Assigned Protection Factor
Workplace level of respiratory protection that a respirator or class of respirators is expected to provide to a population of properly fitted and trained users.
NOTE For example, an APF of 10 for a respirator means that a user could expect to inhale no more than one tenth of the airborne contaminant present.
Source: API RP 98, Personal Protective Equipment Selection for Oil Spill Responders, First Edition, August 2013. Global Standards