How long would the oxygen last me in an average sized scuba tank?

Question

also, what would be the best size and how much would it cost?

Answer 1

I think you mean air, which is mostly nitrogen and some oxygen. (about 79% N and 21%O2), unless you're talking about Nitrox (which refers to a different proportion of nitrogen to oxygen).

Keep in mind, you should only use one tank for regular air and  a separate one for Nitrox. Talk to a dive shop/dealer about the risks, benefits or classes/certifications in Nitrox.

The amount of time a tank can last you depends on how experienced you are as a diver, how deep you go or shallow you stay, how active you are during the dive and in some cases on if you're male or female.

If you are a new diver, you're more likely to use up your tank sooner because of your comfort level in the water. Experienced divers usually are very relaxed and new divers can be scared or panicky. (This ca vary from under an hour to less than 20 minutes, depending on depth and how often you adjust/fiddle with your BC (buoyancy compensator).)

Air usage also varies with depth because the deeper you go, the more pressure is on your lungs, so you actually breathe in a higher concentration of air to compensate for the pressure change. If you're diving one tank above 25 feet, you could possibly last almost an hour. If you're diving 60 feet or below, you'll be very lucky to have 15 minutes with enough air to get back to surface (ascend) safely.

Activity also affects tank usage. If you're relaxed, taking your time enjoying a reef, you'll last much longer than if you're swimming fast against a current or even spearfishing. Your body uses and requires more oxygen during increased activity, and as your heart rate increases, so does your breathing, hence the emptying of the tank.

Your s*x may also affect you. For some reason, a lot of experienced divers have noticed that women (when compared to men of the same diving experience) usually use up less air. This could be to lung size difference between the sexes or level of comfort in the water. Either way, the last one is only an observation.

Air tank size and type (aluminum or steel) depends on where you dive. One is better in colder waters, like California, and the other is better in warmer waters, like Florida. Also, one is actually lighter because of the material it's made from. However, one changes more with the air used up, which can affect your buoyancy (you'd start out overweighted and then end up under weighted, possibly risking not being able to control your rate of ascent).

Talk to your local dive shop/dive dealer. (I don't recommend Sport Chalet.) Try out a few tanks before committing, because experience can help. Prices will vary among cylinder types and from shop to shop. In this case, you might want to check out Sport Chalet, or if you're buying more than a tank, see if a dive shop will give you a deal.

Answer 2

Oxygen (pure) cannot be breathed safely