Padi Advanced OW - Deep stops??

[rjack321]

+1.

In the interest of nitpicking, Marroni's study concluded that for 25-minute dives to 25 metres, faster ascent rate with "deep" and shallow stops produced less Doppler echoes than slow linear ascents. That idea extrapolated to deeper and longer dives resulted in NEDU study and "deep stops considered harmful". If both are true, then you can't expect deep stops to do any good for any dive profiles other than Marroni's 25/25. They may, they may not.

Basically you still have to get off the darn bottom efficiently. Most beginning divers ascend too fast (60+ft/min). Once we/they get our buoyancy wired divers usually ascend slower than optimal (10-20ft/min).

 

[Diver0001]

+1.

In the interest of nitpicking, Marroni's study concluded that for 25-minute dives to 25 metres, faster ascent rate with "deep" and shallow stops produced less Doppler echoes than slow linear ascents. .

If I'm not mistaken, they showed that a linear ascent with the same duration as stepped ascent with the steps being taken at a rapid pace will result in lower doppler scores. It seems counter intuitive because we have all been trained to ascend slowly. However, when you do the math I think you'll see that a linear ascent results in a deeper average depth and THAT seems to be the main factor at work here. Put that way, it doesn't seem counter intuitive at all. Lower average depth with the same total ascent speed = lower doppler scores.

R..

 

[Centrals]

$200.00 is the absolute maximum I would pay for a nitrox compatible computer. Gauge mode is an added bonus and even more so if it also displays average depth BUT only if you need those features at all.

 

[DrGonzo]

As a side note does anyone do the 1 min stop at 3m or is it just me?
3 min at 6m, 1 min at 3m as the most bubbling off occurs there.
Extra safe or not worth it?

 

[scubadada]

Here is yet another well written article discounting the benefits of a Deep Stops. The question I have is "why stay deeper and take on more N2 loading?". It is better to get out of the on-gas depths when not needed!

From the NEDU (Navy Experimental Diving Unit):
Redistribution of Decompression Stop Time From Shallow to Deep Stops Increases Incidence of Decompression Sickness in Air Decompression Dives

www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA561618

This study has nothing to do with recreational diving and deep stops. There has been extensive discussion of this study and the topic in the technical diving forum and on other diving discussion sites

 

[Diver0001]

As a side note does anyone do the 1 min stop at 3m or is it just me?
3 min at 6m, 1 min at 3m as the most bubbling off occurs there.
Extra safe or not worth it?

This strategy can't hurt but what it basically does is slow down your ascent from 5m to the surface. That, in and of itself, is a good general principle. There isn't a computer or a table on the market that I know of that mandates this but the procedure certainly can't hurt if you have the time to do so.

R..

 

[Diver0001]

This study has nothing to do with recreational diving and deep stops. There has been extensive discussion of this study and the topic in the technical diving forum and on other diving discussion sites

Correct.

The confusion I was talking about in my long post above is the confusion created by the definition of a "deep stop".

Depending on the algorithm, a computer in decompression mode will sometimes prescribe a "deep stop" or in other, more accurate words, a "deep ascent curve". In this definition, the stop is part of an ascent strategy intended to get the diver from depth to the surface without developing decompression sickness. These stops are not normally considered to be optional by people using these ascent strategies.

In the context of a recreational dive the computer may also suggest a "deep stop". (note, I'm using the word "suggest" here and "prescribe" in my previous statement). In this definition the stop is intended to build in an extra buffer of safety during an ascent where *all* "stops" are optional.

"Extra safety" is good (provided, of course that there isn't a compelling reason to ascend faster), but there is a non-semantic difference between "extra safety" and "avoiding clinical DCS".

The unfortunate thing here is that we use the term "deep stop" to mean both things. That's why in threads like this we see people citing the Marroni study and the NEDU study as arguments related to the same concept. They are not. The NEDU study, as pointed out by @scubadada is a study about the first definition and offered conclusive results. The Marroni study looked at the second and with inconclusive results.

It would be better for the discussion as a whole if we talked about "deep curve" in the first case and "deep stop" in the second, or some such thing. They really should be given two different labels at this point.

R..

 

[boulderjohn]

It would be better for the discussion as a whole if we talked about "deep curve" in the first case and "deep stop" in the second, or some such thing. They really should be given two different labels at this point.

During the raging deep stops debate in the technical diving forum, I started a thread so that we could agree on a definition for the phrase "deep stop." That effort was a failure.

During the discussion among the experts in the 2008 DAN Deep Stop workshop that was intended to come to a consensus statement for the results of that workshop, the problem of the definition of the phrase was raised. They could not come to a consensus of a definition then, either. Some suggested just eliminating the phrase altogether. I think I am moving in that direction myself.

We all know that when we ascend, we must use some sort of strategy so that we can reach the surface without DCS. We all would agree that ascending a few feet and then stopping for 10 minutes is stopping too deep for too long. We would all agree that going directly to the surface from all but the shallowest dives would be stopping too shallow for too little time. Somewhere in between those extremes is the best strategy for that diver on that dive. The problem is we really don't know what that strategy is. Some people think that the first stop should be deeper than other people believe it should be. For me, that is all that is needed in a discussion, and trying to pin down a definition is not only unnecessary, it is counterproductive. In the raging debate in the technical diving discussion, that simple difference was missed by people who insisted that everyone follow their definition of deep stops rather than just talk about the search for an optimal decompression strategy.

 

[Diver0001]

Glad I was able to draw you out of the woodwork on this discussion, John. If there is anyone on Scubaboard who can explain these things to the masses, it's you.

R..

 

[scubadada]

My Oceanic computers offer an optional deep stop for no deco dives only. It is a 2 minute stop at half the maximum depth of greater than or equal to 80 feet. The owner's manual cites the Morroni & Bennett study. I have never utilized this option. I do spend an extra couple of minutes at my SS if I have come within several minutes of deco. When doing light deco, I pad the shallow stop by 3-5 minutes, kind of like adding a SS after clearing the deco obligation. I dive the DSAT decompression algorithm. So far, so good, for me