An actual legitimate use for spare air???

[Boston Breakwater]

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?

Hello. I think we just beat this to death about a month ago?
Anyway.......I recall reading Spare air is highly recommended for cleaning salt water fish tanks, generally in the 250 to 1000 gallon range.
Cheers.

 

[lexvil]

And most people have 0

Point?

 

[BRT]

I carry a cup of gas in my van, just in case I run out on the highway.

Another mile or 2 down the road. Makes for a lot shorter walk.

 

[BRT]

Point?

3 is more than most people have.

 

[spitfiremac]

I really do love this and appreciate the humor...

...and if you had to sit and idle for 3 minutes outside the station, this might not such a bad idea.

But point taken none-the-less.

 

[lexvil]

3 is more than most people have.

Likely more than most need but more is more

 

[Graeme Fraser]

STAS. I would say handy for offshore helicopter ditching or high speed capsize but can't think of much else.

 

[BoltSnap]

Spare air is nothing more than a false sense of security to the diver. For about the same amount of money, one can have a viable and true independent air supply for emergencies (once in a lifetime event at the most), a pony bottle with regulator.

 

[lowwall]

The problem with the Spare Air is that it is never the answer if you are properly planning and executing a dive.

If you are paying even a little bit of attention to what is going on, you aren't going to drain your gas so the only situation you might need external gas is a major equipment malfunction. The normal plan for that is avoiding it entirely by maintaining and inspecting your equipment at reasonable intervals.

The fallback to that is your buddy. But what if you don't have or trust your buddy? In that case, a reasonable backup plan means carrying enough gas to get you to the surface using a normal ascent from the deepest part of your dive. In other words, a pony bottle rather than a Spare Air.

 

[tbone1004]

Spare air is nothing more than a false sense of security to the diver. For about the same amount of money, one can have a true independent air supply for emergencies (once in a lifetime event at the most) a pony bottle with regulator.

and for free they can plan their dive properly so they don't have to worry about it in the first place...