Scuba Geek

Gradient Factors Explained July 19, 2006

Posted by Andy Carroll in : Decompression , trackback

Over at Yorkshire Divers Garf and Mark Powell have collaborated to produce a nice explanation of Gradient Factors. Gradient factors are used in some decompression software packages to adjust the Buhlmann algorithm, usually with the aim of inserting ‘deep stops’.

Here’s an exceprt;

Now ye old buhlmann tables took you straight up from a deep dive to the M value, and kept you there until offgassing was complete, hence the reason many people refer to them as a “bend and mend model”. This had the advantage of getting you shallow fast, and offgassing fast, but really took you to the edge of being bent. This is why buhlmann tables, and buhlmann based computers, such as the suuntos, get you very shallow, very fast. This is also why many people consider Suuntos to be far too aggressive for decompression diving.

Now, lets call the point of saturation, where everything is equal as being 0%, and the point of supersaturation, or M value, where we are on the point of being bent, as being 100. The fact that buhlmann tables take you straight to the M value means that you are being taken immediately to 100% of the distance between saturation and the M value, hence the reason buhlmann tables are often called 100/100, becuase all of the stops are done at this 100% point. However. There is a “grey area” around the M value, as it is only a theoretical line, and the problem is the many people feel like shit diving buhlmann tables, and indeed people got bent. So Gradient factors were introduced as a fudge to make the model safer. Gradient factors are represented by a LOW factor figure and a HIGH factor figure, which sit as two lines betweem the point of saturation (equilibrium) and the point of supersaturation (whoops I’m bent). the intention is to keep you in the deco zone but stop you getting too close to the M Value

Its worth reading through if you have any interest in decompression models and the like.