What kind of air or gas does a dive tank contain?
A dive tank contains compressed air, not oxygen. Compressed air is exactly the same as the ambient air we normally breathe, but it is compressed to enable the diver to take as much air with him under water as possible. Ambient air consists of roughly 80% nitrogen and 20% oxygen. You will, however, often encounter tanks filled with 100% oxygen on, for example, dive charter boats, but these are only used in emergencies for injured divers (for example, divers with decompression illness).
