Diving 32% Nitrox with "Air" Algorithms

[Angelo Farina]

I don't normally disagree with you, but in this case....
(1) The benefits you ignore are longer bottom times and/or shorter Surface Intervals, or some combination. the additional risk that concerns you should be balanced against those benefits, not "no" benefits.
(2) Just as there is an Equivalent Air Depth concept, which means at what shallower depth with air would the PPN2 be the same as that for Nitrox at some greater depth, you can work that equation alternately to ask at what greater depth with air would the PPO2 of air be the same as with Nitrox at a shallower depth. Example: for Nitrox 32% at 20m, the PPO2 is 3x0.32=0.96. With air, you get the same PPO2 at 38m. So, diving 32% to 20m is no worse on your body (with respect to possible bad effects of O2) than diving to 38m on air.

Of course there are benefits if you profit of Nitrox for making longer dives, or more dives per day with shorter intervals. When you get these benefits, of course the balance between risks and benefits is in favour of nitrox.
But please, see instead my point: at my age I will never make more than one dive per day.
And the time-depth profile will always be at least 15-20 minutes away from NDL.
At this point all the benefits of Nitrox disappear, while the potential risks are still there.
I have nothing against Nitrox when it provides tangible benefits, but when it is useless, I do not see the point of insisting in using it.

 

[scubadada]

...I have nothing against Nitrox when it provides tangible benefits, but when it is useless, I do not see the point of insisting in using it...

I can only do 57 min on air at 60 ft without going into deco, that is just too short (this is DSAT). And that's the first clean dive. Unless I had a long SI, the 2nd dive would be very short.

 

[davehicks]

I leave my computer set on 31, and am happy diving up to 32.5 with that. I find the Buddy Dive blends to nearly always be under 32.

Agreed, i just set my computer to 31 or so and don't sweat the margin of error.

As for Angelo's voodoo gas paranoia, please ignore. There is no justification for any of that.

 

[Angelo Farina]

Of course there are benefits if you profit of Nitrox for making longer dives, or more dives per day with shorter intervals. When you get these benefits, of course the balance between risks and benefits is in favour of nitrox.
But please, see instead my point: at my age I will never make more than one dive per day.
And the time-depth profile will always be at least 15-20 minutes away from NDL.
At this point all the benefits of Nitrox disappear, while the potential risks are still there.
I have nothing against Nitrox when it provides tangible benefits, but when it is useless, I do not see the point of insisting in using it.

Regarding the concept of the equivalent depth, this works well for ppN2.
Swapping it to ppO2, it means that diving at 20 m with Nitrox-32 exposes my body to a ppO2 of 0.96 bars, which is equivalent to diving at 36 m in air, a depth which possibly I would avoid to reach, considering my age and health issues.
But the inflammatory effect of which I was worrying is not only related to ppO2, but also to oxygen percentage. In practice, the higher the oxygen percentage, the larger this effect even if the ppO2 stays well below toxicity limits. Taking into account also this fact, I estimate that the exposure to oxygen at 20m, 32% oxygen is roughly equibvalent to exposure at 40m with air.

I have no plan to expose my body to such high oxygen effects. So I prefer to dive at 20, max 25 m in air, staying down for a limited time, and avoid Nitrox.
Of course everyone should weight risks and benefits of his choices, taking into account depth, duration and mixture employed.

 

[Angelo Farina]

I can only do 57 min on air at 60 ft without going into deco, that is just too short (this is DSAT). And that's the first clean dive. Unless I had a long SI, the 2nd dive would be very short.

57 minutes is A LONG time in the mediterranean, using just a light wet suit or no suit at all.
I did not make a dive so long in the last 15 years.
I am getting older and older, and I continue simplifying my equipment, I suppose the next summer I well get rid also of the BCD, and remove the second independent reg, adopting the American approach of a single first stage with two second stages, with DIN connector.
I suppose that my max diving time will be around 30 minutes max at 20-22 meters.
So what's the point of using Nitrox for that dive profile?
Nitrox is very useful at larger depths (say 30 m) for longer dives, and more than one dive per day.

 

[scubadada]

Hi @Angelo Farina

I'm 69, how about you?

Do you have data regarding the exposure to oxygen for rec dives?

 

[formernuke]

This is basic so mods feel free to delete.

When diving CCR (very new to me) I keep my PPO2 at 1.3 but my off board backup computer is set to 1.2. Which means one computer is essentially doing what the OP mentions for deco and O2 calculations......

 

[Centrals]

I'm not sure what your point is.

Are you suggesting that it is good safety practice to lie to your computer? Are you saying computers with GF are a waste of money?

#6, 12 and 19.
I only said my three dc does not have safety factor and suggested to the OP that it is better to have a 2nd computer set on nitrox to track the O2 intake. Period.
Where did I say lying to my computer? You made that up. Shame on you.
GF? Waste of money? Of course it is for me.
Are you using GF?

 

[Angelo Farina]

As for Angelo's voodoo gas paranoia, please ignore. There is no justification for any of that.

Although nowadays my position of avoiding Nitrox when not needed has very few supporters, this was the official position of Padi and other major diving organisations 30 years ago, when Nitrox started to be available.
At the time I was an active instructor, I studied the topic with the help of a hyperbaric physician friend, and I concluded that hyperoxygenated mixtures are worth the risks only for well defined diving profiles.
Nothing happened in the last 30 years which made me to modify this position...
I admit that in the last 10 years I did not spend time updating my knowledge on recent scientific research, so perhaps I missed some new discovery. Please point me to novel information on this topic, if any.
But what my friend Marco, the hyperbaric doctor who informed me at the time, recently reported on his two-years battle working in the Covid hospital in Mantova, is that oxygen given to Covid patients often exhacerbated inflammation of lung tissues, worsening the situation.
And this confirms what I know on the topic of avoiding exposure to high oxygen when unneeded.

 

[Belzelbub]

In the interest of adding "conservatism" to our diving, my wife and I when diving the tropics (mostly shore diving on Bonaire ) dive 32% Nitrox. But to increase safety, we still keep our computers set to Air.

Anyone else do this........or does anyone have a reason why not to do this?

I’ve heard of others doing this, but I prefer setting my computer to the actual mix I’m breathing. My computers allow a lot of adjustment to conservatism, so I don’t really see a reason to lie to my computer.

With the amount of information available on my computers, I can easily adjust my personal threshold by deciding on what SurfGF I’m comfortable ending the dive with.