What dose of oxygen toxicity can manifest symptoms like visual changes?

The onset of symptoms related to oxygen toxicity is closely linked to the partial pressure of oxygen (PPO2) experienced during a dive. Symptoms such as visual changes, which are indicative of central nervous system (CNS) oxygen toxicity, typically begin to manifest at partial pressures that exceed safe levels.

A partial pressure of oxygen greater than 1.4 ATA, which is equivalent to approximately 1.4 times atmospheric pressure, is known to significantly increase the risk of CNS toxicity. While lower levels can pose dangers, 1.4 ATA is commonly recognized as a threshold above which divers may start to experience negative effects, including visual disturbances, seizure potential, and other central nervous system issues.

In practical diving situations, maintaining a PPO2 below this level is critical to reducing the incidence of these toxic effects, especially during the more demanding aspects of a dive. Thus, the correct choice correctly identifies the point at which visual changes can start to occur due to oxygen toxicity, emphasizing the importance of monitoring PPO2 levels to ensure diver safety.