Scuba - Self-Contained Underwater Breathing Apparatus 07
Scuba - Self-Contained Underwater Breathing Apparatus 07 : Etymology: (2) Rebreather: Rebreather. Less common are closed circuit (CCR) and semi-closed (SCR) rebreathers, which unlike open-circuit sets that vent off all exhaled gases, process each exhaled breath for re-use by removing the carbon dioxide and replacing the oxygen used by the diver. Rebreathers release little or no gas bubbles into the water, and use much less stored gas volume for an equivalent depth and time because exhaled oxygen is recovered; this has advantages for research, military, photography, and other applications. The first modern rebreather was the MK-19 that was developed at S-Tron by Ralph Osterhout and used the first electronic control system. Rebreathers are more complex and more expensive than open-circuit scuba, and special training and correct maintenance are required for them to be safely used, due to the larger variety of potential failure modes. In a closed-circuit rebreather the oxygen partial pressure in the rebreather is controlled, so it can be increased to a safe continuous maximum, which reduces the inert gas (nitrogen and/or helium) partial pressure in the breathing loop. Minimising the inert gas loading of the diver's tissues for a given dive profile reduces the decompression obligation. This requires continuous monitoring of actual partial pressures with time and for maximum effectiveness requires real-time computer processing by the diver's decompression computer. Decompression can be much reduced compared to fixed ratio gas mixes used in other scuba systems and, as a result, divers can stay down longer or decompress faster. A semi-closed circuit rebreather injects a constant flow of a fixed nitrox mixture into the breathing loop, or changes a fixed percentage of the respired volume, so the partial pressure of oxygen at any time during the dive depends on the diver's oxygen consumption or breathing rate. Planning decompression requirements requires a more conservative approach for a SCR than for a CCR, but decompression computers with a real time oxygen partial pressure input can optimise decompression for these systems
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