Editing Nitrox (section)

==Choice of mixture==
{{See also|Scuba gas planning}}
[[File:Decompression Dive-Preparation.JPG|300px|thumb|left|[[Technical diving|Technical divers]] preparing for a mixed-gas [[Decompression schedule|decompression dive]] in [[Bohol]], [[Philippines]]. Note the [[backplate and wing]] setup with [[Side mount diving|side mounted]] [[Diving cylinder#Purposes of diving cylinders|stage tanks]] containing EAN50 (left side) and pure [[oxygen]] (right side).]]
The two most common [[recreational diving]] nitrox mixes contain 32% and 36% oxygen, which have [[maximum operating depth]]s (MODs) of {{convert|34|m|ft}} and {{convert|29|m|ft}} respectively when limited to a maximum partial pressure of oxygen of {{convert|1.4|bar|abbr=on|lk=in}}. Divers may calculate an [[equivalent air depth]] to determine their decompression requirements or may use nitrox [[Dive tables|tables]] or a nitrox-capable [[dive computer]].<ref name=noaa/><ref name=dan/><ref name="Logan1961" /><ref name="Berghage and McCraken 1979" />

Nitrox with more than 40% oxygen is uncommon within recreational diving. There are two main reasons for this: the first is that all pieces of [[diving equipment]] that come into contact with mixes containing higher proportions of oxygen, particularly at high pressure, need special cleaning and servicing to reduce the risk of [[fire]].<ref name=noaa/><ref name=dan/> The second reason is that richer mixes extend the time the diver can stay underwater without needing [[decompression stop]]s far further than the duration permitted by the capacity of typical [[diving cylinder]]s. For example, based on the PADI nitrox recommendations, the maximum operating depth for EAN45 would be {{convert|21|m|ft}} and the maximum dive time available at this depth even with EAN36 is nearly 1 hour 15 minutes: a diver with a breathing rate of 20 litres per minute using twin 10-litre, 230-bar (about double 85 cu. ft.) cylinders would have completely emptied the cylinders after 1 hour 14 minutes at this depth.

Use of nitrox mixtures containing 50% to 80% oxygen is common in [[technical diving]] as decompression gas, which by virtue of its lower partial pressure of inert gases such as nitrogen and helium, allows for more efficient (faster) elimination of these gases from the tissues than leaner oxygen mixtures.

In deep [[Scuba set#Types|open circuit]] technical diving, where [[Breathing gas#Oxygen|hypoxic]] gases are breathed during the bottom portion of the dive, a Nitrox mix with 50% or less oxygen called a "travel mix" is sometimes breathed during the beginning of the descent in order to avoid [[Hypoxia (medical)|hypoxia]]. Normally, however, the most oxygen-lean of the diver's decompression gases would be used for this purpose, since descent time spent reaching a depth where bottom mix is no longer hypoxic is normally small, and the distance between this depth and the MOD of any nitrox decompression gas is likely to be very short, if it occurs at all.

===Best mix===
The composition of a nitrox mix can be optimized for a given planned dive profile. This is termed "Best mix", for the dive, and provides the maximum no-decompression time compatible with acceptable oxygen exposure. An acceptable maximum partial pressure of oxygen is selected based on depth and planned bottom time, and this value is used to calculate the oxygen content of the best mix for the dive:<ref name="Becker" />

:<math>f_{\text{O}_2,\text{max}} = \frac{p_{\text{O}_2,\text{max}}}{p} = \frac{\text{Maximum acceptable partial pressure of oxygen}}{\text{Maximum ambient pressure of the dive}}</math>