Many elements exist as gases in their natural state, and because gases mix easily, in nature, gases normally occur mixed rather than in isolation. On earth, the most common gas mixture is air, which consists of nitrogen, oxygen, argon, carbon dioxide, neon, helium, krypton, hydrogen,xenon, radon, and carbon monoxide among others. However, many of these gases exist in such small portions that they are normally inconsequential. So, from a practical point of view, it’s only necessary to address those gases that affect diving, either in respiration or through special applications to diving. These gases include: oxygen, nitrogen, carbon dioxide, carbon monoxide, helium,hydrogen, argon and neon.