Deep stops and ascents...

[The Chairman]

This is not saturation at depth, but substantially below that. If our tissues were saturated to 4atm (or 3.9999) at that point, then additional time spent at depth would not add any more decompression liability. That is obviously not true in this case.

The partial pressure of Nitrogen at 4 atm of air is 3.12 and NOT 4 atm. We will constantly metabolise Oxygen and do not need to factor it into any decompression models. The calculated pressure of 2.99 is only 0.13 atm away from full saturation. I hope this helps you understand the math.

 

[Charlie99]

Assuming that the controlling tissue doesnt change, a slow ascent should indeed work better. Taken to a hypothetical extreme, if there was a tissue with a superfast half-time, a slow ascent would result in the tissue pressure equalizing more or less in sync wih the divers ascent. Slow tissues are less likely to be affected. So, depending on the function, either there is an optimal range of controlling tissues where the above doesnt hold; or it doesnt hold at all; or the controlling tissue changes which puts the math far beyond my abilities.

The controlling tissue does indeed change. The slower the ascent, the more it will change towards the slower compartments. The whole purpose of the ascent is to balance coming up to reduce loadings in the medium to slower compartments, while giving the faster compartments enough time to offgas.

Go up too fast, and the faster compartments get too high of overpressure. Go up too slow and you continue to load up the slower compartments and will eventually take them to their limits.

To help put this is perspective, below is a table showing compartments of various halftimes, and the fsw (absolute) N2 surfacing pressure limit for each compartment, and the depth on air and on EAN32 at which you have that inspired N2 partial pressure. Shallower than that depth, you can stay indefinitely and never exceed the compartment limit. For example, at 90' on either air or EAN32, you will never exceed the allowable pressure for direct ascent in the 5 minute compartment.

HT ... DSAT M0 (fsw).. AIR DEPTH ..EAN32
60 .......... 51.44 ........ 32' ....... 43'
40 .......... 55.73 ........ 37.5' ..... 49'
30 .......... 59.74 ........ 43' ....... 55'
20 .......... 66.89 ......... 52' ....... 65'
10 .......... 82.63 ....... . 72' ....... 88.5'
5 ........... 99.08 ........ 92' ....... 113

 

[vkalia]

The partial pressure of Nitrogen at 4 atm of air is 3.12 and NOT 4 atm. We will constantly metabolise Oxygen and do not need to factor it into any decompression models. The calculated pressure of 2.99 is only 0.13 atm away from full saturation. I hope this helps you understand the math.

Yes, oops on my part, I was typing in a bit of a hurry. The tissues will of course pressurize to the ppN2, not to ambient pressure. I got thrown off by the saturation comment.

Ok, so you are talking something that is 95% saturated, ie, a 5 min tissue, more or less. That makes sense now

 

[grazie42]

What I was taught in OW: 3 mins @ 15 ft

What I do:
-From 60ft-18ft: I make sure that my ascent rate stays below 18ft/minute

-From 18-9ft: I spend between 3-5 minutes, the classical "safetystop" (Number of minutes depending on the circumstances but 5 when conditions allow). It is not so much a stop as a slow, gradual ascent from 18-9ft, with the time distributed pretty evenly but with an emphasis on 12ft...

-From 9ft: I make sure I see every 0,1m/2"-increment on my computer from 9ft and up, it takes as long as it takes...(but I won´t descend if I miss a number and this too depends on the conditions for the dive)

Why I do it?
Because, after a full day of diving, I still feel refreshed and ready to party, instead of in danger of falling asleep on my feet.

ymmv...

 

[Cacia]

Great post Charlie99.

Most of the time I dive intuitively, on the timing of the slope and at times have made the error of going too slow. I am getting it down.

I really like see people have "activities" they look forward to for that last 3-5 minutes. When you can not wait to practice skills, (SMB, heli turns, air share) then you naturally spend the adequate time. The natural light available at this shallow depth makes for great diver portraits, etc.

I sure notice the difference in my energy level since slowing down on the ascents.

I actually look forward to seeing my profiles downloaded someday and plan to delegate that to JB! The balancing of compartments is really where it seems the razor's edge exsists.

 

[Jim Lapenta]

It was not covered in my ow or any other class. In fact my ow instructor just heard of it from me about two weeks ago. On dives below 90 ft I do 1-2 minutes at 1/2 max depth. Another minute at 1/2 that and then 3-5 at 15 or 13 ft if at altitude. So a dive to 116 ft(last deep dive) would give me a 1-2 minute stop at 58-60 ft. 1 at 30 an then final at 13-15. I first learned of this on my keys trip in may. The boat we were on did the 1/2 max stop and then 15. I added the extra interval based on some v-planner profiles I generated for dives I was planning that may have went into deco.

 

[ArcticDiver]

Maybe with the chills, but feeling "out of it/stoned" and "tired" are not really clinical symptoms. And I didn't have a fever over 99...



I should have mentioned that I normally don't get up at 6am though. Taking a nap after getting up at 6am is totally normal for me.

If I've had enough sleep and I still need to take a nap after diving, then that's a sign that something may be up.

Finally got down the priority list far enough to get back to this. Thanks for the links and the comments. They have been educational.

I fully agree that when one experiences fatigue that isn't usual as this post says "...something may be up". The question is: What?

Remember, when we started this thread fatigue was listed as a sole symptom. Even then it was considered "sub-clinical". In other words:"I'm more tired that I usually am. Wonder why?" and no clinical measurement is out of range. As the thread progressed other symptoms were thrown in. My original comments were in the context of the original comment.

Nothing I've read, or discussed with hyperbaric physicians, leads me to believe anything other than that fatigue, by itself is only a Maybe Something Is Up thing. We all experience "sub-clinical symptoms" of many things on a frequent basis.

Now if fatigue is just a part of a panopoly of symptoms that are assessed that is another matter. Even then considering the rarity of DCS one has to first think that something else is going on. Especially if we are in the Sub-Clinical range. Reminds me of my favorite doc.

He said the two biggest problems he has are the folks who are the Worried Well and those who are constantly chasing illnesses that clinical tests won't confirm. He really has no way of dealing with either.

So, thanks for the references. They confirm that, unlike the trauma that is DCI, DCS is much talked about, but very rare. They show that we have many good ideas of what May contribute to DCS. But we don't yet have firm confirmation. That it may be interestung to conjecture about isolated sub-clinical symptoms but they are much more likely to indicate that the "...something..." that is up is not DCS.

 

[drbill]

I do a series of deep stops depending on depth. If I go to 130, I do a stop at 90 ft, one at 60-70, one at 40 ft and then do the rest of my dive at 20-40 feet with a 3 min stop at 15 ft. If I go to 180 ft, I do a stop at 120 ft, then follow the stops outlined previously. Each of the deeper stops is for a minimum of 1 min with the max at that depth determined by whether I find anything I want to film there.