Nitrox diving

[weazelz]

1) Would everyone agree that when the diver leaves the bottom they would have the same amount of nitrogen loaded in their tissues?

for the controlling compartment, yes, I think the loading would be similar [1]. other compartment loadings would be different

[1] the controlling compartment may not be the same for the two scenarios

2) Would they have the same amount of nitrogen in their tissues after their identical stop(s)/ascent?

in view of (1), no

[David]

I think decoplanner does it. This thread needs a graph.

I am sure a graph and a heron will follow very soon :-)

[karlw]

Just played with these on Suuntos DM, the 32% gives you a higher tissue loading at the end, and shows some supersaturated tissues by the end of the bottom time.

So 1) No
2) No

[Naomi S]

Arrrrgh my brain hurts!

So the longer nitrox dive will mean you have more N2 loading in the slow tissues (well and the fast tissues but they are not so much the issue AIUI) but also AIUI you will offgas quicker on the ascent than you would on air so it is entirely possible that both divers have the same N2 loading when they get out.

Please feel free to point out any glaring errors in my understanding of deco theory! This is just AIUI.

Edit: This is not what I meant at all! Must stop trying to understand deco theory when I am trying to concentrate at work at the same time

[nigelH]

I can't explain it without lots of maths. I can see I'm just going to have to write something that shows all the compartments as nice curvy graphs.

The nearest I ever got to it was here but it doesn't do nitrox.

[neilh]

I am sure a graph and a heron will follow very soon :-)

Et Voila

Couple of charts showing the loading at the end of each bottom time assuming a 15m/min descent rate.

Air:


EANx32:


Huge disclaimer here that this is my own application - so the chances of the above being in any way accurate are pretty slim

[Kev]

I have had a play in decoplanner and although pretty close the gas loadings are not the same. I am trying to upload the exel file but I am too much of a Luddite.

Therefore answers 1 and 2 are no!

Best

Kev

[Naomi S]

Et Voila

Couple of charts showing the loading at the end of each bottom time assuming a 15m/min descent rate.

Air:


EANx32:


Huge disclaimer here that this is my own application - so the chances of the above being in any way accurate are pretty slim

...and what about after the ascent?

[Kev]

Et Voila

Couple of charts showing the loading at the end of each bottom time assuming a 15m/min descent rate.

Air:


EANx32:


Huge disclaimer here that this is my own application - so the chances of the above being in any way accurate are pretty slim

Very good. Where is the heron?

[Doppler]

I'm pretty sure that given the scenario as painted by the OP that at the start of the final stage of decompression... surface interval... the diver who breathed nitrox and who performed the same stops 'as if on air' would have cleaner tissues than his counterpart who breathed air throughout. At least, that's what the algorithm says... your mileage will vary but this is a supportable assumption.

This is based on the required stops for the ean diver being about 4 to 5 minutes shorter than actually performed... they spent longer offgassing in water than required by the tables. (I'm basing this on VPM maths). This additional time at 6 metres and above breathing a mix delivering a nitrogen partial pressure about 85 percent of what an air diver would be breathing, sort of seals the deal...

And therefore: nitrogen loading for both divers upon leaving the bottom is close but not identical and nitrogen loading upon surfacing is certainly less close.

To find out more, read Mark Powell's excellent book, Deco for Divers