Deep stops, Pyle stops, Gradient Factor
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Figured it was in there somewhere; just couldn't find it. I shouldn't have limited my search to the one forum...
Dr Deco
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Dear dandydon:
Half- Depth Stops
The stop is an improvement over the Haldane rapid rise to the surface. Nuclei are constantly shrinking because of the inward pressure exerted by surface tension. This is the Laplace pressure. If nuclei are allowed to expand because of Boyles Law, the Laplace pressure is reduced. Should that reduction be sufficient such that the partial pressure of nitrogen in the tissue fluid exceeds that of gaseous nitrogen in the microbubble, than that bubble will grow by inward diffusion of nitrogen. One can maintain a high internal pressure in the nuclei by never allowing the Laplace pressure to fall and the inward migration o nitrogen to occur.
The secret to all of this is a slow ascent rate or an intermediate stop. You can see this for yourself with a bottle of carbonated soda. Slow releasing the pressure keeps the nuclei small and few bubbles will form . Note that you are not really eliminating any dissolved carbon dioxide from the liquid. Just reclose, shake, and reopen. You will convince yourself that all of the carbon dioxide is still there.
Dr Deco :doctor:
Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm
Half- Depth Stops
The stop is an improvement over the Haldane rapid rise to the surface. Nuclei are constantly shrinking because of the inward pressure exerted by surface tension. This is the Laplace pressure. If nuclei are allowed to expand because of Boyles Law, the Laplace pressure is reduced. Should that reduction be sufficient such that the partial pressure of nitrogen in the tissue fluid exceeds that of gaseous nitrogen in the microbubble, than that bubble will grow by inward diffusion of nitrogen. One can maintain a high internal pressure in the nuclei by never allowing the Laplace pressure to fall and the inward migration o nitrogen to occur.
The secret to all of this is a slow ascent rate or an intermediate stop. You can see this for yourself with a bottle of carbonated soda. Slow releasing the pressure keeps the nuclei small and few bubbles will form . Note that you are not really eliminating any dissolved carbon dioxide from the liquid. Just reclose, shake, and reopen. You will convince yourself that all of the carbon dioxide is still there.
Dr Deco :doctor:
Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm
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The thread in the other forum pretty well answered my question, but I certainly appreciate YOUR explanation. Just may have to read it over a few times 
but thanks again!!
D-Don
but thanks again!!D-Don
I don't normally make this statement as I think in many cases there is real value in revisiting a subject and it often seems a little cold to people just seeking information.....But you may want to do a search for "deep stop" as the topic has been covered in the past.
Also, check this thread from a couple weeks ago:
http://www.scubaboard.com/t34069/s.html
And this one from a couple months ago:
http://www.scubaboard.com/showthread.php?s=&threadid=28939&highlight=stop+and+half
Also, check this thread from a couple weeks ago:
http://www.scubaboard.com/t34069/s.html
And this one from a couple months ago:
http://www.scubaboard.com/showthread.php?s=&threadid=28939&highlight=stop+and+half
Charlie99
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One way is to download a deco program such GAP deco program.
Using gradient factor conservatism, such as 0.20/0.80 will automatically generate deep stops, even for dives that are within the no-deco limits. VPM is also a good program, but doesn't seem to generate as nice a series of deep stops on a typical 80' 30 minute profile.
Looking at GAP on a wide variety of my typical profiles, I find that 1 minute at 40-50', 1 at 25-30', then 3 minutes at 15' are good for most dives. If the dive is beyond 100', (and it isn't a multilevel dive) I add another 1 minute stop a bit deeper.
On a multilevel dive, for the purposes of deep stops, I ignore all deeper depths once I've been at a shallower level for more than 5 minutes.
Another crude method of generating deep stops is to simply stop halfway between your bottom depth and the safety stop depth for a minute. If that stop is 40' or deeper, then add another 1 minute halfway between it and the safety stop.
Dr Deco
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Hi LightBlue:
Deep Stops
There are various ideas about this. JS Haldane actually put in deeper stops but these were eliminated when the allowable supersaturations were increased in the fast compartments. A deep stop was empirically added by the DFVLR (a German group) in the 1970s. Deep stops were also found empirically by Pyle while collecting fish in Hawaii. They now for a part of the two-phase decompression models.
The means by which they are calculated are empirical. I am not aware of any laboratory studies that actually attempted to determine the best way of doing this.
Other responders have indicated how the stops can be calculated by various algorithms.
Dr Deco :doctor:
Please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm
Deep Stops
There are various ideas about this. JS Haldane actually put in deeper stops but these were eliminated when the allowable supersaturations were increased in the fast compartments. A deep stop was empirically added by the DFVLR (a German group) in the 1970s. Deep stops were also found empirically by Pyle while collecting fish in Hawaii. They now for a part of the two-phase decompression models.
The means by which they are calculated are empirical. I am not aware of any laboratory studies that actually attempted to determine the best way of doing this.
Other responders have indicated how the stops can be calculated by various algorithms.
Dr Deco :doctor:
Please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm
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