impurities which are initially in the apparatus or exhaled by the subject. A carbon dioxide removal system in the apparatus prevents channeling of exhaled gases through scrubber material, thereby insuring efficient carbon dioxide removal. The condition of the carbon dioxide absorption material can be determined by visual inspection by an attendant while the subject is connected to the apparatus.

Abstract: Oxygen is mixed into hydrogen for use as breathing gas for divers, pressure chambers and the like in precise and regulated amounts. Provision is also made to prevent explosion of these mutually reactive gases during mixing.