Nitrox main tank.....air in pony...?

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RICHinNC

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RAEFORD. NC
A while back I did a thread about the pros and cons of diving nitrox (32%) but using an air computer. The idea was......a lot of people say they are less tired with nitrox....and using an air computer would add an additional safety margin. There was a lot of good discussion on that. (my lds hates nitrox and when I asked the question there, the owner indicated it is the only way he would recommend diving nitrox)

But, my question here is.......if one does dive nitrox in the main tank.....is it ok to still just have "air" in a pony bottle? And, when I say pony bottle I dont mean a deco stage bottle.....just a small 13 cu ft bail your butt out of a jam bottle.

Would switching to the pony in an emergency and breathing air after having breathed nitrox for a while cause any problems?

(my thought is it wouldnt....you breath "air" when you surface, but there might be something I am missing there.)
 
I'm no expert at all .. but I would think it's fine to switch to air as air has a deeper MOD than Nitrox mixes. So there would be no decom issues, it would be mainly a matter of nitrogen loading and how you go about assessing it.

Interesting to hear what others say...
 
why not just put 28% in your pony and not worry about it?
 
RICHinNC once bubbled...
A while back I did a thread about the pros and cons of diving nitrox (32%) but using an air computer. The idea was......a lot of people say they are less tired with nitrox....and using an air computer would add an additional safety margin. There was a lot of good discussion on that. (my lds hates nitrox and when I asked the question there, the owner indicated it is the only way he would recommend diving nitrox)

But, my question here is.......if one does dive nitrox in the main tank.....is it ok to still just have "air" in a pony bottle? And, when I say pony bottle I dont mean a deco stage bottle.....just a small 13 cu ft bail your butt out of a jam bottle.

Would switching to the pony in an emergency and breathing air after having breathed nitrox for a while cause any problems?

(my thought is it wouldnt....you breath "air" when you surface, but there might be something I am missing there.)

Firstly, I love nitrox and only dive air when I can't get it. Even offshore in NC I do 30%. I also let my computers know what I am diving in order to maximize the benifits from the reduced nitrogen.

Why does your LDS hate nitrox? Don't sell it, but the competition does?

That said, you question could be a loaded one. If you are using computer settings for the mix you're diving, and you have a deco obligation on you computer, then switching to air could be a problem because you won't outgas at the rate your computer is calculating.

If you use the pony bottle air to complete any dive, deco or not, if you are using mix settings instead of air settings on your computer, then you computer doesn't know where you are.

It seems to me that a higher mix in the pony would make more sense. If you had to use it at depth, below it's MOD, the exposure would be minimal because you would be in ascent. If the O2 is a higher mix than your computer has set then what is being fooled is the O2 clock. I would use a higher mix, say 40%.
 
Don't quite understand the LDS not liking nitrox - sounds like someone stuck in the dark ages.

If you are diving Nitrox but left your computer on air, than having air in the pony is a mute question as the computer assumed you were diving air the whole time anyway. There is no problem with switching during the dive.

I have to disagree with putting a higher mix in the pony if there is a chance of exceeding the MOD as it only takes a few breaths for a CNS hit and there is no reason to put yourself at this risk no matter how small the risk is. I would reccomend the same mix as is in your main tank.
 
is that you will have an incentive to ALWAYS get it topped off.

A small pony is not good if its not FULL. And I do mean FULL!

A 13cf pony is BARELY big enough to be useful. If its down 500 psi, its a lot less useful, perhaps enough to make the difference between making it and not.

A pony is not the "right device", in general, for deco diving. It doesn't have enough gas to cover you if you have a problem with the main tank, which is NECESSARY or your NEXT pony ride will likely be of the iron variety!

But for NDL diving, yes, air in the pony is just fine, PROVIDED that you immediately call the dive when you pull it, AND you either end your diving day when you use it OR are EXTREMELY conservative from that point forward (better to call the diving day) as your computer's tissue loading numbers will be a bit off.

With that said, if your shop BANKS Nitrox, then topping a pony with 32% is pretty easy, and if that was the case (I had banked 32%) I'd fill and top the pony with that instead. 32% is ok to breathe down to 130 in a pinch (1.6 PO2) which will cover you to basically any recreational depth.

If your shop PP mixes their Nitrox then topping a pony is a pain in the butt and usually involves partially or totally dumping the existing gas. That gets out of hand fast and the shop is going to charge you for a fill, as its not just a couple of cf nor is it nearly as quick. In that case I'd fill it with air.
 
Maybe I wasnt quite clear enuf....

The pony is a pure bail out....total main failure...last resort thing. There would be no need ever to finish a dive with a 13 cuft pony with good air usage monitoring.

As to why my lds hates nitrox is hard to tell. He gets too emotional and hasnt really conveyed why to me. Plus, I dont think he wants to cost involved of offering nitrox as he is barely keeping his business head above water...sorry about the pun. The last time we did talk nitrox....and I asked this question....he was emphatic that if he ever dived...or recommended diving nitrox...it would be only with the use of an air computer following air limitations.

The comment about the % is interesting. I was in Ocean City MD a while back and stopped into an lds. We talked about nitrox and the owner said he never fills less than 40%. When I asked why not....he just gave me a disgusted look and commented that anyone filling under 40% needs to take a nitrox class. First of all I thought that you only could get nitrox IF you have taken a class. And, I thought the "standard" fills were 32 and 36 %.... that the 40% is the limit one can use before having to have DEDICATED equipment for nitrox only.......as it applies to non tek fills.

As for keeping the pony filled with say a 32% blend is an interesting thought. My questions there would be.... what is the effect on valves and regs with relative long term storage with nitrox??? I usually fill my pony at the beginning of my dive season....breath off it once or twice to check it out each dive....top it off after every 3rd or so dive.....and drain during the off season. Would it be worth while to do nitrox that way in a pony.

Since I have been curious about this, no one in my discussions has come up and given any definitive comments and reasoning. Which in itself I find pretty interesting. It could be because no one has done any studies around this subject. But it makes me wonder what they know definitively about anything else they seem to be experts on. Just the cynical side of me sneaking out!!

Appreciate your responses.
 
Definitely something low o2 so you can have more depth flexibility.
 
No issues with keeping 32% in a tank.

Consider that the 100% O2 that comes in my supply tanks has an expiration date of several YEARS from the date of production (typically 3 or so.)

If you can get banked Nitrox, fill it with that. If not, then fill it with air. Its far more important that you keep it FULL than what gas is in there, provided its BAIL OUT ONLY.

If you EVER are tempted to breathe it as a "dive extender", then you need to disabuse yourself of that notion rather than trying to allow for it somehow.
 
1. You're on the way to the surface.

2. You're diving No-Decompression Limits, under recreational circumstances.

3. Depending on the depth at which your "Oh $hit" occurs, you'll be breathing off the contents of the tank for little more than two minutes (at a recreationally-oriented ascent rate of 60' per minute, which is two minutes to the surface from 120').

4. With only 13 cu ft to begin with, and hyper-awareness and elevated respiration rate resulting from your "Oh $hit", whether or not you'd have enough in the pony for a 3 minute safety stop is rather academic.

5. It's irrelevant whether you have air in it or EAN during a 2 minute straight shot ascent.

So put air in it.

Doc



P.S. What about your buddy? Use his Nitrox.
 

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