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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 (recycling) of the substantially unused oxygen content of each breath. Oxygen is added to replenish the amount metabolised by the user. This differs from open-circuit breathing apparatus, where the exhaled gas is discharged directly into the environment.
Rebreather technology may be used where breathing gas supply is limited, such as underwater or in space, where the environment is toxic or hypoxic, as in firefighting, mine rescue and high altitude operations, or where the breathing gas is specially enriched or contains expensive components, such as helium diluent or anaesthetic gases.
- Underwater:
- As self-contained breathing apparatus – where it is variously known as "closed circuit scuba", "closed circuit rebreather" (CCR), "semi-closed scuba", "semi-closed rebreather" (SCR), "closed circuit underwater breathing apparatus" (CCUBA - a military term), or just "rebreather", as opposed to "open circuit scuba" where the diver exhales breathing gas into the surrounding water.
- Surface supplied diving equipment may incorporate rebreather technology either as a gas reclaim system, where the surface supplied breathing gas is returned and scrubbed at the surface, or as a self-contained diver bailout system.
Other uses for rebreather technology:
- Mine rescue and other industrial applications – where poisonous gases may be present or oxygen may be absent.
- Crewed spacecraft and space suits – outer space is, effectively, a vacuum without oxygen to support life.
- Hospital anaesthesia breathing systems – to supply controlled concentrations of anaesthetic gases to patients without contaminating the air that the staff breathe.
- Himalayan mountaineering. High altitude reduces the partial pressure of oxygen in the ambient air, which reduces the ability of the climber to function effectively. Mountaineering rebreathers provide a higher partial pressure of oxygen to the climber.
- Submarines, underwater habitats and saturation diving systems use a scrubber system working on the same principles as a rebreather.
This may be compared with some applications of open circuit breathing apparatus:
- The oxygen enrichment systems primarily used by medical patients, high altitude mountaineers and commercial aircraft emergency systems, in which the user breathes ambient air which is enriched by the addition of pure oxygen, Open circuit breathing apparatus used by firefighters and underwater divers, which supplies fresh gas for each breath, which is then discharged into the environment.
- Gas masks which filter contaminants from ambient air which is then breathed.
The recycling of breathing gas comes at the cost of mass, bulk, technological complexity and specific hazards, which depend on the specific application and type of rebreather used.
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