What phenomenon might a diver experience when breathing a gas mixture with a nitrogen partial pressure greater than approximately 4 ata?

When breathing a gas mixture with a nitrogen partial pressure greater than approximately 4 ata (atmospheres absolute), a diver is likely to experience nitrogen narcosis. This phenomenon occurs because nitrogen behaves as an anesthetic at elevated pressures, which can impair cognitive and motor functions. As a diver descends, the increased pressure causes more nitrogen to dissolve in the body's tissues, leading to an effect similar to intoxication. Symptoms can include confusion, poor judgment, and a decreased ability to perform complicated tasks, which can pose significant risks during a dive.

Understanding nitrogen narcosis is crucial for divers because it highlights the effects of depth on nitrogen absorption and the importance of monitoring depth and gas mixtures to ensure a safe diving experience. This knowledge helps divers make informed decisions about their dive profiles and manage potential risks associated with deeper dives.