Deep stops really worth it?

[GCullen94]

Came across a study showing done by the U.S. Navy Experimental Diving Unit looking into the effectiveness of deep stops. I was wondering who here uses a deep stop strategy in technical diving or recreational safety deep stops? Or if you run a computer on a deep stop setting, use a deep stop program such as VPM, or run with the GF's set to produce deep stops?

Here's the link to the original article
NEDU study

Thanks,
GC

 

[Chugwhump]

---------- Post added December 20th, 2013 at 12:15 AM ----------

Deep stops worth it?
GC

Yes.
They are worth it.
What do you have to lose other than some more time diving?

Chug
Stops when deep.

 

[DevonDiver]

I tend to use VPM-B to calculate my schedules.

I don't add manual, arbitrary, deep-stops to either technical nor recreational dives.

I do add shallow stops (beyond a 'minimal' 3min/5m safety stop) to recreational dives.

I do believe that there is more to be considered with arrested ascents on a deco profile than "losing a few extra minutes diving"...

 

[GCullen94]

"Both DCS incidence and median VGE scores were higher after the deep stops schedule than after the shallow stops schedule. This is the largest man-trial of individual decompression schedules of which we are aware and the only laboratory comparison of deep stops and shallow stops that is not confounded by differences in TST. Present results failed to support any potential benefit of the bubble model schedule over the gas content schedule for air decompression diving. Since the purpose of a decompression stop is to limit the formation of bubbles while allowing washout of gases from tissues,interpreting this result requires a clear picture of the relationship between tissue gas kinetics and bubble formation. "

That is from the conclusion of the article, done by NEDU

The usefulness of deep stops is one that is still debated today and is a very interesting discussion.

The Navy found that deep stops actually increase the risk of decompression sickness, as well as having larger VGE bubbles in the blood after surfacing possibly causing more fatigue after a dive.

 

[Eric Sedletzky]

I absolutely do deep stops. Ever since I read a very good report in DAN about the effectiveness of deep stops to prevent bubble formation.
I don't do any tech diving anymore, but even on my fairly deep recreational dives I always incorporate a few deep stops.
On any dive to 60 or 70 feet for anything close to the NDL I'll stop at 30 then 20 then 10 for the remainder just as a normal practice.
On dives 80 feet or deeper that get close to NDL I'll stop at half the deepest depth then work up.
I don't know anything about the new computer models. When I was doing tech there were no computers that would recognize deep stops so we used bottom timers and tables.

 

[GCullen94]

It seems like on recreational profiles, the deep stop is effective at aiding in off gassing however in technical profiles, deep stops actually cause the slow compartments to continue to on gas while fast compartments are off gassing. This causes the VGE scores in the slow compartments to be higher when the diver is at the surface and subsequently more risk of DCS. Temperature also plays a roll in the effectiveness of deep stops as the cold will cause decompression to not be as effective. Because the divers were in the water longer on a deep stop profile, they got colder and this caused the shallow portion of their decompression to not be as effective.

 

[TSandM]

The study cited is very interesting, because it's really pretty well designed. They did a large number of dives with the same bottom time, and the "deep stops" profile was one I think most of us with technical training would have chosen, starting the stops at 70 feet. The shallow stops profile started at 40, but heavily loaded the very shallow stops, as traditional Buhlmann-esque profiles do. Their results are pretty compelling, both in symptomatic DCS and bubble grade. Pure Buhlmann did better.

However, they did not use any decompression gas, as far as I can tell; all the deco was done on the same air that was breathed during the bottom time. I wonder if that would have made a difference.

At any rate, I have long found the evidence for very deep stops less than compelling, and this study is even more of an eyebrow-raiser.

 

[dumpsterDiver]

My personal experience with aggressive diving, doing 3-6 dives per day in depths of 90 to 135 with close to deco or maybe into deco a little on some dives.... I noticed a marked decrease in the occurrence of "pole spear" elbow... a dull ache in my elbow that I would have liked to attribute to over use... but I'm pretty sure (now) it was more than that...

I had a buddy who used to definitely get bent in the elbow doing similar dives and once he started doing a tiny bit of exercise on the stop and a deep stop, he wasn't getting bent anymore and having to sit out a day of diving.

2-3 minutes at 50 feet is what I use for a deep stop. My computer does not call for it, but it should be adjusting the calculations for it when I do them.

Unless I have shark problems or REALLY want to save air for another dive on the same tank; I stop about half way up for a little.

 

[dmainou]

Guys, sorry to point to another forum however on this occasion I believe it's worth it.

Please have a read. It gets a bit repetitive but it is certainly good.

Amongst other contributors you have Dr Simon Mitchell and David Dollette (sorry if I misspelled it). On the other side of the fence you'll find Ross Hemingway who sells v- planner.

http://www.rebreatherworld.com/showthread.php?t=46994Deep stops debate (split from ascent rate thread)

Sent from my GT-I9300 using Tapatalk

 

[Kevrumbo]

Look at the Bottom Mix Gas used in the NEDU Study (essentially Deep Air):

(Abstract, p.i)). . .Divers wearing swimsuits and tshirts, breathing surface-supplied air via MK 20 UBA, and immersed in 86 °F water were compressed at 57 fsw/min to 170 fsw for a 30 minute bottom time during which they performed 130 watt cycle ergometer work. . . Results indicate that slower tissue gas washout or continued gas uptake offsets the benefits of reduced bubble growth at deep stops.

(Conclusion p.18) The practical conclusion of this study is that controlling bubble formation in fast​

compartments with deep stops is unwarranted for air decompression dives.
​

This is the simple main point IMO/IME, to take away from the study:

Of course you're going to have significant residual inert Nitrogen and potentially on-gas N2 at your deep stop & even at intermediate deco stops on Eanx50 which may encroach on critical slow tissue M-values --if you were using a working bottom mix with a high fractional N2 content to begin with like Air. Plan accordingly, use a computer to track your inert tissue loading (i.g. Shearwater Petrel) and be prepared to extend your 6m depth 100% Oxygen deco profile along with a stand-by In-Water-Recompression Table as a DCS treatment contingency if necessary should you choose to use Deep Air on mandatory decompression dives, especially on multiple dives per day over a week or more.