General

Heliox
Heliox is a mixture of Helium and Oxygen used for deep-sea diving, usually to greater than 200 feet. Helium's advantage is that it does not lead to Nitrogen Norcosis. Diving with Heliox is strictly for technical and professional divers.

The disadvantages of Helium are voice distortion, high thermal conductivity and expense.

Nitrox
Nitrox is usually prepared by mixing pure Oxygen from one source with air until the desired Oxygen concentration is reached [either 32% (I) or 36% (II)]. Nitrox is not air. Nitrox is used for technical and professional diving in depth more than 130 feet.