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Scuba Tanks

The most easily identifiable piece of diving equipment is the scuba tank. This is a canister of compressed air that the diver takes down with them so that they can breathe underwater. Combined with a tube and a mouth piece, the scuba tank is the core of any set of diving equipment.

Scuba tanks contain a mixture of compressed oxygen and other gasses. Depending on the type of diving done, the expected amount of bottom time, and the breathing system the mixture of gasses differ. For open circuit breathing systems the typical mixture is nitrogen and oxygen in a ratio of 78% to 22%. This is a safe mixture to use up to a depth of 120 feet below the surface.

For deeper diving, scuba tanks are filled with other mixtures.  Some examples of deep sea diving air mixtures are hydreliox- a mixture of helium, hydrogen, and oxygen; and trimix- which is a nitrogen oxygen mixture with helium added to increase the safe bottom operation of the mix.

The reason for adding helium to regular breathing air is that both nitrogen and oxygen become toxic to the body if ingested at a high enough pressure. As you descend deeper underwater, the air intake system of your diving suit adjusts the pressure of the air to the surrounding water pressure. At a certain concentration oxygen and nitrogen begin causing problems with your body’s nervous and respiratory systems. Adding helium to an air mixture allows a diver to go deeper before hitting the toxicity threshold because there is a lower concentration of both oxygen and nitrogen in each breath.

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