Hence many of the variables that can adversely affect protection actually provided to workers in typical respirator programs are not reflected in WPF studies.
In 1985, the AIHA Respirator Technical Committee, chaired by H. P. Guy, prepared a "consensus terminology" for respirator performance in consultation with the principals from Los Alamos National Laboratory and NIOSH.[1] The Guy Committee
recommended that the terminology be published in the AIHA Journal and ultimately adopted for manuscripts submitted to the Journal. The Guy Committee provided the following APF definition:
The minimum expected workplace protection level of respiratory protection that would be provided by a properly functioning respirator or class of respirators, to a stated percentage of properly fitted and trained users. The maximum use concentration for a respirator is generally determined by multiplying a contaminant's exposure limit by the protection factor assigned to the respirator.[2]
The Guy Committee also recommended the following definition for workplace protection factors:
A measure of the protection provided in the workplace, under the conditions of the workplace, by a properly selected, fit tested and functioning respirator when correctly worn and used. It is defined as the workplace contaminant concentration which the user would inhale if he were not wearing the respirator (C0) divided by the workplace contaminant concentration inside the respirator facepiece (C1). Both C0 and C1, are determined from samples taken simultaneously, only while the respirator is properly worn and used during normal work activities.[3]
Regarding NIOSH's 1987 recommended APF values,[4] NIOSH stated:
