5
64 NAUI Nitrox Diver
To use the NAUI RGBM tables, you must follow
certain specific rules, but planning dives with the tables is
simplicity itself.
The important RGBM table rules are:
• A minimum surface interval of one hour is
required between each dive.
• If the actual dive depth is not listed, select the
next greater depth.
• The depth of each repetitive dive must be
no greater than the depth shown on the row
immediately to the right of the previous dive’s
depth; of course, it may be shallower than this
maximum repetitive-dive depth.
• As the tables are designed, there can be no
shallow dive followed by a deeper dive.
• The maximum ascent rate is 9 meters (30 feet)
per minute.
• All dives require a 3-minute safety stop at
5 meters (± 1 meter)/15 feet (± 3 feet).
• On the sea level to 610 meters (2000 feet) tables,
no more than three repetitive dives within a
12-hour period. In actual practice, the “third
dive” may be a series of repetitive dives not
exceeding the total maximum dive time of
150 minutes.
The flying after diving rule is to wait at least 12
hours after a single dive within the prior 18-hour period,
15 hours after two dives, and 18 hours after three dives.
Example: A diver using EAN32 is planning a dive
to 24 meters (80 feet). The maximum dive time for this
first dive is 47 minutes. Moving horizontally to the right
on the same row: after a one-hour surface interval, the
diver can dive to a maximum depth of 18 meters (60 feet)
with a maximum dive time of 85 minutes. Following
another one-hour surface interval, the diver can dive to a
maximum depth of 12 meters (40 feet) for a dive time up
to 150 minutes or make a series of dives to 40 fsw for up
to a total of 150 minutes.
When using the NAUI RGBM Tables (with onehour
surface intervals), you may also switch tables from
leaner to richer oxygen fractions from dive one to dive
two (or dive two to dive three) by simply following the
maximum depth constraints as you move between the
appropriate dive tables, since depth (pressure) is the
only controlling factor. For example, it is possible to use
air and the NAUI RGBM Air Table on Dive One, then
switch to EAN36 and use the RGBM EAN36 Table on
Dive Two.
Comparing this dive series to one derived from the
standard NAUI EAN32 Dive Tables: On the first dive
to 24 meters (80 feet), the diver would have a maximum
dive time of 50 minutes and emerge from the dive as a
“J” diver. One hour later, the diver would be an “H” diver
and, if planning an 18 meter (60 foot) dive, would have
an adjusted maximum dive time of only 34 minutes. In
order to attain an adjusted maximum time equivalent
to the RGBM diver’s 85 minutes, the surface interval
between the first and the second dive would have to be at
least 5 hours 41 minutes. Sometimes simpler is better.
THE RULE OF HALVES
In 2003, NAUI introduced the “Rule of Halves” into its
recommended diving procedures. The NAUI Rule of
Halves is based on RGBM theory and provides an extra
margin of safety for divers by further controlling both
dissolved-phase and free-phase nitrogen in the body. It
can be used with any dive deeper than 12 meters (40 feet)
and with any dive tables or dive computer.
To use the Rule of Halves, when ending any
no-decompression dive in excess of 12 meters (40 feet),
halve the distance from the dive’s deepest depth to the
surface. Ascend to that depth and make a two to three
minute stop (with two and one-half minutes being
optimum). Then continue your ascent to the 3-6 meter
(10-20 feet) safety stop for one minute before surfacing.
For example, following a dive to 30 msw (100 fsw),
you would perform a two and a half minute stop at about
15 msw (50 fsw) and then ascend to 5 msw (15 fsw) for a
one minute stop before surfacing.
DIVE COMPUTERS AND NITROX
Dive computers perform real-time dive calculations
(Figure 5-9). Generally, their algorithms are quite
conservative, but because they sample the diver’s
Figure 5-9 Examples of nitrox dive computers.