This is done by increasing the amount of oxygen, and the resultant gas is called nitrox. A diver can use a nitrox mix to build in an extra safety margin by applying decompression calculations for air. Alternatively, by applying decompression calculations for the relevant nitrox mix, he can enjoy extended bottom time. Another way to use nitrox is to breathe a mix rich in oxygen during a decompression stop to increase the rate at which nitrogen is eliminated from the body. Surprisingly, oxygen is hazardous when breathed under pressure at depth.
Oxygen poisoning under water can be terminal.
The equipment you use with nitrox may differ from that used for normal compressed-air diving, so special nitrox training is essential.