4
Chapter 4 Choosing the Best Nitrox Mix 47
LEARNING GOALS
Comprehension Objectives
Learn about Maximum Operating Depth and
determining it for any nitrox mixture.
Learn how to use the NAUI MobileTM App tools.
Understand what “Best Mix” means and how to
calculate it.
Integrate the ODIGTML dive planning format into
your nitrox dive planning
Up to this point, you have learned theory and concepts
related to diving with oxygen-enriched air. This included
such topics as gases, gas mixtures, partial pressure,
physiology, decompression sickness, oxygen toxicity, and
recommended maximum oxygen partial pressures.
With this chapter, you will begin learning how to
use this knowledge to plan and execute safe dives using
nitrox. This and the remaining chapters of this book are
more practical in nature.
For instance, you already know that you should limit
the partial pressure of the oxygen that you breathe at
depth in order to minimize the risk of oxygen toxicity.
In this chapter we will present how to determine the
maximum depth to which you should dive with any
given nitrox mix. We will also show how to approach this
from the other direction, that is, how you can optimize
your nitrox benefit by choosing the best fraction of
oxygen for your blend if you are planning to dive to a
known depth. In later chapters, you will learn how to use
nitrox dive tables in your dive planning as well as how
to use standard air dive tables when diving with nitrox,
precautions that you must use when handling oxygen and
oxygen rich mixtures, and how oxygen-enriched air is
prepared.
Actually, diving with enriched air nitrox is similar
to diving with air. In all diving, we plan our dives using
dive tables or dive computers to monitor and control
our nitrogen loading. We dive with an awareness of
and respect for the environment and the limitations of
our training and ability. We are responsible divers –
responsible for our own safety, responsible to our dive
partner, and responsible in our attitude and impact
on the ocean or aquatic environment we are visiting.
The added difference is that with nitrox there are more
variables involved because we are now in control of what
we are breathing. Also, using oxygen means that we must
be aware of certain special precautions regarding its use.
It is sometimes said: “Once you strap the tank on your
back, diving with nitrox is just like diving with air.” To a
large degree this is true – if you have properly prepared
and planned your dive and follow your plan.
THE ODIGTML DIVE PLANNING
SYSTEM
ODIGTML is a proven format for dive planning
organization and has an unmatched performance history
for all types of diving from recreational to technical and
expeditionary dives. The ODIGTML system grows with
your training and experience. At the NAUI Nitrox Diver
level, dive plans are straightforward and completed in a
short amount of time, with only slight additions to how
you learned dive planning in your NAUI Open Water
Diver course.
As you progress as a diver, this tool will adapt to
your current level of training. There are seven general
categories within the system, each addressing specific
considerations. As you complete each section in the
system, check off that section when you feel satisfied
that you have addressed the particular area in that area
(Figure 4-1). A memory aid to help remember the steps
is: On Dives I Go Through My Life. Each of the letters
corresponds to an important part of the dive plan as seen
below:
• Oxygen
• Decompression
• Inert gas narcosis
• Gas management
• Thermal
• Mission
• Logistics
Although a diver may enter the ODIGTML system
at any point, all components must be considered and
completed. The order was originally determined to
Figure 4-1 Sample ODIGTML Dive Planner. See
Appendix for larger version.