An actual legitimate use for spare air???

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Location
Monterey, CA
Want to run something by the community...

I've been thinking about those little 3 cu ft. bottles and if they have any legitimate use at all in actual SCUBA, whether it be rec or beyond. General consensus is that anything smaller than a 19 cu ft pony bottle absolutely doesn't given proper safety procedure, buddy protocol, on and on.

I generally agree with this assessment. Spare air may only be for free divers/snorkelers, BUT there is one case that I think is worth mentioning.

In the case of a SCUBA emergency, two divers sharing one tank, depending on max depths and dive times before the OOA situation, stressed air consumption, etc, etc, Spare Air could be usable in the very limited context of ENABLING A PROPER SAFETY STOP at 15 ft by extending the air margin, and thereby avoiding a whole host of other issues on the surface.

Here are my calculations:

.5L x 3,000 psi (compression) / 14.7 psi (atmo pressure) =
102L (compressed air) in a Spare Air or SMACO bottle

102L = 3.6 cu ft of compressed air in said bottles

3,000 psi = 206.84 bar in bottles (for calculating SAC rate, which I did online here)

at a 22.98 L/min SAC rate (this is a baseline, not accounting for elevated breathing rates)

...that's (102L) / (22.98 L/min) = 4.43 min of air at a safety stop depth of 15 ft

At many rec depths, that could enable the completion of a safe ascent without the prospect of DCS for one or two people...

that being said, it has to be noted that this is if the slim Spare Air is ONLY looked at as a safety stop enabler or safety stop finisher... much like the altitude auto-deploy on a reserve parachute container, something no plane jumper in their right mind (absent product testers) would rely on for anything but primary and reserve pull-chord malfunction or unconscious freefall.

As far as using it to ascend, hey, if the situation is that bad at depth all bets are off, but you're not going to care about anything but air at that point. Thinking of this as a little bit of margin at 15 ft seems to me to be the only legit rec diving use of this, but not a bad one at all for the cost of a slim bottle and 2 extra pounds on land.

Thoughts?
 
Safety stops are not required. They are recommended and a very good idea but in a recreational low-on-air or out-of-air emergency you aren't going to get bent or die from not doing a safety stop. Carrying a spare air for just this purpose is without merit. If this situation occurs just blow your safety stop.
 
in the eternal words of @cerich that is an equipment solution to a skills problem. Failure to adequately plan rock bottom reserves have caused you to need more gas. This could have been solved by proper dive planning... If you want to do a safety stop, then add it to your rock bottom gas requirements, I do.
 
Thoughts?

I just don’t get them. Diving with a 3cf Spare Air makes about as much sense to me as someone perpetually driving around with their vehicle on empty, because you don’t plan to drive more than 20 miles...so why would you need more fuel?

You carry a decent size pony bottle and your buddy gets into an issue at depth...you can pass them the regulator, clip off the bottle to them, and have an untethered and leisurely ascent. Or you can have a leisurely ascent...if need be.
 
The argument that a small spare are could be used to make a more controlled CESA makes sense. Instead of bolting from depth, it is easier to come up slow, taking a breathe and continuing to exhale as long as you can before another breath. However, if you took the time to think of that plan and acquire the gear necessary for it, then why would you not just get a proper pony bottle? If its life safety then dont short change yourself just to save 8 lbs...
 
The argument that a small spare are could be used to make a more controlled CESA makes sense. Instead of bolting from depth, it is easier to come up slow, taking a breathe and continuing to exhale as long as you can before another breath. However, if you took the time to think of that plan and acquire the gear necessary for it, then why would you not just get a proper pony bottle? If its life safety then dont short change yourself just to save 8 lbs...

Exactly. A brand new AL40 is the same price as a Spare Air. An AL19 is cheaper than a Spare Air. A pony bottle reg setup is not expensive, in the grand scheme of things.
 
Thoughts?

If you like the idea of using a spare air, go ahead and use it.

If/when people laugh at you for having it, just flip them a bird. You don't need to justify your gear to anyone. So what if they can buy bigger and better stuff for the same cost of spare air, you get your thing and that's that.

I always thought it would be cool to have one in a car, just in case you fall in a canal and can't find the glass braker in the console/glove compartment, you can breath long enough to kick the windshield out, and swim away. Like in the movies.
 
https://www.shearwater.com/products/perdix-ai/

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