If You Understood NITROX,
You'd Be Using It, Too

Nitrox is any combination of nitrogen and oxygen.

The air that we breathe is approximately 21% oxygen and 79% nitrogen. In the language of nitrox, this may be described as EAN21, or normoxic nitrox, so you have been breathing nitrox since the day you were born.

In Recreational Scuba Diving nitrox is used to increase a divers allowable bottom time. Depending on the mixture, one may be able to extend the bottom time to the double and still maintain a safe nitrogen absorption

In scientific diving, nitrox usually refers to a breathing mixture with less than 21% oxygen.

In technical diving, nitrox usually refers to a breathing mixture with more than 40% oxygen.

Nitrox mixtures with more than 21%, but no more than 40% oxygen are called
Enriched Air Nitrox (EANx)

The commonly used EANx mixtures are:
EAN32 (32% oxygen / 68% nitrogen) also known as NOAA I and
EAN36 (36% oxygen / 64% nitrogen) also known as NOAA II
The U.S.-based National Oceanic and Atmospheric Administration published tables for these mixes in the late 1970s, hence the names NOAA I and NOAA II
As Enriched Air is a subset of nitrox, it becomes important to use the proper terminology. In the recreational diving community however, the term Nitrox most frequently is synonymous with Enriched Air. One Diver Training Organization has coined the name "Safe-Air" to mean Enriched Air.

It has been understood, for a long time, that by lowering the nitrogen content, divers can extend the no decompression limits and/or reduce the time needed for decompression. The use of oxygen to shorten the time required for decompression was first mentioned in 1878 by Paul Bert.

Oxygen is non toxic under usual conditions. Breathing pure oxygen at one atmosphere, however, may produce cough and chest pain within 8 - 24 hours. Concentration of 60% may produce these symptoms in several days. At two atmospheres symptoms will occur in 2-3 hours. Partial pressure of oxygen in excess of two atmospheres may produce a variety of central nervous system manifestations including tingling of fingers and toes, visual and hearing disturbance, abnormal sensations, impaired coordination, confusion, muscle twitching, and seizures resembling those of epilepsy. Severe hazards may be present when confusion and impaired judgment lead to operational errors.

In 1943, Chris Lamberston (U.S. Navy) added oxygen to air for improved physiological and operating advantages.

In 1957, The Frenchman Andre Galerne used for the first time a 50/50 Nitrox during a commercial diving operation

In 1962, the Navy began using enriched air in its Mark V (hard-hat) diving system

In 1970, Dr. Morgan Wells, Ph.D., Diving officer for the National Oceanographic and Atmospheric Administration (NOAA) began using oxygen enriched air during diving operations.

In 1978 NOAA publishes NOAA Nitrox I Dive Tables

In 1985, Richard Rutkowski, the Deputy Diving Coordinator for Dr. Morgan Wells, retired from NOAA and took the first steps to bring "Nitrox Diving" to sports divers.

In 1988 Ed Betts and Doug Pettit joined Richard Rutkowski to form the American Nitrox Divers Institute (ANDI). Their aim was to standardize sports diver training, instructor training and refill station dispensing procedures for Nitrox.

In 1990 NOAA publishes NOAA Nitrox II Dive Tables

Enriched Air is NOT useful for deep diving. With an increased percentage of oxygen and hence an increase in the oxygen partial pressure, the potential for oxygen toxicity becomes a limiting factor with regards to depths.

In the March/April -98 issue of Alert Diver (The Magazine of Divers Alert Network) Barbara Wellington of DAN points out that First Aid with Enriched Air is effective up to a point in reducing the amount of nitrogen bubbles in the blood stream. The more oxygen and less nitrogen in the First Aid breathing mix, the faster the this process will occur.

If you want to know more about Enriched Air (nitrox) diving, consider taking our PADI Enriched Air Diver Specialty Course.