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Chapter 1 Introduction 21
one changes between gas mixes during the dive, dives that
use an oxygen percentage greater than 40%, or dives into
overhead environments such as caves or wrecks.
Myth 2: “Nitrox is for deep diving.”
Quite the opposite. Because of the increased
concentration of oxygen in nitrox, there are stringent
depth limits imposed to prevent oxygen toxicity. Nitrox
is a mid-range breathing gas and provides the greatest
advantages for dives in the 15- to 33-meter (50- to 110-
foot) depth range. Beyond that depth the decompression
advantage gain is minimal, and the risk of oxygen toxicity
problems increases rapidly. Later in this book you will
learn how to determine maximum operating depth
(MOD) for various nitrox mixes.
Myth 3: “If you dive with nitrox you
won’t get bent.”
Enriched air nitrox only reduces the fraction of
nitrogen in the gas you breathe; it does not eliminate
it. Moreover, no breathing gas mixture, dive table, or
dive computer can absolutely eliminate the possibility
of decompression sickness. Nitrox has advantages over
air because the partial pressure of the nitrogen is less for
any given depth. Nitrogen accumulation is slower, but
you must still monitor depth and time – as well as the
specifics of your breathing mixture – to avoid excessive
nitrogen accumulation in your body. The knowledge and
procedures in this text will help you control the risks of
decompression sickness while maximizing the safety and
enjoyment of your dives.
Myth 4: “Nitrox is safer than air.”
Nothing that we do is entirely without risk. All diving
involves some risk, and as noted above, there are risks
associated with nitrox. In this course, you will learn
procedures and techniques to responsibly manage and
minimize the risks of using oxygen-enriched air. Nitrox
has advantages over air in many diving applications,
such as increased available dive time and decompression
advantages, but with these advantages comes your added
responsibility to be mindful of oxygen levels and depth
and time limits, analyze you own gas mixture, properly
maintain your equipment, and dive prudently.
Myth 5: “If you dive with nitrox you
won’t get narcosis.”
It is easy to assume that the reduced nitrogen in nitrox
should reduce narcosis just as it provides advantages
in other areas. The fact is that narcosis involves many
factors, some of which are psychological. Evidence on
nitrox and narcosis is sparse, but it is best to regard the
narcotic potency of nitrox as the same as that of air.
While it has been theorized that unmetabolized oxygen
may be as narcotic as nitrogen, recreational nitrox divers
do not subject themselves to oxygen pressures where
this could be a factor. In order to reduce narcosis on
deep dives, technical divers use trimix to lower both the
nitrogen and the oxygen content of their breathing gas.
Myth 6: “It is hard to dive with nitrox.”
This book will help you to learn the proper planning and
procedures for conducting dives with enriched air nitrox.
Most of the procedures are simple, and where there are
calculations involved, the formulas are usually backed up
with tables where you can look up the necessary derived
information. Using nitrox involves an understanding
of partial pressures and oxygen limits, somewhat more
advance planning and preparation than air diving, and an
acceptance of your added responsibility for safe diving.
But the training to become a nitrox diver is far less than
the initial training that prepared you to be a scuba diver.
Once you are in the water, the rule of nitrox diving is the
same as any other diving: Plan your dive, and dive your
plan.
TERMINOLOGY
You will meet a number of new or unfamiliar terms in
this book. Some of them, such as “partial pressure,” you
encountered in your first scuba course, but you may have
not used or seen them since then. Important terms will
be emphasized in bold type at least the first time they are
used in this book and defined in context when necessary.
Figure 1-9 One benefit of nitrox is the possibility of a
shorter required surface interval.