When do symptoms of hypoxia generally begin to appear for most people?

The onset of hypoxia, which is a deficiency of oxygen reaching the tissues, is typically associated with specific partial pressures of oxygen (PO2). For most individuals, symptoms of hypoxia generally become noticeable when the PO2 falls to approximately 0.16 atmospheres absolute (ata).

At this level of PO2, the oxygen available is insufficient to meet the metabolic needs of the body, leading to symptoms such as confusion, dizziness, and impaired judgment. This threshold can vary among individuals, but 0.16 ata is recognized as a standard point where symptoms are likely to manifest for most people.

Understanding this is crucial for divers because it highlights the importance of monitoring oxygen levels and ensuring that adequate breathing gas is available during dives to prevent hypoxic conditions.