What percentage of oxygen concentration is considered normal for breathing air?

The correct answer is 21% because atmospheric air typically consists of roughly 21% oxygen, which is essential for human respiration and various combustion processes. This concentration allows the body to effectively utilize oxygen for cellular functions, and it is a critical component in maintaining normal physiological and metabolic activities.

Understanding the importance of this percentage is fundamental for firefighters, as it relates to fire behavior and the health of persons in smoke-filled environments. Oxygen levels below this percentage can lead to hypoxia, while levels significantly above can create a risk of fire and combustion. Thus, knowledge of the normal concentration helps firefighters assess risks and make informed decisions in emergency situations.