Argox is the informal name for a

scuba diving Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface air supply. The name "scuba", an acronym for "Self-Contained Underwater Breathing Apparatus", was coined by Chris ...

breathing gas A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed h ...

consisting of

argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...

and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

. 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 Nitrox refers to any gas mixture composed (excepting trace gases) of nitrogen and oxygen. This includes atmospheric air, which is approximately 78% nitrogen, 21% oxygen, and 1% other gases, primarily argon. In the usual application, underwater ...

, 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.

Possible uses

Human exploration of Mars

Argox, or half-argox/half-

is a possible oxygen mixture for human exploration of

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atm ...

due to the relative abundance of Argon in the

Martian atmosphere The atmosphere of Mars is the layer of gases surrounding Mars. It is primarily composed of carbon dioxide (95%), molecular nitrogen (2.8%), and argon (2%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen, and no ...

. The Martian atmosphere is composed of approximately: 95% , 1.9%

, 1.9%

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at sevent ...

. While it is possible for humans to breathe pure oxygen, a pure oxygen atmosphere was implicated in the

Apollo 1 Apollo 1, initially designated AS-204, was intended to be the first crewed mission of the Apollo program, the American undertaking to land the first man on the Moon. It was planned to launch on February 21, 1967, as the first low Earth orbit ...

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 A carbon dioxide scrubber is a piece of equipment that absorbs carbon dioxide (CO2). It is used to treat exhaust gases from industrial plants or from exhaled air in life support systems such as rebreathers or in spacecraft, submersible craft or ...

filters the astronauts' air, the other is vented to the Mars atmosphere.

Drysuit inflation

The

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table ...

in the 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

cylinder A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infi ...

, dedicated to drysuit inflation, containing argon. A second class of divers at intermediate depths of which do not require trimix sometimes carry a

pony bottle A pony bottle is a small diving cylinder which is fitted with an independent regulator, and carried by a scuba diver as an extension to the scuba set. In an emergency, such as depletion of the diver's main air supply, it can be used as an alte ...

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. Some 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

narcotic The term narcotic (, from ancient Greek ναρκῶ ''narkō'', "to make numb") originally referred medically to any psychoactive compound with numbing or paralyzing properties. In the United States, it has since become associated with opiates ...

gas, meaning that it could only be breathed at comparatively shallow depths above . However, in an emergency this is enough for adequate decompression time at typical decompression levels between and , 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

, 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 In underwater diving activities such as saturation diving, technical diving and nitrox diving, the maximum operating depth (MOD) of a breathing gas is the depth below which the partial pressure of oxygen (pO2) of the gas mix exceeds an acceptable l ...

for air owing to narcosis is taken to be , then for 20% argox (20% O₂, 80% Ar) it would be .

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 gas There are several categories of decompression equipment used to help divers decompress, which is the process required to allow divers to return to the surface safely after spending time underwater at higher ambient pressures. Decompression o ...

, instead of nitrox. 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. 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. 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. 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.

Notes

References

External links

* Why Argon? Diving applications
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. Breathing gases