Evolving Thoughts on Deep Decompression Stops

[Manatee Diver]

It's not impossible, but ascent time and rate usually get factored in. So e.g. if at 60 fpm you hit an M-value at 18 m, you'll get the stop at 18 m. If, on the same ascent but at 30 fpm you hit an M-value at 12 m, you'll get the stop at 12 m instead. In other words you'd have to mis-calculate your profile, or blow your safe ascent rate in order for it to work as you say. I think -- ICBW and all the usual disclaimers, of course.

Pyle stops weren't calculated as part of the profile.

They were 1-2 minutes stops half way between your max depth, and your profile's first stop. And then half again, and if needed half again.

 

[dmaziuk]

Pyle stops weren't calculated as part of the profile.

They were 1-2 minutes stops half way between your max depth, and your profile's first stop. And then half again, and if needed half again.

My point is that if the first stop is calculated correctly for the 60 fpm ascent rate in the first place, then adding Pyle stop to "slow down" should not make things "better".

Edit: on 2nd thought, Buhlmann's formula gives you the safe ascent ceiling "right now", so in theory even if you could teleport from your max depth to the first stop in zero time, you should still be under M-values in every tissue compartment.

It's the clever implementations that factor in ascent time and recompute your next stop depth, that are affected by ascent rate.

 

[gypsyjim]

Much of the terminology in the linked article is above my head, and I am not a "technical diver" on any level.
Still, I was taught, not that long ago to add a deep stop ( called a Haldanian stop by my instructor) at 1/2 my deepest depth when diving in the 100'+ range.

I have also since that training heard debate that suggested such deep stops are not as beneficial as I was taught.

In your article I did see this from the Navy tests, and I found it pretty enlightening:

"The study concluded: “The deep stops schedule had a greater risk of DCS than the matched conventional schedule. Slower gas washout or continued gas uptake offset benefits of reduced bubble growth at deep stops.”


Thank you.

 

[tursiops]

John:
Very nice. Thank you.
You've got footnotes that evidently refer to references, but the reference list is bulleted, not numbered.

 

[Jay]

Thank you @boulderjohn. It was a great read.

 

[Wathdoc]

John, a well written and well referenced article if I may say so. What is often not mentioned is the role of the vascular inflammatory response in the production of DCI. One of the references alludes to this. Its a poorly understood reaction regards DCI and involves the compliment activation system(part of the immune system). Like others have said it does seem sensible to avoid on gassing of the none fast tissues ,whilst avoiding DCI risk to the brain and spinal chord.

 

[rjack321]

My point is that if the first stop is calculated correctly for the 60 fpm ascent rate in the first place, then adding Pyle stop to "slow down" should not make things "better"..

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. Even digital depth gauges were practically in their infancy so reliably measuring and logging ascent rates was basically impossible for a free swimming diver. Plus, I have no idea what Pyle was using back when those were thought up, its possible they were Bill Hamilton tables or some other proprietary pre-buhlmann dissolved gas table. Even on a 300ft dive they don't often add up to more than 3 or maybe 4 mins anyway, so within margins of measurement.

 

[boulderjohn]

Although he did not say it, I believe Pyle was using Bühlmann as his primary decompression program. He was adding stops deeper than the Bühlmann tables.

The U.S. Navy was the source of the 60 FPM rule, an unscientific decision based on a compromise between scuba and hard hat diving. In contrast, Bühlmann used a 30 FPM scent rate.

 

[rjack321]

Although he did not say it, I believe Pyle was using Bühlmann as his primary decompression program. He was adding stops deeper than the Bühlmann tables.

Then deeper than 100/100 presumably? I don't think GFs were a published "thing" at that time

 

[boulderjohn]

Then deeper than 100/100 presumably? I don't think GFs were a published "thing" at that time

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