What Gases Are in a SCUBA Tank?
Most recreational SCUBA diving is done with air that is compressed, but otherwise regular. However, commercial diving and wreck diving take people to deep environments and high pressure, where regular air can be limiting and even dangerous. These dives are greatly improved through the use of special gas mixes.
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Compressed Air
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Most of the time, a SCUBA air cylinder is filled with compressed air. This is identical to ordinary air: 78 percent nitrogen, 21 percent oxygen, 1 percent other gases.
Nitrox
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To help counter the effects of nitrogen narcosis and decompression sickness on deep dives, the most popular special gas mix is Nitrox. Oxygen is boosted to between 32 and 36 percent, with a corresponding decrease in the proportion of nitrogen.
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Trimix
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For demanding deep dives, a gas cocktail called Trimix is used. This is a mixture of helium, oxygen and nitrogen, with the exact mixture depending on what is desired.
Helium in Trimix
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A greater proportion of helium in Trimix minimizes the effects of nitrogen narcosis, decompression sickness, oxygen toxicity and breathing resistance. However, high helium proportions introduces the problem of hyperbaric arthralgia.
Oxygen in Trimix
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Divers need oxygen for respiration, but the proportion of oxygen in the Trimix imposes a maximum depth limit on the dive. Lowering the amount of oxygen reduces the dangers of oxygen toxicity, and therefore increases maximum dive depth.
Nitrogen in Trimix
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Keeping a little nitrogen in Trimix prevents high pressure nervous syndrome.
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