The Beginner's Mixture

[gcbryan]

I am wiling to accept the fact that o2 may be SLIGHTLY narcotic, but no one will every convince me that the narcotic properties are ANYWHERE near that of n2..

WHen the conditions permit, there is a drill I do with my Technical rebreather students.. I bring them to 45m/150 fsw (give or take a bit) using AIR diluent.. we start with a po2 of 1.3... this means we have about 23% o2 in the loop, I have the breath the loop down to somewhere between a .7 and a 1.0 (somewhere between 13-18% 02)..
at this point the PN2 is at least a 4.5 (for a 1.0 po2), All divers report afterwards of high narcosis and skills done at depth show this.... We then quickly raise the po2 to a 1.4- 1.5, this drops the pn2 down to a 4.0-4.1, EVERY diver has reported feeling noticibly clearer headed and skills done under these conditions show drastic improvement

Here's the question I would have with this. Why do people use 30/30 if EAN 30 would do the trick?

When moving from air to EAN 32 oxygen is only displacing 11% of the N2 and in a range where N2 isn't all that debilitating yet. Even with He mixtures is 11% enough to be that noticeable? I assume with He the answer is probably yes but this oxygen not being narcotic subject just doesn't line up very well logically for me given that to test it you are in a range where narcosis isn't a big factor anyway (not referring to your example in this case).

I can't really address your test although on the face of it it's logical enough though highly subjective.

As a practical matter I don't think nitrox reduces narcosis to any substantial degree because narcosis is limited in EAN ranges and because the deeper you go the less O2 in the mix anyway and to say that you won't get "narced" on nitrox is completely wrong no matter how you look at it.

Anxiety and CO2 being large components of most people experiencing being narced this is not reduced in any way by nitrox and the nitrogen in the mix is only being marginally reduced by the oxygen (even if it weren't narcotic at all) there wouldn't be a great effect.

 

[MSilvia]

Here's the question I would have with this. Why do people use 30/30 if EAN 30 would do the trick?

How about this: People use 30/30 instead of EAN30 because 30/30 replaces an additional 30% of the tank's contents that had been nitrogen with an easily offgassed inert gas, resulting both in a dramatic decrease in the mixture's narcotic potential, and (a stupid thing I retract). Frankly, I don't understand why read padiscubapro's post as saying EAN30 would "do the trick".

 

[DandyDon]

How about this: People use 30/30 instead of EAN30 because 30/30 replaces an additional 30% of the tank's contents that had been nitrogen with an easily offgassed inert gas, resulting both in a dramatic decrease in the mixture's narcotic potential, and a dramatic increase in the MOD of the mix. Frankly, I don't understand why read padiscubapro's post as saying EAN30 would "do the trick".

Y'all realize that this is Basic Scuba forum? I hardly think that tri-mix discussions are appropriate, but then - 30/30 is 30% O2, right? How could that give a "increase in the MOD of the mix"...?

 

[DCBC]

As a practical matter I don't think nitrox reduces narcosis to any substantial degree because narcosis is limited in EAN ranges and because the deeper you go the less O2 in the mix anyway and to say that you won't get "narced" on nitrox is completely wrong no matter how you look at it.

You guys are starting to confuse me. GC, you're right. Nitrox reduces N2 narcosis, as the PN2 is reduced and is replaced with O2. Some say that this doesn't matter as the PO2 increases and the diver can suffer from O2 narcosis (which has been discussed in this thread).

As the Nitrox diver descends the P2 of both O2 and N2 increase, but before N2 narcosis begins to affect most divers, the PO2 may become toxic in-which Hyperoxia will occur.

Nitrox I (EAN32) has a MOD of 33.75 Meters (110 feet) and Nitrox II (EAN36) has a MOD of 28.88 Meters (95 feet); to keep the PO2 at the maximum of 1.4 ATM. If you were using EAN30 your MOD would be 120 feet. In any case most divers would be limited by the PO2 maximum before they developed narcosis.

 

[MSilvia]

30/30 is 30% O2, right? How could that give a "increase in the MOD of the mix"...?

It doesn't... brain fart on my part. Good catch Don.

 

[sailingk8]

The rest of that post sounded great, but the bolded part didn't. If anyone was ill after diving, I'd wonder about the air source - but then I am a cynic about such, as little enforcement as there is in that area.

Elimination of narcosis? For many it lowers your gas consumption?

Don, my comment about getting sick on air was after I dove at three completely separate sites on three separate sources of air. Not boat either as one dive was at Jules Underwater Hotel from dock using their air. I figured it was just my body getting used to breathing underwater. All I know is that after diving on Nix, I don't feel sick. I have a couple of short dives coming up using air, I'll let you know how that goes.

 

[padiscubapro]

When moving from air to EAN 32 oxygen is only displacing 11% of the N2 and in a range where N2 isn't all that debilitating yet. Even with He mixtures is 11% enough to be that noticeable? I assume with He the answer is probably yes but this oxygen not being narcotic subject just doesn't line up very well logically for me given that to test it you are in a range where narcosis isn't a big factor anyway (not referring to your example in this case).

I can't really address your test although on the face of it it's logical enough though highly subjective.

.

Its NOT the percentage of the gas thats important, its the partial pressure thats important.. The deeper you go, the smaller the change in percentage of an individual gas needs to be to make a profound change..

at a PN2 of 3.2 narcosis is measurable but not always felt, thats 100fsw on air or about 118 fsw on about 31% o2.. The PN2 usually has to be alot higher for most people to realize they have impairment..

The test above is not entirely subjective, there are skills that are done that ARE measurable.. Its a combination of subjective feeling and measurable tasks..

 

[DandyDon]

Don, my comment about getting sick on air was after I dove at three completely separate sites on three separate sources of air. Not boat either as one dive was at Jules Underwater Hotel from dock using their air. I figured it was just my body getting used to breathing underwater. All I know is that after diving on Nix, I don't feel sick. I have a couple of short dives coming up using air, I'll let you know how that goes.

No, I doubt that you could get bad air from three different sources. Odd that Nitrox could make a difference, even with only anecdotal evidence. I don't know of any real evidence that increasing O2 intake helps divers or athletes actually feel better, but we keep hearing that. "There are more things on heaven and earth..."

 

[DCBC]

I don't know of any real evidence that increasing O2 intake helps divers or athletes actually feel better, but we keep hearing that.

"There are effects of increased Po2 on the pulmonary responses to exercise and on the acid-base responses. There is evidence that one or both of these mechanisms could play an important role in the changes in performance"

The American College of Sports Medicine 1982 - Volume 14 - Issue 4 > Hyperoxia and Human Performance

It makes sense that when we exercise oxygen is consumed (that's why our breathing rate increases). It also follows, that if there is more O2 in what we breath, that this would have a positive affect.

 

[DandyDon]

"There are effects of increased Po2 on the pulmonary responses to exercise and on the acid-base responses. There is evidence that one or both of these mechanisms could play an important role in the changes in performance"

The American College of Sports Medicine 1982 - Volume 14 - Issue 4 > Hyperoxia and Human Performance

It makes sense that when we exercise oxygen is consumed (that's why our breathing rate increases). It also follows, that if there is more O2 in what we breath, that this would have a positive affect.

Well, I'm not going to try to debate that in this Basic Scuba thread.

The lady said...

After my first 5 dives I was either physically sick or felt like I wanted to be. I also felt exhausted. (It's really a wonder I kept going back for more!) After nitrox dives I felt no different physically than before the dive.

I wondered about air quality, but she said she got the air from 3 different sources so probly not the problem. Lots of other possibilities with those first 5 dives? I've had a nagging bug for 12 days now; never seriously ill but pushing myself at all can make me feel like I'm going to be. Maybe she was just healthier by the time she started Nitrox? Or maybe she relaxed enough to stop skip breathing by then. Can't say. Now, she probly expects to be ill on air, not ill on Nitrox - so the trend is set regardless of what the actual causes were? Really, it's be nice to see SailingK8 start a new thread with full details in Dive Medicine for a more objective discussion.

I think that the Nitrox card is a great tool for any new diver and am glad to see more newbies acquiring it, as well as the price and requirements more reasonable than when I got mine. Now if we can make it more affordable on Cozumel, cool!