What is Enriched Air Nitrox?

You may have spotted the telltale green and yellow SCUBA cylinder stickers that signal somebody is diving with enriched air nitrox, also called oxygen enriched air, enriched air, EAN, EANx, NX or just plain "nitrox" for short. It’s been used in recreational and technical diving for decades, and every major training agency has a training program for learning to safely dive the gas, but what is enriched air nitrox? lets find out!

What is the composition of the air we breath?
The air that we breath is made up 78.08% Nitrogen, 20.95% Oxygen, 0.93% Argon, 0.04% Carbon Dioxide, 0.018% Neon, plus other trace gases including Helium, Methane, Krypton, Hydrogen, Nitros Oxide, Carbon Monoxide and Zenon.

With regards to SCUBA diving we simplify the above and define "air" as simply being made up of 79% Nitrogen and 21% Oxygen (easier to remember huh?). When we learn to SCUBA dive, this is the gas we breath. Many divers stick to using normal air but there are other gases that can be used, one being Enriched Air Nitrox.

What is Enriched Air Nitrox?
In recreational diving terms, enriched air nitrox (EANx) refers to any nitrogen/oxygen gas mixture with more than the 21% oxygen found in normal air. For example, enriched air nitrox 32% contains 32% oxygen and an enriched air nitrox 36% contains 36% oxygen. 

By increasing the amount (%) of oxygen in the breathing gas we reduce the amount (%) of nitrogen in the gas. This is a good thing as we need oxygen to sustain life, our bodies metabolise the oxygen keeping us alive, awake and in good working order. 

The nitrogen however is an inert gas and our bodies do not and can not use it, we therefor breath it in, absorb it into our tissues and after a dive we eventually "off gas" breathing it back out again. It's this "off gassing" that can potentially cause decompression sickness when ascending too fast from a dive and failing to make required decompression stops. 

Therefor enriched air nitrox can be a safer gas to use when correctly trained.

What are the benefits of using enriched air nitrox?

• Longer bottom times/more dive time: 
  The reduced percentage of nitrogen in enriched air nitrox allows divers to extend their no decompression limits (or dive time) by reducing the amount of nitrogen absorbed. 
• Shorter surface intervals between dives:
  A diver who uses enriched air nitrox absorbs less nitrogen for a given depth and dive time than a diver using normal air. This means that the enriched air nitrox diver does not have as much nitrogen to “off-gas” during a surface interval, which can shorten the required surface interval significantly.
• Longer Repetitive Dive Times:
  Enriched air nitrox becomes especially useful for divers who complete more than one dive per a day and is most commonly used on boat diving adventures where it is common to do multiple dives per day.
  A diver using enriched air nitrox will have a longer allowable bottom time on a repetitive dive than a diver using normal air because the diver using enriched air nitrox has absorbed less nitrogen.
• Less post dive fatigue:
  Although not scientifically proved and a possible placebo effect, many divers claim to feel less tired after diving on enriched air nitrox than after a similar dive on normal air. By reducing a diver’s nitrogen absorption, enriched air nitrox may also reduce a diver’s post-dive exhaustion. 
• Safety benefits:
  All trained and certified SCUBA divers understand the sport’s most-common risk, which is decompression sickness (The Bends).
  Decompression sickness is a condition that results when too rapid decompression causes nitrogen bubbles to form in the tissues of the body and can cause pain in the muscles and joints, cramp, numbness, nausea, and paralysis.. Breathing air which is enriched with more oxygen reduces the amount of nitrogen and therefore reduces the risk. Diving on enriched air nitrox can increase safety margins therefor a dive on enriched air nitrox will be much safer than the same dive profile on normal air.