What percentage of oxygen is typical in a normal atmosphere?

In a typical atmosphere at sea level, the composition of air consists of about 21% oxygen. This percentage is established by various studies and measurements of the earth's atmosphere. The presence of oxygen at this level is crucial for sustaining life, as it provides the necessary element for respiration in most living organisms.

A concentration of 21% oxygen allows for sufficient availability in various environments, ensuring a balance for both human health and the environment. For instance, this level of oxygen supports human activities, combustion processes, and biological functions in ecosystems. Understanding the exact percentage of oxygen is particularly important in firefighting, emergency management, and safety protocols, as any deviations can indicate hazardous conditions, such as in confined spaces or areas affected by fire.

The other percentages provided do not reflect the typical composition of the atmosphere, making the 21% figure a fundamental aspect of foundational knowledge in fields related to environmental science and safety.