What is the definition of oxygen deficient air?

Oxygen deficient air is defined as air with less than 19.5% oxygen. This threshold is significant because it marks the point at which oxygen levels can become insufficient to support normal respiratory function in most people. Oxygen levels in the atmosphere are typically around 21%, and when they fall below this level, especially to 19.5% or lower, individuals may experience symptoms of hypoxia, which can lead to impaired cognitive and physical performance.

This concept is especially relevant in occupational safety and health, as environments with low oxygen levels pose serious risks to workers. Recognizing the dangers associated with oxygen-deficient atmospheres is crucial for ensuring safety standards are maintained in various industries, especially in confined spaces or areas with limited airflow.

The other options do not accurately define oxygen deficient air. While air with pollutants or at high altitudes may have different properties, they do not specifically relate to oxygen deficiency in the same way as the correct answer does.