Gradient Factors - What is Everyone Using?

[Tom_Ivan]

58/70. Which I believe is in in line with the current research.

The two experts in the field that I know of are Dr David Doolette and @Dr Simon Mitchell

Dr David Doolette suggests that GFlow should be 83% of your GFhigh.
Last I know Simon Mitchell suggested he uses 50/70. But that was at a talk in South Africa and is a few years out of date.

 

[inquis]

It would be nice to see computer manufacturers introduce GFs which can be scaled to depth or total deco time

Decreasing the GF based on X total deco time would only increase the deco time further. At that point, your gas supply is already fixed and may be insufficient to handle the additional time.

 

[dmaziuk]

It would be nice to see computer manufacturers introduce GFs which can be scaled to depth or total deco time.
NDL 85, then once exceeded that the plan shifts to 80, if more that X total deco shift to 75 etc.

You've done the research to show that results in fewer DCS incidents than sticking to 85?

For that matter, do you have the research showing that 75 results in fewer DCS incidents than 85?

 

[scubadada]

...For that matter, do you have the research showing that 75 results in fewer DCS incidents than 85?

A probabilistic deco algorithm like SAUL would tend to support that premise. However, the rates of DCS with available dive computers are all quite low for no stop diving.

Conservatism

I had a dialog with a fellow diver on consevatism. He is an fierce advocate of eliminating risks, and consequently diving conservatively. He recommended to set my my Shearwater computer at high conservatism AND set max ppO2 at 1,2. This made me wonder afterwards, how does each of this impact...

scubaboard.com

DAN's project dive exploration was unable to demonstrate such an effect

Project Dive Exploration (PDE)

Researchers sought to understand if there was a correlation between how recreational divers dive and the prevalence of decompression sickness (DCS).

dan.org

 

[grantmac]

Decreasing the GF based on X total deco time would only increase the deco time further. At that point, your gas supply is already fixed and may be insufficient to handle the additional time.

Talking about adding deco conservativism, not a holistic dive planning solution (although with AI I'm sure that's possible).

Personally I'm diving 70/85 for everything. But I'm only just getting into basic deco without trimix and up to 100% O2 at less than 40m.

 

[J-Vo]

I'm more in the set it and forget it camp. Even if you can get away with less deco on smaller dives, GFs makes less total difference in those dives anyway.

I'm running 50/65 at least until my PFO closure is verified. I doubt I'll go above GF high of 70 after that though.

 

[dmaziuk]

A probabilistic deco algorithm like SAUL would tend to support that premise. However, the rates of DCS with available dive computers are all quite low for no stop diving.

Conservatism

I had a dialog with a fellow diver on consevatism. He is an fierce advocate of eliminating risks, and consequently diving conservatively. He recommended to set my my Shearwater computer at high conservatism AND set max ppO2 at 1,2. This made me wonder afterwards, how does each of this impact...

scubaboard.com

DAN's project dive exploration was unable to demonstrate such an effect

Project Dive Exploration (PDE)

Researchers sought to understand if there was a correlation between how recreational divers dive and the prevalence of decompression sickness (DCS).

dan.org

Check out Robert's blog if you haven't already: The Theoretical Diver – Theorizing about scuba diving (the Probabilistic Models post).

I think similar critique applies just as well to conservatism settings on the "deterministic" models: the chosen M-values were verified to produce x DCS incidents in y dives at -- speaking ZH-L+GF -- 100/100. We're assuming that the probability decreases linearly when reducing M-values (which is what GFs actually do), and that assumption is based on exactly zero exploded goats and bent caisson workers. I.e. no "scientific" evidence whatsoever, we just do it because "it stands to reason".

 

[NitroxOnly]

I'm interested in what gradient factor settings everyone is running and why? Does the type of dive you're doing affect your settings (e.g., cold vs. warm water, technical vs. recreational, clear vs. silty, other)? I've heard everyone is all over the map with regard to the settings they are using and I'm curious to hear if there's any sort of consensus.

I've been reading some of the past threads regarding gradient factors and decompression theory but didn't see this aspect specifically addressed, though admittedly I didn't read back super far. However, some of the threads regarding the efficacy of deep stops have been super interesting.

One thing that came to mind while reading those threads is it would be super interesting for Shearwater for example to sponsor some deco research. Many people upload their dive profile and data to their cloud based app. It might be interesting to have a short survey people could fill out after their dive with questions related to how they felt post dive, if someone had skin bends, other DCS symptoms, etc. You may only get people that have issues filling out the surveys, but I wonder if you would see some strong correlations between certain gradient factor settings and problems with DCS or even just feeling lousy after your dive (sub clinical DCS maybe?).

The problem with gradient factors is that without data on how your body actually processes inert gas you’re basically shooting in the dark. For example, how fast do you drive over the speed limit? Is it 10 mph over before you get a ticket? Or twelve? The only real way to know is to get the ticket. That’s not the best way to figure out your personal gradient factor. I use a product called O’Dive. It’s an ultrasound device that you use to measure bubbles in the subclavian artery and vein, post dive. You get hard data and you can play “what if” with the data. What if I add additional stop time, what if I change my mix, what if I edit my high or low factors. You can see the result and make the change without getting bent. For me, I’ve edited the high number down to 60. The low number…from 30-50 doesnt effect your profile all that much, it will allow you to carry less bailout or deco gases. I know the argument of your slower compartments will still be on gassing, but in reality they are almost never your controlling compartments. No I am not a salesperson for O’Dive. We had a buddy that would get bent frequently and we could not figure out why. He was very slow in his ascents, conservative stops,etc.. After getting the data, he’s not been bent since.

 

[iointerrupt]

We're assuming that the probability decreases linearly when reducing M-values (which is what GFs actually do),

Do we? I assume GFHi of 75 results in less DCS than 85, but a linearly less amount?

Is the implied suggestion to forget about Gradient Factors because they've never been chamber tested, and only dive 100/100 because it was?

Decompression models are extremely crude compared to reality, but at least GFs give the individual something to work with. You can dive 95/95, and if you get back on the boat and are exhausted, you can go "next time lets try 85 and see how that feels".

 

[inquis]

That’s not the best way to figure out your personal gradient factor. I use a product called O’Dive. It’s an ultrasound device that you use to measure bubbles in the subclavian artery and vein, post dive. You get hard data and you can play “what if” with the data

Dr. Doolette addressed this topic extensively in his talk at RB4. Two quotes I found to be particularly interesting (around the 17 min mark):

• "[VGE are] not very useful for an individual person"
• "If you have a portable device [... and you change your GF...] and you got a lower bubble grade, that doesn't tell you anything"

There is so much variability, even for the same diver and even for the identical dive (controlled time and workload). Additionally, he showed the majority of the no-DCS cases had Grade 3 bubbles; i.e., "a lot", since Grade 4 is "too many to count" (his words).

Based on that, it doesn't seem like O'Dive is a great way to figure out my personal gradient factor. YMMV.