2—Nonregulatory APF values used during the 1970s and 1980s.
Assigned protection factors are a necessity for correct respirator selection and proper use. In 1976, OSHA gave the following guidance on the use of respirator-class APFs to its compliance officers during an evaluation of an employer's respiratory protection program for acceptability:
(4) Compare air contaminant exposure measurements collected during the inspection to the [assigned] protection factor for the respirator device. [Assigned Protection factors ([A]PFs) should be considered as an element in determining complaince with 29 CFR 1910.134(c).
(a) A protection factor is the ratio of the ambient airborne concentration of the contaminant to
the concentration of that contaminant inside the facepiece. It is a measure of the facepiece fit of a respirator based on quantitative respirator fit tests. The product of the [A]PF and the permissible exposure limit (PEL) is the maximum use concentration (MUC).[1]
Prior to the revised APFs for filter respirators recommended in this evaluation, there have been numerous APF tables recommended by NIOSH, OSHA, and the American National Standards Institute (ANSI). These are given as follows:
| Tables in this evaluation | Recommending Organization |
| A, B | OSHA (1976) |
| C | ANSI (1980), OSHA (1984) |
| D | ANSI (1991) |
| E, F | NIOSH (1976) |
| J, K | NIOSH (1987) |
OSHA has previously used APFs to derive respirator-selection tables in numerous contaminant-specific regulations.[2] OSHA has also published APFs in their 1976
- ↑ OSHA: Industrial Hygiene Manual, Chapter III—OSHA Standard Method for Determination of Respiratory Protection Program Acceptability (June 28, 1976), p. 82.
- ↑ To determine the "required apparatus" or "required respirator" for differing "atmospheric concentrations" of a specified contaminant. For example, but not limited to: 29 CFR 1910.1017(g)(4), 29 CFR 1910.1018(h)(2)(i), 29 CFR 1910.1025(f)(2), 29 CFR 1910.1043(f)(2), 29 CFR 1910.1044(h)(2)(i).
