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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 an 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. Rebreather technology is used in many environments: *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. *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. ==General concept== As a person breathes, the body consumes oxygen and produces carbon dioxide. Base metabolism requires about 0.25 L/min of oxygen from a breathing rate of about 6 L/min, and a fit person working hard may ventilate at a rate of 95 L/min but will only metabolise about 4 L/min of oxygen 〔''NOAA Diving Manual, 4th Edition'' CD-ROM prepared and distributed by the National Technical Information Service (NTIS)in partnership with NOAA and Best Publishing Company〕 The oxygen metabolised is generally about 4% to 5% of the inspired volume at normal atmospheric pressure, or about 20% of the available oxygen in sea level air. Exhaled air at sea level still contains roughly 16% oxygen. The situation is even more wasteful of oxygen when the oxygen fraction of the breathing gas is higher, and in underwater diving, the compression of breathing gas due to depth makes the recirculation of exhaled gas even more desirable, as an even larger proportion of open circuit gas is wasted. Continued rebreathing of the same gas will deplete the oxygen to a level which will no longer support consciousness, and eventually life, so gas containing oxygen must be added to the breathing gas to maintain the required concentration of oxygen. However, if this is done without removing the carbon dioxide, it will rapidly build up in the recycled gas, resulting almost immediately in mild respiratory distress, and rapidly developing into further stages of hypercapnia, or carbon dioxide toxicity. A high ventilation rate is usually necessary to eliminate the metabolic product carbon dioxide (CO2). The breathing reflex is triggered by CO2 concentration in the blood, not by the oxygen concentration, therefore even a small buildup of CO2 in the inhaled gas quickly becomes intolerable; if a person tries to directly rebreathe their exhaled breathing gas, they will soon feel an acute sense of suffocation, therefore rebreathers must chemically remove the CO2 in a component known as a carbon dioxide scrubber. By adding sufficient oxygen to compensate for the metabolic usage, removing the carbon dioxide, and rebreathing the gas, most of the volume is conserved. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「rebreather」の詳細全文を読む スポンサード リンク
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