Deep Stop on Dive over 100 ft? California Wreck

[clownfishsydney]

I have been doing dives over 40+ metres (135 feet) since 1992. Even when the craze was for deep stops, I was never in favour of them as I figured you were still taking on a lot of nitrogen. My plan (and the vast majority of people I dived with then and still do now) was to ascend from 40 metres to 18 metres fairly fast and then go slower to the first stop. We have never had a problem with this (no-one ever bent) and still use it.

 

[markmud]

Been reading this thread.... it strikes me that the OP has a listed total of 0-24 dives, and self-admits not knowing how to calculate detailed air consumption, has a high consumption rate, and the solution is to just carry 130 cf and a pony. Add in task saturation with spearfishing, and we're talking a potential for some potential risk here. Not telling anyone how to dive, but rather suggest to tread lightly! I'd think that spearfishing at 130' fsw is prime for some EANX discussion.

Hello RVbuilder,

I concur with your assessment.

May we use the correct nomenclature for the term "pony bottle" as it relates to the OP's description for his planned actions? The OP is using his second rig not as redundant gear, but as as a stage bottle. A stage bottle to be used when he sucks his primary system "dry". Where is his redundant gear? Is he following the rule of thirds? He is talking about using technical diving tactics with seemingly no competent knowledge of technical diving protocols.

I do deep stops while recreational diving all the time. The format I am following is multi-level diving. However, I don't think the OP is planning on using half, or some other portion thereof, of his NDL time at 130 fsw and then ascending to 85 fsw for a typical multi-level dive format.

Disclaimer: I don't go to 130' and then burn-up my entire NDL and plan on doing deep stops up to the surface. When my computer's NDL graph is flashing yellow, with staged decompression on the so-called horizon, I forget deep stops, or multi-level diving, and safely ascend to the surface (by following NDL protocols which includes an optional safety stop).

OP: Diving to 60' is relatively benign. CESAs, if performed properly can save your life and you may avoid serious injury (in many cases [caveat emptor]). A speedy ascent from 60' while constantly inhaling and exhaling gas is quite survivable. At 130 feet, and deeper, real SCUBA diving begins. Compound issues and mistakes can turn fatal. And quickly.

Please, get more experience and training from a competent technical diving instructor before doing what you are planning.

thanks,
markm

 

[boulderjohn]

Furthermore, there is just as little evidence for effectiveness of safety stops at 15’. That’s not to say there is zero evidence for either....go back to the DAN article on deep stops from 2011, where the addition of a deep stop and a shallow stop decreased incidence of bubbling as seen on Doppler from 30% to zero. It was more effective than a slow ascent, or a slow ascent with only a shallow safety stop.

That study, which if you find the original DAN article on that study(the study was done nearly a decade before 2011) you will see is now marked as not reflecting current thinking, is the only study ever done to show such a benefit. Those results were contradicted by a later study. (This has been discussed in recent ScubaBoard discussions, including some involving Dr. Simon Mitchell.) There is no research other than that study to suggest a benefit to deep stops by recreational divers.

There frankly has not been a lot of research on the use of deep stops in recreational diving. The first people to advocate it were doing so after what we think of as traditional ascents had been used for about 100 years, with many, many studies by different people during that time. As far as I can see, the trend to put in deep stops in recreational diving was based on the theory that if they are good in decompression diving, they are probably good in recreational diving, too. The theory that they are good in decompression diving became popular at just about the same time, and that idea was based on pure theory--there was no scientific research behind it whatsoever. The various decompression algorithms that grew out of that theory were never really tested before being implemented.

So now all the recent research on deep stops in decompression diving suggest that they do more harm than good, and the reasons for it make sense for recreational dives as well. When you do a deep stop, you are giving your faster tissues a little time to off gas more and get farther from critical saturation levels, but your slower tissues are still on-gassing, and the slower tissue on-gassing seems to be more important than was earlier thought.

One of the theorists who jumped on the deep stops bandwagon immediately designed decompression software that is still in use in many computers. Some of those models include a further deep stop option. Although he participated very briefly in one of the ScubaBoard discussions on the growing disfavor of deep stops, he did not make a meaningful contribution to the discussion and bowed out early. As far as I know, he has been publically silent on the issue in recent years. I am told he is still on the Board of Directors of a scuba agency. It would be interesting to see what kind of input he is currently giving them on this issue.

 

[tomfcrist]

That study, which if you find the original DAN article on that study(the study was done nearly a decade before 2011) you will see is now marked as not reflecting current thinking, is the only study ever done to show such a benefit.

That study used Doppler scores as a metric. So did the NEDU study. If the NEDU study had any validity as a debunker for the study we are talking about, the deep stops profiles from the 2011 article would have had higher Doppler scores than the profile with stops only at 6m...as was generally observed in the NEDU study. That simply was not the case. The scores were lower...by a lot.

The bandwagon reaction of “this doesn’t reflect our current thinking” somehow invalidates scientifically collected and reviewed data? Let’s not forget that this was all AFTER the NEDU study had ended. So why did Mitchell and Doolette not call BS on it as soon as it was published?

 

[Wookie]

That study used Doppler scores as a metric. So did the NEDU study. If the NEDU study had any validity as a debunker for the study we are talking about, the deep stops profiles from the 2011 article would have had higher Doppler scores than the profile with stops only at 6m...as was generally observed in the NEDU study. That simply was not the case. The scores were lower...by a lot.

The bandwagon reaction of “this doesn’t reflect our current thinking” somehow invalidates scientifically collected and reviewed data? Let’s not forget that this was all AFTER the NEDU study had ended. So why did Mitchell and Doolette not call BS on it as soon as it was published?

Real scientists do not publicly call bs on other peer reviewed science just because it doesn’t agree with theirs. They present theirs, and let the readers decide which is right.

 

[tomfcrist]

Real scientists do not publicly call bs on other peer reviewed science just because it doesn’t agree with theirs. They present theirs, and let the readers decide which is right.

Then why call it “peer reviewed”?

 

[Chilly_Diver]

Then why call it “peer reviewed”?

That’s not how peer review works....

 

[rossh]

So now all the recent research on deep stops in decompression diving suggest that they do more harm than good, and the reasons for it make sense for recreational dives as well. When you do a deep stop, you are giving your faster tissues a little time to off gas more and get farther from critical saturation levels, but your slower tissues are still on-gassing, and the slower tissue on-gassing seems to be more important than was earlier thought.

John,

You write these broad comments like its all been proven. In fact, all we really have is opinions and certain peoples interpretations of the science, and a new direction driven by nothing to show its in any way superior. DCS is pretty rare, no matter what ascent type one uses today, so exactly what do you think all this new change is fixing?

But let me focus on the OP question and the paragraph above, and highlight some of the false reasoning used to justify this new changes.

In NDL diving, and those just on the edge of deco, they do not have any slow tissue involvement. They simply do not stay in the water long enough to accumulate any amount of slow tissue gas that matters. An NDL diver who suffers injury, is at the mercy of fast tissue problems. Even the multi-dive NDL profiles, the slow tissues still do not reach supersaturation levels. So trying to use the slow tissue reason on NDL divers, is nonsense. Just thought I should clear that up.

.

 

[tomfcrist]

That’s not how peer review works....

I’m aware of that. Here’s what I have a problem with.

Study A was done comparing NDL dives/divers and had lower Doppler scores using deep stop methods.

Study B was done comparing working divers in deco with a substantial exaggeration in deco time in comparison to any available deco algorithm on the market.

The torch carriers for study B now say that study A is invalid? They are two different things completely. Study A imposes short duration stops on NDL dives and calls them deep stops...2 of them. One at 1/2 max depth for 2 minutes, and 1 at 6M for 3-5 minutes.

Study B in contrast takes an unused and unknown bubble model and plays with the gradient to meet an arbitrary total dive time. This results in multiple stops of long duration at much deeper depths then study A would consider stopping a diver. They determined that the bubble model profile was less advantageous than a shallower profile.

How do these two studies relate? Using critical thinking, it would be logical to assume that if better outcomes were attained using study As method, that deep stops are beneficial in short durations...where as deep stops for long durations are not beneficial.

Not that any of that is relevant, because study B didn’t use deep stops...or Pyle stops, or whatever you choose to call them... they used a bubble model.

 

[IncreaseMyT]

Please, get more experience and training from a competent technical diving instructor before doing what you are planning.

thanks,
markm

LOL wait what? Last time I checked 130 ft was still a recreational dive. Furthermore, no one said anything about running their air dry at 130 foot and then switching to secondary air.

I think you are confused about the discussion and rather than me go get some tech diving instructions for a recreational dive we would both be better served if you went back and read the thread and actually paid attention. Just FYI my watch displays my ATR there is no need for me to calculate air time remaining, I was referring to pre-calculating how much air would be used on the deep stop and what that translates to at 35 ft, if you were paying attention you would know that.

For everyone else that gave me really solid advice, my friend, who has been diving since before I was born, agreed completely with the deep stop and that it isn't necessary.

So I appreciate all the great feedback thank you.