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A store of oxygen, usually as compressed gas in a high pressure cylinder, but sometimes as liquid oxygen, that feeds gaseous oxygen into the ambient pressure breathing volume, either continuously, or when the user operates the oxygen addition valve, or via a demand valve in an oxygen rebreather, when the volume of gas in the breathing circuit ...
Underwater breathing apparatus can be classified as open circuit, semi-closed circuit, (including gas extenders) or closed circuit (including reclaim systems), based on whether any of the exhaled gas is recycled, and as self-contained or remotely supplied (usually surface-supplied, but also possibly from a lock-out submersible or an underwater habitat), depending on where the source of the ...
[3] [4] The inert gas and unused oxygen is kept for reuse, and the rebreather adds gas to replace the oxygen that was consumed, and removes the carbon dioxide. [3] Thus, the gas recirculated in the rebreather remains breathable and supports life and the diver needs only to carry a fraction of the gas that would be needed for an open-circuit system.
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 [10] The oxygen metabolised is generally about 4% to 5% of the inspired volume at normal atmospheric pressure, or ...
A sodium chlorate oxygen candle in the base of the unit generates oxygen on start-up as the canister has to reach a high internal temperature before it will start generating oxygen. The circulation of exhaled air containing carbon dioxide through the canister starts the chemical process, usually taking less than five minutes to reach a stable ...
non-rebreather mask A non-rebreather mask (NRB) is a device used to deliver supplemental oxygen to a spontaneously breathing person. An NRB allows the delivery of relatively high concentrations of oxygen while using a constant flow rate, with relatively low waste, by accumulating the oxygen flow during exhalation in a soft bag, to be inhaled at ...
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Oxygen rebreathers can also use less reactive scrubber absorbent which only removes carbon dioxide, but must then have an alternative supply of oxygen, usually compressed gas from a high pressure cylinder. Submarine escape sets had a mouthpiece, so the user had to also wear a noseclip to prevent breathing water through the nose. The endurance ...