Deep Stops Recreational Divers

[dmaziuk]

Under the right conditions that ascent rate would be harmful. Could those conditions be met on a rec dive??????

Theoretically if you use a very fast tissue compartment, like RGBM's or ZH-L12's 2.5 minutes, it will on-gas very fast and reach NDL very quickly. That NDL will not be meaningful because the compartment will also off-gas very fast on ascent. i.e. with slow enough ascent rate it'll never actually hit its M-value. But if you blow that ascent rate it can.

Now whether there is an actual "2.5-minute tissue", or whether coming up 3 meters in 2 seconds really matters is another question.

(Note that dive computers tend to average ascent rates over longer-than-a-couple-of-seconds intervals before turning on ascent rate alarm. I expect such averaging has not been applied to the "200 fpm" number because, well, the surface is too close.)

 

[boulderjohn]

I think Deco for Divers quotes a study that found most recreational divers ascend from their safety stop to the surface at 200 fpm. Perhaps we should be amazed that we don't see more obvious signs of decompression stress when this is the case?

I would like to see the actual wording of that. With millions of recreational dives done around the world every year, how could you possibly know the ascent rate of most of the the divers after a safety stop? Where would that information be found?

I cannot guess what percentage of my total dives are recreational dives with safety stops, but I have completed quite a few in many places around the world--check my profile to see. I have seen many thousands of divers surface following safety stops. I certainly don't time them, but I do not often see people doing such ascents at what I would consider an alarming rate. If someone were going at 200 that fast, I would probably feel compelled to seek out such a person after a dive to give a polite warning, and I have never even felt the urge to do so.

 

[VsubT]

With a known + trusted group:
No. Nice 30 fpm ascent to ~30’ depth, then ease up to a safety stop.

With known clowns or an unknown group:
Yes. A 1 minute stop at half depth. Less to do with decompression than keeping folks from getting separated or ascending too fast. Easier than a surface rescue and less paperwork.

Lance

 

[tursiops]

If someone were going at 200 that fast, I would probably feel compelled to seek out such a person after a dive to give a polite warning, and I have never even felt the urge to do so.

I have, in fact, made comments to people after their ascent from a SS.

 

[dmaziuk]

I would like to see the actual wording of that. With millions of recreational dives done around the world every year, how could you possibly know the ascent rate of most of the the divers after a safety stop? Where would that information be found?

In my dive log, subsurface draws yellow vertical lines there. Including the dives where we followed the sand to waist-deep and then stood up: that standing-up part gets logged as ascent rate violation drawn as a yellow vertical line. My computer may be moving up at 300 fpm, even, at that point.

 

[scubadada]

Suunto RGBM Dive Algorithms

 

[rjack321]

I have, in fact, made comments to people after their ascent from a SS.

I can raise my arm at 200ft/min
Back in the early-mid 1990s when I had an analog gauge I'd say I was off and on ascending in the 100ft+/min range (but probably not 200ft/min). I've seen plenty of people cork, feet full of air, in their first drysuit from 30ft in 15sconds (120ft/min)

 

[Nirvana]

Why do you think that Suunto RGBM is a version of RGBM, and so a bubble model calibrated to give deep stops? Surely if it were it would not need to introduce them in the style of Pyle stops as this computer does.

According to the HelO2 manual, section 10.2:

"The Suunto Reduced Gradient Bubble Model (RGBM) is a modern algorithm for predicting both dissolved and free gas in the tissues and blood of divers. It was developed in co-operation between Suunto and Bruce R. Wienke BSc, MSc, PhD. It is based on both laboratory experiments and diving data, including data from DAN. It is a significant advance on the classical Haldane models, which do not predict free gas (microbubbles)."

In a later passage, section 10.2.1:

"Suunto's decompression model development originates from the 1980s when Suunto implemented Bühlmann's model based on M-values in Suunto SME. Since then research and development has been ongoing with the help of external and internal experts. In the late 1990s Suunto implemented Dr. Bruce Wienke's RGBM bubble model to work with the M model."

 

[dewdropsonrosa]

I would like to see the actual wording of that. With millions of recreational dives done around the world every year, how could you possibly know the ascent rate of most of the the divers after a safety stop? Where would that information be found?

I cannot guess what percentage of my total dives are recreational dives with safety stops, but I have completed quite a few in many places around the world--check my profile to see. I have seen many thousands of divers surface following safety stops. I certainly don't time them, but I do not often see people doing such ascents at what I would consider an alarming rate. If someone were going at 200 that fast, I would probably feel compelled to seek out such a person after a dive to give a polite warning, and I have never even felt the urge to do so.

I'll look for it when I get home tonight, I know I read it fairly recently.

However, I will amend my prior wording to indicate that the results pertained to the recreational divers in the study. Depending on the methods, this may or may not be a good sample of the gen pop.

 

[shurite7]

With millions of recreational dives done around the world every year, how could you possibly know the ascent rate of most of the the divers after a safety stop? Where would that information be found?

Good question. This would be a good study, if it could ever be done. In my experience while working in the islands is more than half the people ascend rather quickly from the safety stop. We used to remind customers to slow down. On GUE's video Mysterious Malady's of Decompression one of the doctors from DAN mentions this issue. This is an interesting video for those who haven't seen it.