In mixed gas diving, what is the main reason for using helium?

In mixed gas diving, the primary reason for incorporating helium is to prevent nitrogen narcosis. Nitrogen narcosis occurs when divers breathe compressed air at depths typically exceeding 30 meters (100 feet), leading to cognitive impairment and other negative effects caused by the high partial pressure of nitrogen. Helium, being a lighter and less narcotic gas than nitrogen, mitigates this risk. By replacing a portion of nitrogen with helium in the breathing gas mixture, divers can safely reach greater depths without experiencing the debilitating effects of narcosis, thereby enhancing their safety and performance underwater.

The use of helium does not primarily relate to increasing buoyancy, reducing costs, or improving visibility, which are concerns that do not factor into the critical nature of preventing narcosis during deep dives. Thus, the inclusion of helium in mixed gas diving is fundamentally aimed at enhancing safety and operational efficiency in deeper dives.