How much N2 would you exhale through decompression?

[BlueTrin]

Silly question here, when off-gassing I think most of the N2 and other gas would be exhale through our lungs.

I was wondering if anyone had an idea of how much volume of gas we are talking about if I was for example doing 1 hour dive at 35m followed by 30 minutes of decompression.

I am mostly looking for an order of magnitude, I was wondering if this noticeable for example on a CCR if it was going through the loop.

 

[Underwater Tourist]

Since on-gassing and off-gassing speeds depends on the pressure difference between your tissues and the environment, I think it will be difficult to give an estimate because it will depend on your GF settings, gas mixture, etc. Not even mentioning physical activity (current/no current), plus your own physiology.. I remember Simon Mitchell would show a slide demonstrating enormous individual variability when it comes to CO2 retention, I would guess there is probably as much variability when it comes to nitrogen absorption

I can give you an upper limit for your estimate though = total volume of nitrogen you have in your tanks

edit: misread your question and thought you were asking throughout the entire dive, not just at deco

 

[L13]

I did a quick estimate here:

Question - Deco gas as diluent for deco

Thanks all for the answers. It makes perfect sense as I had not considered that in deco diluent is not used except for flushes. For those wondering where the hell the question was coming from, it's from this table I built to show what percentage of O2 you need depending on your setpoint as a...

scubaboard.com

There was some useful critique of my estimate as well.

Short answer:

40m ==> ~8 liters of N2 released ~= 0.3 cuft​

 

[BlueTrin]

I did a quick estimate here:

Question - Deco gas as diluent for deco

Thanks all for the answers. It makes perfect sense as I had not considered that in deco diluent is not used except for flushes. For those wondering where the hell the question was coming from, it's from this table I built to show what percentage of O2 you need depending on your setpoint as a...

scubaboard.com

There was some useful critique of my estimate as well.

Short answer:

40m ==> ~8 liters of N2 released ~= 0.3 cuft​

That’s quite a lot actually

 

[L13]

That’s quite a lot actually

It is probably less than that. I assumed saturation, which would be close for fast tissues, but not even close for slow tissues. And a lot of guesstimates. However someone else quoted a value from another source in that thread that was in the ballpark of my estimate.

 

[tmassey]

I am mostly looking for an order of magnitude, I was wondering if this noticeable for example on a CCR if it was going through the loop.

I can’t give you any numbers, but I can tell you this: rebreather divers who dive on helium have to dump their loop from time to time during deco. The helium, and I would imagine nitrogen, that they are offgassing starts to push their maximum PO2 lower, because the loop is no longer pure O2. Once it drops low enough, they will dump the loop and refill it with oxygen in order to keep the offgassing as rapid as possible. (ETA: of course, the loop drops because you’re consuming the O2, like always; the difference is, you can’t raise it back up to the maximum because there’s still inert gas that won’t go away.)

So, your intuitive feeling about that is very much correct. And that would probably be the easiest way to determine how much inert gas you’re offgassing. You know the volume of your loop, you know you just dumped the entire loop for pure 02, and you can keep track of how long it takes for the maximum PO2 to drop. A tiny bit of mathematics and you know roughly how much inert gas you added in that time.