What is defined as an oxygen-deficient atmosphere?

An oxygen-deficient atmosphere is defined as one that contains 19.5% oxygen concentration or less. The standard threshold for normal atmospheric oxygen is around 21%. When the oxygen level drops to 19.5% or below, it can lead to impaired physiological functions and increase the risk of asphyxiation, particularly in environments where individuals may be engaged in physical activities or wearing heavy protective gear.

An atmosphere with more than 22% oxygen content would be considered oxygen-enriched rather than deficient, which can create its own hazards, such as increased fire risk. High levels of carbon monoxide, while dangerous, do not specifically define an oxygen-deficient atmosphere as they pertain to the presence of a different hazard. Lastly, humidity levels are unrelated to the definition of oxygen concentration, so an atmosphere with less than 10% humidity does not indicate the oxygen content and would not qualify as an oxygen-deficient atmosphere.