O2 deco

[major111]

If my computer says just go to 10 feet for deco stop (and am doing it on 100 %) is there any gain to staying at/just above 20' for a while? Pure 02 is pure 02 but release of pressure is obviously less at 2o than 10. I'm not arguing with computer, I'm just wondering why it doesn't follow "My" logic of letting "some" N2 out into lungs devoid of N2 due the 100 % 02 at 20', then letting some more out at 10' or does it just not matter because the lungs don't have any incoming N2 so they can handle the release?

I'm talking about dives that for whatever reason don't require a 20' stop. My Suunto, for example, just brings me up to 10 and holds me there for a while. These are intentional deco dives with tables but not so serious that I can't take the Suunto along and use as backup since it's so conservative I stay longer than table. Dive profile is 100 foot max with an average depth of 70 or so for an hour.

MD1

 

[Dr Deco]

Hello major111:

Actually I believe that you are inquiring about a form of “deep stop.” A deeper stop [20 fsw] will cause the microbubbles to remain small and have a greater internal pressure because of the effect of surface tension. They will off gas faster.

The fact that the table and meter do not agree is simply a fact of the difference in algorithm and ascent criteria.

There is a considerable degree of “freedom” and safety in tables and meters. The big culprit is stress-assisted nucleation from physical activity while on the surface. This is not included in the table but is rather controlled by the diver. Don’t perform work on the surface, e.g., carrying loads or walking up hills.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[major111]

Doc, suppose I have 8 minutes of deco to do on 100 % Can I do some of it at 20' to get the benefit of bubbles having greater internal pressure/smaller size and then do some at 10'? If yes, is there a a "logic" for how much at what depth? Or, is total best off gassing done at 20' (whole deco time) and then I just come up to surface? And not even do a stop at 10? My question is more of a " if I do all deco at 20' then come to surface, is there still N2 that would have wated to come out at 10' with the pressure reduction or is it pretty much "out" if I did all the deco time at 20'?

How do you get around the "no activity" climbing out of a cave site (like Ginnie, etc.). I do what I was taught; make a seperate trip back for deco bottle but I (and everyone else) carries their doubles out and back to the tables after a few minutes sitting on surface chatting.

Should everyone be leaving doubles and pick them up after some time?

MD1

Hello major111:

Actually I believe that you are inquiring about a form of “deep stop.” A deeper stop [20 fsw] will cause the microbubbles to remain small and have a greater internal pressure because of the effect of surface tension. They will off gas faster.

The fact that the table and meter do not agree is simply a fact of the difference in algorithm and ascent criteria.

There is a considerable degree of “freedom” and safety in tables and meters. The big culprit is stress-assisted nucleation from physical activity while on the surface. This is not included in the table but is rather controlled by the diver. Don’t perform work on the surface, e.g., carrying loads or walking up hills.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[jerryn]

Major,

You are asking for a quickie deco rule of thumb. There is none.

I would take issue with the statement that you made that the deco is not serious. I know what you meant, but the fact that you are in deco (a virtual overhead environment) means that it is serious.

You should understand and study the decompression models and decide which offers you the level of risk you are willing to live with. Then you will have the answer to these questions. As you study the models you will see what happens to both bubble formation and tissue off gassing in the last 20 feet and be able to come to some conclusion about where you want to do your last stops. The fact that Suunto says it does not make it the best thing for you. Remember the Suunto's are designed for recreational diving and as I recall the manual specifically says that you should not be using it for doing decompression diving.

With respect to strenuous activity after the dive, that's a tough one. I am frequently climbing on a boat with my doubles and stages in choppy seas and there is no way around the exertion. I often keep my deco reg in my mouth so I'm breathing o2 enriched or o2 gas and I try to breathe continuously. But until they get scuba sherpas out here, I think we are stuck. When I do get to the place where I can sit, I try to sit for a while.

Jerry

 

[Dr Deco]

Hello Major:

Reduction of strenuous activity following diving, especially extensive diving, is important. That is major finding in our NASA research. It is also a finding traceable back to DCS research during WW II.

If one were faced with the problem of hauling gear following diving, the prudent move would be to wait for at least a half hour and move around a bit to promote blood circulation. By this, I mean moving arms and legs while sitting – not doing jumping jacks.

This “nucleation aspect” is what I might term “The Myth of Gas Loading.” By this I mean, the vast majority of divers consider only gas loads as indicated by their deco meters. They ignore the effects of nuclei formation, and then will offer that they received an “undeserved hit.” :11:

Unfortunately, nuclei formation is really only stressed on this SCUBA SOURCE forum as far as recreational diving is concerned. Training agencies have not yet picked this up (to my understanding).

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[cerich]

It seems to me that we are falling in the gap between your training/knowledge.

Most after training recreational cave dives(ginnie, little river, peacock etc.) are what you called "not serious" deco, but as pointed out all deco is serious. You are diving following a computer that is developed for the recreational market but should be able to fairly well model those dives however.

I tend to conservative on those types of dives, I plan my deco to air, dive 32% watch my PPO2 and O2 clock(at those locations with the depth/time,deco on 100%, multi dives you CAN run up againts the clock, unlike all one gas recreational no stop nitrox diving so calculate the darn thing!). I personally do my deco on 100% at 20, I have done it at 10 and 15 but "notice" I feel better doing it at 20(highly subjective).My research also seems to indicate that deco will be more efficient. That being said my training/experience level with multi gas diving is high. I also make sure my buddy has that training as well. 100% O2 at 20 is a high PPO2 and you can and people do tox! If you are fighting to remain in position because of high flow you would do well to move more shallow to decrease the PPO2 and probability of tox. I keep my assent rate at 30FPM below 20 Feet and then as slow as I can tolerate (<10 FPM) from there to the surface after my stop or deco whatever it is I need to do

You'll need to do your own research and has been mentioned decide what risk you are comfortable with.

As far as dragging the gear, yeah you are better to wait for a while. (although I prefer to think that is what students are for...

Another very important factor is hydration may be fairly new to you as well. You need to be peeing often and clear when you are diving. Drinks lots of water and a good sports drink. It's hot there, the gear is heavy the scuba air is dry and it is much easier to get dehydrated than it seems. That will also greatly increase risk of DCS.

 

[ScubaDadMiami]

This is the problem with computer diving. The computers are set in their ways. They "instruct" you to do something that is not necessarily optimal for your profile.

For all I know, the manufacturers were concerned with getting sued for somebody taking an O2 toxicity hit. So, they bent the algorithm to force a ten foot stop instead of 20 even if 20 would make better sense for the dive profile. Most of them claim to be one algorithm or another, but most have some proprietary alterations added.

I stopped using computers some time ago. I now plan my dive with software, V-Planner in particular, and the diver can set the software to account for stops that are optimal. I can tell the software if I want to make my last stop at 20 or 10. I am more in control after learning about the pros and cons of my dive behaviors.