Air is a mixture of primarily two gases, approximately 21% oxygen and 79% nitrogen. Nitrogen is the culprit in causing decompression sickness, more commonly know as the “bends”. This fact will be important as we discuss enriched air advantages. Enriched air is the result of adding oxygen to air, raising the level of oxygen in the mixture to between 22% and 99%. However, for recreational purposes enriched air blends range from 22% to 40% oxygen. Nitrox is often referred to as “enriched air”; however there is a difference between the two. Nitrox refers to any nitrogen-oxygen mixture, while enriched air is air that has some oxygen added. Therefore by definition enriched air can only contain greater than 21% oxygen. The two most common blends are 32% oxygen (EANx32) and 36% (EANx36). The abbreviation EAN stands for Enriched Air Nitrox.
The primary advantage of enriched air is to extend the no stop limits beyond the normal no stop limits associated with air. Since enriched air has a lower level of nitrogen than air, you absorb less nitrogen while your body is able to metabolize the extra oxygen, assuming you are diving within recreational enriched air...