There's more to respirators than meets the eye.
Rekus
J F
JF
D004867:Equipment Design; D005069:Evaluation Studies as Topic; D006801:Humans; D011482:Protective Devices / Q000592:standards*; D012134:Respiratory Protective Devices / Q000592:standards*; D014481:United States; D014489:United States Occupational Safety and Health Administration