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10.2.1. Suunto Technical RGBM decompression model
Suunto's decompression model development originates from the 1980s when Suunto im-
plemented Bühlmann's model based on M-values in Suunto SME. Since then research
and development has been ongoing with the help of external and internal experts. In the
late 1990s Suunto implemented Dr. Bruce Wienke's RGBM bubble model to work with the
M model. The first commercial products with the feature were Vyper and Stinger. With
these products the improvement of diver safety was significant.
Now Suunto has taken another leap in decompression modeling by introducing Suunto
Technical RGBM decompression model with He tissues.
Suunto Technical RGBM model is a modified version of the M-value model. Calculation
of the M-value model can be found in common dive literature. Modifications have been
made to have the model follow RGBM theory as closely as possible. The modifications
have been conducted with the help of Dr. Bruce Wienke. Functionality of Suunto Technical
RGBM has been validated and verified to the depth of 120 m/393 ft with hundreds of test
dives both in the field and in laboratory. The algorithm should not be used in deeper depths
than the verified depth.
Suunto technical algorithm models the human body by using nine tissue groups. In theory
the model is accurate if there are more tissue groups, but using more than nine tissue
groups has no practical significance.
Tissue calculation aims to model the amount of nitrogen (N
in tissues. Ongasing and offgasing of saturated gas is modelled using the ideal gas
equation. In practice this means that the total pressure of the nitrogen and helium tissues
can be higher than the total pressure of the breathing gas, even without any exposure to
pressure. For example, when a diver dives an air dive soon after a demanding trimix dive,
the residual pressure of helium combined with a high nitrogen content cause the diver a
decompression obligation very fast.
10.2.2. Diver safety and Suunto Technical RGBM model
Because any decompression model is purely theoretical and does not monitor the actual
body of a diver, no decompression model can guarantee the absence of DCI. Suunto
Technical RGBM model has many features that reduce the risk of DCI. The Suunto
Technical RGBM algorithm adapts its predictions of both the effects of microbubble build-
up and adverse dive profiles in the current dive series. The pattern and speed of decom-
pression is adjusted according to the microbubble influence. The adjustment is also applied
to the maximum combined nitrogen and helium overpressure in each theoretical tissue
group. To add diver safety, offgasing is also slowed down compared to ongasing and the
amount of slowing down depends on the tissue group.
Experimentally it has been shown that the body adapts to decompression to some degree
when diving is constant and frequent. Two personal adjustment settings (P-1 and P-2) are
available for divers who dive constantly and are ready to accept greater personal risk.
CAUTION
Always use the same personal and altitude adjustment settings for
the actual dive than for the planning. Increasing the personal adjust-
ment setting from the planned setting as well as increasing the altitude
adjustment setting can lead to longer decompression times deeper
and thus to larger required gas volume. You can run out of breathing
gas underwater if the personal adjustment setting has been changed
after dive planning.
) and helium (He) saturated
2
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