Rebreather
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A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen is added to... Wikipedia
Acronym: CCUBA (closed circuit underwater breathing apparatus); CCR (closed circuit rebreather), SCR (semi-closed rebreather)
Uses: Breathing set