What air is in scuba divig tanks?

Answer 1

The answer is sort of in the question... air, which is 78% nitrogen and 21% oxygen. Normal air is most commonly used to fill cylinders because it is the cheapest gas to fill cylinders with.

Although air is what most diving cylinders have inside them, some people do something called nitrox diving. This is where the air is enriched with pure oxygen. This increases the time a diver can stay at any depth without needing to decompress. Adding pure oxygen means that special equipment is required to fill the cylinders and also breathe it because it needs to be 'oxygen clean'.

For very deep diving the mixtures change to tri-mix which is a blend of nitrox and helium or heliox which is just helium and oxygen. These mixtures are used because nitrogen causes intoxication at depth. By reducing the amount of it and replacing it with helium these effects are reduced or eliminated. Helium is a rare and expensive gas so these mixtures would only be used when they are required.