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Specializing in Enriched Air

,Technical, and Mixed Gas Diving

Training by

Dennis H. Hocker
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RxSCUBA offers Enriched Air training
 "NITROX" in PADI and/or IANTD Formats

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NITROX for Recreational SCUBA Diving
By  Dennis H. Hocker
Web Site
Phone 510.rxscuba (797 2822)
IANTD Technical Instructor No. 1031
IANTD  Instructor Trainer No. 234
IANTD  Gas Blending Instructor
PADI     Master Instructor No. 5870
DAN  O2  Instructor Trainer No. 7335
Universal Diver Training CD No. 8

There are questions being asked by the recreational diving community  as well as some misconceptions about the use of Enriched Air (nitrox) for recreational diving. In the following article I will hopefully answer these questions and set straight the misconceptions about the use of Enriched Air (nitrox) in recreational diving. First, lets define recreational diving. With the advent of nationally recognized training agencies who have very successfully set up their own standards and the ability to police themselves through the establishment of minimum standards they must all meet, recreational SCUBA diving was defined as:  the use of open circuit Self Contained Underwater Breathing Apparatus using compressed air to a maximum depth of 130 feet sea water. In resent years (the year varies by training agency) the Recreational SCUBA Diving definition has been modified to include compressed air as well as the use of Enriched Air (nitrox) with an Oxygen content of up to 40%.

Next we need to define the word nitrox and understand what nitrox really is: the words Nitrogen and Oxygen were combined to form the acronym Nitrox. In review of your basic chemistry class in school Nitrogen is a colorless, odorless, tasteless gaseous element that constitutes about four-fifths of the volume of the Earth's atmosphere. Oxygen is also a colorless, odorless, tasteless gaseous element constituting about one-fifth of the volume of the Earth's atmosphere. Oxygen is also an required element to sustain animal life.

Looking at the above definitions we see that  nitrox is a combination of Oxygen and Nitrogen -- to be specific, any combination of Oxygen and Nitrogen results in Nitrox. We also see that Nitrogen is the major element accounting for about four-fifths of the Earth's atmosphere -- to be more accurate about 78.1% of the Earth's atmosphere. Oxygen makes up 20.9% of the Earth's atmosphere. If one quickly does the math we find that there is 1% unaccounted for. This remaining 1% is made up of carbon dioxide (0.033%), and various inert and rare trace gases.

Mother Nature provided the planet Earth with a nitrox atmosphere known as air. (Though she never said that this nitrox mixture was the best breathing medium for divers.) As you read this article and continue the involuntary breathing reflex, you are breathing nitrox. In fact, you have been breathing Nitrox from the time you took your first breath of air following your birth into this world. Every time a SCUBA dive is done on compressed air the diver is breathing a nitrox mixture containing 79% Nitrogen and 21% Oxygen.

Air has been used as a breathing gas by divers since the beginning of diving. Its principal advantage is that it is readily available and inexpensive to compress into cylinders or use directly from compressors with surface-supplied equipment. Air is not the "ideal" breathing mixture because of the decompression liability which it imposes.

A diver learns early in their open water training that Nitrogen is absorbed by their blood and body tissues. Since the rate that Nitrogen absorbed is dependent on the inspired partial pressure of  Nitrogen and time, not  "depth and time," this Nitrogen uptake can be reduced by reducing the Nitrogen content of the diver's breathing gas. To reduce the Nitrogen content  in the breathing gas, the content of a gas which is metabolized away by the body would be increased (i.e. Oxygen) thus producing an Nitrox mixture with an Oxygen content greater than 21% or Enriched Air Nitrox (EANx) Hence, EANx is a more accurate term to use to address breathing mediums other than air for recreational diving. When the Oxygen content is known the "x" in EANx is replaced with that value, i.e., an EAN mixture with an Oxygen content of 32% would be expressed as EAN32.The concept of EANx is by no means new. EANx was first prepared by an English chemist  named Joseph Priestly in 1773. By 1794 EANx was being used as part of standard medical procedures. In 1879 Henry Fleuss made the first EANx wet dive. Over the years the development and understanding the effects of EANx diving continued. Throughout World War II the British Navy used EANx. In 1943 research by Chris Lambertsen of the U.S. Navy proved that you could put Oxygen on top of  air and create a mixture equal to breathing air at a shallower depth. This concept was published in the 1959 edition of the U.S. Navy diving manual. 1962 U.S. Navy began using EANx. About 1970 National Oceanic and Atmospheric Administration (NOAA)  began to realize they were spending a lot of money to get scientist into the sea but were getting about half the amount of bottom time that they could by using Nitrox mixtures other than air. NOAA continued its development in the usage of Nitrox and in 1978 J. Morgan Wells published the first set of  dive tables for use with a breathing medium other than air. These tables were for use with NOAA Nitrox I (68% Nitrogen, 32% Oxygen). These tables were included in the NOAA diving manual. Dick Rutkowski founded the International Association of Nitrox Divers (IAND) in 1985 and introduced EANx to the recreational diving community. In 1991, at the request of Dick Rutkowski, Tom Mount developed the first set of standards for recreational use of breathing gases other than air. IAND was expanded to encompass technical diving and the name was changed to International Association of Nitrox & Technical Divers (IANTD).

At this point I would like to dispel the common misconception that EANx (Nitrox) is for deep diving. The truth is that EANx is not for deep diving but is ideal for depths within the recreational depth limit of 130 feet sea water. In fact, the greatest benefits of using EANx are realized in the 50 to 80 foot range.

Lets look at the benefits of diving using EANx. The first thing to keep in mind is that it is not the fact that EANx contains a higher percentage of Oxygen than air but it is the fact that EANx contains a lower percentage of Nitrogen than air that gives EANx the benefit over the use of air for diving. The benefits of using EANx include increased bottom times without exceeding the no decompression stop limits of the dive tables, reduced residual nitrogen time on repetitive dives and shorter surface intervals. Many divers report less post-dive fatigue and post-dive headache when using EANx. A few divers feel they are warmer and consume less gas when diving on EANx.

For those divers that like to take the conservative approach, one can use the air tables or use a regular dive computer that does its computations based on diving with compressed air thus giving themselves an additional margin of safety. For those divers who are in less than good physical condition or getting up in age, conservatism is something to be considered.

For those who would like to fully realize the benefits of diving EANx, lets do a quick comparison of air versus EANx using the latest dive tables based on Buehlmann's ZHL-16 Algorithm. A diver diving to a depth of 50 feet on air has a no decompression stop limit bottom time of 75 minutes. If this dive was done using EAN32, the bottom time would be 125 minutes which is an increase of 65%. If the dive was to 80 feet, the bottom time on air would be 25 minutes maximum; on EAN32, the maximum bottom time would be 35 minutes; and if EAN36 was used, the maximum bottom time would be 51 minutes, which is double the time available using compressed air. Where one realizes substantial benefits of EANx is on repetitive dives. Due to less Nitrogen uptake shorter surface intervals are required between dives; thus, one can get in an additional dive or two per day on that great live aboard dive trip to wherever.

Diving EANx does slow the Nitrogen uptake but does not eliminate it. One still needs to plan their dives and stay within the dive tables for the breathing gas being used or through the use of EANx programmable dive computers of which there are an increasing number available.

Before using EANx (Nitrox) one needs to be trained and certified in it use. There are advantages to diving using EANx but Oxygen at high partial pressure becomes toxic to the central nervous system resulting in convulsions. Convulsions while under water usually result in death by drowning. Oxygen levels can be easily tracked and Oxygen toxicity prevented through proper training. A mistake using EANx may not be as forgiving as a mistake using compressed air (a case of the bends can be treated), the benefits outweigh the risk.

Due to space considerations, this is just a brief overview of Nitrox for recreational diving .  For further clarification or specific questions, I can be reached by email at or phone at 510-RxSCUBA (797 2822)


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