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associated with computed APFs. Thus the internal validity of the APFs is subject to question. It has been said that "the science of statistics deals with making decisions based on observed data in the face of uncertainty."[1] If decisions regarding the observed levels of 5th-percentile sample WPF values (or other percentiles such as the 1st or one tenth of 1%) are not made with regard to the margins of error associated with them, then the credibility of those decisions is suspect. In all modern scientific professions, the accepted standard of practice regarding research data is to consider the uncertainty in the data when making comparative decisions (i.e., establish internal validity with confidence intervals and hypothesis testing).
With regard to the research settings and study conditions of WPF research conducted by NIOSH staff in the 1980s and into the 1990s, it was stated in 1984:
The methods and materials identified for collecting the workplace protection factor (WPF) data represent an optimized set of conditions in which the respirator is used while its field performance is being measured. Therefore, the best possible results should be obtained.[2]
Additionally, a noted respirator expert stated in 1989:
Since the administrative deficiencies that reduce respiratory protection will be suppressed in a closely monitored field test, the WPF [workplace protection factor] may not reflect actual working conditions.[3]
Gaboury and Burd also stated in 1989:
As mentioned before, these 5th percentile WPF's represent what can be achieved in the under good worker compliance and tight administrative controls. Real life WPFs may be less than 275 [for a helmeted PAPR with organic vapor/HEPA cartridges] and 9 (for non-powered halfmasks with organic vapor cartridges and DM or DFM prefilters] respectively for the tested respiratory protective devices for the following reasons:
- — Close surveillance of workers under normal working conditions is not usually performed by supervision (sic);
- — Cleaning of the respirators during the rest period is not always done prior to the worker returning to the workplace;
- ↑ Bowker, A. H. and G. J. Lieberman: Engineering Statistics, 2nd edition, Prentice-Hall, Inc., Englewood Cliffs, New Jersey (1972), p. 1.
- ↑ Myers, W.R., M. J. Peach, III, and J. Allender: Workplace Protection Factor Measurements on Powered Air-Purifying Respirators at a Secondary Lead Smelter—Test Protocol, Am. Ind. Hyg. Assoc. J. 45(4):236-241 (1984), p. 237.
- ↑ O'Leary, C.C.: New Concepts—Open Forum: Respirator Testing, Ind. Safety and Health News (May 1989).