DIR- Generic gradient factors

[PfcAJ]

I use high 85, and I change my GF low to get the first stop at 21, where i usually do the gas switch

This approach makes no sense.

Manipulating the algorithm so your stop depth (which is controlled by physics and physiology) is at the same depth as a gas switch (which is user choice, you could choose any gas, and by extension, any depth) is backwards thinking.

If you didn't have 50% would you adjust your GF low so your 1st stop is at 6m?

 

[ls23]

The newly released article on the GUE blog finally has something "official" on the GF 20/85 training standard:

"During the early 2000’s, GUE developed a reference standard based upon Buhlmann algorithms. The intent was to ensure divers reference profiles with the most successful history. From this base, consideration for team control and unity during ascent, as well as the potential utility of bubble control were considered. Balancing these factors resulted in a gradient factor of 20/85. These settings will not only result in deeper stops but will also account for these stops with additional decompression time.

Current research challenges the value of deep stops, suggesting they may be less efficient. GUE has been slow to adjust parameters for dives conducted during training because the relatively short profiles of students and their need to gain proficiency with a controlled ascent speaks against the value of faster ascents and/or shorter total decompression time. Balancing the experience in our community, while considering the most useful priorities for students, supports a deeper gradient than might be otherwise encouraged by developing research.

GUE protocols maintain a 20/85 reference gradient for training dives where the priority is ascent training and team refinement and where a slight increase in additional decompression time is not problematic. As divers gain experience. they are free to adjust gradients in a way that is suitable to the team while considering personal experience, team preference, mission objectives, and evolving research."

and

"Low gradients such as 20/85 should not be confused with studies like that done at NEDU. The NEDU research greatly delayed the ascent, adding 3.4 x’s the stop time in the first three stops alone, as compared to a similar 20/85 profile. More importantly, the NEDU study did not account for the additional decompression time these low-gradient stops develop because it was testing whether the value of deep stops in controlling bubbles was enough to overcome the increased on-gassing at these deeper depths. Yet, a 20/85 profile is very different, since it will increase the decompression time as a consequence of the lower gradient at depth while actually “insisting” upon a relatively low compartment pressure upon surfacing. One can certainly argue that these deep stops are not useful or that they delayed the ascent unnecessarily, but it is difficult to argue that they are more dangerous, unless the diver ignores the resulting shallow decompression time. The problem with low gradients is mainly an issue of decompression time, with risk accruing when divers add deep stops while ignoring the consequences of that gas loading. This reduced time was the hope and advertised benefit with deep stops, but shortening shallow time is not necessary with the inclusion of deep stops."

Part Three: Bubble-wise, pound-foolish. Are deep stops dangerous?

 

[JohnnyC]

"We're gonna keep using 20/85 because deep stops make students work more." Huh? C'mon dude.......

The article is a Ross Hemingway-style cop out. I think it's funny that he proudly talks about pushing boundaries and moving forward by extrapolating data (in another part of the series) to create ratio decompression, but refuses to extrapolate the findings of the NEDU study. Which is literally in the study's title.

I think the most telling line in the entire article is this,"What we can say now is that it is unlikely anyone study could convince those that perceive years of success with a given approach." His bias is pretty clear. Using words like "aggressive" to talk about higher GF-Lo's, etc. The entire article is contradictory in nature.

 

[jgttrey]

One can certainly argue that these deep stops are not useful or that they delayed the ascent unnecessarily, but it is difficult to argue that they are more dangerous, unless the diver ignores the resulting shallow decompression time. The problem with low gradients is mainly an issue of decompression time, with risk accruing when divers add deep stops while ignoring the consequences of that gas loading. This reduced time was the hope and advertised benefit with deep stops, but shortening shallow time is not necessary with the inclusion of deep stops.

Sigh. Apparently, we've come a long way from justifying deep stops by attacking "bend and mend" models.

Now that research suggests that deep stops potentially cause more issues than they cure, the solution is "don't worry, we'll just do more mending on the shallow stop." Sounds like the worst of all worlds when it comes to efficient deco.