What factor most increases the risk of nitrogen narcosis during a dive?

• A. Temperature
• B. Depth
• C. Dive duration
• D. Gas mix

Answer: (B)

Nitrogen narcosis is caused by dissolved nitrogen affecting the nervous system when under high pressure. The amount of narcosis you experience scales with the nitrogen partial pressure, which is the product of how much nitrogen is in the breathing gas and the ambient pressure. As you go deeper, ambient pressure increases roughly 1 atmosphere every 10 meters, so the nitrogen partial pressure rises. That higher PN2 makes narcosis more likely and more pronounced.

Gas mix can influence how much nitrogen you’re inhaling at any depth, so using a mix with less nitrogen or including helium can reduce narcosis, but the depth itself is the primary driver because it directly raises the pressure—and thus the nitrogen partial pressure—inside your body. Temperature and dive duration may affect comfort or perception, but they don’t change the fundamental pressure-nitrogen relationship driving narcosis.