Page:NIOSH DM DFM respirator evaluation draft.pdf/63

cated that observed WPFs properly adjusted for wall deposition could typically be only one third to one fifth of the uncorrected values."^[1]
  Fifth, in 1981 it was stated that the saccharin QLFT "would reject any respirator having a leakage rate in excess of one percent (any PF less than 100]."147 However, in the five studies of Table O that utilized the saccharin test, the true failure rates could have ranged from about 1 to 14 users per 100 users for an APF of only 10. Failure rates for an APF of 100 would be substantially higher. Additionally, with respect to the issue of external validity, it should be noted that there are several reasons why the higher control failure rate estimates in Table O possibly underestimate the highest failure rates that can occur with NIOSH-certified halfmasks available to purchasers and users. These reasons relate to process ele- ments 1 and 3 in Table L of this evaluation, which are necessary for evaluating res- pirator performance. First, the studies presented in Table O were not based on a representative sample of all non-powered, halfmask facepieces certified under 30 CFR Part 11. Second, the reported results are from a very limited number of the scores of halfmask makes and models certified by NIOSH. Third, it was not the objective of any of the studies to test or identify the halfmasks with the highest control failure rates. Thus, other: makes and models of untested halfmasks with higher control failure rates might easily have been excluded from the nine studies. Fourth, the studies generally measured respirator performance on any available facial sizes. Based on the Institute's experience in this area and, absent information to the contrary reported in the studies, one can surmise that smaller and larger fa- cial sizes were probably not included in the test subjects. Compared to average fa- cial sizes, extreme facial sizes are generally expected to show substantially higher control failure rates due to excessive face-seal leakage. In summary, NIOSH con- cludes that it is highly probable that higher control failure rates would have been reported than those presented in Table O of this evaluation if the nine studies had been able to test non-powered halfmasks from more manufacturers and sample respi- rator performance on a wider range of facial sizes with each mask. In three of the nine studies presented in Table O, the small-sample point estimates for the control failure rates were about 5 per 100 users, even though every measured respirator user had passed an OSHA-approved fit test (i.e., QNFT or QLFT). More importantly, the 1-sided, 95% upper confidence limits (UCL196) for the true failure

1473M Company: Comment of Minnesota Mining and Manufacturing Company with Respect to the Permanent Lead Standard Quantitative Fit Test Provision, OSHA Docket No. H-048A, Exhibit 6-16,

(July 1, 1981), p. 4.