OOA at 75'

[H2O 70]

I'll read the article again, and maybe we can discuss it on a thread on Basic Scuba - but I am not going to stop doing them just because my computer is not set up to suggest them. I think they are a very good idea...!

It wasn't that the computers weren't set up to suggest them, it was that they weren't set up to account for them in their algorithm. It was an interesting point.

 

[DandyDon]

It wasn't that the computers weren't set up to suggest them, it was that they weren't set up to account for them in their algorithm. It was an interesting point.

Well, SDiver and I happen to have the same brand, but his is newer and does allow for deep stops I think. My older ones do not, but they do not penalize either - and I use the computer to assist me in my diving, not control me, so I'll still do them. When I did a TDI Deco class, they were not suggested, but I still did them on my dives - with my Inst blessings.

They are a relatively new idea...

 

[Bubbletrubble]

With an OOA (or severely low on air) diver at 75 fsw, doing a deep stop should not have been a priority. So long as the OOA diver hadn't tripped into deco (which would have made two critical errors), the priority during the air-share is making a controlled ascent to the surface and doing a 3-minute safety stop if possible. Considering the depth of the dive, it probably wouldn't have been a bad idea to extend that stop to 5 minutes or longer, gas supply of the donor permitting (which was the case since the donor surfaced with 1000 psi).

I agree that there was little need to return the low on air diver to his back gas. Not sure why that occurred.

I have no problem with deep stops. I do my version of them when I think it might be useful. My computer does not give credit for the deep stop, per se. It considers the stop as part of the multi-level dive profile. I dictate how long I want to stay at a particular depth and then will take note of any "suggestions" that the computer spits out. FWIW, my computer only specifies a 3 minute safety stop, but I will usually conduct a 5 - 7 minute stop, splitting that time between 20 fsw and 10 fsw.

I have a problem with people overstating the research that's been done on deep stops. There is insufficient evidence indicating that deep stops lower the incidence of DCS in recreational divers. The certainty with which Ayisha wrote is frankly not supported in the literature. Part of being able to use research effectively is to understand what has been tested, how it was tested, and what reasonable conclusions could be made from the data. All of us should be mindful of overstating the significance of the data, since it's very easy to make this mistake. Heck, even Peter Bennett, who has co-authored a couple of deep stop papers, misspoke in the Alert Diver article in question.
The interviewer asked: "Should recreational divers staying within no-decompression limits be concerned about deep stops?" Bennett responded:

There is no more reason for concern about deep stops than for the widely accepted shallow safety stop. Both were developed based on the reduction of bubbles in the blood vessels seen in research studies. The research on the deep stop is, in fact, more extensive and is based also on actual recreational dives. The deep stop at half the depth for 2.5 minutes significantly reduces not only bubbles, but also the critical gas supersaturation in the "fast" tissue compartments (like the spinal cord's 13.5 minutes) without increasing the "slow" compartments usually related to limb pain. More recent research is concerned with the damaging effects of bubbles on the endothelial lining of blood vessels. Reduction of such bubbles will prevent this.

(I added the bold-faced text for emphasis.)
Where Bennett errs is when he uses information taken from a theoretical model to support the notion that recreational divers should be doing deep stops. That's backwards. He should have stuck with citing the bubble studies and the possible link between bubbles and DCS. At the very least, he should have made it clear that, based on deco algorithms utilizing various tissue compartments, deep stops could be helpful. Furthermore, he does not qualify his statements regarding the deep stop bubble studies by acknowledging that very few deep stop profiles have been rigorously evaluated. Moreover, the track record for divers doing 10-20 fsw shallow safety stops is far more extensive than that for half-depth deep stops. Yet another point is that it's quite possible that deep stops at half depth might not be optimal for significantly reducing DCS.

Sorry for the off-topic discussion.

 

[DandyDon]

I agree that there was little need to return the low on air diver to his back gas. Not sure why that occurred.

Oh, I've done that at time. Give him my pony as he he gets low, allowing him to keep at least 500# in his back gas not being used until after the SS, then switching him back to his own for surfacing, inflating and boarding. I really like keeping the reg in the mouth until fully on the boat well.

 

[TSandM]

I think the real life challenge is discussing all the minutae of solid dive team planning and execution with an insta-buddy who just wants to jump in the water. Especially when I turned out to be over-confident in his skill set. Remember, it was the MOST EXPERIENCED diver who went OOA of on this dive. Hmmm...

This is why I am a PITA to everybody I dive with. I want a dive plan and an equipment check. I'm so known for it that when Peter dove with one of our companions on the trip we just finished (because I was out with a knee injury) the guy started saying, "Well, I know you're going to want a dive plan . . ." and Peter said, "Jump in and swim around and take pictures work for you?" And my dear mentor, NW Grateful Diver, said, "Bric, he ain't Lynne."

Lynne wants a dive plan, even if it's as simple as max depth, estimated time, starting gas and a simple gas utilization strategy, and identifying a leader. And I don't start the dive until I have one, and I can be quite mulish about it. Better to have irritated buddies than issues underwater.

 

[Ayisha]

I use the computer to assist me in my diving, not control me, so I'll still do them.

Good thinking, Don. Most computers continually re-calculate NDL's throughout the dive, so it is not necessary to have the computer be able to plan or recognize it as a deep stop. The computer will simply recalculate your theoretical NDL's based on your actual dive profile, whether it includes a deep stop or not. There is really not much difference between a deep stop and a multilevel dive. A multilevel dive is usually considered to be beneficial to off-gassing as opposed to a square profile or sawtooth profile dive.

With an OOA (or severely low on air) diver at 75 fsw, doing a deep stop should not have been a priority.

The deep stop suggestion was not about dealing with a LOA emergency, it was in regard to PLANNING as others had already discussed. If the dive plan included reserving the gas for a deep stop, a slow graduated ascent and extended safety stop, as well as rock bottom that had previously been suggested, and the gas supply of each diver was monitored to enable this plan, short of a catastrophic occurrence, the LOA would not have happened in the first place. However, in this case, there was no issue with being able to perform any stops that the divers planned since the donor had plenty of gas to bring both of them to the surface including completing any stops.

Deep or haldane model stops have occurred since the beginning of diving. There was an early movement away from them, and in recent years, there has been a movement back to them, first with a one minute deep stop, and then toward the 2 1/2 minute deep stop in the last 18 months or so. I also originally resisted increasing my deep stops from 1 minute to 2 1/2 minutes because of the concerns at the time, but the more I read, the more it made sense. The concerns seemed to be more of an issue for tech divers, and performing a deep stop at or above half-depth in recreational diving seems to really not be an issue. Do you really think that a stop at let's say 50 or 60 feet for 2 1/2 minutes is really going to affect your off-gassing negatively any differently than a multi-level dive?

No, a deep stop or anything other than the most basic dive planning is not necessary in recreational diving. However, it has not been shown to be harmful, just as a multilevel dive has not been shown to be harmful, and there is evidence that a deep stop can help in off-gassing more efficiently in recreational dives.

BTW, at the Hyperbaric Medicine conference last fall here in Toronto, which involved doctors/speakers from around the world, it was emphasized that a deep stop for 2 1/2 minutes and an extended safety stop were some of the most important things one can do to avoid DCS.

 

[openmindOW]

I want a dive plan and an equipment check. ... Lynne wants a dive plan, even if it's as simple as max depth, estimated time, starting gas and a simple gas utilization strategy, and identifying a leader. And I don't start the dive until I have one, and I can be quite mulish about it. Better to have irritated buddies than issues underwater.

Amen.

 

[DandyDon]

...a deep stop for 2 1/2 minutes and an extended safety stop were some of the most important things one can do to avoid DCS - probly right after hydrate hydrate hydrate.

 

[Peter_C]

Do what you feel is right for your kind of diving...For recreational diving, I was trained to hold half depth for thirty seconds, then slowly ascend for thirty seconds to the next ten foot level and hold that for thirty seconds, then thirty seconds to the next level and hold for thirty seconds, etc. So another way of putting it is 1 minute stops every 10 feet starting at half depth and throw in a couple extra minutes at the 20' (If there is big swells) or 10' stop for extra security if coming up from a longer deeper dive~100' for 35 minutes on 32%.

 

[Diver Tim]

(Last time I looked, Lamont's article wasn't available any more.)

I think you can still get it here: Rock Bottom and Gas Management for Recreational Divers