R
Reduced Gradient Bubble Model (RGBM): A
set of decompression algorithms and diving tables
based on a dual-phase model of tissue ingassing and
offgassing–that is, based not only on gases dissolved
in one’s tissues but also on the ever-present gaseous
micronuclei or “bubble seeds” in our bodies.
Repetitive Dive: Any dive following a previous dive
before complete offgassing of nitrogen. According to
the NAUI Dive Tables, any dive within 24 hours of a
previous dive is a repetitive dive.
Residual Nitrogen: The nitrogen remaining in the
body because of a previous dive or dives.
Residual Nitrogen Time (RNT): The amount of
time a diver must consider as already having been
spent at depth for a planned repetitive dive. The
time is based on the residual nitrogen remaining in
the diver’s body from the previous dive.
Rule of Halves: A modification to the safety stop procedure
to further reduce bubble formation. By the
Rule of Halves, the ascending diver stops for two to
three minutes (with two and one-half minutes being
optimum) at a depth that is one half the deepest
depth of the dive, followed by a one-minute stop at a
depth of 3-6 msw (10-20 fsw) before surfacing.
S
Safety Stop: A precautionary delay in ascent from a
no-stop dive. The safety stop is taken at approximately
5 msw (15 fsw) for three to five minutes at
the end of the dive.
Saturation: In diving, the presence of the most dissolved
gas possible in the body tissues of the diver
for the existent depth/pressure.
SIT: Surface interval time: See Surface Interval.
Solubility: The amount of one substance that will
dissolve in another substance under specified conditions.
See also Henry’s Law.
Solute: A dissolved substance.
Solvent: The liquid substance that dissolves another
substance.
Square Profile Dive: A dive that involves descending
to one particular depth, staying there for the
entire dive time and then ascending directly to the
surface, with the exception of safety and decompression
stops. All dives are treated as square profile
dives when using dive tables.
Surface Interval: The time spent on the surface
between dives. A surface interval must be at least 10
minutes to qualify the next descent as a repetitive
dive. NAUI recommends that the surface interval be
a minimum of one hour.
T
Technical Diving: A mode of diving using advanced
techniques, equipment, and training. “Technical
dives” include planned decompression dives, deep
dives where both nitrogen and oxygen in the
breathing gas are diluted with helium (trimix),
dives in which the diver changes gas mixes during
the dive, dives that use an oxygen percentage
greater than 40%, or dives into overhead environments
such as caves or wrecks. The term is also
applied to diving with a rebreather.
Total Nitrogen Time (TNT): The sum of residual
nitrogen time from previous dives and the dive time
for the present dive.
Trimix: A breathing mixture of three gases: oxygen,
helium, and nitrogen.
NAUI Nitrox Diver
90 GLOSSARY