Diving technology and equipment are constantly improving. The industry is also learning more and more about the long term effects of pressure on the human body. One of the newer discoveries is Nitrox. In 1996 Nitrox was accepted into the recreational dive industry. It is a mixed gas that contains more oxygen and less nitrogen than regular compressed air.
Less nitrogen allows for longer bottom times.
There is still quite a bit of controversy about using Nitrox for pushing the standard dive limits. On the other hand there is a solid agreement that using Nitrox with standard limits actually improves safety. Using Nitrox in conjunction with standard dive tables for compressed air will reduce the amount of nitrogen that is absorbed and therefore reduce the chances of decompression sickness. As in any new technology or technique, do your homework before you make a decision. Nitrox does require additional training.