The risk of CNS oxygen toxicity increases significantly above which level?

The correct answer highlights that the risk of central nervous system (CNS) oxygen toxicity notably increases at a partial pressure of oxygen (ppO2) of 1.4 bar. This is a critical threshold defined in diving regulations and guidelines.

Understanding the significance of this level involves recognizing how oxygen behaves under pressure. As divers descend, the partial pressure of the gases they breathe also increases. While oxygen is essential for respiratory functions, elevated levels (particularly above 1.4 bar) start posing risks to the CNS, including symptoms like visual disturbance, dizziness, and convulsions, which could lead to accidents while diving.

The choice of a ppO2 of 1.6 bar represents an even higher level of risk, which further exacerbates the potential for CNS toxicity. Generally, diving guidelines suggest avoiding prolonged exposure to this level of oxygen in order to minimize risks.

While the other options touch on aspects related to diving and oxygen exposure, they do not represent recognized thresholds for increased risk of CNS oxygen toxicity as effectively as the indicated ppO2 of 1.4 bar. For example, diving at specific depths or durations affects other physiological aspects but is not as directly correlated to the immediate risk of CNS oxygen toxicity.