A half-face, negative pressure, HEPA cartridge respirator has a protection factor of 10. This means:

• A. The mask will protect the worker up to 10 times the OSHA PEL
• B. The mask filters 10 percent of particles
• C. It provides 10 times the hazard protection
• D. It only works under positive pressure

Answer: (A)

Protection factor describes how much a respirator lowers your exposure, not how many particles it filters per cent. A half-face negative-pressure respirator with a protection factor of 10 reduces the concentration of contaminant you breathe by a factor of 10.

That means if the workplace air has up to about ten times the OSHA permissible exposure limit, the air inside the facepiece would be at or below the PEL, assuming a good seal and proper use. In short, you can work in air up to 10x the PEL and still be protected to the PEL inside the respirator.

This isn’t about filtering a fixed percentage of particles, and it isn’t about operating under positive pressure.