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Appendix – RGBM Model
The Reduced Gradient Bubble Model is an algorithm developed by Dr. Bruce R. Wienke that is used
to calculate the decompression stops needed for a particular dive profile. It assumes asymmetric off
gassing and compensates for nitrogen microbubbles, which can reduce the rate of off gassing.
The RGBM has gained tremendous popularity in the recreational and technical diving worlds in just the
past few years.
The RGBM algorithm considers various factors, including the maximum depth reached during the dive and
the length of time underwater. For repetitive dives it also includes the
above the water between the previous dive and the start of the current dive. This information is used to
calculate the amount of residual nitrogen build-up in the diver's tissues after completing a dive.
The RGBM:
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Monitors continuous multiday diving
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Computes for closely spaced multiple dives
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Computes for a dive that is deeper than the previous one
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Adapts for rapid ascents which build up microbubbles
The algorithm provides additional safety features though its ability to be set for a variety of situations and
dive profiles.
Depending on the situation, the RGBM adapts decompression data by:
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Reducing no-decompression stop dive times,
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Adding mandatory safety stops
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Increasing decompression stop times
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Increasing the surface interval
The UDI-14™ allows the diver to choose between the traditional recommended safety stop and deep
stops. Deep stops occur deeper than traditional stops to minimize microbubble formation.
The RGBM model calculates deep stops iteratively, placing the first stop at approximately halfway between
the maximum depth and the ceiling depth. After completing the first deep stops, another deep stop is set
halfway to the ceiling and so on.
Personal adjustment
Divers can input personal adjustments into the RGBM decompression model. There are 5 modes to choose
from. Factors which can affect which mode to choose vary between divers, and for the same diver from
one day to the next. The factors which can increase susceptibility to decompression illness include, but are
not limited to:
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Cold exposure
•
Fitness level
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Fatigue
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Dehydration
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Previous cases of decompression illness
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Stress
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Obesity
The model should be adjusted to a conservative level, according to personal experience and ability. Under
ideal conditions, use the default value of mode 2.
If conditions are more difficult, choose a more conservative model. The UDI-14™ adjusts the RGBM model
according to the mode entered, and provides appropriate decompression times.
surface interval
57
, or the time spent
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