Basic Firefighter Written Practice Exam

What percentage of normal air is comprised of oxygen?

1. 10%

2. 21%

3. 30%

4. 50%

The correct answer is: 21%

Normal air is comprised of approximately 21% oxygen by volume. This percentage is a critical aspect of understanding combustion and respiration, as it highlights the availability of oxygen for supporting fire and life. Oxygen is a vital component that fuels combustion; without sufficient oxygen, fires cannot sustain themselves. In the context of firefighting, recognizing that air consists mainly of nitrogen (about 78%) with only a small fraction being oxygen helps firefighters understand the conditions needed for fire to ignite and continue burning. This knowledge is essential when preparing for fire response scenarios, ensuring that firefighters effectively manage ventilation and air supply to control fire behavior and safety.