Diving 32% Nitrox with "Air" Algorithms

[scubadada]

You can't do both.
If you dive up to the NDLs for nitrox your DCS risk is not (measurably) less than your DCS risk for diving up to the NDLs for air. Your 20min NDL on air at 100ft is functionally equal N2 accumulation to 30min NDL on 32% at 100ft. That's the entire basis for nitrox tables which were derived via the "equivalent air depth".

If you want to be more conservative, using nitrox, you have to accept less bottom time compared to the nitrox NDL.

I often dive nitrox to the same limit as I would dive air. I do not pretend that nitrox has less risk of DCS than air in those cases, but I do very much appreciate the extra dive time. I often do not dive nitrox to the same limit as I would dive air on the same dive and do believe those dives may be safer.

There is data from the SAUL probabilistic deco algorithm that diving nitrox to the NDL limit is safer than diving air to the limit Diving with Nitrox – What You Don’t Know | Modern Decompression This becomes quite clear if you look at the probability of DCS at the NDLs for 32% vs. air SAUL Recreational Dive Planner | Modern Decompression

 

[MaxBottomtime]

The fact that she is breathing in 14% less nitrogen makes it inherently safer on the same depth and time profile.

How much safer? It's like driving 64mph instead of 65 on the freeway.

 

[arew+4]

How much safer? It's like driving 64mph instead of 65 on the freeway.

1.5% 14% same/same

 

[Angelo Farina]

What are these new and or increased risks you speak of in shallow less than say 30M Dives?

Inflammation of airways and lungs due to oxygen.
Increased metabolism and consequent reduction of sugar.
Hypoxic drive, causing shallow breathing, CO2 retention and consequent narcosys.
All the side effects reported with oxygen therapy: What are the Possible Side Effects Of Oxygen Therapy? | VitalAire Canada

 

[boulderjohn]

EANx 32 has a MOD of 33.8 m @ PPO2 of 1.4. 130 feet is about 40m right? That would create a PPO2 of 1.6. There's a risk...

It's a little less than 1.6, and 1.6 is considered the contingency depth. If you take a nitrox class, which apparently you have not, you will be taught that although 1.4 is the standard, it is acceptable to go to 1.6 when needed. (That is with almost all agencies.)

When PADI made their EANx tables, they were considered to be nitrox-phobic, so it was a big step for them. As I pointed out before, their tables give you 18 minutes at 130 feet while diving EANx 32. Are you saying that their decisiopn making was flawed? IF so, please identify the data that led to their poor decision making and why their decision was wrong.

How big is that risk? I sadly know of more than a few cases of technical divers dying from oxygen toxicity. I do not know of any cases of recreational, NDL divers dying of oxygen toxicity. If you know of one, please post a link to it. (I have made this challenge several times in the past; so far, nothing.)

 

[dmaziuk]

Aside from oxygen toxicity acute from high ppo2, and cumulative from excessive number of repetitive dives? Which we have already covered?

~70 years of research? Oxidative stress, aging, and diseases - PubMed

 

[NW Dive Dawg]

Buy a computer, enter your mix and don’t play games with ox tox
If you can’t afford a computer or are unable to plan your gas recipe off a plastic card and a timing device, stay home.

While I'm staying at home I'll also be sure to drink my Ovaltine, and not run with scissors or shoot my eye out..

Maybe I didn't make it crystal clear in my original post that we are talking about recreational NDL diving on Bonaire. I dive an AL80 and my wife dives a 63. We have a self-imposed MOD of 100ft and we rarely feel the need on Bonaire to go much deeper than 80. All of our dives on Bon are NDL and our profiles with the 80 and the 63 are usually spot on to get us to our SS with around 500psi each and plenty of NDL time remaining on the AIR algorithm. We do 2-3 dives max a day on Bon and typically have long surface intervals.

When we first visited Bon back in 1999 - 2000, all we had was our basic Palagic "pucks" with no option for Nitrox.... (I actually still have three of the pucks and they all still work perfectly.) Anyway, Nitrox was free from Buddies and we were both PADI EAN certified. We discussed it.....and along with our typical profiles and conservative MOD, we agreed it was perfectly safe with basically little to no additional risk of O2 tox issues.

Once we finally did go to Nitrox computers we just kept using the Air algorithm since we felt it was completely safe and also added some additional conservatism and safety.....

(Pic of my good ol'e pucks)

So then I made the original post here on SB to talk about this and for the folks here who actually offered sound advice or even constructive criticism.......Thanks! And.....that's exactly why I added the below posts in this thread OVER TWO WEEKS AGO! ...

Thanks for all the responses. I guess my thinking has been that leaving our computers set to air, and staying above the MOD for 32, was really just another means of having my computer set to very conservative. But after a better understanding from all of these responses here, we'll be setting our computers conservatively to the gas we are actually diving.. We will however be keeping our personally agreed MOD for 32% at 100ft.....

What I have learned from this thread...... and other threads....... is that many of my "old school" ideas and personal opinions, combined with my inherent stubbornness and tendency to debate and challenge those that have a "high horse my way or the highway attitude" may not always be the best option. I really do sincerely appreciate the responses from those that are respectful, constructive and instructive. Thanks!

Anyway, thanks again!!

 

[BRT]

How much safer? It's like driving 64mph instead of 65 on the freeway.

Talk to @Wookie. I believe that after he switched to pumping only nitrox on his boat they had no more DCS incidents. None.

 

[arew+4]

~70 years of research? Oxidative stress, aging, and diseases - PubMed

Nicely irrelevant!

 

[tursiops]

Nicely irrelevant!

That was also a response to post #224, which also was a response to you.