Editing Scuba set (section)

==Gas endurance of a scuba set==
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{{Main|Scuba gas planning}}
{{see also|Diving cylinder#Gas calculations}}

Gas endurance of a scuba set is the time that the gas supply will last during a dive. This is influenced by the type of scuba set and the circumstances in which it is used.

===Open circuit===
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The gas endurance of open-circuit-demand scuba depends on factors such as the capacity (volume of gas) in the [[diving cylinder]], the depth of the dive and the breathing rate of the diver, which is dependent on exertion, fitness, physical size of the diver, state of mind, and experience, among other factors.  New divers frequently consume all the air in a standard "aluminum 80" cylinder in 30 minutes or less on a typical dive, while experienced divers frequently dive for 60 to 70 minutes at the same average depth, using the same capacity cylinder, as they have learned more efficient diving techniques.{{citation needed|date=August 2016}}

An open-circuit diver whose breathing rate at the surface (atmospheric pressure) is 15 litres per minute will consume 3 × 15 = 45 litres of gas per minute at 20 metres. [(20 m/10 m per bar) + 1 bar atmospheric pressure] × 15 L/min = 45 L/min).  If an 11-litre cylinder filled to 200 bar is to be used until there is a reserve of 17% there is (83% × 200 × 11) = 1826 litres available. At 45 L/min the dive at depth will be a maximum of 40.5 minutes (1826/45). These depths and times are typical of experienced recreational divers leisurely exploring a [[coral reef]] using standard 200 bar "aluminum 80" cylinders as may be rented from a commercial recreational diving operation in most [[tropical]] island or coastal resorts.{{citation needed|date=August 2016}}

===Semi-closed rebreather===
A semi-closed circuit rebreather may have an endurance of about 3 to 10 times that of the equivalent open-circuit dive, and is less affected by depth; gas is recycled but fresh gas must be constantly injected to replace at least the oxygen used, and any excess gas from this must be vented. Although it uses gas more economically, the weight of the rebreather encourages the diver to carry smaller cylinders. Still, most semi-closed systems allow at least twice the duration of average sized open-circuit systems (around two hours) and are often limited by scrubber endurance.{{citation needed|date=December 2016}}

===Closed circuit rebreathers===
An oxygen rebreather diver or a fully closed circuit rebreather diver consumes about 1 litre of oxygen corrected to atmospheric pressure per minute. Except during ascent or descent, the fully closed circuit rebreather that is operating correctly uses very little or no diluent. A diver with a 3-litre oxygen cylinder filled to 200 bar who leaves 25% in reserve will be able to do a 450-minute = 7.5 hour dive (75% × 3 litres × 200 bar × 1 litre per minute = 450 minutes). This endurance is independent of depth. The life of the [[soda lime]] scrubber is likely to be less than this and so will be the limiting factor of the dive.{{citation needed|date=December 2016}}

In practice, dive times for rebreathers are more often influenced by other factors, such as [[hypothermia|water temperature]] and the need for safe ascent (see [[Decompression (diving)]]), and this is generally also true for large-capacity open-circuit sets.{{citation needed|date=December 2016}}