At what oxygen level can a person experience respiratory arrest or death?

The correct answer reflects the level of oxygen in the atmosphere at which critical life-supporting functions begin to fail. Under normal conditions, the air we breathe contains approximately 21% oxygen, which is vital for human survival. When the oxygen level declines significantly, physiological effects become noticeable.

At an oxygen level of around 12%, individuals may begin to experience symptoms such as increased heart rate, shortness of breath, and impaired cognitive function. As the oxygen level falls further, reaching around 6%, the body cannot obtain sufficient oxygen, leading to severe hypoxia, confusion, and potentially loss of consciousness.

At just 4% of oxygen, the situation is dire, and individuals can rapidly experience life-threatening conditions including respiratory arrest or death due to the inability of the body to sustain vital processes. This is why the 4% threshold is identified as fatal, highlighting the importance of maintaining a safe and adequate oxygen level for human survival.