When do symptoms of hypoxia typically appear?

Symptoms of hypoxia typically appear when the partial pressure of oxygen (PPO2) drops to 0.16 atmospheres absolute (ata). At this level, the body's ability to adequately utilize oxygen begins to diminish significantly, leading to various symptoms of hypoxia, which can include confusion, impaired coordination, and shortness of breath.

As the PPO2 decreases, the availability of oxygen for cellular metabolism is compromised, and these physiological effects become more pronounced. Although lower PPO2 levels can lead to severe hypoxia, the threshold of 0.16 ata is widely recognized as the limit at which noticeable symptoms begin to show in individuals, particularly in high-altitude or underwater environments. Understanding this critical point is essential for safety during diving operations and for recognizing when immediate intervention is needed to improve oxygen supply.