Enriched Air Nitrox Totally Explained

Everything about Nitrox totally explained

Nitrox refers to any gas mixture composed (excluding trace gases) of nitrogen and oxygen; this includes normal air which is approximately 78% nitrogen and 21% oxygen, with around 1% inert gases, primarily argon. However, in SCUBA diving, nitrox is normally differentiated and handled differently from air. There has, however, been some suggestion that post dive fatigue is due to sub-clinical decompression sickness (DCS) (for example micro bubbles in the blood insufficient to cause symptoms of DCS); the fact that the study mentioned was conducted in a dry chamber with an ideal decompression profile may have been sufficient to reduce sub-clinical DCS and prevent fatigue in both nitrox and air divers.
Further studies with a number of different dive profiles, and also different levels of exertion, would be necessary to fully investigate this issue. For example, there's much better scientific evidence that breathing high-oxygen gases increase exercise tolerance, during aerobic exertion. Though even moderate exertion while breathing from the regulator is a relatively uncommon occurrence in scuba, as divers usually try to minimize it in order to conserve gas, episodes of exertion while regulator-breathing do occasionally occur in sport diving. Examples are surface-swimming a distance to a boat or beach after surfacing, where residual "safety" cylinder gas is often used freely, since the remainder will be wasted anyway when the dive is completed. It is possible that these so-far un-studied situations have contributed to some of the positive reputation of nitrox.

Naming

Nitrox is known by many names: Enhanced Air Nitrox, Oxygen Enriched Air, Nitrox, EANx or Safe Air. The name "nitrox" is sometimes capitalized in English; in this article the uncapitalized convention will be used except when specific mixtures are referred to (such as Nitrox32).
   In its early days of introduction to non-technical divers, nitrox has occasionally also been known by detractors by less complimentary terms, such as "devil gas" or "voodoo gas" (a term now sometimes used with pride).
   Although "nitrox" usually refers to a mixture of nitrogen and oxygen with more than 21% oxygen, it can refer to mixtures that are leaner in oxygen than air.
   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., CMAS, SSI and NAUI train their divers to personally check the oxygen percentage content of each nitrox cylinder before every dive. If the oxygen percentage is 1% or more higher than the value written on the cylinder by the gas blender, the scuba diver must either recalculate his or her bottom times with the new mix, or else abort the dive to remain safe and avoid oxygen toxicity or decompression sickness. Under IANTD and ANDI (External Link

) rules for use of nitrox, which are followed by most dive resorts around the world, filled nitrox cylinders are signed out personally in a gas blender log book, which contains, for each cylinder and fill, the cylinder number, the measured oxygen percent composition, the signature of the receiving diver (who should have personally measured the oxygen percent with an instrument at the fill-shop), and finally a calculation of the maximum operating depth for that fill/cylinder. All of these steps minimize danger but increase complexity of operations (for example, personalized cylinders for each diver must generally be kept track of on dive boats with nitrox, which isn't the case with generic compressed air cylinders).

Fire and or toxic cylinder contamination from oxygen reactions

Diving cylinders are usually filled with nitrox by a gas blending technique such as partial pressure blending or premix decanting (in which a nitrox mix is supplied to the filler in pressurized larger cylinders). A few facilities have begun to fill cylinders with air which has been enriched with oxygen by a pre-mixing process, so that it's pressurized as nitrox for the first time in the diving cylinder. The pre-mixing is accomplished either by a membrane system which removes nitrogen from the air during compression or by a 'stick' blending technique where pure oxygen is mixed with air in a baffled chamber attached to the compressor intake.
   With the use of pure oxygen during "partial pressure blending" (where pure oxygen is added to the nearly empty dive cylinder to 300-500 p.s.i. (20-35 bar), from a large pure oxygen cylinder before air is added, by compressor) there's an especially increased risk of fire. Partial blending using pure oxygen is often used to provide nitrox for multiple dives on live-aboard dive boats, but it's also used in some smaller diver shops.
   However, any gas which contains a significantly larger percentage of oxygen than air is a fire hazard. Furthermore, such gases can also react with hydrocarbons or incorrect lubricants inside a dive cylinder to produce carbon monoxide, even if a recognized fire doesn't happen. At present, there's some discussion over whether or not mixtures of gas which contain less than 40% oxygen may sometimes be exempt from oxygen clean standards. Some of the controversy comes from a single U.S. regulation intended for commercial divers (not recreational divers) years ago. However, the U.S. Compressed Gas Association (CGA) and two international nitrox teaching agencies (IANTD and ANDI) now support the standard that any gas containing more than 23.5% oxygen should be treated as nitrox (which is to say, no differently from pure oxygen) for purposes of oxygen cleanliness and oxygen compatibility (for example, oxygen "servicability"). However, the largest training agency - PADI - is still teaching that pre-mixed nitrox (for example nitrox which is mixed before being put into the cylinder) below 40% oxygen doesn't require a specially cleaned cylinder or other equipment.
   In 1970, Dr. Morgan Wells, who was the first director of the National Oceanographic and Atmospheric Administration (NOAA) Diving Center, began instituting diving procedures for oxygen-enriched air. He also developed a process for mixing oxygen and air which he called a continuous blending system. For many years Dr. Wells' invention was the only practical alternative to partial pressure blending. In 1979 NOAA published Wells' procedures for the scientific use of Nitrox in the NOAA Diving Manual., it was PADI's endorsement that put nitrox over the top as a standard sport diving "option." (External Link

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Nitrox in nature

Sometimes in the geologic past the Earth's atmosphere contained much more than 20% oxygen: for example up to 35% in the Upper Carboniferous. This let animals absorb oxygen much easier and influenced evolution.

Further Information

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