Assigned Protection Factor. This is a numerical value assigned to a specific class of respiratory, and represents by increasing value, the relative protection that the type of device affords when its fit is verified by fit testing
Grainger, Inc. (Maintenance, Repair and Operating MRO), Glossary of Safety Terms, IL, USA 2012. www.grainger.com/images/GlossaryofSafetyTermsPDF.p df, (IndS/Maint, Repr and Opr - Amer) {79}