What gas do divers commonly notice narcosis from at a depth of about 30 meters?

At depths around 30 meters, divers frequently experience nitrogen narcosis, a condition caused by the effects of increased pressure on nitrogen. As divers descend, the partial pressure of nitrogen in the body's tissues rises, leading to a narcotic effect comparable to alcohol intoxication. This can impair a diver's cognitive and motor functions, resulting in reduced judgment, coordination, and reaction time.

Understanding the mechanism of nitrogen narcosis is crucial for divers, as it highlights the importance of managing depth and bottom time during dives, especially at greater depths. While oxygen, carbon dioxide, and helium play roles in diving physiology, they do not exhibit the same narcotic effects as nitrogen at the typical recreational diving depths. Oxygen can be toxic at very high pressures, carbon dioxide is more about hypercapnia and its effects, and while helium is sometimes used in deep diving mixes to reduce narcosis (due to its low narcotic effect), nitrogen remains the primary gas responsible for narcosis at the stated depth.