Diving with nitrox

The safety increases with Nitrox while diving, similar to the airbag while driving

Nitrox the safe and easy way of Diving

Nitrox? Here is all you need to know

What Is Nitrox?

Nitrox refers to any gas mixture composed (excluding trace gases) of nitrogen and oxygen; this includes normal air which is approximately 78% nitrogen, 21% oxygen, and 1% other gases, primarily argon. However, in scuba diving, nitrox is normally differentiated and handled differently from air. The most common use of nitrox mixtures containing higher than normal levels of oxygen is in scuba, where the reduced percentage of nitrogen is advantageous in reducing nitrogen uptake in the body’s tissues and so extending the possible dive time, and/or reducing the risk of decompression sickness (also known as the bends).


Enriched Air, with an oxygen content above 21%, is mainly used in scuba diving to reduce the proportion of nitrogen in the breathing gas mixture. Reducing the proportion of nitrogen by increasing the proportion of oxygen reduces the risk of decompression sickness for the same dive profile, or allows extended dive times without increasing the need for decompression stops for the same risk. EANx is not a safer gas than compressed air in all respects; although its use can reduce the risk of decompression sickness, it increases the risk of oxygen toxicity and fire, which are further discussed below.

Breathing EANx is not thought to reduce the effects of narcosis, as oxygen seems to have equally narcotic properties under pressure as nitrogen; thus one should not expect a reduction in narcotic effects due only to the use of nitrox. Nonetheless, there are people in the diving community who insist that they feel reduced narcotic effects at depths breathing Enriched Air. This may be due to a dissociation of the subjective and behavioural effects of narcosis. However, it should be noted that because of risks associated with oxygen toxicity, divers tend not to utilize nitrox at greater depths where more pronounced narcosis symptoms are more likely to occur. For a reduction in narcotic effects trimix or heliox, gases which also contain helium, are generally used by divers.

There is anecdotal evidence that the use of nitrox reduces post-dive fatigue, particularly in older and or obese divers; however a double-blind study to test this found no statistically significant reduction in reported fatigue.There was, however, some suggestion that post dive fatigue is due to sub-clinical decompression sickness (DCS) (i.e. 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. In 2008, a study was published using wet divers at the same depth and confirmed that no statistically significant reduction in reported fatigue is seen.

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 is 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 EANx.

Nitox is known by many names: Enriched Air, Oxygen Enriched Air, EANx or Safe Air. Since the word is a compound contraction or coined word and not an acronym, it should not be written in all upper case characters as “NITROX”, but may be initially capitalized when referring to specific mixtures such as Nitrox32, which contains 68% nitrogen and 32% oxygen. When one figure is stated, it refers to the oxygen percentage, not the nitrogen percentage. The original convention, Nitrox68/32 became shortened as the first figure is redundant.

The term “nitrox” was originally used to refer to the breathing gas in a seafloor habitat where the oxygen has to be kept to a lower fraction than in air to avoid long term oxygen toxicity problems. It was later used by Dr Morgan Wells of NOAA for mixtures with an oxygen fraction higher than air, and has become a generic term for binary mixtures of nitrogen and oxygen with any oxygen fraction,[3] and in the context of recreational and technical diving, now usually refers to a mixture of nitrogen and oxygen with more than 21% oxygen. “Enriched Air Nitrox” or “EAN”, and “Oxygen Enriched Air” are used to emphasise richer than air mixtures. In “EANx”, the “x” was original the x of nitrox, but has come to indicate the percentage of oxygen in the mix and is replaced by a number when the percentage is known; for example a 40% oxygen mix is called EAN40. The two most popular blends are EAN32 and EAN36, developed by NOAA for scientific diving, and also named NitroxI and NitroxII, respectively, or Nitrox68/32 and Nitrox64/36.

The term Oxygen Enriched Air (OEN) was accepted by the (American) scientific diving community, but although it is probably the most unambiguous and simply descriptive term yet proposed, it was resisted by the recreational diving community, sometimes in favour of less appropriate terminology.

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).

American Nitrox Divers International (ANDI) uses the term “SafeAir”, but considering the complexities and hazards of mixing, handling, analyzing, and using oxygen enriched air, this name is considered inappropriate by those who consider that it is not inherently “safe”, but merely has decompression advantages.

The constituent gas percentages are what the gas blender aims for, but the final actual mix may vary from the specification, and so a small flow of gas from the cylinder must be measured with an oxygen analyzer, before the cylinder is used underwater.