Which gas is considered narcotic when exposed to increased pressure?

Nitrogen is considered a narcotic gas when exposed to increased pressure, a phenomenon known as nitrogen narcosis or "the bends." This condition typically occurs at depths beyond 30 meters (about 100 feet), where the partial pressure of nitrogen in the breathing gas increases significantly. Under these conditions, nitrogen can have an anesthetic effect on the central nervous system, leading to impaired judgment, decreased motor skills, and altered consciousness. Divers may experience a feeling similar to intoxication, which can affect their ability to make sound decisions underwater.

This narcotic effect happens because nitrogen is not metabolized by the body and remains in the bloodstream, where it can alter the function of nerve cells. Understanding this effect is crucial for divers, as it emphasizes the importance of managing dive depth and duration to minimize risks associated with nitrogen narcosis.

In contrast, while oxygen can also have dangerous effects at high pressures such as toxicity, it does not produce the narcotic effects characteristic of nitrogen. Helium, when used in dives, is typically considered to have very minimal narcotic properties and is often used to mitigate the risks of nitrogen narcosis. Carbon dioxide, while potentially harmful in high concentrations, primarily leads to hypercapnia rather than narcotic effects.