What is a significant risk of exceeding oxygen limits during a dive?

Exceeding oxygen limits during a dive can lead to convulsions, which is a major risk associated with oxygen toxicity. Oxygen toxicity occurs when a diver breathes in an elevated partial pressure of oxygen, typically above 1.4 ATA (atmospheres absolute) on enriched air nitrox. As the pressure of oxygen increases, it can affect the central nervous system, leading to symptoms such as visual disturbances and muscle twitching, which may culminate in a convulsion. This convulsion can significantly impair the diver's ability to manage their buoyancy and could lead to a loss of consciousness, increasing the risk of drowning.

Understanding the physiological effects of different gas mixtures and their limits is crucial for divers using enriched air nitrox. The other risks listed, while serious, are not directly related to the limits of oxygen itself as they occur due to different physiological mechanisms or situations encountered during diving. Recognizing the dangers associated with oxygen exposure helps divers make informed decisions about their gas mixes and diving practices.