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{{short description|Gas mixture occasionally used by scuba divers for dry-suit inflation}}
'''Argox''' is the informal name for a [[scuba diving]] [[breathing gas]] consisting of [[argon]] and [[oxygen]]. <!-- Since ''argon'' is not capitalized, in theory ''argox'' should not be capitalized either. --> Occasionally the term ''argonox'' has been used to mean the same mix. The blend may consist of varying fractions of argon and oxygen, depending on its intended use. The mixture is made with the same gas blending techniques used to make [[nitrox]], except that for argox, the argon is added to the initial pure oxygen partial-fill, instead of air.
Argox is essentially a theoretical diving gas, being rarely, if ever, used, and usually thought to have no practical applications where its benefits outweigh its drawbacks.{{Citation needed|date=September 2008}}
==Possible uses==
===Human exploration of Mars===
Argox, or half-argox/half-[[nitrox]] is a possible oxygen mixture for human exploration of [[Mars]] due to the relative abundance of argon in the [[Atmosphere of Mars|Martian atmosphere]].  The Martian atmosphere is composed of approximately: 95% {{CO2|link=yes}}, 1.9% [[argon]], 1.9% [[nitrogen]]. While it is possible for humans to breathe pure oxygen, a pure oxygen atmosphere was implicated in the [[Apollo 1]] fire. As such, Mars habitats may have a need for additional gases. One possibility is to take nitrogen and argon from the atmosphere of Mars; however, they are hard to separate from each other. As a result, a Mars habitat may use 40% argon, 40% nitrogen, and 20% oxygen. Another concept for breathing air is to use re-usable amine bead carbon dioxide scrubbers. While one [[carbon dioxide scrubber]] filters the astronauts' air, the other is vented to the Mars atmosphere.<ref>"The Caves of Mars - Martian Air Breathing Mice". highmars.org. Archived from the original on 24 July 2007. Retrieved 12 June 2015</ref><ref>{{cite journal |last1=Courtland |first1=Rachel |title=Suiting Up for the Red Planet |journal=IEEE Spectrum |date=30 September 2015 |volume=52 |issue=10 |pages=36–38 |doi=10.1109/MSPEC.2015.7274192 |s2cid=46224902 |url=https://spectrum.ieee.org/suiting-up-for-the-red-planet |access-date=9 January 2019}}</ref>
===Drysuit inflation===
The [[helium]] in the breathing gas [[Trimix (breathing gas)|trimix]], which is used to avoid [[nitrogen narcosis]] on deep dives, gives the gas a high thermal conductivity compared with air, making it inappropriate for drysuit inflation. Divers breathing trimix with drysuits usually inflate their drysuits with their decompression gas (usually nitrox or oxygen). A few carry yet another small [[Diving cylinder|cylinder]], dedicated to drysuit inflation, containing argon.<ref>{{cite journal |author=Nuckols, Marshall L |author2=Giblo, J |author3=Wood-Putnam, JL |title=Thermal characteristics of diving garments when using argon as a suit inflation gas (abstract) |journal=Undersea and Hyperbaric Medicine |year=2008 |volume=35 |issue=4 |url=http://archive.rubicon-foundation.org/7789 |access-date=2008-10-24 |archive-url=https://web.archive.org/web/20090412110050/http://archive.rubicon-foundation.org/7789 |archive-date=2009-04-12 |url-status=usurped }}</ref>
A second class of divers at intermediate depths of {{convert|30|-|45|m|ft|-1}} which do not require trimix sometimes carry a [[pony bottle]] for emergencies, as is taught in many deep diving courses. Such second bottles are often 3 litres, and may be mounted in various ways from tank bracket to sling mounting. This second bottle can be used for argox, if a drysuit is used.{{Original research inline|date=May 2016}}
Some{{who|date=May 2016}} argue that an argox blend with oxygen content similar to that of air could be used as a suit inflation gas in place of pure argon, as such a blend would only have a slightly higher thermal conductivity than pure argon, and unlike pure argon, would be breathable in an emergency. However, there are many problems with the use of suit inflation gas as an emergency breathing gas. Argon is a very [[Nitrogen narcosis|narcotic]] gas, meaning that it could only be breathed at comparatively shallow depths above {{convert|20|m|ft}}. However, in an emergency this is enough for adequate decompression time at typical decompression levels between {{convert|3|m|ft|0}} and {{convert|9|m|ft}}, and would save a diver from a direct ascent. The small size of typical very small suit inflation cylinders mean that their contents would quickly be exhausted if breathed, but this is not so of larger ponies.
The thermal conductivity of argon is 68% of that of air or [[nitrox]], hence its use in drysuit inflation. Using argox 20% would slightly degrade this to 74% of that of air.
Argon is far more narcotic (about 2.3 times more) than the cheaper and more readily available nitrogen at depth, so it loses out to nitrogen in all roles as a primary breathing gas. If the [[maximum operating depth]] for air owing to narcosis is taken to be {{convert|40|m|ft}}, then for 20% argox (20% O<sub>2</sub>, 80% Ar) it would be {{convert|14.5|m|ft}}.{{efn|1=Assuming oxygen, nitrogen and air all have roughly equal narcotic potential, and argon is 2.3 times that, the pressure (P) at which the narcotic potential of 20% argox is the same as air at 5 bar (i.e. 40 metres) can be found from P x (0.2 + (0.8 x 2.3)) = 5. That gives P=2.45 bar, which corresponds to 14.5 metres.}}
===Decompression gas===
It has been theorised on the basis of the theory of [[isobaric counterdiffusion]] that argon, because of its higher molecular mass compared with nitrogen (40 vs. 28 '''u'''), may cause less inert gas on-loading, if used as a [[Decompression stop|decompression gas]], instead of nitrox.<ref>{{cite journal |vauthors=D'Aoust BG, Stayton L, Smith LS |title=Separation of basic parameters of decompression using fingerling salmon |journal=Undersea Biomed Res |volume=7 |issue=3 |pages=199–209 |date=September 1980 |pmid=7423658 |url=http://archive.rubicon-foundation.org/2869 |archive-url=https://web.archive.org/web/20090423095711/http://archive.rubicon-foundation.org/2869 |url-status=usurped |archive-date=April 23, 2009 |access-date=2008-08-28}}</ref> The MOD of argox mixes containing more than about 47% oxygen are limited by oxygen MOD (assuming 1.5 atm ppO2) rather than by argon narcosis MOD. The maximal MOD for argox mixes occurs at 47% oxygen and 53% argon, and is about 73 fsw (22 m). This depth is the theoretical maximum which can be safely attained with any two-component argon/oxygen mix: a larger fraction of oxygen than about 50% will result in oxygen toxicity before this depth, and a larger fraction of argon than about 50% will result in argon narcosis before this depth. <!-- exercise left for student-- however the calculation of the argon 80% and 53% MOD is OR here also, so we've already busted that one. See TALK-->
However, as argox is more narcotic than nitrogen (causing it to be more dangerous if a decompression mix is accidentally breathed), and because argox is moderately more expensive than nitrox, and mostly because there has been little research done into the actual (vs. theoretical) physiological aspects of breathing argon during decompression, argox is not currently recommended by any professional agency for this purpose.<ref>{{cite journal |vauthors=Rahn H, Rokitka MA |title=Narcotic potency of N<sub>2</sub>, A, and N<sub>2</sub>O evaluated by the physical performance of mouse colonies at simulated depths |journal=Undersea Biomed Res |volume=3 |issue=1 |pages=25–34 |date=March 1976 |pmid=1273982 |url=http://archive.rubicon-foundation.org/2768 |archive-url=https://web.archive.org/web/20090427024327/http://archive.rubicon-foundation.org/2768 |url-status=usurped |archive-date=April 27, 2009 |access-date=2008-08-28}}</ref>
Although there is little research relating to ''divers'' decompressing using argon mixes, there have been scientific studies of ''astronauts'' decompressing using argox.  The provisional results of those studies indicated higher levels of decompression sickness when argox was used, rather than pure oxygen; however, using pure oxygen is not an option for decompression at the pressures for which argox would be used in diving, and no direct comparison of argon to nitrogen was done.<ref name="pmid14692466">{{cite journal |vauthors=Pilmanis Andrew A, Balldin UI, Webb James T, Krause KM |title=Staged decompression to 3.5 psi using argon-oxygen and 100% oxygen breathing mixtures |journal=Aviat Space Environ Med |volume=74 |issue=12 |pages=1243–50 |date=December 2003 |pmid=14692466 |url=http://www.ingentaconnect.com/content/asma/asem/2003/00000074/00000012/art00004 |access-date=2008-08-28}}</ref>  There is also a certain amount of anecdotal evidence within the diving community that informal experimentation with decompression on argon mixtures has resulted in a high incidence of decompression sickness, but no formal studies.<ref>{{cite web|url=http://www.scubaboard.com/forums/5136597-post48.html|title=Accelerated decompression on an argon mix?|author=Scubaboard.com|date=2010-03-25|access-date=2011-02-02}}</ref>
==See also==
*{{annotated link|Heliox}}
*{{annotated link|Hydreliox}}
*{{annotated link|Hydrox (breathing gas)|Hydrox}}
*{{annotated link|Nitrox}}
*{{annotated link|Trimix (breathing gas)|Trimix}}
== Notes ==
{{notelist}}
== References ==
{{Reflist}}
== External links ==
* Why Argon? Diving applications: [http://www.decompression.org/maiken/Why_Argon.htm Why Argon?]
* {{cite web|url=http://www.techdiver.ws/exotic_gases.shtml |author=Tech Diver |title=Exotic Gases |access-date=2008-08-28 |archive-url=https://web.archive.org/web/20080914174633/http://www.techdiver.ws/exotic_gases.shtml |archive-date=14 September 2008 |url-status=dead }} - A discussion of various rarely used and theoretical diving gases.
[[Category:Breathing gases]]