How is the protection factor of a respirator calculated?

• A. Outside/Inside
• B. Inside/Outside
• C. Outside x Inside
• D. Inside - Outside

Answer: (A)

Protection factor is the ratio of contaminant levels outside the respirator to those inside the respirator. It shows how much the respirator reduces your exposure. Mathematically, PF = C_out / C_in, where C_out is the concentration in the ambient air and C_in is the concentration you breathe inside the mask. A larger ratio means greater protection; for example, if outside the air has 1000 units of contaminant and inside the respirator it’s 10 units, the protection factor is 100, meaning a 100-fold reduction in exposure. The other options don’t measure protection in this way—multiplying, subtracting, or taking the inside concentration over the outside does not reflect how well a respirator reduces contaminant exposure.