Does Nitrox help air consumption?

I was diving at a local quarry (I live in IN) and I was talking to a diver who was diving Nitrox while on my surface interval. I inquired to why he was using nitrox since the quarry was only 35 ft deep. He told me it was for more bottom time (which is true) and then he said that a single 80cf tank lasts him about 3 hrs on nitrox and helps his air consumption. I am new to the sport (I have 19 dives), but I think he was blowing smoke. I know that nitox has a higher percenatge of O2 in it than normal air to help with deco diving, but does the increase in O2 cause your CO2 produced to be less so you feel the need to breathe less often or was this diver just full of it?


Thank You

Frank

Mileage seems to vary. Some of the divers in my area showed substantial improvement in air consumption with Nitrox, some showed improvement at depth only and some showed no improvement at all. So there are, in my opinion, a lot of other factors involved and a simple statement that nitrox improves air consumption cannot be made.

My air consumption is already quite good (SAC rate of .53) but I also show substantial improvement over that when diving Nitrox. The increase in P02 has little to do with the stimulus to breathe however as that is triggered by CO2 levels. So based on this, my experience, and my limited observations of other divers Nitrox and air consumption, my Unified Theory of Nitrox Versus Air Consumption is that Nitrox potentially improves air consumption in divers who already have a high tolerance for elevated CO2 levels (in my case from freediving for several years before moving to scuba) and can therfore breathe slow enough and dive efficiently enough to reap the benefits of the extra O2 in their lungs by being able to tolerate elevated CO2 levels.

The ability of the diver to limit his or her movement under water and keep extraneous motion (and muscle activity) to a minimum is also key as it will reduce the amount of CO2 produed. So I also suspect divers with good air consumption are the one likely to see further improvement with Nitrox. In my observations, it has not been a cure for being an air hog.

The bad news is that there is also research that indicates that elevated CO2 levels are a factor in O2 hits. So skip breathing, artifically lowering your breathing rate on Nitrox, or just having a very low breathing rate (and consequently getting great air consumption on Nitrox) may increase your suceptibility to an O2 hit.

This was one of the reasons for the US Navy not pursuing enriched air to any great operational extent in the 50's and 60's as they found sensitivity to oxygen toxicity to be quite variable. They also used divers in the test program who were helmet divers and who had consequently also developed a high tolerance for elevated CO2 levels and were consequently at greater risk than the average diver.

So in short, if you get great air consumption on Nitrox you, in my opinion, need to be conservative with PO2 levels.

Yes, it can under certain circumstances.

RSD did a study of the benefits of EAN several years ago. Among other things, they found that in double-blind in-water tests conducted between 33 and 99 feet, comparing air (21 percent oxygen) and EAN 36 (36 percent oxygen) divers at-rest at 99 feet revealed no difference between the basic breathing rates on air and on nitrox. However, in controlled course runs, swimming at one mph, nitrox divers averaged 2 psi per minute better gas consumption than air divers. This result was based on 54 trials.

If this nitrox advantage held true over an entire dive of 60 minutes at 66 feet, there would be 360 psi more gas available to the nitrox user, a 12 percent improvement when using a standard aluminum 80.

Best regards.

DocVikingo

DocVikingo once bubbled...
Yes, it does.
>snip<
a 12 percent improvement when using a standard aluminum 80.

Click to expand...

The wise diver, however, won't count on it.
E.

Thanks for all the info. It helps clear up a lot of thoughts and questions i had. I would like to take the nitox class, but would like to wait until I get more expierence under my belt.



Frank

Assuming this diver spends most thier time at 2 ATA, that's a working SAC of .22, which would be pretty amazing even for a very small woman.

Of course the assumption that they're at 2 ATA could be very wrong...

In the aquarium scrubbing and siphoning, with a (WAG) average depth of about 10 feet an AL80 lasts me between 2 and 2.5 hours.

Unless they're sleeping at 10 feet, 3 hours sounds a bit over the top.

Roak

If nitrox reduces air consumption, which I doubt, the reduction will be insignificant compared to the reduction you would get having good technique. IMO, the way to reduce air consumption is good trim and efficient finning technique.

BTW, regarding the Rodale's test, how much gas is 360 psi? What was the mean difference in RMV. Was a significance test done on the data? Standard deviation of both groups?

roakey once bubbled...
Assuming this diver spends most thier time at 2 ATA, that's a working SAC of .22, which would be pretty amazing even for a very small woman.

Click to expand...

Or the diver does what I do --- figures that an AL80 lasts about 3 hours. ON THE SURFACE.

While non-standard, I find it easiest to do all my gas calculations in a ficticious unit called "surface minutes". This is how many cu ft a profile would use at 1 cu ft / minute. Then I apply whatever SAC I choose to use for planning.

180 minutes "surface minutes" out of an AL80 is a not uncommon 0.36 cu ft /minute, just using 65 cu ft and leaving a 500psi reserve. Using the whole tank, it is 0.43 cu ft/min, which is more than I normally use swimming lazily on a tropical reef dive.

is anywhere from 0.5 to 0.7, depending on what I'm doing. Just lazily swimming along, it tends to be towards the bottom of the range. Spearfishing when I actually have to work can push it towards the top of the range.

I've found that Nitrox doesn't change this materially - for ME. It may for you though.

I must be a major air hog then because I go from 3000psi to 925psi in about 40 min at about 20 ft. Hopefully that will reduce in time.

Frank