Editing Scuba set (section)

===Breathing gases for scuba===
{{further|Breathing gas#Breathing gases for diving and other hyperbaric use}}
Until [[Nitrox]], which contains more oxygen than air, was widely accepted in the late 1990s,<ref name="Lang 2000" /> almost all recreational scuba used simple compressed and filtered air. Other gas mixtures, typically used for deeper dives by [[Technical diving|technical]] divers, may substitute helium for some or all of the nitrogen (called [[Trimix (breathing gas)|Trimix]], or [[Heliox]] if there is no nitrogen), or use lower proportions of oxygen than air. In these situations divers often carry additional scuba sets, called stages, with gas mixtures with higher levels of oxygen that are primarily used to reduce decompression time in staged [[Decompression (diving)|decompression diving]].<ref name="Jablonski 2006" /> These gas mixes allow longer dives, better management of the risks of [[decompression sickness]], [[oxygen toxicity]] or lack of oxygen ([[Hypoxia (medical)|hypoxia]]), and the severity of [[nitrogen narcosis]]. Closed circuit scuba sets ([[Diving rebreather|rebreathers]]) provide a gas mix that is controlled to optimise the mix for the actual depth at the time.