Enriched air (Nitrox) is air enriched with oxygen to give it a higher percentage of oxygen than normal air.

Increasing the oxygen percentage of the air consequently decreases the percentage of nitrogen that the diver is breathing.

As allowable no decompression dive time is dependant on the amount of nitrogen the diver has been exposed to at a particular depth reducing the nitrogen percentage therefore increases the divers no stop dive time.

The increase in allowable dive time can be appreciable, for example at a depth of around 30m the allowable dive time can be increased from a maximum of twenty minutes to a maximum of thirty minutes with the appropriate oxygen percentage of enriched air nitrox used by the diver.