An Introduction to Enriched Air Nitrox

Call it Nirtox, Oxygen Enriched Air or Enriched Air Nitrox, this gas has taken the Sport SCUBA Diving community by storm. In fact on most of the local North Carolina wreck diving charters we see more divers using Enriched Air than not! Enriched Air Nitrox is a breathing gas consisting of air mixed with a higher percentage of oxygen. By adding additional oxygen to the mixture the rate of nitrogen absorption into the body is reduced. Nitrox is commonly used by recreational divers for one of two purposes: to increase the length of time one may stay at depth without requiring decompression stops and/or to reduce the risk of decompression sickness by lowering the overall nitrogen levels within the body's tissues.

A common misconception among divers is that Enriched Air Nitrox (EANx) is a deep diving gas. In fact, EANx is best applied to shallower dives. As an example of the improved bottom time one may realize by using EANx a diver making a dive to 60 feet on air has a no decompression limit of 55 minutes. In contrast, a diver making the same dive on Nitrox containing 36% oxygen would have a no decompression limit of 115 minutes. That's an hour more bottom time! (Results based on the PADI Recreational Dive Planner)

Nitrox is also commonly used to accelerate (shorten) the amount of time required at stops during planned stage decompression dives. By reducing the amount of nitrogen being breathed by the diver, the excess nitrogen loaded in the tissues is expelled faster. An additional benefit to the process, oxygen tends to reduce the size of any bubbles that may have formed in the divers blood stream during the ascent, reducing the odds of these "Silent bubbles" from reaching a size large enough to cause decompression sickness. Cave and technical divers using enriched air for this purpose will typically use a mix containing 40% to 100% oxygen.