LEARNING GOALS
In this chapter, you will learn:
• About NAUI EANx Dive Tables and NAUI RGBM
EANx Dive Tables.
• What Equivalent Air Depth is and how it is used
with Air Dive Tables.
• How to determine and calculate Equivalent Air
Depth.
• How to use the NAUI RGBM Nitrox Dive Tables.
• What is the “Rule of Halves” and how to use it in
all of your diving.
• About using dive computers for EANx diving.
DIVE TABLES
In your entry-level Scuba Diver course, you learned
how to use dive tables to plan and execute dives. You
learned that dive tables are used to monitor and control
the amount of nitrogen in our bodies in order to minimize
the risk of decompression sickness. This chapter
will build on that knowledge and acquaint you with
using dive tables designed for diving with oxygenenriched
air.
There are many different dive tables in use today.
They are based on varying models of nitrogen absorption
and elimination. If you were certified as a NAUI Scuba
Diver, then you probably used either the NAUI Dive
Tables or the NAUI RGBM Dive Tables to plan your dives.
Or, you might have learned to use the U.S. Navy Tables
(on which the NAUI Dive Tables are based), the
Canadian Defence and Civil Institute for Environmental
Medicine (DCIEM) Tables, or tables developed by Dr. A.
A. Bühlmann of Switzerland (which were also designed
to accommodate altitude diving). All three of these tables
are endorsed for use by NAUI in NAUI courses. Another
algorithm, which was developed under the auspices of
the Diving Science and Technology Corporation, is used
in the PADI Recreational Dive Planner. The British Sub
Aqua Club has its own tables; the British Royal Navy has
its; Stolt Offshore has its. In fact, many navies and most
commercial diving operations have developed proprietary
dive tables for their own use. Most have also developed
tables for use with oxygen-enriched air.
If you want to learn more about decompression theory
and dive table development, you can advance your
knowledge in a NAUI Master Scuba Diver course. There
are also texts that present advanced decompression theory,
and good information can be found on many web
sites. In this course, we will consider only the classic
NAUI Dive Tables and the NAUI RGBM Dive Tables,
which use the more modern concept of dual-phase modeling
and the Reduced Gradient Bubble Model developed
by Dr. Bruce Wienke. We also assume that you already
know how to use dive tables to plan your dives. If you
are out of practice in the use of dive tables and dive table
terminology, you should go back and review the information
in your basic scuba textbook.
Remember that if you are diving at higher altitudes
(above about 300 meters or 1000 feet), you will have to
use special altitude dive tables or apply a conversion for
theoretical depth. NAUI RGBM Tables are available that
cover three altitude ranges up to a maximum of 3048
meters (10,000 feet) above sea level.
Also, planned required-decompression diving,
whether breathing air or nitrox, is an advanced skill that
requires additional training. Recreational divers use
oxygen-enriched air to increase the safety margin of
no-required-decompression dives or to extend maximum
dive time without encountering a mandatory
decompression obligation.
ENRICHED AIR NITROX DIVE TABLES
So-called “standard dive tables” are designed for
diving while breathing air. The mathematics and the formulas
that were used in their development assume the
diver is breathing a mixture that is 79% nitrogen/inert
gas and 21% oxygen. When NOAA introduced procedures
for diving with an enriched air nitrox mix of 32% oxygen/
68% nitrogen (NOAA Nitrox I) in 1979, they also
published a set of derivative nitrox dive tables that took
into account the reduced percentage (and therefore partial
pressure) of nitrogen. The tables were based on the
concept of equivalent air depth. That is, because the
NOAA Nitrox I diver would be breathing only 68/79ths of
air’s partial pressure of nitrogen at any depth, the diver
NAUI Nitrox Diver
54 Dive Tables and Dive Computers