What is the lowest breathable level of partial pressure of oxygen (ppO2) that can lead to hypoxia?

The lowest breathable level of partial pressure of oxygen that can lead to hypoxia is typically recognized to be around 0.16 ata. At this level, the oxygen available in the breathing mixture is insufficient to meet the metabolic needs of the body, which may start to result in symptoms of hypoxia. As ppO2 decreases below this threshold, the risks of hypoxia escalate, leading to cognitive and physical impairments.

Understanding partial pressure is crucial in diving because it relates directly to the amount of oxygen available to the body. As divers descend to greater depths, the ambient pressure increases, which affects the ppO2 of the breathing gas mixture. Maintaining an appropriate level of ppO2 is essential for ensuring that divers avoid hypoxia, which can impair their cognitive functions and can be dangerous underwater.

The other options fall below the recognized threshold, making them insufficient for maintaining safe oxygen levels in the body as depth increases. Therefore, 0.16 ata serves as a critical limit when considering the onset of hypoxia in diving scenarios.