Asphyxia is generally limited to enclosed spaces, and the deficiency of breathable air in an enclosed space can occur with any of the following conditions. Indicate the condition that will NOT cause asphyxia.

Correct Answer: Option A — When 21% of oxygen is present.

Asphyxia occurs when oxygen levels drop below the breathable threshold, typically 19.5%. An atmosphere containing 21% oxygen is normal, ambient air. Conversely, inert gas, cargo vapors, or oxidation (rusting) consume or displace oxygen, creating an oxygen-deficient environment that poses a lethal risk to personnel entering enclosed spaces.