The Beginner's Mixture

[Cave Diver]

My preference for bailout would be EAN21. You can still use it as an emergency breathing gas down to around 218 fsw. Where as with most other Nitrox mixes the MOD would be much shallower than that. So why use Nitrox for a bailout gas?

If I'm going to be anywhere near 200' on CCR, I'm going to have a trimix dil and trimix bailout. I personally wouldnt risk the narcotic hit of switching to an air bailout at that depth, and I don't want the narcotic impairment of an air dil on CCR that deep.

Individual choices for dil and bailout will be driven by their training, experience and the particular dive they are doing.

In regards to "why Nitrox as a bailout?" I'll throw a few thoughts out there.

Doing a cave dive with an average depth around 90'. If I have to bailout and travel any significant distance to exit, I'll incur less deco obligation on a nitrox bailout.

If I have to bailout and I'm using nitrox, my PO2 will remain closer to what I was already breathing on the loop.

If I'm diving with an OC buddy, they will most likely be on nitrox. Using their same gas for my OC bailout simplifies things in the event I have to donate gas to them.

 

[Cave Diver]

6. In theory, the effects of a barotrauma may be reduced, due to the improved circulation of breathing enriched air.

Can you expand on this?

I seem to recall reading an article a long time ago, that the higher PP and oxygen absorption could actually contribute to inner ear DCS. Something about the soft tissues in the ear off gassing the excess oxygen before the body could consume it, which led to some sort of barotrauma. As I remember it, it related to long exposures to 100% oxygen during extensive deco, but prolonged nitrox use could also cause it.

*Edit* I found the article I was referencing in the above comment. Scanning through it quickly indicates that the scenario I described is most likely to be caused through isobaric counter-diffusion when using helium rich mixtures, not oxygen. I'm including the link in case anyone wishes to read it. http://jap.physiology.org/cgi/reprint/94/6/2145.pdf

 

[ptyx]

Will Nitrox take the place of Air, as the preferred "beginners mixture?" Why or Why not?

Not anytime soon.

For most beginners, the benefits of Nitrox don't out-weight the extra effort and cost required.

Nitrox starts to be really interesting on dives where the NDL is the limiting factor. Most beginners don't go that deep or are limited by gas - especially with the standard AL80 rental.

A 'niche' where Nitrox as a standard finds its place is liveaboards or places like Bonaire, where diving air can get limiting fast - and the gas budget is negligible compared to the cost of the trip.

 

[muddiver]

If I'm going to be anywhere near 200' on CCR, I'm going to have a trimix dil and trimix bailout. I personally wouldnt risk the narcotic hit of switching to an air bailout at that depth, and I don't want the narcotic impairment of an air dil on CCR that deep.

Individual choices for dil and bailout will be driven by their training, experience and the particular dive they are doing.

In regards to "why Nitrox as a bailout?" I'll throw a few thoughts out there.

Doing a cave dive with an average depth around 90'. If I have to bailout and travel any significant distance to exit, I'll incur less deco obligation on a nitrox bailout.

If I have to bailout and I'm using nitrox, my PO2 will remain closer to what I was already breathing on the loop.

If I'm diving with an OC buddy, they will most likely be on nitrox. Using their same gas for my OC bailout simplifies things in the event I have to donate gas to them.

Ok, now that you qualified and narrowed your original one word answer, I agree with your perspective.

Back to the OP's question, if one is using the, please pardon the agency reference, SSI/ANDI training progression, it is perfectly acceptable and safe to introduce Nitrox (standard mixes like NOAA Nitrox I and Nitrox II) to begining divers. The only difference is the discussion of MOD for any mix that is shallower than the approx. 60' recreational recommended limit for new divers, Ox-tox below that, analyze your cylinder and the change in NDL's based on the equavilant air tables. Everything else blends right in wiith the physics and physiology of diving.

 

[DCBC]

We were taught in our Nitrox class (PADI) that oxygen has roughly the same narcotic effect as nitrogen, so we were to figure that oxygen enrichments was a wash when it comes to being narked.

Was PADI telling a fib?

I've spoken with several hyperbaric physicians about this including: Drs. David Sawatzky, George Harpur, Hal Koch, Claes Lundgren and others during my tenure at DCIEM and since then. This is a complex issue and the testing information seems to be conflicting.

Perhaps you would find Dr Sawatzky's book "Oxygen Narcosis: Fact or Fiction" worthwhile. In this book he states "The scientific data available does NOT support the conclusion that oxygen is narcotic." Although some have claimed to have experienced oxygen narcosis, he concludes that in any event "there is less narcosis when oxygen is substituted for nitrogen in the breathing gas."

Personally 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...

 

[Ana]

Wow... So you do those 200 minute NDL's with one tank of ean? And the new diver should not run into deco obligations. Their limit is 18 meters and most of those dive 12 meters and above. hundreds of minutes- one tank. Ean or air would not matter... They are out in less than an hour anyway.

I get the feeling you and I are in different worlds.

Don't know what 200 minutes you refer to.

I didn't say a new diver should run into deco obligations.

Didn't know there was an 18 meter limit, the new divers in my world (ie: my 2 sons) have a 130 feet limit, a hair less than 40 meters.

Around me, most of the dives are not to 12 meters, most of the shallow dives are around 20 meters.

I understand they are out in less than an hour, which is why I said:

..the new diver starts up inhaling a full bottle in a blink of an eye so for the very first few dives probably it makes no difference

If you think having new divers go with NITROX is a bad idea, that's cool. I don't think is a bad idea.

 

[DCBC]

Can you expand on this

Thanks for the article Cave Diver.

The basis of this presumes that the effects of a barotrauma may be reduced because increased circulation is caused by higher blood oxygenation, as well as a lower nitrogen levels which provide a lower level of nitrogen that can cause bubbles to be formed.

 

[Teamcasa]

Will Nitrox take the place of Air, as the preferred "beginners mixture?" Why or Why not?

Why? I doubt it. - It would cause too many arguments about O2 clean tanks and regulators.

Why Not?
- New divers simply don't stay down long enough for the benefits to take hold.
- Why would they spend the extra money?
- Too many Instructors and Dive Shops would actually have to learn more about it.
- The cost of OW Classes would have to go up.

 

[Cave Diver]

I get the feeling you and I are in different worlds.

Don't know what 200 minutes you refer to.

200 minutes is the NDL listed for a 35' dive.

I didn't say a new diver should run into deco obligations.

Didn't know there was an 18 meter limit, the new divers in my world (ie: my 2 sons) have a 130 feet limit, a hair less than 40 meters.

Standard for some agencies recommend a 60' depth limit for an OW diver and 100' recommended with 130' max limit for AOW.

 

[Cave Diver]

as well as a lower nitrogen levels which provide a lower level of nitrogen that can cause bubbles to be formed.

"I see!" said the blind man.