It varies. Divers use different breathing gases depending upon their needs.
For standard air, it is 21% oxygen and 79% nitrogen.
For nitrox, it can be any higher mix of oxygen, but typically either 32% or 36% oxygen, and the balance nitrogen.
For trimix, you can have almost any combination of oxygen, nitrogen and helium to suit your depth, and manage your risk to oxygen toxicity and nitrogen narcosis.
Because that is the main chemical in the air humans like to breath. Our atmosphere (near the ground anyway) is made up of 71% nitrogen. Compressed air in a Scuba tank is the same air you are breathing right now just without the oils and moisture.
If you replace some of the Nitrogen with Oxygen that is called Nitrox.
http://en.wikipedia.org/wiki/Nitrox
If you replace some of the Nitrogen with Helium that is called Trimix. http://en.wikipedia.org/wiki/Trimix_%28breathing_gas%29
Addition
Air is made up of approximately 79% nitrogen. This percentage stays the same regardless of altitude.
I would think so, because there are two of them mixed together. Air in a scuba tank or anywhere else should be heterogeneous. A scuba tank filled with either oxygen or nitrogen would be homogeneous.
The numbers on a scuba tank reveal 3 things. Serial no. of the tank. Type metal. and the current hydro date.
From a regulator attached to a scuba tank.
A scuba tank holds compressed air or a mix of gases, typically oxygen and nitrogen, that divers breathe underwater. The tank allows divers to stay submerged for extended periods by providing them with a continuous air supply.
The empty weight of a 100 cubic foot steel SCUBA tank is approximately 33lbs.
Depends on the size of the tank.
Depends on the size of the tank.
the silly answer is you can store anything in a scuba tank that you can get in it!!. BUTthe serious answer is scuba tank were designed for compressed air and nothing else... using a scuba tank for natural gas is like driving around with a bomb in your car!!, the valves and collars of the bottles are not strong enough if there was a crash
No.
The simple answer is ... you don't. A majority of scuba dives use compressed air in the cylinders. Therefore you don't need "oxygen" cylinders. HOWEVER, if you are a diver that is diving on Nitrox, in which divers change the amount of oxygen vs nitrogen in their air, then your tank needs to be "oxygen clean" because you are putting oxygen in first, then nitrogen.
its the scuba tank on the swimming guys back.
You can use a scuba tank, but that is it.