Bühlmann decompression algorithm: Difference between revisions

Revision as of 04:19, 19 August 2023

Revision as of 20:12, 20 August 2023

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User input of [[gradient factor]]s is sometimes available for planning and real time applications.

Gradient factors are a calculation trick (Erik C. Baker) consistingthat inconsists of taking a percentage of each M-Value (e.g. 90%) in order to increase conservatism (shorter duration without mandatory stops, longer and/or deeper stops) by reducing the maximum quantityamount of neutral (inert) gas (e.g. nitrogen) accepted when approaching surface (Maximum Value of each tissue compartment at... 9 m, 6 m, 3 m, surface).<ref name="Foret-1" />.

It is generally possible to define two GFs: GFlow and GFhigh. GFlow applies to the first (deepest) stop, GFhigh to the last stop (closest to the surface). Any intermediate GFs (between GFlow and GFhigh) are calculated by linear interpolation.

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For dives without mandatory stops, only GFhigh is used, even if a GFlow is defined.

Twin GFs (e.g. 80/80) have the same effect than artificially increasing dive time (time taken into account is greater than actual time). UsingWhen using printed dive tables, it is like an "impromptu addition of extra increments of depth and time beyond those actually required by the dive, universally known as ''Jesus-factoring''".<ref name="Shields" />

AsymmetricalAsymmetric GFs (e.g. 30/70) can be used to force deep stops (e.g. helioxHeliox or trimixTrimix dives when the algorithm used is not sufficiently conservative enough). Deep stops can be defined as follows: “one or more voluntary or empirically derived decompression stops that are deeper than any prescribed by the algorithm utilized”.<ref name="Deep-Stops" />

GFs can be implemented in dive computers in three ways:

* with a preset mode (e.g. L0, L1, L2 ... or P0, P1, P2 ...) corresponding to a decreasing twinpair of GFs: 90/90; 85/85; 80/80... ;

* leaving GFlow and GFhigh free for input;

* by integratingincluding intoin the algorithm a modification of the GFs according to diver's behavior (profile, ascent speed, etc.).

In all cases, the choice of GF values is arbitrary.

The term "ZH-L 16 with GF" is misleading. It may give the impression that there is a specific set of parameters for use with GFs. There isn't. Any set of parameters with M-Values (ZH-L, US-Navy, Hahn, RGBM, Comex...) can be used with GF.

==References==