How to choose gradient factors

[Novice_diver]

In most decompression software one can change the gradient factors to personal preference. I'm wondering how one chooses the gradient factors, is this by trial and error or are there ways to "calculate" them.

 

[Azza]

In most decompression software one can change the gradient factors to personal preference. I'm wondering how one chooses the gradient factors, is this by trial and error or are there ways to "calculate" them.

If you are playing around with Gradient factors then you are using a deco software that is modelled on victorian era physics,ie Neo-Haldane, and trying to make them fit the 21st century, ie Bubble Models such as RGBM and VPM(B).
Dump the software and buy a bubble model software such as GAP or V-Planner.
Seriously.

 

[Novice_diver]

If you are playing around with Gradient factors then you are using a deco software that is modelled on victorian era physics,ie Neo-Haldane, and trying to make them fit the 21st century, ie Bubble Models such as RGBM and VPM(B).
Dump the software and buy a bubble model software such as GAP or V-Planner.
Seriously.

Thanks for your advice. I already decided to use GAP if i'm going to do decompression diving. At this moment i'm not doing decompression dives. I didn't ask because i'm going to play around with the gradient factors. I just want to understand the mechanics behind them. I do understand how they work but i've read some different ways in which people use them. So i would like to know on which grounds someone uses a high gradient of 95 instead of 80. There must be a reason why they can be changed. Once I understand the mecanics I'll consider decompression diving. But until now I've got to many questions about it.

 

[Uncle Pug]

Play with GF. See what changes in the generated ascent when you do.

 

[MikeFerrara]

There's a good article on gradient factors on the GAP web site. A straight haldanian table will bring you up to the point where the controlling compartment is at it's M value. Gradient factors allow you to adjust that. Two are used. The first controls what percentage of the M value the first stop happens at and the second controls the last stop. Stops inbetween are adjusted based on the slope of the line between the two gradient factors.

By setting both factors to a value of 1, you get the straight model. By setting the 1st gradient factor to a value less than one you start your stops deeper. By setting the second (or upper) factor less than 1 you stay at your last stop longer....as apposed to getting out of the water when the leading compartment is at it's M value.

The article on the GAP site shows this graphically and of course explains it more thoroughly.

We use Dplan (the palm version) as a reference and while it isn't the same as a bubble model we don't dive any of them "as is" anyway.

Vplanner is slick but I wish Ross would come out with a version for a palm.

 

[Novice_diver]

Thanks Mike,
i understand how they work and i have been playing a lot with them (using M-plan on my palm) But i would like to know how one chooses the factors that are right for him? Do they depend on weight? Physical condition? Diving conditions?
There must be a relation between these factors and the gradient factors that one uses.

 

[Dr Deco]

Hello Novice Diver:

I do not believe that there are any current methods to decide “gradient factors.” [Depending on the decompression system that you are using, these might also be referred to as “conservative and liberal.”] There is not any correlation that I have ever seen between anything that is obvious and the risk of DCS with the exception of age. People have looked for blood factors but nothing has yet been found. I truly suspect that some day, something will be found in blood serum, but that day has not yet arrived.

Fitness Level

The best measure to date of DCS risk is physical fitness based on maximum oxygen consumption. Most people are not able to measure this, since it requires the need of an oxygen gas analyzer and a bicycle ergometer. Some measure can be found by determining how fast one can WALK a mile. Someone in good cardiovascular shape can do this in fifteen minutes. Not so good a time is 25 minutes and poor fitness is indicated by the need for 35 minutes.

Adjustments

There is more to DCS risk that fitness, but, in the absence of anything else, one might propose that those in poor shape take a very much reduced gradient (or conservative setting). I have never tested this idea, but there is evidence for it in the literature (concerning fitness and Doppler bubbles).

Dr Deco :doctor:



References :book3:

Carturan D, Boussuges A, Vanuxem P, Bar-Hen A, Burnet H, Gardette B. Ascent rate, age, maximal oxygen uptake, adiposity, and circulating venous bubbles after diving. J Appl Physiol. (2002) Oct; 93(4): 1349-56.

Carturan D, Boussuges A, Burnet H, Fondarai J, Vanuxem P, Gardette B.Circulating venous bubbles in recreational diving: relationships with age, weight, maximal oxygen uptake and body fat percentage. Int J Sports Med. 1999 Aug;20(6):410-4.

 

[Novice_diver]

Hello Dr.Deco,
i already thought so, one can adjust his gradient factors but there is no way to establish if the chosen factors are the right ones (other then getting DCS and them knowing they were wrong)
Thnx for your reply.

 

[Dr Deco]

Hello novice diver :

If the truth be known, there is nothing in diving that you know is safe until twenty four hours have passed. :280:

Dr Deco :doctor: