When WPF data existed, NIOSH selected a confidence limit of p=0.95.[1] Thus for a given set of data and given class of respirators, NIOSH would expect that 95% of the WPF's would exceed the calculated point estimate.[2]
NIOSH has concluded that APFS based on APF definitions from Myers et al. and the Guy Committee are derived from WPF data that were obtained after each test subject has been properly fitted and trained. "Properly fitted" for these APF defini- tions has generally been interpreted as fit screening with OSHA-approved qualitative or quantitative fit tests. As reported by respirator researchers in the 1980s, WPF values are measurements of the actual protection provided in the workplace by a properly-functioning respirator when correctly worn by a properly trained user after proper fit testing. This is in marked contrast to the LASL laboratory face-seal data for halfmasks that were obtained before proper fit testing was performed. NIOSH has concluded that the Hyatt/LASL-recommended APFS were values that at least 90% of all workers were expected to achieve before proper fit testing was performed. That is, up to 5% of a face-seal-performance test panel not achieving an APF plus the 5% of all American workers with extreme facial sizes not represented on a test panel were expected to not be able to achieve a given LASL-recommended APF. However, for a given respirator, it was expected and required that these 10% maximum of all potential wearers would be identified and not permitted to wear the respirator in the workplace. NIOSH has concluded that the Hyatt/LASL and ANSI 1980 APF recommendations were predicated on the requirement that 100% of respirator users in the workplace must attain protection exceeding a class APF after proper fitting (i.e., fit testing) has been performed by the employer. That is, the Hyatt/LASL and 1980 ANSI APFs expressed the level of respiratory protection expected to be achieved by 100% of prop- erly-fitted users (i.e., those with satisfactory fits exceeding the class APF). A noted respirator expert stated the following in 1989 with regard to the impact of workplace-testing results on the Hyatt/LASL APFs developed in the 1970s: The subject of testing the efficiency of respirators while worn in the workplace has become a hot topic of conversation.... This subject has been brought into close scrutiny by the significant work of several investigators which shows essentially no correlation between the "Simulated Workplace Protection Factor" (SWPF) determined in a semi-laboratory situation, that is, quanti-
tative respirator fit testing (QNFT) results, as compared to the WPFs obtained in the workplace.
- ↑ This is an incorrect statement. NIOSH personnel did not compute confidence limits at a confidence level for the NIOSH-recommended APFs based on WPF data. The statement should read, ". . . NIOSH selected a population proportion of p = 0.95."
- ↑ NIOSH Respirator Decision Logic, DHHS (NIOSH) Publication # 87-108, Cincinnati, OH (May, 1987), p. 29.
