1) Breathing gas 
==Use== Enriched Air Nitrox, nitrox with an oxygen content above 21%, is mainly used in scuba diving to reduce the proportion of nitrogen in the breathing gas mixture. Reducing the proportion of nitrogen by increasing the proportion of oxygen reduces the risk of decompression sickness for the same dive profile, or allows extended dive times withou...
any mixture of nitrogen and oxygen that contains less than the 78% of Nitrogen.No-mount diving
For recreational diving, Nitrox (or Enriched Air Nitrox) refers to a mixture of nitrogen and oxygen where the oxygen concentration is more than 21 percent (which is the percentage of oxygen found in normal air). Most commonly refers to 32 percent oxygen in a tank.
A breathing gas consisting of oxygen and nitrogen