text: Good question actually. A reputable dive shop shouldn't be selling them to a non certified diver. They have a reg similar to that used on a set of normal regs, which require some training on, to be familiar with it's use and limitations. You also need to be familiar with how a compressed gas works on the body and some of the physics involved.\n There are a couple of sizes of spare air, so gas volume will be part of how long a can will last as well as the depth it's used at.\n Mine is the 3 cubic foot (largest I think) and allegedly holds 50 typical breaths when used at the surface. This number goes down substantially when you  hit 2 atm and so on. About 25% per atm approximately. I don't think they are what you want, for what you intend on doing. They are refillable, but I don't think the cost is worth it for you overall. Mine's sole purpose is to get me out of a tight spot, should the need arise. Fortunately (knock on wood) I haven't had to take it out of the holster.\n You could get certified for just a little more than the cost of one of these. Just a thought.