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Chapter 1 Introduction 15
LEARNING GOALS
Comprehension Objectives
Learn what nitrox is.
Discover other names for nitrox.
Learn about the early history of diving with gases
other than air.
Learn when NAUI sanctioned nitrox diving.
Understand 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-of-choice
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 nitrogenoxygen
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 subjective 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 dangerous. 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 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
(Figure 1-1). 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.
Figure 1-1 Nitrox diving methods were first
published by the U.S. Navy in 1959 just as
recreational diving instruction (NAUI) was
also developing.