At what partial pressure of oxygen (PPO2) is the risk of oxygen toxicity significantly increased?

The risk of oxygen toxicity is significantly increased at a partial pressure of oxygen (PPO2) above 1.4 ATA. This level of PPO2 is critical because it represents a threshold where there is a notable increase in the likelihood of central nervous system toxicity, which can lead to symptoms such as visual changes, twitching, and potentially seizures.

At PPO2 levels above 1.4 ATA, divers are advised to manage their exposure time carefully to mitigate the risks associated with high oxygen concentrations. While lower pressures like 1.1 ATA or 1.2 ATA do carry some risk, it is mainly at and beyond 1.4 ATA that divers begin to encounter significant safety concerns. Levels above 1.6 ATA and 2.0 ATA represent even higher risks, but the critical threshold for prudent management and consideration of oxygen toxicity symptoms starts at 1.4 ATA.