Brand new to nitrox

[drrich2]

It doesn't enable me to stay down longer or anything, right?

It's been quite some years since I took my nitrox course, and I don't know how the educational material may've changed. I've learned some things on Scuba Board that have helped me gain some perspective, and from elsewhere. Maybe a bit of that might help you see why more oxygen doesn't make your tank last longer.

1.) Many people believe respiration (inhale/exhale cyclically) is about renewing the oxygen content in our lungs.

2.) But for most people, that's not what drives respiration. It's not marked oxygen depletion that makes you feel the need to take another breath. You inhale 21% oxygen & exhale ~ 16-17% oxygen (I think I've seen both figures).

3.) It's CO2 buildup that drives your respiration. CO2 is not just some 'waste gas' plants use to make their food. It's important in regulating the acidity of our blood. Hyperventilating, which can drive down CO2 levels in the blood, can make you pass out. Skip breathing, which can raise CO2 levels in your blood, can give intense head aches.

4.) Much of the oxygen carried in our blood is carried by hemoglobin, a pigment contained in red blood cells. It has the interesting property of binding to oxygen at high oxygen partial pressures (e.g.: your lungs) and letting go of it at low oxygen PP's (e.g.: in your tissues where it's being consumed). So your red blood cells are key in moving oxygen from your lungs to your tissues.

5.) In normal, healthy people, the blood hemoglobin has a saturation rate in the high 90's on room air on the surface (with a partial pressure O2 of 21% inhaled). So nitrox providing a higher oxygen mix (e.g.: EAN 32%) is not going to meaningfully increase that.

6.) But be mindful oxygen dissolved into the liquid component of your blood, and elsewhere, still matters. Oxygen toxicity is serious, potentially fatal (e.g.: underwater seizure) and respecting maximum operating depths for a given mix well advised.

So, at least in theory, if you 'slipped' a nitrox tank onto a diver who thought he was diving air (don't!), and he didn't exceed the MOD, that tank should in theory last him the same time (assuming he ends his dive due to running low on gas) an air tank would have.

Richard.

 

[Steve_C]

Above assumes that you are diving an AL80 which is 77. In some areas it is mostly students on AL80s. Locally most of the divers in NC are diving 100s or larger. That affects things a lot. I will often ride NDLs on nitrox and come up with over 1000 psi.

 

[drrich2]

True, I was thinking in terms of shallow to moderate (max. 70 feet maybe, average depth over dive 30 something feet) multi-level reef dives on an 80-cf tank, where many divers run low on gas before NDL.

People with very low SAC rates, or larger tanks, doing dives with greater depth (both max. and average), those things are game changers even on the 1st dive of the day.

Richard.

 

[TMHeimer]

All good info., most of which (including your OP questions) is basic stuff that should've been covered (it's all in my paper manual from 2006). Most important with nitrox is convulsions from oxygen toxicity, likely to cause mouthpiece loss and drowning. In my manual they go overboard explaining the dangers. I rarely use nitrox, but when I have, I wanted to know the max depth of the site. If that's decently deeper than my MOD allowed then I worry less about OxTox--but still monitor depth constantly. You should also have in your course materials the (what I call) complicated formula for figuring out what mix to use for really deep depths like 120-130'. I have used 28% for such dives, I think.

Side note-- I figure a "full face" mask would keep you breathing if you went unconscious from toxicity, but they are expensive. I bungee my mouthpiece in my mouth, thinking that may keep me alive if I become unconscious. I do this on all my dives, 95% of which are 20-30' and not nitrox.

 

[sheeper]

1) get your money back for your class. all that should have been covered.
2) nitrox is not about the O2. It's all about N2. The less N2 you have the more bottom time you have and/or a shorter surface interval is needed.
3) there is some recent decompression theory science that suggests nitrox provides additional benefits. some of this is improved eyesight (unconfirmed), being less tired (some medical confirmation), and lower risk of DCS (some confirmation).
4) most of all, friends don't let friends dive air!

 

[RayfromTX]

There is also a recent study I read that attributed some but not a lot of improved mental function on nitrox. The difference was slight and as I recall was more apparent later in the dive and during the ascent. I don't believe it has yet been replicated in followup testing and the numbers were not large. I am not free to share the document that was sent to me. I don't believe it is substantial enough to modify my planning or to dive nitrox for that reason alone. I do enjoy the benefits of nitrox and like seeing the ndl extension that it makes possible now that my air consumption is low enough to make my dives ndl limited.

 

[Just phil]

Guys, THANK YOU!
I mean that, thank you all!

I'm simply going to take the course again...
There is a different LDC not too far from home

I don't mind paying twice for it. It's obvious that I wasn't "getting it" AND I do not want to take money from a LDC.

I really do want to thank you all for your help with this.

Cheers
Phil

 

[RayfromTX]

wise man

 

[uncfnp]

If you are book smart and by this I mean good reading comprehension, I recommend a book review and then more questions on SB. It is amazing the amount of good review you can get this way. Plus ways of approaching a subject that a standard course may not cover.

I don’t know anyone that comes away from a course knowing it all.

And of course there is always the online course.

 

[MaxBottomtime]

Guys, THANK YOU!
I mean that, thank you all!

I'm simply going to take the course again...
There is a different LDC not too far from home

I don't mind paying twice for it. It's obvious that I wasn't "getting it" AND I do not want to take money from a LDC.

I really do want to thank you all for your help with this.

Cheers
Phil

There are tons of people who take the Nitrox course and don't "get" it, so don't fret too much. Although the textbooks say that there is a placebo effect, many insist they don't feel tired after diving nitrox. Now someone has posted that Nitrox improves eyesight. Sheesh! Who knew it was such a miracle drug.
Breathing nitrox lowers your nitrogen intake, giving you longer ndl or a shorter surface interval. Your body can't metabolize any more oxygen than it already does. It is a great tool for dives in the 60-100' range.