Scuba gas management

Scuba gas management is the aspect of scuba diving which includes the gas planning, blending, filling, analysing, marking, storage, and transportation of gas cylinders for a dive, the monitoring and switching of breathing gases during a dive, efficient and correct use of the gas, and the provision of emergency gas to another member of the dive team. The primary aim is to ensure that everyone has enough to breathe of a gas suitable for the current depth at all times, and is aware of the gas mixture in use and its effect on decompression obligations, nitrogen narcosis, and oxygen toxicity risk. Some of these functions may be delegated to others, such as the filling of cylinders, or transportation to the dive site, but others are the direct responsibility of the diver using the gas.

Management of breathing gas during the dive is a critical skill to avoid potentially fatal consequences. For the basic case of no-decompression open-water diving, which allows a free emergency ascent, this requires ensuring sufficient gas remains for a safe ascent (plus a contingency reserve) and for the possibility of an assisted ascent, where the diver shares gas with another diver. Gas management becomes more complex when solo diving, decompression diving, penetration diving, or diving with more than one gas mixture.^[1][2] Other necessary knowledge includes awareness of personal and other team members' gas consumption rates under varying conditions, such as at the surface, at varying depths, for different dive task loadings and personal physical effort and mental states. ^{[3]: Sect.3 [4]}

Divers need to be aware of the remaining gas available, so a submersible pressure gauge is fitted to each diving cylinder to indicate the remaining gas pressure, and the cylinder is clearly labelled to indicate the gas mixture. The amount of available gas remaining can be calculated from the cylinder pressure, the cylinder internal volume, and the planned reserve allowance. The time that a diver can dive on the available gas depends on the depth, work load, the fitness of the diver and that the gas is safe to breathe at that depth. Breathing rates can vary considerably, and estimates are largely derived from experience. Conservative estimates are generally used for planning purposes. The divers must turn the dive and start the exit and ascent while there is enough gas to surface safely. This may require the calculation of minimum acceptable pressures for various stages of a dive, known as critical pressures.^[5][1][2]

To limit the risk of equipment malfunctions that could cause a loss of breathing gas, divers maintain their breathing apparatus in good order, assemble it with care and test it before use. This does not entirely eliminate the possibility of a malfunction that could cause a loss of gas, so the requisite skills for dealing with the reasonably foreseeable malfunctions should be learned and maintained, and redundant supplies carried to allow for circumstances of unrecoverable malfunction.^[3][4]