Diving 32% Nitrox with "Air" Algorithms

[Raphus]

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......

On ccr otu and cns can be a real issue. I would absolutely not lie to the computer!
It's not good practice in rec diving, but 100% a very bad idea in tech diving. If your controller fails and you backup has wrong information about oxygen loading, this could be your last dive.

 

[Angelo Farina]

Hi @Angelo Farina

I'm 69, how about you?

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

I am 64 now.
But my health had several issues, including lung embolism twice.
I follow the recommendations of my friend Marco, another diving instructor graduated with me at the 1978 instructor course in Nervi.
He has been an hyperbaric physician, who later also got specialization in pneumology and recently ended his career working three years in the hospital of Mantova, treating Covid patients.
He was always quite adverse to hyperoxygenated mixtures and has a long clinical evidence of the damages caused by oxygen to his patients. So not a direct evaluation of damages inflicted to recreational divers, but enough reasons for avoiding unnecessary exposure, when it does not provide any tangible benefit.
It is a precaution principle.

 

[formernuke]

On ccr otu and cns can be a real issue. I would absolutely not lie to the computer!
It's not good practice in rec diving, but 100% a very bad idea in tech diving. If your controller fails and you backup has wrong information about oxygen loading, this could be your last dive.

Well if I set my offload to 1.3 I'm lying to it as well because I won't be 1.3 the entire time especially if I bail out.

 

[scubadada]

Well if I set my offload to 1.3 I'm lying to it as well because I won't be 1.3 the entire time especially if I bail out.

Basic Scuba...

 

[formernuke]

Basic Scuba...

Recall when I posted I mentioned that exact thing.

 

[Belzelbub]

I know people who set their clocks 10 minutes ahead of the actual time to avoid being late. This is just regressive laziness and a sad attempt to fool yourself out of bad habits. Doing the equivalent on your dive computer is just as backwards and ridiculous. Sorry!

That’s a great point. My mom was perpetually late to everything as I was growing up, and still to this day. She did set her watch ahead to try and correct this, but it didn’t work. Problem was, she knew how much she had advanced the watch, so she’d tell herself she had a few more minutes. The result was that she was just as late as before.

I could see a diver doing this as well. Setting for air, when diving EAN. Then, as they are at NDL, they spot an interesting critter, and stay a bit longer. May still be under NDL, but they don’t know at that point.

 

[scubadada]

Recall when I posted I mentioned that exact thing.

Why didn't you abide by it??

 

[formernuke]

Why didn't you abide by it??

Make the conversation more interesting, have people think.

 

[davehicks]

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.

Many thousands of Rebreather divers (myself included) spend untold hours huffing and puffing on high PPO2 mixes day in and day out. There is not a plague of lung inflammation or other problems associated with breathing enriched gas mixes.

As for the science, NASA decided in 1968 (after the Apollo1 disaster) to run the Apollo space program with an atmosphere of 60% O2 / 40% nitrogen at 16psi for all ground operations. Once in space the atmosphere was switched over to 100% O2 at 5psi. If it's good enough for astronauts, it's good enough for divers.

No new science needed, this stuff has been known for decades. The science is clear and your basic Nitrox class teaches you about OTU's and CNS levels etc that represent the actual limitations of oxygen use.

50th anniversary of NASA deciding on a mixed-gas atmosphere for Apollo, a direct result of the Apollo fire. - NASA

50 years ago, on the way to the Moon…..

www.nasa.gov

 

[Angelo Farina]

Many thousands of Rebreather divers (myself included) spend untold hours huffing and puffing on high PPO2 mixes day in and day out. There is not a plague of lung inflammation or other problems associated with breathing enriched gas mixes.

As for the science, NASA decided in 1968 (after the Apollo1 disaster) to run the Apollo space program with an atmosphere of 60% O2 / 40% nitrogen at 16psi for all ground operations. Once in space the atmosphere was switched over to 100% O2 at 5psi. If it's good enough for astronauts, it's good enough for divers.

No new science needed, this stuff has been known for decades. The science is clear and your basic Nitrox class teaches you about OTU's and CNS levels etc that represent the actual limitations of oxygen use.

50th anniversary of NASA deciding on a mixed-gas atmosphere for Apollo, a direct result of the Apollo fire. - NASA

50 years ago, on the way to the Moon…..

www.nasa.gov

I understand very well the benefits of high oxygen percentages when using CC rebreathers: in my OW course, in 1985, training was done mostly using pure-oxygen CC rebreathers (ARO).
Oxygen can be very useful for some dive profiles, increasing bottom time and reducing deco time.
But when the diving profile is so modest that DCS is entirely not an issue, what's the point of using Nitrox for a relaxed rec dive?
I repeat, Nitrox is great for more "aggressive" dive profiles, making them safer and more enjoyable.
But when instead there is no benefit, why one should get the risk, even if small?
Remember, we are in Basic Scuba, discussing rec diving at small depths and very "conservative" regarding DCS.
The original poster is doing something wrong and pointless, that is diving Nitrox with the computer set to air.
Many answers pointed out the flaws of this approach.
But the general suggestion is to solve the discrepancy by setting the computer to the real oxygen percentage, while still using Nitrox.
I am simply suggesting another solution to the discrepancy: leave the computer set to air and just use air tanks.
If the dive profile is still far from NDL, this is also a viable solution.
Both solutions provide some benefits and some drawbacks...
And both are an improvement over the practice employed by the OP.