rebreather 
noun
An aqualung in which the diver’s exhaled breath is partially purified of carbon dioxide, mixed with more oxygen, and then breathed again by the diver.Have you heard that British dive shops are being asked for names of people buying the more expensive items of dive gear, particularly rebreathers and diver scooters?...
- Unlike conventional scuba gear, rebreathers recycle exhaled gas by chemically scrubbing it of carbon dioxide with soda lime.
- Without it, Shirley would have to constantly monitor the oxygen levels in his rebreather and inject oxygen into his breathing loop manually.