Oxygen level threshold below which respirators must be worn?

Oxygen level threshold below which respirators must be worn?

• A. 19.5%
• B. 18%
• C. 16%
• D. 21%

Answer: (A)

Understanding when respirators are required hinges on ambient oxygen levels. Normal air has about 21% oxygen. An atmosphere is considered oxygen-deficient when oxygen drops below 19.5%. In such environments, workers must wear a respirator that provides breathable air (like supplied-air or SCBA), because air-purifying respirators can’t supply enough oxygen. Values like 18% or 16% describe even more severe deficiency, but the trigger used is 19.5%. At 21%, no respirator is required.

Understanding when respirators are required hinges on ambient oxygen levels. Normal air has about 21% oxygen. An atmosphere is considered oxygen-deficient when oxygen drops below 19.5%. In such environments, workers must wear a respirator that provides breathable air (like supplied-air or SCBA), because air-purifying respirators can’t supply enough oxygen. Values like 18% or 16% describe even more severe deficiency, but the trigger used is 19.5%. At 21%, no respirator is required.