What concentration of oxygen defines an oxygen-deficient atmosphere?

An oxygen-deficient atmosphere is defined as having a concentration of oxygen that is below 19.5%. In normal atmospheric conditions, the typical concentration of oxygen is around 20.9%. When the level drops below 19.5%, it can pose various health risks, including dizziness, shortness of breath, and in severe cases, loss of consciousness or death. This threshold is critical for ensuring safety in environments where oxygen levels could be depleted, such as confined spaces or during certain industrial activities. Understanding this threshold is essential for firefighters and safety personnel to ensure a safe working environment when responding to emergencies or operating in potentially hazardous areas.