What does the Assigned Protection Factor (APF) of a Respirator mean, including disposable masks?

It is the level of protection that a wearer can reasonably expect in the workplace. It is different from the Nominal Protection Factor (NPF) which is a value determined by the performance of the respirator in a standardised test.

The APF is used to select an adequate and suitable respirator after the required protection factor (RPF) has been determined. Different countries will have varying APF’s. Some countries will convert WEL’s (workplace exposure limit) and convert them to the nearest APF’s.