People have used compressed air as their breathing medium since the advent of diving in the 1950s. Its main advantage is that it is readily available and relatively inexpensive to compress into cylinders. Nevertheless, air is not the "ideal" breathing mixture for diving. With a concentration of approximately 79 percent nitrogen, compressed air poses two potential problems for all divers: susceptibility to nitrogen narcosis (a condition resembling alcoholic intoxication) at deeper depths; and decompression sickness (DCS). Both of these can prove fatal to a diver. In an effort to reduce the ill effects of nitrogen on divers, nitrox was developed.
Nitrox is a generic term that can be used to describe any gaseous mixture of nitrogen and oxygen. In the context of technical diving, nitox is a mixture containing more oxygen than air. The two most commonly used nitrogen-oxygen mixtures contain 32 percent and 36 percent oxygen by volume. This differs significantly from compressed air, which contains approximately 21 percent oxygen by volume. While an increase of 12 to 16 percent oxygen by volume may not seem drastic, it allows divers to significantly extend their bottom time, and decreases their risk of developing DCS.
While diving with nitrox has definite benefits, it also has clearly associated risks. The major hazard is oxygen toxicity. This comes about when oxygen is inhaled in high concentrations for an extended period of time; this occurs primarily when a diver exceeds the recreational limits for depth. Under these circumstances, a diver can experience an epileptic-like seizure, which may lead to drowning. Due to this potentially fatal hazard, divers using nitrox must adhere to special dive tables. These tables list the maximum safe amount of time that a diver can stay underwater at a certain depth.