The Beginner's Mixture

[DandyDon]

Hi Don, Perhaps you can read all my posts on the subject and comment. Elimination was the wrong choice of words (which I also mentioned), but with the PO2, N2 narcosis isn't really a factor.

True, I did reply to that one post after someone recently referrenced it here ("post #23"), and this is an old old subject to trash about again here - but while Nitrox is a wonderful tool to use appropriately, I see no need in exaggerating claims...

Nitrogen narcosis is certainly possible on Nitrox;

Oxygen narcosis is also possible;

And I am not aware of anyone claiming to lower gas consumption on Nitrox...​

If you corrected those in the 100 posts between, sorry - missed it. :blush:

 

[gcbryan]

I think the bottom line is there is no reason for it not to be included in OW and it's benefits are sometimes exaggerated.

It's generally a pretty good choice for multi-dive/days vacations. It's also a good choice for instructors bouncing up and down in the water all day.

It may be a good choice for certain specific dives...30 vs 20 minutes on a wreck at a fixed depth (100 fsw).

Otherwise, in many cases it's just not particularly needed and the hassles of getting it may not be worth the benefits. Extending a dive that didn't really need to be extended and therefore resulted in no net reduction in nitrogen would be an example.

 

[Thalassamania]

I rarely use EAN to extend a dive, I use it to stay further back from the limit. In terms of "feeling good," that's controversial ... some deny any effect, so rave about it. All I can say is that for multi dive, multi day projects when I use air I eat supper and then I'm in bed within an hour or two, when I use EAN I stay up later and seem to get up better rested. If I had to hip shoot a cause ... less loss of lung surface area to venous side bubbles.

 

[DCBC]

True, I did reply to that one post after someone recently referrenced it here ("post #23"), and this is an old old subject to trash about again here - but while Nitrox is a wonderful tool to use appropriately, I see no need in exaggerating claims...

Nitrogen narcosis is certainly possible on Nitrox;

Oxygen narcosis is also possible;

And I am not aware of anyone claiming to lower gas consumption on Nitrox...​

If you corrected those in the 100 posts between, sorry - missed it. :blush:

I think I addressed these issues, but the list of posts is a long one indeed...

 

[padiscubapro]

No, I was told that: "The scientific data available does NOT support the conclusion that oxygen is narcotic" (quoting Dr Sawatzky's book "Oxygen Narcosis: Fact or Fiction").

I also mentioned that: "I have not experienced the same affect with O2 as I have with N2. The fear I have with O2 is that I will go unconscious with no warning once the PO2 goes past tolerance. I have experienced this on more than one occasion over the years while in a chamber. I was not even smiling at the time..."

In other words, although I've experienced toxic PO2 levels that have caused unconsciousness, I have never been affected in a similar way as experiencing N2 narcosis. Although some people have suggested that O2 narcosis exists, no scientific evidence is available to support this claim (although claims have been made).

In any regard, I've suggested that nitrox provides an advantage in eliminating nitrogen narcosis (although a small percentage of Divers may experience this within the maximum range of the gas). When a diver is diving deep with nitrox, the greatest hazard is not narcosis, rather O2 toxicity.

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

 

[DandyDon]

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

Interesting, but confusing: If you're on a closed circuit rebreather, what do you mean by breath the loop down from 23% to 13-18% 02? Converting O2 to C02? Where did the N2 increase come from? Do I need a rebreather course to continue here?

 

[Cave Diver]

Interesting, but confusing: If you're on a closed circuit rebreather, what do you mean by breath the loop down from 23% to 13-18% 02? Converting O2 to C02? Where did the N2 increase come from? Do I need a rebreather course to continue here?

The O2 is metabolized by your body. To maintain the oxygen percentage in the loop, additional O2 is added via one of the tanks you carry. Every breath uses up a small percentage of your total oxygen and as you absorb the gas, the loop volume gets a bit smaller with every breath.

CO2 is removed by passing the gas through the scrubber. If you continue breathing without adding additional O2, your loop volume will decrease slightly, as will the oxygen content. Decreasing oxygen content is one of the dangers CCR divers have to watch out for.

 

[tgsmith]

Interesting, but confusing: If you're on a closed circuit rebreather, what do you mean by breath the loop down from 23% to 13-18% 02? Converting O2 to C02? Where did the N2 increase come from? Do I need a rebreather course to continue here?

You add less 02 than your body metabolizes. The po2 will slowly drop.

Let's say you want to keep your po2 at 1.2 for a dive. The diver will need to add 02 every so often to the loop in order to offset the 02 that his/her body is metabolizing. This can be done using a computer controlled solenoid as on an eCCR or in the case of a mCCR, there is(usually) a slow bleed of 02 into loop that measures slightly less than what you metabolize. This way you only need to add 02 to the loop every so often in order to keep the desired po2.

Thus, if you shut off the 02 supply completely, you will slowly metabolize the 02 remaining in the loop until you pass out from a po2 too low to sustain consciousness.

 

[DandyDon]

So that's kind of like the reverse of making Nitrox: removal of some O2 which leaves a higher rate of N2...?

 

[DCBC]

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..

I agree; but it's really hard to say exactly as the precise mechanism of narcosis is not well understood. It appears to be a direct effect of gas dissolving into nerve membranes and causing temporary disruption in nerve transmissions. There has been much discussion on this topic and the "expert opinions" vary widely on what the science actually is. It continues to be a complex issue.

As I've mentioned, I've not experienced oxygen to be a narcotic in a similar way as I have nitrogen. Even when I have been subjected to potentially lethal Po2s that have caused me to black-out I never felt any giddiness or change to my mental functions. It would seem that if O2 narcosis is possible, it is a result of an interaction with other gases at specific partial pressures; I can't be sure. The experts can't even come to an agreement, so I'm not going to try.