Air supplied respirators must be used when the atmosphere contains less than ___% oxygen.

Air supplied respirators are essential in situations where the oxygen level in the atmosphere falls below a safe threshold. The crucial point is that an atmosphere with less than 19.5% oxygen is considered hazardous for breathing. This specific percentage is aligned with guidance from safety and health organizations, which state that any level of oxygen below this mark can lead to insufficient oxygen for normal physiological function.

As the level of oxygen decreases, the risks of unconsciousness, incapacitation, and severe health issues increase significantly. Using air supplied respirators in environments with oxygen levels under this threshold provides a safer alternative by supplying breathable air, thus protecting workers from the dangers posed by inadequate oxygen levels and potential harmful atmospheric contaminants.

Understanding this threshold is vital for maintaining safety protocols in various occupational settings, especially those involving confined spaces or atmospheres with potential respiratory hazards.