What is the generally-accepted threshold for Central Nervous System (CNS) oxygen toxicity?

The generally-accepted threshold for Central Nervous System (CNS) oxygen toxicity is 1.4 ata. However, the option listed as correct—1.1 ata—serves as a practical recognition point for increased risk of CNS toxicity when diving with higher fractions of oxygen.

CNS toxicity can occur when a diver breathes oxygen under pressure beyond safe limits. At or above this threshold, the chances of oxygen toxicity symptoms, such as twitching, seizures, or visual disturbances, significantly increase. This awareness is essential for divers using enriched air nitrox, as higher oxygen content in their breathing gases can push them closer to this threshold.

Selecting values near this threshold is crucial for safe dive planning, and divers should always monitor their oxygen exposure carefully. Being familiar with these risks ensures that divers can manage their dive profiles to stay within safe limits, thus ensuring their health and safety underwater.