At what percentage is the air considered oxygen deficient?

Oxygen deficiency in the air is typically defined as having an oxygen concentration below 19.5%. This threshold is significant because at this level, individuals may begin to experience symptoms of hypoxia, which can impair cognitive function, coordination, and overall physical health. When the oxygen level drops to 19.5%, it is universally recognized as hazardous for human occupancy, making it crucial for safety protocols in environments where potential oxygen depletion can occur, such as in confined spaces or during hazardous materials incidents. Maintaining awareness of these levels is a vital component of the training for hazardous materials responders to ensure safe operational practices.