Evolving Thoughts on Deep Decompression Stops

[rjack321]

This was well before GFs. GF's were added to make Bühlmann a part of the deep stop craze.

On a 20min 350ft dive using 32%, 50%, 100% deco gasses as might have been used in the 1990s a 100/100 profile generates a first stop at 130ft (36seconds at 140ft actually but going to assume that clears).
Pyle stops (rounding slightly) would be at 240, 180, 160 and 140 then, about 4 mins more on that ascent

A 30/100 profile would have 48sec at 220, then 1 min every 10ft all the way up to 150. and 2mins at 140. 10mins added below 130.

50/100 has 5 mins added below the 130 stop/switch starting at 190. So pretty close to the Pyle stop time overall and only minute at 240 is deeper.

At least for this depth/time/gas combo, the "modern" raising of the GF low is pretty close to the pyle stop approach from decades ago. Total time is 110-120 mins.

Contrast with VPM+2 which (for the same bottom time and 3 deco gasses has 22 mins below the 130ft switch! Starting at 270ft. There's also more time overall with a 147min runtime.

Net:
100/100 no adjustments = 350ft 20min OC "base" 1990s profile, first stop is 130ft
Pyle stops add 4 mins below 130ft first stop -which is also 32% switch depth
GF low of 30 adds 10mins below 130ft switch
GF low 50 adds 5 mins below 130ft switch
VPM+2 adds 22 mins below 130ft.

Saying Pyle stops are the same as "deep stops" is not appreciating their overall duration and likely effect.

 

[dmaziuk]

This was well before GFs. GF's were added to make Bühlmann a part of the deep stop craze.

In all fairness, they were built on the general idea of adding conservatism, and don't have to be used to generate deep stops. They're flexible enough to generate extended shallow stops instead by using GH Lo > GF Hi. Or use GF Hi=GF Lo to add conservatism without changing the shape of the profile.

Driving motivation was the deep stop/bubble model argument, but the tool itself is better than that.

 

[dmaziuk]

It doesn't matter the calculated ascent rate. If (Pyle way back in the 1990s) was ascending faster than the stipulated ascent rate, "stops" which effectively slowed that down would make it "better" - or at least closer to what was intended.

Indeed. That's why you can't discount the possibility that on his dives the half-depth stop did in fact work by slowing down ascent rate. We can only tell that if you do it by the modern book, it shouldn't work that way.

 

[Manatee Diver]

Indeed. That's why you can't discount the possibility that on his dives the half-depth stop did in fact work by slowing down ascent rate. We can only tell that if you do it by the modern book, it shouldn't work that way.

I agree, which was pretty much the guess I was trying to make. Pyle stops might have been a bandaide for a time before you can easily monitor your ascent rate, and on top of that the allowed ascent rate is much higher.

Now with modern computers that are so accurate that they will yell at your if you raise your arm to quickly during an ascent, and a lower allowable ascent rate that their purpose has been served.

Of course this is just a random stab in the dark to try to explain why it worked for Pyle, and the early advocates.

 

[tursiops]

Of course this is just a random stab in the dark to try to explain why it worked for Pyle, and the early advocates.

What I'm learning from reading here and elsewhere is that it worked for Pyle and others because he was using an overly aggressive deco model (Buhlmann 100/100) so his deep stops backed off from that level of aggression. This got formalized into Baker's GF, and there is still some uncertainty about how much backing off from 100/100 Pyle was using, is "optimal," and is bad for you.
It is beginning to appear that 20/X is too much back-off, and 70/X is too little. And what is X? Well, 50 is too little, and 95 is pushing it. that's what I'm learning. Any more detailed than that depends on individual physiology and on that particular dive. So, 50/70 is maybe a good middle ground to start with, and make your personal adjustments from there.

Is what I'm learning similar to what others are learning?

 

[rjack321]

Of course this is just a random stab in the dark to try to explain why it worked for Pyle, and the early advocates.

1) They don't add that much time relatively speaking
2) Dr. Pyle is an N of 1 (who also got bent quite a bit)

 

[rjack321]

What I'm learning from reading here and elsewhere is that it worked for Pyle and others because he was using an overly aggressive deco model (Buhlmann 100/100) so his deep stops backed off from that level of aggression. This got formalized into Baker's GF, and there is still some uncertainty about how much backing off from 100/100 Pyle was using, is "optimal," and is bad for you.
It is beginning to appear that 20/X is too much back-off, and 70/X is too little. And what is X? Well, 50 is too little, and 95 is pushing it. that's what I'm learning. Any more detailed than that depends on individual physiology and on that particular dive. So, 50/70 is maybe a good middle ground to start with, and make your personal adjustments from there.

Is what I'm learning similar to what others are learning?

I'm using 50/75 lately and combined with suit heat have been feeling way better at 50yrs old than I did when I was younger and fitter at 40yo. My personal N=1

 

[DavidFL]

Thanks for writing this John. I've seen and read most of the content of your article elsewhere, but spread out over multiple threads and videos and my own searches, ad many times with so many other follow up posts and threads that it is hard to keep it sorted.

 

[boulderjohn]

I'm using 50/75 lately and combined with suit heat have been feeling way better at 50yrs old than I did when I was younger and fitter at 40yo. My personal N=1

I am going to go at either 50/75 or 50/70 when I get back to deco diving. I had been using 50/80 before that.

 

[boulderjohn]

Is what I'm learning similar to what others are learning?

What I like about that simple sentence is the difference in attitude compared to my first foray into tech. Then I was given absolute "this is what you MUST do!" dogma. Bring up anything else, and you got an insult for a response.

It has been more than 100 years since the first ascent tables (Haldane's) appeared, and they were used with more or less success by the British Royal Navy until 1955. For most of a century, information was gleaned through research a little at a time, with one tweak leading to another. People like Hill, Workman, Spencer, Rogers, Bühlmann and others did extensive research to add to a knowledge base. Lots of people got bent creating that knowledge base. Then suddenly everything changed, and radically different approaches were developed, all with little to no actual research. I don't know what everyone's else's experiences were, but for me, it was the rigidity I mentioned above.

And that still exists. The reception of this article in this and other public forums has been pleasant, but I can assure you that all is not wonderful in the arena of private correspondence, where insult is still the primary mode of persuasion.