Nitrox - Is it "worth it"?

[Gdog]

Geezer Gas. Im all in!

 

[BlueTrin]

Your body can only metabolize so much oxygen. Breathing more only means you will exhale more. It's not the extra O2 that makes nitrox useful, it's the lower percentage of nitrogen.

In Mark Powell’s ‘Deco for divers’, he mentions that actually breathing high PPO2 will increase the partial pressure difference between arteries and veins and reduce bubbling.

But he does not provides any references for this claim.

 

[Bob DBF]

And your post further reinforces what I was saying. Dive air or nitrox to the NDL and the nitrogen loading is the same. And the off gassing during ascent is the same as well.

Now I see what you are talking about, and why is there even a question? I thought I read every post. NDL is calculated the same way regardless what Nitrox mix you are using, and off gassed the same way, all Nitrox does is slow the on gassing of N2 by reducing the amount you breathe.

Your one minute difference is just a function of your algorithm, mine is 0, but considering it's an approximation of ones body offgassing, it's close enough for government work. If one is using Nitrox and diving it to NDL, the point is to get longer bottom times, which it does.


Cheers

Bob

 

[BlueTrin]

Offgassing on ascent is the same?

It is not but he is saying that for rec dives the effect is minimal.

 

[Johnny Geodive]

3) what depths are you typically diving? Below 120' (130' actual), that tank of EANx on your back is poison.

Using a ppO2 of 1.4 at 40metres is perfectly safe, thus you could use 28% EAN.
Using a percentage eg 27% will give you an EAD of 36.2 metres or 119 feet and an MOD of 41.85 metres.
This would give you an NDL of around 12 minutes as opposed to air (21%) 9 minutes at 40m.
Whilst the increase in NDL is only 30%, having a reduced nitrogen component in your mix which sounds like a good thing to me.

 

[Tribal]

The ascent on one dive was on air and the other on 32%,

if you keep it rec diving then the entire dive of the one on 32% would be on 32% so he would have had a longer bottom time or he would have had less No2 loading.

Switching from air to 32% only for the short ascent is useless ofcourse.

 

[BlueTrin]

if you keep it rec diving then the entire dive of the one on 32% would be on 32% so he would have had a longer bottom time or he would have had less No2 loading.

Switching from air to 32% only for the short ascent is useless ofcourse.

You are right. In this discussion, I think OP was talking about Nitrox as main gas, not as a stage for accelerated decompression though.

 

[Lorenzoid]

Does anyone here routinely dive nitrox on air settings as a safety margin?

I sometimes did when I was diving nitrox with an air buddy or group, but only to have a better idea of their status.

However, I have a feeling that the Perdix on med conservatism is a bit more conservative than the average DC out there, at least for the first dive, because I often find myself shallowing out to get my NDL back up when others are still staying deeper. Maybe they are more daring near the NDL. So I keep the Nitrox setting now.

I set my computer for the percentage as analyzed, and then use my judgment for maintaining a safety buffer away from NDL.

 

[Diver-Drex]

I’ll explain in a little more detail.

I did a comparison of two ascent rates, one on air and one in 32%.

My thesis was that, for rec dives the difference in the rate of off gassing, measured indirectly by total time to surface, is negligible between the two gasses.

As the control I used an 80fsw dive on air for 25 minutes using GF 60/80. This meant that nitrogen loading is the same for both dives and that the allowed Surfacing GF would be the same, the residual nitrogen upon surfacing is the same.

The variable is the gas used for ascent, air or 32%. If the nitrogen loading at the start and end of the ascents are the same, then the rate of off gassing that occurs during ascent is a function of the gas being used. The difference in the rate of off gassing would be reflecting in the total time to surface, ie a shorter TTS for a faster rate of off gassing.

The results were that the total times to surface were - 5 minutes on air and 4 minutes on 32%.

My conclusion is that this is a small difference and supports my thesis. For rec dives the difference in off gassing during ascent between air and 32% is negligible.

 

[Diver-Drex]

Does anyone here routinely dive nitrox on air settings as a safety margin?

When I first started doing deco dives this is exactly what I was taught to do. And then when I started using computers it was the primary set to air and the backup on your actual back gas.