Which condition indicates an oxygen-deficient atmosphere?

An oxygen-deficient atmosphere is characterized by oxygen levels that fall below the normal atmospheric concentration of approximately 21%. Levels below 19.5% indicate a deficiency that can pose health risks, such as impaired cognitive functions or unconsciousness, in humans. It is vital to monitor oxygen levels in environments where the risk of deficiency exists, such as confined spaces or certain industrial settings.

While elevated oxygen levels (over 21%) may indicate a potentially enriched atmosphere, and high levels of carbon dioxide could suggest ventilation issues, they do not specifically point to an atmosphere that is deficient in oxygen. Additionally, gas leaks might pose different dangers unrelated to the oxygen concentration itself. Thus, monitoring for levels below 19.5% is crucial for safety in environments where oxygen deficiency could occur.