What percentage of the atmosphere is composed of oxygen?

The correct answer highlights that the atmosphere is composed of approximately 21% oxygen and 79% nitrogen. This composition is essential for life on Earth, as oxygen is crucial for respiration in most living organisms. Nitrogen, while not directly participating in respiration, serves as a major component of the atmosphere, providing stability and dilution of oxygen, which helps prevent combustion or other reactions that could be harmful.

Understanding the atmospheric composition is vital, especially in fire safety contexts. Since fires require oxygen to ignite and sustain combustion, knowing that oxygen levels are typically around 21% helps fire safety directors assess risks and manage emergency situations effectively. In environments with away from the normative atmosphere, such as high-rise buildings during a fire, these percentages can provide insights into potential fire behavior and ventilation needs.