Scuba Diving with Enriched Air

 By: James Smi
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 limits. This results in longer no decompression limits while diving on enriched air. The primary disadvantage of diving with enriched air is potential exposure to oxygen toxicity. Oxygen can be toxic based on depth and duration under water, and by increasing the level of oxygen in the gas you breathe, you are constrained by your depth and duration. This is why you must calculate both your no decompression limit due to nitrogen, and your oxygen exposure limit called partial pressure. For most non-repetitive dives under 100 feet, you will be limited by the amount of gas as opposed to either the no decompression limit or the partial pressure limits. Enriched air is particularly effective in enhancing the frequency and duration of repetitive dives, since nitrogen buildup is lessened.

Enriched air diving within the recreational limit of under 40% oxygen requires some special equipment, but for the most part you can use the equipment you purchased for diving air. The only new piece of equipment that you will definitely need is a tank. One reason for this is the special markings that must go on an enriched air tank; the other is that the tank must be cleaned and lubricated for oxygen exposure to facilitate partial pressure blending which involves adding pure oxygen to air. A common scuba community guideline is that regulators, BCDs, SPGs and alternate air sources may be used with enriched air blends up to 40% oxygen without modification. However, you should verify that the manufacturer of each piece of equipment has certified that equipment for use with enriched air. For gas mixes with more then 40% oxygen, special equipment is required. As with any scuba equipment, regular servicing is highly recommended, including O-rings and other critical components. During your enriched air training, you will learn how to properly fill and verify the blend of gas in your tank. The verification step is extremely important and must be done by you the diver; you shouldn't rely on anyone else to verify your gas blend.

Remember, you should never dive with enriched air unless you have been certified by a reputable certification organization. While the benefits of diving enriched air are significant, so are the risks.
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