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Air to Spare

Should you bring a Spare Air on your next dive?

Cover image by Stephen Frink

A Spare Air is a small air tank, only a fraction of the size of a scuba tank, but made from the same material and construction, and intended as a backup alternate-air source in case a diver runs out of air during a dive, allowing the diver to surface safely. These units have been around for some time, but have yet to become a must-have in every diver’s gear bag. So what’s it like to dive with one?


The construction is simple and sturdy, and the bright yellow tank looks like something out of a Bond movie. There’s a mouthpiece attached, and the Spare Air comes with a carrying pouch that can be fastened to a tank, leg, or wherever you find it most convenient. It’s larger than I had expected, and heavier, and really does add a bit of bulk and weight to your collection of gear. But if that’s the price of safety, so be it.


Filling it

Filling the Spare Air is pretty straightforward. You simply attach an inflow valve to the unit and attach it to your main tank the same way you would a regulator set and fill it that way. However, the model I tested didn’t have a pressure-release valve, so once the unit is filled and the main tank closed, it’s very difficult to remove the unit again, as the system is now pressurized. That you fill your spare from your own tank is a bit of a drawback, since you’re essentially just redistributing your own air, not taking additional air with you. So if you’re likely to consume most of the air in your tank on your dive, by filling your Spare Air from it you’re simultaneously working to prevent an out-of-gas situation and making that little bit more likely. If at all possible, fill it from a spare tank or fill station.

Diving with it

As stated previously, a diver is meant to wear the Spare Air on his gear or person until it’s needed. I tried fitting it to my tank, but decided, after a few tries, that it would be very difficult for me to reach it there. I did manage — with a bit of help from a buddy — but the presence of a buddy close enough to help me would negate the need for a Spare Air, as he or she would (or at least should) be able to supply me with air through their octopus.

The leg seemed the best place for the unit during the dive. It filled nearly the length of my shin, but once it was attached, it rested comfortably there and I hardly noticed it. It does stick out some, though, making it a bit of an entanglement risk, something I discovered when I managed to get it snagged on a piece of sea kelp during the dive. Nothing critical, but in areas with many stray fishing lines or net, or other entanglement risks, this could be problematic.

Using it

The idea of the Spare Air is simple; if you run out of air and your buddy is nowhere to be seen, or is too far away to reach, you pull out the Spare Air, pop it in your mouth and start breathing. No need to open a valve or anything like that: it’s always ready to go. Deploying it is quick and easy, and I was able, after a few practice runs, to deploy it and start breathing from it in a matter of seconds. That’s faster than most people can get to their buddy, communicate their need for air and receive a regulator. If nothing else, the Spare Air can buy you precious minutes to do just that, or to ascend on your own.

I was comfortably able to swim up from a depth of 22 feet (7 meters) with the Spare Air. I chose not to exceed 33 feet (10 meters) on these test dives so I wouldn’t have to skip a safety stop, which you would naturally do in an emergency. The unit is surprisingly comfortable. One of my initial concerns with this type of unit was that its weight would mean you needed to keep a hand on it to keep the tank from pulling the mouthpiece out of your mouth, but that proved to be no problem at all. Breathing resistance is a little high, probably to prevent free-flows during diving, but not uncomfortably so.

Air to spare, but how much?

As noted, I was able to ascend from shallow water with no problem. My next test was to see just how long I’d be able to breathe on it, so I plopped down to few meters depth and sat at the bottom while I breathed from a freshly filled Spare Air. I got about 10 good breaths before it ran dry. Breathing resistance increased a little on the last few breaths, giving me warning that my air was almost gone. The big question is how deep you’d be able to surface from, safely, using the Spare Air. The unit contains 3 cubic ft. (85 liters) of air, compared to 2,400 liters in a standard scuba tank. Now, I’m an experienced diver and very comfortable in the water. I’m 6’2” and weigh about 180 lbs. On most dives, I consume (adjusted for depth) about 16 liters per minute. So on the surface, I would have enough air for about 5+ minutes. But at 66 feet, I’d have air for only a couple of minutes at best, and that’s under ideal conditions, i.e. swimming at a normal pace, being physically and emotionally relaxed, etc. In the event of an out-of-gas situation, it’s probably safe to assume that I wouldn’t be quite so relaxed, which would make my air consumption increase dramatically. Still, even from reasonable depths, there should be enough air to surface.

Overall impressions

The Spare Air is one of those inventions that, in hindsight, seems to fill an obvious niche. It makes for a great little self-contained, backup-air unit. And there’s no denying the Bond-like quality of it. I took it for a swim after my test, and swimming around in my swim trunks, with my dive mask on and my Spare Air gripped in my teeth, I was humming the Bond theme all along. And let me say that I am seriously considering sticking one of these in the glove compartment of every car I’ll ever own, as it would be a true lifesaver should you ever drive into a body of water.

For diving, it delivers what it says it will very well. There’s plenty of air to surface on; it’s easy to use; construction seems solid. However, there’s the entanglement issue, which is a drawback for me. Also, the cost is somewhat high at $310 online, and for it to really make sense, you should fill it from a separate, dedicated tank or at the fill station, which makes it slightly less convenient. So for a unit that you should (hopefully) never need, it has a few too many drawbacks, in this reviewer’s opinion. For a recreational diver, there’s no real reason to spring for one, as all training organizations teach out-of-gas management, both with a buddy (shared-air ascent) and without (controlled-emergency ascent). As a recreational diver, you should never put yourself in a situation where you aren’t able to head straight for the surface if you must. For photographers or solo divers it may be worthwhile to bring one, but in that case, I’d prefer a completely separate air source, such as a pony bottle or a set of double tanks.

One group of water sports enthusiasts I spoke to who seemed very interested in the concept was snorkelers and skin divers, who saw it as a way of extending their dives. However, this shouldn’t be undertaken without caution, and ideally with prior scuba training, as adding a Spare Air to a snorkeling situation makes it something close to a dive situation since you’ll be breathing compressed air under pressure. All in all, the Spare Air is a great idea — well constructed, but ultimately not necessary enough for most divers to warrant the cost and maintenance. In the glove box of my car, though…