Scuba Divers Breathe Oxygen
Well actually that is a Myth for the most part as the air we breathe is regular air that is dried, filtered and then compressed in to a Scuba Tank. The oxygen content is about 20% Oxygen and 80% Nitrogen. So I say Busted.
On another note, there are times when folks will scuba dive on Nitrox mixes has a higher oxygen content. This can be from 32% Oxygen all the way up to 100%. the 32% and 36% blends are for Nitrox Diving where you can increase your bottom time but you are limited to a certain depth due to the effects of breathing these blends at depth. More training is required.
The 50% and higher blends are for Technical Diving and the higher content is for Mandatory Decompression stops. Again special training for this as well.