Air backup for a nitrox dive?

[Brian G]

The only issue I can think of is that your computer will still be calculating NDL based on nitrox instead of air. It's hard to imagine that would make much of a difference over the short amount of time that you would be taking on extra nitrogen at depth with a spare air.

 

[Barnaby'sDad]

Yeah... considering a Spare Air is filled from a main tank, i.e. no one in their right mind would will a SA with partial pressure blending... I think every SA is a "nitrox SA".

Silly. But a good test of how well someone paid attention in their nitrox class.

You’re assuming that the OP filled it from their Nitrox tank. Given the OP/question, I have to assume that they had it filled from a regular air cylinder.

 

[The Chairman]

Most bail out bottles should be filled with air since air is safe at any recreational depth. Deco bottles are another thing entirely.

Whatever your switch, there are some procedures to follow. Before the dive, charge the regulator and then turn it off. This will stop water intrusion into the first stage and up the hose. After you're on the "new" gas, be sure to change your PDC to reflect the actual gas you're breathing. There are additional procedures for deco gasses.

I won't use anything smaller than an AL40 as a bailout. Getting used to slinging an AL40 is great preparation for tech classes.

 

[PfcAJ]

Say I have Spare Air (the air model, not nitrox) and I have an OOA situation on a nitrox dive. Am I correct in assuming that it's safe to switch to the 20.9% backup for my ascent? I can't wrap my head around it at the moment.

Bruh youre OUT OF GAS and about to be out of gas again because spare air sucks. No time to fiddle with buttons on your computer.

Up you go to the big air tank in the sky.

 

[Caveeagle]

If you were properly trained for nitrox, or trained at all you probably shouldn’t be asking this question. And that’s not being rude, it’s just reality. Put simply, with increased O2 you cannot go down as far.

Good grief, let’s all pile on and beat up the OP for an honest question. (Sarcasm). . I am sure you all retained 100% of the information in your Nitrox class. You are all aware you can get a Nitrox card online for about a $100 and under an hr. ‍

To the OP.. as you have probably figured out by now, a spare air isn’t really much help for most real world emergencies. Best case it gets you a few breaths and time to get to the surface.

If your diving 32% and within your NDLs, two or three breaths of air is not likely to get you bent, and is certainly better than drowning.

Yes. An AL40 is also my preferred bail out bottle for OW diving. However a al30 or even 20 would be far better than a spare air. They really get you true redundancy, so if you have a problem you have time to sort it out and not be a panicked Polaris missile.

 

[iamrushman]

what ever it takes to get to the surface...air is 21% nitrox....so go for it....of course, gas planning and management is the best option....

 

[caruso]

As to the question asked in the first post. For all practical purposes the short amount of time and the relatively small amount of gas breathed during ascent from a SpareAir filled with air won't make any difference.

As to the off topic comments about Spare Air being useless, I suggest you simply ignore them. It's a good product, it does have it's place in recreational diving, it's infinitely better in an OOA situation than no gas at all. Just know the limits and consider using a larger source of backup gas if you're spending some time at depth.

 

[caruso]

If you were properly trained for nitrox, or trained at all you probably shouldn’t be asking this question. And that’s not being rude, it’s just reality. Put simply, with increased O2 you cannot go down as far.

I don't recall the contents of a pony bottle being mentioned by the instructor or written anywhere in the Nitrox manual. Either my memory is poor or my training wasn't proper either (by your standards).

And you're wrong - with more 02 you can in fact go "as far" as you can with air. It's all about the amount of time you can stay there. Even if the Spare Air was filled with a high percentage of EAN the odds are almost nonexistant that there would be any issues with CNS toxicity from the small amount of time and gas involved at recreational limits or less.

 

[jlcnuke]

I don't recall the contents of a pony bottle being mentioned by the instructor or written anywhere in the Nitrox manual. Either my memory is poor or my training wasn't proper either (by your standards).

And you're wrong - with more 02 you can in fact go "as far" as you can with air. It's all about the amount of time you can stay there. Even if the Spare Air was filled with a high percentage of EAN the odds are almost nonexistant that there would be any issues with CNS toxicity from the small amount of time and gas involved at recreational limits or less.

You'd be comfortable breathing 40% (what nitrox cert allows to be used) at 130' (still in rec depths)?

 

[caruso]

You'd be comfortable breathing 40% (what nitrox cert allows to be used) at 130' (still in rec depths)?

Let's think this through. I've got 40% Nitrox in my spare air at 130' and I'm OOA with no other options. First thing I'm doing is going up. I doubt I'd even take 1 breath at that depth I'd be already 5-10 feet shallower and moving upwards at a pace far greater than the recommended 60 fpm.

Odds are I won't take more than around a half dozen breaths at a depth that exceeds PO2 1.6, and remember PO2 is a function of exposure over time. Those numbers are going to calculate at close to zero.

Most importantly- if you're at 130', OOA and reliant on a Spare Air for your only survival you've got bigger issues than worrying about exceeding your MOD.