A few months ago I purchased the Spare Air model 300 to attach to my BCD as a completely redundant alternate air source for my dives. Since I do a lot of Nitrox or Enriched Air diving I chose the 300-N model because it comes Nitrox ready.
The Model 300 is a 3 cubic foot or 85 liter capacity scuba tank that can be pressurized up to 3,000 psi, and will give a diver approximately 57 breaths while at the surface. The deeper you are the more the surrounding water pressure will affect the number of available breaths. With this in mind, I only use my Spare Air on shallow dives of less than about 80 feet.
I purchase my Spare Air as a complete kit, which included the Spare Air unit that has the simple to use on-demand regulator with purge button right on top of it, high-visibility yellow mounting holster, coiled safety leash, attached mouthpiece cover, mounting straps with quick release buckles, pop out pressure indicator, and convenient yoke style Refill Adapter that allows me to attach the Spare Air unit to my scuba tank to fill the Spare Air from.
I opted to include the pressure gauge to my unit to replace the pop out pressure indicator so that I know exactly how much pressure is in the unit at any time, not just when it is full to 3,000 psi.
The aluminum cylinder is manufactured just like any other scuba cylinder and includes the same safety features. It should have a visual inspection every year, and also undergo hydrostatic testing every five years, the same as with your other scuba tanks.
A couple weeks ago a friend of mine was diving up on the North Shore when he had a catastrophic failure of the o-ring where his first stage attaches to the tank, it completely disintegrated. This caused him to loose 1,000 pounds of air per minute. In this type of catastrophic event, with a full cylinder he would only have 3 minutes of air in his cylinder before it was completely empty. Luckily he also carries the same 3 cf Spare Air with him on his dives. He was able to switch over to his Spare Air and return safely to the surface without incident.
Luckily I have never needed the Spare Air in an emergency situation as of yet, but I have run several emergency simulation tests on it from various depths. Because of its small size and thereby limited air capacity it should only be used in an emergency out of air situation.
It will give you those precious breaths needed to return to the surface, but it does not have enough air capacity to allow you to make a 3 minute safety stop on the way up. This is why I choose to only use mine for shallower dives, which do not require a safety stop. If you were to use it on a deeper dive, you would have to just blow right past the safety stop and take your chances for DCS.
I love the Spare Air system for its simplistic design and functionality. For around $300 it can definitely be a life saver, and I wouldn’t do shallow dives without it ever again.
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