Using gas mixtures to eliminate surface intervals?

[jdelprete]

interesting read so far...

 

[Dr Deco]

Hello rjack321:

I do agree with what you say. Possibly, I was interpreting the question(s) differently.

Your remarks appear to be correct to me, i.e., the microbubbles will equilibrate with the current inspired breathing gas.

Dr Deco :doctor:

 

[jimclarke]

Dr. Deco,
Respectfully, I think your missing something here. If all the residual gases stay dissolved on the ascent form dive 2, who cares? Dissolved gas doesn't cause problems. If you do get a bubble, the inert fraction in that bubble is going to offgas like crazy since that inert doesn't exist in the inspired gas. The bubble will quickly become just the inert in the inspired gas. So from a practical persepective,
1) Dive 1 microbubbles will offgas as soon as you start breathing gas 2. And
2) any residual dissolved gas from dive 1 will either stay dissolved and do no harm, or form a mixed gas bubble and quickly turn into a bubble of inert 2.

I follow your argument but believe that it would only apply to microbubbles in the blood. In slow tissues inert gas 1 will not be quickly diminished to reflect the inspired mixture. Any new or preexisting bubble in slow tissues will grow from the combined gas tensions.

 

[Dr Deco]

Hello readers:

How tissue bubbles grow or diminish, or how fast gas is taken up or eliminated will depend on the solubility. A soluble gas such as nitrogen will be taken up slowly in comparison to helium. This is the basis for gas switching to decrease decompression time.

As concerning bubbles in the blood, they essentially are “inert” and without effect with respect to joint pain DCS.

Dr Deco :doctor:

 

[Gene_Hobbs]

Just as a theoretical possibility....

Suppose you made two dives, the first with Nitrox and the second with Heliox (or visa versa).

Would you need to account for the surface interval between dives in the planning for the second dive?

I KNOW this is an old thread but the question was interesting to me... Tonight, ran across this 1998 paper. It is not this exact question but it does seem to offer some similar issues.

Experiment of nitrox saturation diving with trimix excursion.
Shi, ZY
PMID: 10052222
Depth limitations to diving operation with air as the breathing gas are
well known: air density, oxygen toxicity, nitrogen narcosis and
requirement for decompression. The main objectives of our experiment
were to assess the decompression, counterdiffusion and performance
aspect of helium-nitrogen-oxygen excursions from nitrox saturation. The
experiment was carried out in a wet diving stimulator with "igloo"
attached to a 2-lock living chamber. Four subjects of two teams of 2
divers were saturated at 25 msw simulated depth in a nitrogen oxygen
chamber environment for 8 days, during which period they performed 32
divers-excursions to 60 or 80 msw pressure. Excursion gas mix was
trimix of 14.6% oxygen, 50% helium and 35.4% nitrogen, which gave a
bottom oxygen partial pressure of 1.0 bars at 60 msw and 1.3 at 80 msw.
Excursions were for 70 min at 60 msw with three 10-min work periods and
40 min at 80 msw with two 10-min work periods. Work was on a bicycle
ergometer at a moderate level. We calculated the excursion
decompression with M-Values based on methods of Hamilton (Hamilton et
al., 1990). Staged decompression took 70 min for the 60 msw excursion
and 98 min for 80 msw, with stops beginning at 34 or 43 msw
respectively. After the second dive day bubbles were heard mainly in
one diver but in three divers overall, to Spencer Grade III some times.
No symptoms were reported. Saturation decompression using the Repex
procedures began at 40 msw and was uneventful: Grade II and sometimes
III bubbles persisted in 2 of the four divers until 24 hr after
surfacing. We conclude that excursions with mixture rich in helium can
be performed effectively to as deep as 80 msw using these procedures.

Paper is available for download at: http://www.jstage.jst.go.jp/article/ahs/17/6/17_249/_article/-char/en


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[Kendall Raine]

Hello rjack321:

I do agree with what you say. Possibly, I was interpreting the question(s) differently.

Your remarks appear to be correct to me, i.e., the microbubbles will equilibrate with the current inspired breathing gas.

Dr Deco :doctor:

Is there not still a potential problem with inert gas counterdiffusion? At depth or decompression from dive 2. Assuming all residual inert gas is dissolved, or that recompression on dive 2 crushed gas phase residual nitrogen back into dissolved phase is nice, but not necessarily the case.

 

[Saturation]

Just as a theoretical possibility....

Suppose you made two dives, the first with Nitrox and the second with Heliox (or visa versa).

Would you need to account for the surface interval between dives in the planning for the second dive?

My thinking is no. I'd like to hear some expert opinion.

R..

Yes. You still need to calculate residual He or N2. However, roughly 3 hours SITs the residual is small enough to be ignored in routine diving. The theoretical response to various combinations can easily be forecasted with software, like Vplanner.

I do this frequently, but mostly mixes of nitrox and trimix ... a tech dive on trimix followed by a recreational dive on nitrox or air, or vice versa if I do a dive breathing residual mix from a prior dive.