What is the maximum partial pressure of oxygen (PO2) that is typically considered safe for recreational diving?

The maximum partial pressure of oxygen that is typically considered safe for recreational diving is 1.4 ATA (atmospheres absolute). This level is widely accepted to minimize the risks associated with oxygen toxicity, which can lead to central nervous system effects and other potentially hazardous conditions when diving.

At higher partial pressures of oxygen, particularly above 1.4 ATA, the risk of experiencing oxygen toxicity increases significantly. Recreational divers are trained to manage their gas mixtures to ensure that their exposure to oxygen remains within safe limits. While some technical diving practices may occasionally allow for higher values, for the purposes of recreational diving, adhering to the 1.4 ATA guideline ensures a balance between the benefits of using enriched air nitrox for extended bottom times and reduced nitrogen absorption versus the inherent risks of increased oxygen exposure.

The other options suggest higher partial pressures that are beyond the commonly accepted safe limit for recreational diving, increasing the potential for toxic effects and complicating dive planning and safety protocols.