Did you know you have been breathing a form of Nitrox all of your life? Simply stated, Nitrox is any combination of oxygen and nitrogen. So, since the air we breath is approximately 21% oxygen and 79% nitrogen, it is a Nitrox blend. We could call this Natural Nitrox or Normoxic Nitrox. However, the use of this natural Nitrox was covered in your Open Water Diver course. In this course, our focus is using “Enriched Air Nitrox” (abbreviated EANx, where the x designates the oxygen percentage in the


Therefore, looking at our basic definition, Enriched Air Nitrox is a breathing gas blend with the oxygen content of the mixture higher than 21%. The traditional Nitrox blends are EAN 32, 32% oxygen, and EAN 36, 36% oxygen. As an IANTD Nitrox Diver, you will be certified to use oxygen/nitrogen mixtures from 21% to 40% oxygen.

Of course, the big question in your mind is probably “why?” Why do I want to use Nitrox? Why is it different to use than air? Why do I have to take an additional course to use it? The answers to these questions will be covered in more detail later in this manual. Suffice it to say that your body will appreciate the use of Nitrox, and your dive partner will appreciate the added time you both can spend underwater.

In the first instance, your body will appreciate the use of Nitrox because, by increasing the oxygen content of the mixture. Observing Dalton’s Law, you automatically lower the nitrogen content. This, in turn, means that you are not exposing your tissues to as much nitrogen. Also, if you continue to use your air computer or the air tables, you are introducing more safety into your dives.

Secondly, the dive tables and computer algorythms are models used to calculate the amount of nitrogen being added to the body tissues. By lowering the nitrogen levels in the breathing gas, you are effectively adding less nitrogen to the tissues. Your body will “feel” as though it is diving shallower than you really are. This process is explored later in the Planning Nitrox Dives section.

However, this equivalent nitrogen concept allows you to stay underwater longer.

So, if Nitrox is so wonderful, why do divers not use it all of the time? Because, with the benefits, there are some trade-offs. Remember that we mentioned that, traditionally, there are two mixtures? This indicates that there are some decisions to make when selecting Nitrox blends. As you will discover in later chapters, all dives require some choices, and using Nitrox is no different. The depth of your dive, the type of diving, and the equipment you will be using all affect the gas mixture you select.