What is the oxygen concentration percentage at which breathing becomes difficult and potential fainting occurs?

Breathing becomes increasingly difficult and the risk of fainting occurs when the oxygen concentration in the air drops significantly below the normal atmospheric level of 21%. At 18% oxygen concentration, individuals may start to feel symptoms such as shortness of breath and decreased cognitive function because the body isn't receiving the oxygen it needs for proper functioning. However, it is typically at around 10% oxygen concentration that severe hypoxia can occur; this level is dangerously low and can lead to unconsciousness or fainting due to insufficient oxygen reaching the brain and vital organs. The body does not function well at these critically low levels, and prolonged exposure can be life-threatening. Thus, understanding that 10% oxygen concentration signifies an extreme risk for fainting underscores the importance of maintaining adequate oxygen levels for safe breathing.