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The absolute pressure on an ambient pressure diver is the sum of the local atmospheric pressure and hydrostatic pressure. [ 5 ] [ 6 ] Hydrostatic pressure is the component of ambient pressure due to the weight of the water column above the depth, and is commonly described in terms of metres or feet of sea water .
The pressure of seawater at a depth of 33 feet equals one atmosphere. The absolute pressure at 33 feet depth in sea water is the sum of atmospheric and hydrostatic pressure for that depth, and is 66 fsw, or two atmospheres absolute. For every additional 33 feet of depth, another atmosphere of pressure accumulates. [6]
In scuba diving, bar is also the most widely used unit to express pressure, e.g. 200 bar being a full standard scuba tank, and depth increments of 10 metre of seawater being equivalent to 1 bar of pressure. Many engineers worldwide use the bar as a unit of pressure because, in much of their work, using pascals would involve using very large ...
The formula simply divides the absolute partial pressure of oxygen which can be tolerated (expressed in atm or bar) by the fraction of oxygen in the breathing gas, to calculate the absolute pressure at which the mix can be breathed. (for example, 50% nitrox can be breathed at twice the pressure of 100% oxygen, so divide by 0.5, etc.).
critical pressure. See: Scuba gas planning#Critical pressures. Cylinder gas pressure which determines a safe limit to an underwater activity on scuba, such as start of ascent or turnaround during a penetration. critical ratio hypothesis. See: Decompression theory#Critical ratio hypothesis
Technology to display gas pressure in a scuba cylinder on a dive computer, and in some cases make further use of the information for gas management. gas fraction. Main article: Gas composition. The fraction by molecular count, volume or pressure (they all come to the same thing) of a specific gas in a mixture of gases. gas matching
Underwater diving is practiced as part of an occupation, or for recreation, where the practitioner submerges below the surface of the water or other liquid for a period which may range between seconds to the order of a day at a time, either exposed to the ambient pressure or isolated by a pressure resistant suit, to interact with the underwater ...
See Scuba gas planning#Reserve pressure and Surface-supplied diving#High-pressure reserve gas. Gas which is not intended to be used during the dive, and is reserved for contingencies. reserve valve. See: Scuba cylinder valve# Cylinder valve with a lever operated bypass valve to release the gas below reserve pressure. [62] residual gas