What is the term for an atmosphere containing less than 19.5% oxygen by volume?

An atmosphere containing less than 19.5% oxygen by volume is referred to as an oxygen-deficient atmosphere. This definition is critical in confined space rescue operations because an oxygen-deficient environment presents serious health hazards, including the risk of unconsciousness or death due to asphyxiation. Normal atmospheric air contains about 20.9% oxygen, and levels below 19.5% indicate insufficient oxygen for human survival, making it essential for rescue technicians to recognize and address such conditions promptly.

Understanding this terminology is vital for safety in confined spaces. It informs the approach to entering and working in these environments, necessitating the use of proper protective equipment, such as supplied-air respirators, and monitoring devices to assess atmospheric conditions before and during rescue operations. Recognizing what constitutes an oxygen-deficient atmosphere helps in planning effective rescue operations and ensuring the team's safety.