Argox (scuba)

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.

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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

Drysuit inflation

The helium 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 bottle(s) (using nitrox or oxygen-- see technical diving). A few carry yet another small cylinder, dedicated to drysuit inflation, containing argon.

A second class of divers at intermediate depths which do not require Trimix (30-45 m) sometimes carry a pony bottle for emergencies, as is taught in the NAUI Master Diver course, and other deep diving courses. Such second bottles may range in size from 13 to 40 cf, 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 an extremely narcotic gas, meaning that it could only be breathed at comparatively shallow depths (above 65 fsw). However, in an emergency this is enough for adequate decompression time at typical decompression levels (i.e. 30 and 20 fsw), 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 extinguished 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 due to narcosis is taken to be 40 m (about 131 fsw), then for 20% argox (20% O₂, 80% Ar) it would be 11 m or 37 feet.

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 used during as a decompression gas, 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).

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.