nitrogen accumulation ? time vs air quantity.

[Thalassamania]

I think by now we lost the OP

His question had already been clearly and fully answered. Now it is time to stretch his (and our) little grey cells a dash.

 

[bobbyp10]

Jonah. Listen to Thal. Here and elsewhere.

He has alot of answers to the questions you are always searching for.

Remember the tables? Only depth and time, plus some SI and RNT for subsequent dives. Nothing mentioned about gas consumption. And of course the special rules - ie add 4m to actual depth for cold/low vis dives

Now, onto more important things. Were you diver 1,2,3 or (polishing knuckle dusters) 4?

 

[eternaljonah]

i was definitely not diver one but i was diver two... been on the boat with like 80 bar these days. only once when aravind and myself raised the anchor (like 20kg) did i finish with 45 bar....

but thanks for all the answers i definitely have a wider understanding now.

 

[Bombay High]

Jonah,
You have some great answers here, and I'm guessing Rob is training you ... not much more you can ask for.
The one thing I can say for sure is avoid the vegemite on all surface intervals ... its got too much nitrogen in it !!
Rob ... I am on for March / April. We are also clear to dive the sunken temples on the west coast. Find out good months for viz.
Best helium prices - 7000/- for a 150bar whopper.

BTW wasn't it Jonah who was swallowed by a whale ?

 

[boulderjohn]

John,

I don't think your analysis is correct. Under standard conditions there is about 100 ml of nitrogen in you at the surface. Contrast this with the approximately 4800 ml of nitrogen in your lungs at full inhalation. Now, making some perhaps unwarranted simplifying assumptions like constant temperature and a complete lack of diffusivity from the blood out in to the tissues, then at say, 99 feet, you could at most (e.g., at total saturation) quadruple the nitrogen in circulation, to about 400 ml, reducing the nitrogen in your lungs to 4500 ml. This is equivalent to an fN2 drop from 78% to 73% (ignoring, of course the respiratory consumption of oxygen, which would serve to raise the fN2 and thus reduce the 5% change).

Now if we look at your thought experiment of a diver doing his entire bottom time on one breath: I do not think that there would be much of a difference, even if the dive were long enough to reach saturation (e.g., 12 hours), rather than a dive that is measured in minutes. The nitrogen levels in the lungs and in the blood would, as you state, move toward equalization, but equalization at saturation consumes less than 5% of the available Nitrogen in the lungs. Consequently, the rate of nitrogen transfer from the air to the blood would NOT drop significantly.

I am trying to wrap my meager brain around this now. I will play with it some more, although I am not sure I want to spend the time to think all the way through a scenario that can't possibly happen. We are all in agreement that there is no difference in a real dive, which is all we really need to know.

 

[Thalassamania]

It is kinda an, "how many angels can dance question." That's why I used the gross simplifications rather than actually calculating out amount N2 that goes into solution at a given pressure and a given time, too much trouble.

Here's a problem that is remarkably similar to a final exam question that we used to have for the upper division Ocean Engineering section of our scientific diving course.

 

[Bombay High]

Jonah. Listen to Thal. Here and elsewhere.

He has alot of answers to the questions you are always searching for.

I agree ... as his status says ... he truly is a diving polymath.

 

[boulderjohn]

It is kinda an how many angels can dance question.

and we both know how we feel about that particular question.

 

[eternaljonah]

yes, but the whale could not keep me down ;-)

 

[cloudflint]

I am trying to wrap my meager brain around this now. I will play with it some more, although I am not sure I want to spend the time to think all the way through a scenario that can't possibly happen. We are all in agreement that there is no difference in a real dive, which is all we really need to know.

I think if im reading that right, one lungful of air would provide enough nitrogen to fully saturate the body? So no matter how fast or slow you breathe (thus restoring the level of nitrogen in your lungs to the original level before some of it was absorbed into the tissues) you would still take on nitrogen at pretty much the same rate, unless you got really close to full saturation at which point the slightly reduced partial pressure of nitrogen would cause the absorption to be slightly slower? So if you could manage to only breathe in once on a dive it would take slightly longer to reach full saturation than if you where breathing normally?

Agh my head hurts now