Nitrox - Is it "worth it"?

[Diver-Drex]

Intuitively the difference isn’t great. For rec dives the ascent time is short and the PPO2 delta isn’t great comparing air and typical EAN.

Before posting that I ran an 80fsw dive for 25 minutes on air with GF 60/80 in MultiDeco. Using air for the ascent a 3 minute stop is required. Switching to 32% requires a 2 minute stop. I don’t consider that to be a material difference. Maybe substitute ‘significant’ for ‘material’?

 

[CptTightPants21]

Inexperienced diver here, with Nitrox certification is next on my todo list - for the simple reason that I am going to be diving with a group or buddy, and not having Nitrox certification limits the dives I can do since other people may choose to use it.

Looking at dive tables, I am underwhelmed by the advantage to Nitrox, especially considering Nitrox limits the depth you can go. Not only are you trading the ability to go deep for more time at medium depth, the increased risk of bad things happening if you go deeper than you intend (either not watching gauge, current, etc) to seems an even trade for the decreased risk of a lower NDL number.

I have done 5 dives in 1 day, and I have done 4 dives on days diving near the recreational depth limits. 4 dives is exhausting, mentally if not physically. I love being under water, but it is nice to relax, eat, drink and talk to other divers. I can't imagine trying to do 8+ dives in the same day, it would start to feel like work and not vacation.

I know Nitrox doesn't mean your gas supply lasts longer, but I am surprised it does not. We breath to exchange CO2 for O2, so more O2 should mean less need to breath as fast. It certainly works the other way - on a high enough mountain I breath harder just walking than I would be running a 6 minute mile at sea level. Does anyone know why Nitrox doesn't slow down breathing?

A couple of different factors at play. The build up of CO2 is what induces the body to want to breathe, not the "lack of O2". So evening breathing 80% O2 won't make a difference if you are generating a lot of CO2 because the body wants to expel the CO2. Your exhale will just have a larger percentage of unused O2.

Breathing aside, there is also the factor of depth and the increase atmospheres which mean that a greater amount of gas is needed to fill the volume of your lungs. No matter what the O2 percentage is you still will need a certain amount to fill your lungs.

 

[bvbellomo]

I am not an expert on Nitrox research, but one thing I've seen with study after study in other areas:

1) A group of scientists wants to confirm an association, for example, Nitrox causes less fatigue.
2) Scientists recruit a relatively small number of subjects, which is all they can get with their budget and resources
3) Scientists are unable to find a statistically significant association, typically a p-value below 0.05 (which 95% odds of an association - they might find a 90% chance Nitrox causes less fatigue, but that is below the commonly accepted threshold).
4) Scientists publish they didn't reach statistical significance, and that more research is needed and hope for funding and resources to do a similar study with more people.
5) The media and whole world jumps on the study, claiming the Scientists proved beyond any possible doubt that no association exists

 

[CptTightPants21]

Inexperienced diver here, with Nitrox certification is next on my todo list - for the simple reason that I am going to be diving with a group or buddy, and not having Nitrox certification limits the dives I can do since other people may choose to use it.

Looking at dive tables, I am underwhelmed by the advantage to Nitrox, especially considering Nitrox limits the depth you can go. Not only are you trading the ability to go deep for more time at medium depth, the increased risk of bad things happening if you go deeper than you intend (either not watching gauge, current, etc) to seems an even trade for the decreased risk of a lower NDL number.

I have done 5 dives in 1 day, and I have done 4 dives on days diving near the recreational depth limits. 4 dives is exhausting, mentally if not physically. I love being under water, but it is nice to relax, eat, drink and talk to other divers. I can't imagine trying to do 8+ dives in the same day, it would start to feel like work and not vacation.

I know Nitrox doesn't mean your gas supply lasts longer, but I am surprised it does not. We breath to exchange CO2 for O2, so more O2 should mean less need to breath as fast. It certainly works the other way - on a high enough mountain I breath harder just walking than I would be running a 6 minute mile at sea level. Does anyone know why Nitrox doesn't slow down breathing?

For scuba trips with a lot of repetitive dives--3-5 dives a day for 6 or 7 days. Nitrox can assist with reducing fatigue and offer an improved safety margin towards the back end of those trips. Using nitrox on strictly NDL basis for 1 or 2 dives a day for a couple of days provides "benefits", but can be described as marginal and could be strongly dependent on the person and dive profile.

 

[Diver-Drex]

@bvbellomo - Looking at tables and calculating best mix and equivalent air depth, the difference is generally 10fsw shallower in the tables.

 

[MaxBottomtime]

Inexperienced diver here, with Nitrox certification is next on my todo list - for the simple reason that I am going to be diving with a group or buddy, and not having Nitrox certification limits the dives I can do since other people may choose to use it.

Looking at dive tables, I am underwhelmed by the advantage to Nitrox, especially considering Nitrox limits the depth you can go. Not only are you trading the ability to go deep for more time at medium depth, the increased risk of bad things happening if you go deeper than you intend (either not watching gauge, current, etc) to seems an even trade for the decreased risk of a lower NDL number.

I have done 5 dives in 1 day, and I have done 4 dives on days diving near the recreational depth limits. 4 dives is exhausting, mentally if not physically. I love being under water, but it is nice to relax, eat, drink and talk to other divers. I can't imagine trying to do 8+ dives in the same day, it would start to feel like work and not vacation.

I know Nitrox doesn't mean your gas supply lasts longer, but I am surprised it does not. We breath to exchange CO2 for O2, so more O2 should mean less need to breath as fast. It certainly works the other way - on a high enough mountain I breath harder just walking than I would be running a 6 minute mile at sea level. Does anyone know why Nitrox doesn't slow down breathing?

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.

I am not an expert on Nitrox research, but one thing I've seen with study after study in other areas:

1) A group of scientists wants to confirm an association, for example, Nitrox causes less fatigue.
2) Scientists recruit a relatively small number of subjects, which is all they can get with their budget and resources
3) Scientists are unable to find a statistically significant association, typically a p-value below 0.05 (which 95% odds of an association - they might find a 90% chance Nitrox causes less fatigue, but that is below the commonly accepted threshold).
4) Scientists publish they didn't reach statistical significance, and that more research is needed and hope for funding and resources to do a similar study with more people.
5) The media and whole world jumps on the study, claiming the Scientists proved beyond any possible doubt that no association exists

Then there is the other group who claims the Scientists proved beyond any possible doubt that an association exists.

 

[Bob DBF]

Intuitively the difference isn’t great. For rec dives the ascent time is short and the PPO2 delta isn’t great comparing air and typical EAN.

Before posting that I ran an 80fsw dive for 25 minutes on air with GF 60/80 in MultiDeco. Using air for the ascent a 3 minute stop is required. Switching to 32% requires a 2 minute stop. I don’t consider that to be a material difference. Maybe substitute ‘significant’ for ‘material’?

I use tables, or a computer that runs DSAT, so 80fsw is 30 min on air, 45 min on N32, a significant difference. 3 minute safety stop for both. So I guess it depends on what algorithm you dive.



Bob

 

[Diver-Drex]

I use tables, or a computer that runs DSAT, so 80fsw is 30 min on air, 45 min on N32, a significant difference. 3 minute safety stop for both. So I guess it depends on what algorithm you dive.


Bob

Of course the NDLs are different. I was specifically addressing off gassing during ascent on air vs 32%. The bottom portion for both dives were the same and both on air. The ascent on one dive was on air and the other on 32%, there was only a 1 minute difference between them. Illustrating my point that the impact of nitrox on off gassing during ascent is minimal in rec dives.

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.

 

[BRT]

Of course the NDLs are different. I was specifically addressing off gassing during ascent on air vs 32%. The bottom portion for both dives were the same and both on air. The ascent on one dive was on air and the other on 32%, there was only a 1 minute difference between them. Illustrating my point that the impact of nitrox on off gassing during ascent is minimal in rec dives.

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.

Offgassing on ascent is the same?

 

[Divectionist]

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.