Contents......iii

Acknowledgments......vii

1-Background......1

2- Nonregulatory APF values used during the 1970s and 1980s......3

3-History of NIOSH's Recommended APFs......13

4-Strategy used by NIOSH for RAPF determinations......19

5-Introduction to respirator-performance evaluations, APF determinations and use of APFs......21

6-Review and evaluation of professional practrices used during the 1970s and 1980s for respirator face-seal evaluations and APF determinations......27

7-Evaluation of face-seal leakage results from nine studies of non-powered, air-purifying halfmasks......51

8-Review and evaluation of two reports, research findings, and recommendations concerning the nature of leakage through DM and DFM filters certified by NIOSH under 30 CFR Part 11......61

9-Derivation and evaluation of two leakage-function models for describing a user's protection factor while wearing a DM- or a DFM-filter mask......71

10-Evaluation factors for DM- and DFM-filter-leakage date......79

11-Results reported from four recent studies of DM- and DFM-filter leakage......87