How does an increase in oxygen concentration affect the dive?

An increase in oxygen concentration during a dive indeed raises the risk of oxygen toxicity. When divers breathe gases with higher concentrations of oxygen—such as those found in enriched air nitrox mixes—they must be aware of the potential for oxygen toxicity, particularly at deeper depths.

Oxygen toxicity can occur when the partial pressure of oxygen exceeds safe limits, potentially leading to symptoms that include visual disturbances, muscle twitching, and in severe cases, seizures. The risk escalates at greater depths, where the partial pressure of oxygen increases as well. Therefore, understanding the impact of varying oxygen concentrations is essential for safe diving practices.

The other options do not accurately reflect the consequences of elevated oxygen levels. While reducing the risk of decompression sickness and enhancing underwater vision might seem desirable, they do not directly relate to the concentration of oxygen in the breathing mix. Similarly, improving diving speed is not a direct effect of increased oxygen concentration. Thus, recognizing the risks associated with higher oxygen environments is crucial for diver safety.