The following should allow anyone who is either unfamiliar with Nitrox, or confused by the terminology, to reach a point where they can follow a discussion on the subject. It may also serve as a starting point for those who wish to learn about Nitrox.

What is Nitrox?

The air we breathe is Nitrox. Air consists primarily of two gases: Nitrogen (79%) and Oxygen (21%), and although some trace gases also make up air, they exist in such small quantities that for practical purposes we can ignore them.

Nitrox is also referred to as "Enriched Air" or air that has been enriched with Oxygen so that it has more than 21% of Oxygen – usually 22% to 40% - blends that are usually used in Recreational No Decompression diving (covered in the PADI Enriched Air Specialty and TDI's Basic Nitrox Course). But really, Nitrox refers to any Nitrogen-Oxygen gas-mix, including blends that have less oxygen than air! For the purpose of Technical Diving, you learn to use Nitrox gas mixes from below 21% (when doing your TDI Advanced Trimix course) to up to 100% (already when doing your TDI Advanced Nitrox course) - although the richer mixes are usually used only for decompression.

Although Enriched Air Nitrox is relatively new to recreational diving, military and research divers have been using it to extend their no decompression limits for over 50 years! In fact, the first recorded Enriched Air mix was recorded by Draeger as early as 1917! The United States Navy and British Royal Navy studied and used Enriched Air in the 1940's and the United States Oceanic and Atmospheric Administration (NOAA) has more than 20 years field experience with Enriched Air used by research divers.

How do you name a Nitrox mix?

To distinguish one blend of Nitrox from another, the diving community uses the abbreviation EANx (for "Enriched Air Nitrox") followed by the Oxygen content percentage.

For Example EANx36 is a Nitrox blend that contains 36% of Oxygen and the balance (64%) of Nitrogen: you would read "EANx36" as "Enriched Air 36" or "Enriched Air Nitrox 36" if saying it aloud.

The most two common blends used in recreational diving are EANx32 and EANx36.

The Advantages Of Nitrox

• You can stay longer underwater. The primary application of Nitrox is that divers use it to extend the no-decompression limit beyond normal air no-decompression limits! As you recall from your Open Water course,Nitrogen dissolves into your body while you are breathing air under pressure. The longer and deeper you dive, the more Nitrogen you absorb. As long as you stay within reasonable limits, when you ascend and surface, your body eliminates the excess Nitrogen through normal respiration without any difficulties. If you exceed reasonable limits, the excess Nitrogen may form bubbles and cause Decompression Sickness (DCS). Dive tables and dive computers help you track time and depth and keep Nitrogen within reasonable limits.Enriched Air replaces some of the Nitrogen you breathe underwater with Oxygen, so that during your dive, you absorb less Nitrogen than you would be breathing normal air. Your body metabolises and otherwise absorbs the extra Oxygen, so that, within the limits of the recreational enriched air diving, it doesn't contribute to bubble formation after a dive. This means that you have longer no decompression limits for each depth than if you do using air. How much longer, depends upon the Enriched Air blend you chose, with more oxygen providing longer no-decompression time.
• You feel less tired after repetitive dives on Nitrox. Well, some might argue that it isn't true, but any instructor who works and completes 3 to 5 dives a day will tell you that they do feel a whole lot better when these are completed using Nitrox. The best way is to try it yourself, but beware that this is only noticeable when completing at least 2 dives in one day – as your body doesn't have to work as hard to flush the excess Nitrogen out of your system, you feel less tired.
• You can have shorter surface intervals between dives. True! The lower level of residual Nitrogen in your system after an Enriched Air Dive, means you can either go back in the water quicker or just use this as a "safety margin" when planning a repetitive dive – this is especially advantageous for older or overweight divers as they tend to retain more Nitrogen than someone who is very fit.

Common Misconceptions

• You do not suffer from Nitrogen Narcosis (Wrong!!!!) Some divers say they experience less narcosis using Enriched Air, but others claim that they've noticed no difference between air and Enriched Air narcosis. Since there have been few, if any, formal objective studies, it is wise to plan your dive accounting for narcosis just as you would using normal air. Although Enriched Air reduces the amount of Nitrogen you breathe underwater, many diving physiologists don't believe that Enriched Air significantly reduces narcosis.
• You use less air. If anything, you will use more! While Enriched Air gives you more no decompression time underwater, you'll probably find that, depending on your depth, your dive is limited by how much Enriched Air you have rather than the decompression limits! Well, that is until you get into the Advanced Nitrox program where at least you have 2 tanks full of Nitrox on your back…!
• Nitrox is only for deep diving. Absolutely not! Actually this is probably the biggest misconception about Enriched Air Nitrox! People have a tendency to think Nitrox is dangerous and is meant to be used by highly trained professional divers and especially divers who want to go deep…! Actually recreational no decompression Enriched Air dives have a maximum limit of 40 meters / 120 feet! The full advantages and benefits of Enriched Air are truly only felt when diving between the depths of 21 and 36 meters or 70 to 110 feet , either on a No Decompression dive, or when Tech Diving as a travel gas or decompression gas!

The Hazards

As mentioned earlier, there is a trade-off - you can't get something for nothing!

• Oxygen Toxicity: Underwater, Oxygen has its own sets of problems, some of which are significantly more hazardous than Nitrogen. As you reduce your Nitrogen exposure, you increase your Oxygen exposure. Much of what you will learn in the PADI Enriched Air course and the TDI Basic Nitrox course deals with keeping your Oxygen exposure within safe limits whilst diving! In fact, Oxygen Toxicity is the most serious of the potential hazards unique to diving on Enriched Air Nitrox and tracking your Oxygen exposure becomes your priority.
• Equipment Considerations: Most of the special procedures you need to dive safely with and handle Enriched Air Nitrox relate to its higher Oxygen content. By itself, Oxygen won't burn or explode, but many substances react with Oxygen and will burn vigorously or explode when in contact with a high amount of Oxygen: any piece of equipment that will come into direct contact with Enriched Air Nitrox, will have to be dedicated solely to diving using Nitrox. Nitrox Cylinders have to be easily visually identifiable – or the consequences could be fatal. Standard Regulators may be used with mixes up to EANx40, depending on the manufacturers recommendations and local diving laws, but any richer mix will require specially serviced and Oxygen cleaned regulators. Other equipment you will learn to use in a Enriched Air Nitrox course are Oxygen Analysers, which enable a diver to personally check the Oxygen content of the tank he is about to dive with – an absolute MUST of diving on Nitrox!
• More Complex Dive Planning: Enriched Air Nitrox dive planning requires a few more planning steps than diving on air, and you will have to use several tables to plan your decompression and Oxygen exposure. Most divers don't find these additional steps too complicated, but the process has more potential for error, and less tolerance for error if you make one. Whatever the circumstances, "Plan your dive and Dive your plan" is always the rule!