Nitrox diving

[Al_Star]

There was a recent discussion around the benefits of nitrox and I'm curious on what people reckon to a scenario:

- Dive to 30m for 20minutes on air. Ascend with a suitable rate and perform some minor stops.
- Dive to 30m for 30minutes on nitrox 32. Ascend with a suitable rate and perform the same stops as if on air.

Theoretically the above two scenarios would represent very close levels of nitrogen loading as the nitrox 32 gives you more deco time at the same depth. The concept of equivalent air depth tells you this and seemed to be something everyone agreed on. So the questions are:

1) Would everyone agree that when the diver leaves the bottom they would have the same amount of nitrogen loaded in their tissues?
2) Would they have the same amount of nitrogen in their tissues after their identical stop(s)/ascent?

Interested in what people think.

Al

[davydiver]

I would imagine that the nitrox diver would have less as they are offgassing more due to decompressing on a higher mix

[Janos]

An interesting question.

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

I don't think this is the case.

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

Hence I don't think this is the case.
---------------------------

Although I'm a big fan of Nitrox, and would try and do either dive on Nitrox, it's not straightforward. Different tissues will have different loadings.

* The fast tissues (half times measured in minutes) are going to be pretty much saturated at the ambient ppN2 (ie 3.2 for the air dive and 2.7ish for the Nitrox dive)

* The slow tissues (half time measured in hours) are going to be nowhere near saturation, but the extra 50% bottom time on the Nitrox dive will mean they are loaded more than on the air dive, despite the reduced ppN2.


My gut feel is that I would prefer to do the 20mins on air dive, but I would need to run it through some tables to check.

Somewhere there is going to be a tipping point. Given the choice between 20mins on air; or 21mins on Nitrox, I'd choose the Nitrox. Given the choice of 20mins on air; or 90mins on Nitrox, I'd choose the air dive.

Janos

[Morag]

There was a recent discussion around the benefits of nitrox and I'm curious on what people reckon to a scenario:

- Dive to 30m for 20minutes on air. Ascend with a suitable rate and perform some minor stops.
- Dive to 30m for 30minutes on nitrox 32. Ascend with a suitable rate and perform the same stops as if on air.

Theoretically the above two scenarios would represent very close levels of nitrogen loading as the nitrox 32 gives you more deco time at the same depth. The concept of equivalent air depth tells you this and seemed to be something everyone agreed on. So the questions are:

1) Would everyone agree that when the diver leaves the bottom they would have the same amount of nitrogen loaded in their tissues?
2) Would they have the same amount of nitrogen in their tissues after their identical stop(s)/ascent?

Interested in what people think.

Al

1)no
2)no, on account of 1)being no.

Simply, using PADI tables (we have all heard how wonderful and important they are in the last few days), they conclude that the EAD of 32% is 24.4m.

After 20 min on air at 30m, your pressure group is N - infact, the NDL at 30 is 20 mins.

Using the green/yellow RD{, especially made for 32%, after 30 mins at 30m, you are in pressure group R.

Therefore your loading is different.

To decide whether you would have different loadings at the end of the dive, assuming you are breathing normal air afterwards, during, lets say, a 1 hour SI, after the air dive you would be in pressure group D, and after the EANx 32 dive (with the same SI, you would be in pressure group F.

That is my opinion. based on my knowledge of the RDP, both niotrox and air, assuming that as you would be diving both as no-stop dives, you would simply be doing a 3 min safety stop in both cases.

Of course, other tables may tell you different (and would also be right).

[Kev]

PADI tables (we have all heard how wonderful and important they are in the last few days)

Told you so.

[Janos]

After 20 min on air at 30m, your pressure group is N - infact, the NDL at 30 is 20 mins.

Fook! I can see why people think 88s are aggressive. After 20mins@30m you're only a G on BSAC tables!

Janos

[Lazlo]

It would be a mistake to assume that a table (or computer, or program) tells you anything other than what is explicitly written on that table (or explicity claimed by the calculation).

If you want to calculate tissue loadings then you need to find calculations that actually do that.

[Dyson Diver]

wish i could be bothered to get the tables or the computer out and work out the difference , but i cant , if its close its close , if its not its not , what odds to either , unless something close to the edge was planned as a second dive . and if that was the case , have another cup of tea at the si .

[Kev]

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

[Naomi S]

There was a recent discussion around the benefits of nitrox and I'm curious on what people reckon to a scenario:

- Dive to 30m for 20minutes on air. Ascend with a suitable rate and perform some minor stops.
- Dive to 30m for 30minutes on nitrox 32. Ascend with a suitable rate and perform the same stops as if on air.

Theoretically the above two scenarios would represent very close levels of nitrogen loading as the nitrox 32 gives you more deco time at the same depth. The concept of equivalent air depth tells you this and seemed to be something everyone agreed on. So the questions are:

1) Would everyone agree that when the diver leaves the bottom they would have the same amount of nitrogen loaded in their tissues?
2) Would they have the same amount of nitrogen in their tissues after their identical stop(s)/ascent?

Interested in what people think.

Al

If we assume for simplicity and arguments sake that the answer to 1) is yes (or the difference between the two is negligible) then I would have thought that on an identical ascent that the diver using 32% will have less nitrogen in their tissues surely?