Nitrox vs Air

[Scuba446]

Moved this thread over to this catagory. BOW certified diver seeking Nitrox certification and am pondering just what I will gain by getting Nitrox certified for my money?

1. Any less risk of nitrogen narcosis diving Nitrox?

2. I know it will increase my BT - but just how much more BT can I hope to gain diving a single AL80 tank anways?

Thoughts? Ideas?

 

[raxafarian]

1. no

2. depends on the depth. First question: Do you run out of air first with your AL80? Or do you usually reach NDL's first?

an example: NDL for air at 90ft. is around 25min. NDL for ean32 would be around 35 min. Don't have tables in front of me, but these should be within a minute.


Depends what kind of diving you're doing. If you're staying shallow... 40ft or less, I'd say skip it. If you dive toward 100ft then take the class.

 

[TwoBitTxn]

First off... $150 That's expensive. I thought paying $100 was alot.

Yes, breathing Nitrox will increase your bottom time. It also adds a margin of safety and helps reduce narcosis at the deeper depths. It also shortens your surface intervals.

My opinions... you get the most out of Nitrox cert once you are able to regulate your breathing rate and you are more bound by no deco limits reather than the air in your cylinder. In other words you run out of time before you run out of air. New divers tend to run out of air before they run out of time. The extended bottom time benefit is essentially meaningless. There is still the increased safety issue.

TwoBit

 

[Rob Meddes]

2. I know it will increase my BT - but just how much more BT can I hope to gain diving a single AL80 tank anways?

All depends on you depth & your mix i'm afraid With the above dive on air you'll have about 12 mins.
On 34% you'll have about 21 mins.

The real benefit comes on repetative dives over a number of days ie. a liveaboard for a week. Or on twinsets to reduce deco times.

These figures are all estimations so feel free to correct me but they're close (i think)
Good diving
Rob

 

[Walter]

Rob,

Your concept is an excellent one, but there's one tiny problem. O2 is also narcotic to approximately the same degree as N2. There is no reduction in narcosis with the use of nitrox.

 

[Spectre]

Other good things are more efficient offgassing on your safety stops, as well as feeling better after diving... Not to mention the understanding you get on oxygen toxicity.

The other side of longer bottom times, if you don't have the tank sizes or air consumption rate to take advantage of it, is that you instead get shorter surface intervals and/or longer repetitive dive times.

There ain't nothin' wrong with increased safety margins!

 

[raxafarian]

Rob Meddes once bubbled...


Yes there is a reduction in narcosis but it may only be by a few meters.

the increased O2 causes about the same level of narcosis.

 

[Rob Meddes]

Your concept is an excellent one, but there's one tiny problem. O2 is also narcotic to approximately the same degree as N2. There is no reduction in narcosis with the use of nitrox.

I've heard theories about the narcotic effect of O2 but have yet to see any proof (not that i go looking).
Having breathed 100% O2 on many occasion for lengths of time up to 60mins. i have never noticed any level of narcosis. Also i think that any narcotic gas would not be supplied to pilots of fighters at 100% if there was the slightest narcotic effect.
I understand this is only at a PPO2 of 1
Surely if the toxicity of O2 is directly in proportion to that of N2 (replace this with this & still be equally narked) then there would be some literature & some menton of it in any of the various agencies Nitrox courses. All i've heard is there MAY be a negligable effect. Do you have any links on the subject?
I'll look into it.
Good diving
Rob

 

[Walter]

"Not to mention the understanding you get on oxygen toxicity."

Except for exposure times, I cover it the same way I cover it in my OW class. It should be a review, there's no new material on ox tox.

 

[Munin]

The narcotic effect of a gas in humans can be predicted by the solubility of that gas in an organic solvent (olive oil, actually). Higher lipid solubility means more narcosis. That's the Meyer-Overton rule. Bunsen solubility coefficients for some gasses of note:

He - .015
N2 - .052
O2 - .110
CO2 - 1.340
Nitrous Oxide - 1.560

Nitrous Oxide is narcotic at 1ATA. He isn't narcotic at depth. Hmmmm..... I wonder what how narcotic O2 is compared to N2....

Theoretically, O2 is 2x as narcotic as N2. However, some is metabolized, reducing the effect.

The best guess on the cause of narcosis is dissolved gas in the cell membranes (lipid) interfering with nerve cell function.