At what percent oxygen concentration does the Occupational Safety and Health Administration require that supplied air be worn?

Supplied air is mandated when the oxygen concentration in the atmosphere falls below 19.5%. This threshold is established by the Occupational Safety and Health Administration (OSHA) as a safety measure to protect individuals working in environments where oxygen levels may be insufficient to support normal respiratory function. At concentrations below 19.5%, the risk of hypoxia increases, posing serious health risks, including impaired cognitive function and loss of consciousness.

The correct answer thus highlights the critical importance of ensuring that personnel have access to breathable air when the environmental conditions are hazardous due to oxygen deficiency. Maintaining a minimum oxygen concentration of 19.5% is essential for safety in workplaces where the atmosphere may be compromised.