NAUI Nitrox Diver
4 Introduction
LEARNING GOALS
In this chapter, you will learn:
• What nitrox is.
• Other names for nitrox.
• The early history of diving with gases
other than air.
• When NAUI sanctioned nitrox diving.
• What nitrox is not.
“Mother Nature provided the planet Earth with a
NITROX atmosphere known as air. She never said
that air was the best medium for divers. Here, as
in many fields of endeavor, human beings have
used their knowledge of natural laws to go one
step beyond what nature has provided for
them.”—J. Morgan Wells, Ph.D. (1987)
WHAT IS NITROX?
Air is a mixture of gases, primarily nitrogen (78%)
and oxygen (21%). Air has been the normal gas-ofchoice
for scuba divers from the very beginning. After
all, we breathe it every day. It is all around us, so it is
easy to compress and purify the air, store it in a cylinder,
then attach a regulator and go diving. But, air has limitations
as a diving gas.
As you learned in your basic scuba course, it is the
nitrogen in the air you are breathing that limits the
depth to which you can dive, the time you can stay at
depth, and the number of dives you can make in a day.
Nitrox has some partial solutions to offer. As the
term is used in recreational diving, nitrox is air in
which the fraction of nitrogen has been reduced.
Commonly, this is accomplished by adding oxygen to
air, but it can just as easily be done by removing some
of the nitrogen. As the nitrogen percentage goes down,
the oxygen percentage goes up. The resulting gas mixture
has been given several names: oxygen-enriched
air, enriched air nitrox, and nitrox. You will also see it
called EANx, where the “x” is usually replaced by the
percentage of oxygen. EAN32 would be a nitrogen-oxygen
mixture that is 32% oxygen. Nitrox is the most widely
used term. Actually, “nitrox” can refer to any mixture
of nitrogen and oxygen, so plain, ordinary air would be
nitrox, and in the past nitrox has even been used to refer
to nitrogen-oxygen mixtures with less oxygen than air
that were used in undersea habitat diving.
Reducing the amount of nitrogen in what you
breathe underwater addresses some of the problems
caused by nitrogen. When using nitrox, it is possible to
dive longer to a given depth or to reduce the required
surface interval between dives. Nitrox may have other
advantages too. Whether it is true or not, many nitrox
divers report that they feel less fatigued after their dives.
However, there are trade-offs. As we reduce the nitrogen
fraction, the oxygen fraction increases. As you will learn
in this course, the higher oxygen content presents its
own limitations. Oxygen breathed under high pressures
can become poisonous. So for example, when diving
with nitrox, we must limit our maximum depth in order
to reduce the possibility of oxygen toxicity.
Today, nitrox is almost universally accepted as a
breathing gas for recreational diving. The benefits and
advantages far outweigh the problems and possible disadvantages.
As a diver, you need a certain amount of
knowledge, awareness, caution, and sensibility to use
nitrox safely, but this is just as true of diving in general.
A BIT OF HISTORY
The development of nitrox use began slowly. It was
first proposed for use in the military in 1943 as a way to
reduce decompression problems. Nitrox diving methods
were published in the U.S. Navy Diving Manual in
1959. In 1975, Morgan Wells and Dick Rutkowski of the
National Oceanographic and Atmospheric Administration
(NOAA) began using nitrox mixes in NOAA diving projects.
In 1979, NOAA published standards for the use of
nitrox in the second edition of its NOAA Diving
Manual. In the 1980s, nitrox began to appear in recreational
diving, but until the mid-1990s its use was frequently
met with wariness, extreme caution, or even
fear. NAUI officially endorsed training in the use of
nitrox in 1992.