Editing Scuba set (section)

===Rebreathers===
[[Image:Inspiration front.JPg|thumbnail|An Inspiration rebreather seen from the front]]
{{Main|Diving rebreather}}

A rebreather recirculates the breathing gas already used by the diver after replacing oxygen used by the diver and removing the carbon dioxide metabolic product. Rebreather diving is used by recreational, military and scientific divers where it can have advantages over open-circuit scuba. Since 80% or more of the oxygen remains in normal exhaled gas, and is thus wasted, rebreathers use gas very economically, making longer dives possible and special mixes cheaper to use at the cost of more complicated technology and more possible failure points. More stringent and specific training and greater experience is required to compensate for the higher risk involved. The rebreather's economic use of gas, typically {{convert|1.6|L|cuft|sigfig=1}} of oxygen per minute, allows dives of much longer duration for an equivalent gas supply than is possible with open-circuit equipment where gas consumption may be ten times higher.<ref name="Parrish and Pyle 2001" />

There are two main variants of rebreather&nbsp;– semi-closed circuit rebreathers, and fully closed circuit rebreathers, which include the subvariant of oxygen rebreathers. Oxygen rebreathers have a [[maximum operating depth|maximum safe operating depth]] of around {{convert|6|m|ft}}, but several types of fully closed circuit rebreathers, when using a [[helium]]-based diluent, can be used deeper than {{convert|100|m|ft}}. The main limiting factors on rebreathers are the duration of the carbon dioxide scrubber, which is generally at least 3 hours, increased work of breathing at depth, reliability of gas mixture control, and the requirement to be able to safely bail out at any point of the dive.<ref name="Heine 2017" />

Rebreathers are generally used for scuba applications, but are also occasionally used for [[bailout system]]s or [[gas extender]]s for surface supplied diving.<ref>{{Cite web |last=dmod85 |date=2023-11-29 |title=43364 U.S. Navy Scuba Diving Mark VI Semi Closed Circuit Apparatus Training Film |url=https://stock.periscopefilm.com/43364-u-s-navy-scuba-diving-mark-vi-semi-closed-circuit-apparatus-training-film/ |access-date=2024-07-29 |website=PeriscopeFilm - Stock Footage }}</ref>

The possible endurance of a rebreather dive is longer than an open-circuit dive, for similar weight and bulk of the set, if the set is bigger than the practical lower limit for rebreather size,<ref name="shreeves2006" /> and a rebreather can be more economical when used with expensive gas mixes such as [[heliox]] and [[trimix (breathing gas)|trimix]],<ref name="shreeves2006" /> but this may require a lot of diving before the break-even point is reached, due to the high initial and running costs of most rebreathers, and this point will be reached sooner for deep dives where the gas saving is more pronounced.<ref name="Parrish and Pyle 2001" />