CHEMICAL BIOLOGICAL CENTER 

U.S. ARMY RESEARCH, DEVELOPMENT AND ENGINEERING COMMAND 

ECBC-CR-085 

RESPIRATOR FILTER EFFICIENCY TESTING 

AGAINST PARTICULATE AND BIOLOGICAL AEROSOLS 

UNDER MODERATE TO HIGH FLOW RATES 

Aaron W. Richardson 

Jonathan P. Eshbaugh 

Kent C. Hofacre 

BATTELLE MEMORIAL INSTITUTE 

Columbus, OH 43201-2693 

Paul D. Gardner 

RESEARCH AND TECHNOLOGY DIRECTORATE 

August 2006 

Approved for public release; 

distribution is unlimited. 

ABERDEEN PROVING GROUND, MD 21010-5424 

EDGEWOOD
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1. REPORT DATE (DD-MM-YYYY)

XX-08-2006 

2. REPORT TYPE

Final 

3. DATES COVERED (From - To)

Dec 2003 - Oct 2005

5a. CONTRACT NUMBER 

SPO700-00-D-3180 

5b. GRANT NUMBER 

4. TITLE AND SUBTITLE 

Respirator Filter Efficiency Testing against Particulate and Biological Aerosols 

under Moderate to High Flow Rates 

5c. PROGRAM ELEMENT NUMBER 

5d. PROJECT NUMBER 

5e. TASK NUMBER 

335 

6. AUTHOR(S)

Richardson, Aaron W.; Eshbaugh, Jonathan P.; Hofacre, Kent C. (Battelle 

Memorial Institute); and Gardner, Paul D. (ECBC) 

5f. WORK UNIT NUMBER

8. PERFORMING ORGANIZATION REPORT 

 NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) AND ADDRESS(ES)

Battelle Memorial Institute, 505 King Avenue, Columbus, OH 43201-2693 

DIR, ECBC, ATTN: AMSRD-ECB-RT-PR, APG, MD 21010-5424 ECBC-CR-085 

10. SPONSOR/MONITOR’S ACRONYM(S)

11. SPONSOR/MONITOR’S REPORT 

 NUMBER(S)

9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 

DIR, ECBC, ATTN: AMSRD-ECB-RT-PR, APG, MD 21010-5424 

12. DISTRIBUTION / AVAILABILITY STATEMENT 

Approved for public release; distribution is unlimited. 

13. SUPPLEMENTARY NOTES

COR: Paul Gardner, AMSRD-ECB-RT-PR, (410) 436-6692 

14. ABSTRACT

The growing terrorism threat associated with biological and chemical agents presents a challenge to emergency responders, 

healthcare workers, and the civilian population. Currently, National Institute for Occupational Safety and Health (NIOSH)-

approved respirators are used in various workplace settings to provide protection against harmful aerosols. The primary 

objective of this project was to evaluate and compare the aerosol filtration performance of NIOSH-approved respirator filters 

with non-biological (inert) and biological test aerosols under breather flow rates associated with high work rates. The inert 

test challenges consisted of solid and oil aerosols having nominal diameters ranging from 0.02 to 3.02 μm, spanning the 

spectrum of potential biological threat agents. As expected, penetration of submicron aerosols was found to increase under 

increased cyclic and constant flow conditions. The magnitude and significance of this increase was dependent on the specific 

filter type and design. The most penetrating particle size was generally between 0.1 and 0.2 μm for the P100 filters and 0.05 

and 0.10 μm for the N95 filters. Inert aerosols of similar aerodynamic diameter were shown to provide a reasonable estimate 

of performance against the biological aerosols tested, Bg spores and MS2 phage. The second objective was to assess the 

extent of reaerosolization of surrogate biological agents from NIOSH-approved filtering facepieces. The extent of 

reaerosolization was dependent on the particle size, particle type, and loading level. 

15. SUBJECT TERMS

Filtration efficiency Bioaerosol Biological aerosol Cyclic High flow 

Aerosol penetration Filter Reaerosolization Breathing Reentrainment 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 

 ABSTRACT 

18. NUMBER OF 

 PAGES 

19a. NAME OF RESPONSIBLE PERSON

Sandra J. Johnson 

a. REPORT 

U 

b. ABSTRACT

U 

c. THIS PAGE

U UL 181 

19b. TELEPHONE NUMBER (include area 

code)

(410) 436-2914 

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39.18
ii 

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iii 

EXECUTIVE SUMMARY 

The growing terrorism threat associated with biological and chemical agents presents a 

challenge to emergency responders, healthcare workers, and the civilian population. The use of 

National Institute for Occupational Safety and Health (NIOSH)-approved respirators, if used 

according to recommended practices, provides protection against harmful agents in different 

workplace settings. Currently, NIOSH certifies respirators based on an inert aerosol test at a 

constant flow rate of 85 L/min. However, measurements of physiological parameters of workers 

show peak inhalation flow rates for short durations in the 300 to 400 L/min range for certain 

activities that demand high work loads. One objective of this study was to investigate the effects 

of high volumetric and peak flow rates on respirator filtration performance. In addition, although 

NIOSH-approved respirator filters have been shown to provide adequate protection against inert 

aerosols, their performance with respect to protection against bioaerosols has not been 

extensively assessed. Thus, another objective of this study was to evaluate and compare the 

aerosol filtration performance of NIOSH-approved respirator filters with non-biological (inert) 

and biological test aerosols. 

 Four cyclic and three constant flow conditions were selected based on an analysis 

completed by the U.S. Army's Edgewood Chemical Biological Center (ECBC) to assess the 

relationship between work load and ventilation rate. The cyclic flow conditions have minute 

volumes ranging from moderate (40 L/min) to high (135 L/min) with peak flows up to 

430 L/min. The respirator filters were selected in coordination with NIOSH and included two 

N95 and two P100 filtering facepieces, and two N95 and two P100 cartridges. The inert aerosol 

challenges had nominal diameters ranging from 0.05 to 3.0 μm and were selected to span a range 

of potential bioaerosol threat agent sizes to include nanoparticles well below the size of 

bioaerosol threat agents. Oil aerosols were used with the P100 filters and solids with the 

N95 filters. The biological aerosols included bacterial B. globigii (Bg) spores and the virus 

MS2 phage. 

 The most penetrating particle size was generally between 0.1 and 0.2 μm for the 

P100 filters and 0.05 and 0.10 μm for the N95 filters. The inert testing demonstrated that the 

penetration of submicron particles tends to increase with flow rate or filtration velocity. The 

magnitude and significance of this increase was dependent on the specific filter design. For 

example, the SEA HE-T P100 cartridge met the P100 requirement (less than 0.03 percent 

penetration) even at the highest cyclic flow conditions. In comparison, the Survivair 1050 

P100 cartridge, which has approximately half of the available surface area, had a penetration in 

excess of 0.1 percent. Although several of the filters had penetrations in excess of the NIOSH 

requirement at the highest flow conditions, the intended use and assigned protection factor of the 

respirator must be considered to determine whether the increase in penetration is significant. 

 Comparison of the penetrations measured under constant and cyclic flow conditions 

showed that the mean and peak inhalation flow (PIF) rates were important parameters. For the 

P100 cartridges, similar penetrations were measured under constant and cyclic flow if the 

constant flow was equivalent to the mean inhalation flow rate. In contrast to the P100 cartridges, 

it may be more important to consider the PIF when testing filtering facepieces or N95 cartridges, 

especially at the high volumetric flow rates that can be experienced during heavy work loads. 
iv 

The N95 filters are not as suitable for the high volumetric flow rate applications as evidenced by 

their lower surface area as compared to the P100 cartridges. Selecting a constant flow equivalent 

to the peak inhalation flow generally provides a conservative estimate of filter performance 

under cyclic flow conditions. 

 The filtration efficiency of the N95 and P100 filters was also assessed against 

bioaerosol challenges, Bg spores and MS2 phage, aerosolized both from liquid suspension and a 

dry powder. The performance of NIOSH-approved N95 and P100 respirator filters was assessed 

against the bioaerosol challenges under high volumetric flow conditions. Mean penetrations 

were below the penetration requirements for the respective filter types (i.e., penetration less than 

5 percent for N95 and less than 0.03 percent for P100 filters) under all flow conditions tested. 

Penetrations of Bg spores through the P100 filters were typically below detectable limits, thus, 

penetrations were at least an order-of-magnitude below the P100 requirement. The N95 filters 

also were very efficient at removing the bacterial aerosol challenges as average penetrations 

were less than 0.5 percent. There were no practical differences in the penetrations measured 

using the "wet" and "dry" Bg spore aerosolization methods. The most penetrating of the 

biological aerosols tested was the "wet" MS2 phage as the particle size was closest to the most 

penetrating particle size (MPPS) as measured using inert aerosol challenges. Average 

penetrations through the N95 and P100 filters were typically less than 2 and 0.03 percent, 

respectively, under all flow conditions. Inert aerosols of similar aerodynamic diameter were 

shown to provide a good estimate of performance against biological aerosols. The Bg spore 

"wet" and "dry" aerosol penetration was generally within a factor of five of the penetrations 

measured using the 1.3 μm PSL. Similarly, the MS2 "wet" aerosol penetration through the 

cartridges was within a factor of five of the inert aerosol penetrations measured using the 

0.3 μm PSL. Comparisons were not made with the MS2 "dry" as aerosol penetration was 

typically below detectable limits. However, this is in agreement with the penetrations measured 

for the 2.3 μm PSL. The results demonstrated that testing with inert particles in the MPPS range 

provide a conservative estimate of biological aerosol penetration for those biological aerosols 

assessed in this study. Finally, the results demonstrated that using an optical light scattering 

instrument such as the LAS to measure bacterial aerosol penetration provides a conservative 

estimate of filter performance. This is notable due to the labor intensive nature of the bioassay 

method. 

 A test method was developed to quantify the extent of reaerosolization from a filtering 

facepiece loaded with either an inert or biological aerosol. Tests were performed to assess the 

effect of particle size, particle type, and loading level. Two brands of filtering facepieces were 

tested, the MSA Affinity Plus and Gerson 1730. The levels and trends of reaerosolization were 

similar for both brands. For the inert aerosols, reaerosolization was observed to increase with 

increased particle size over the range tested (0.8 to 2.2 μm). This trend was consistent with that 

observed by Qian et al. (1997) who attributed this to increased drag force on the larger particles. 

 The extent of reaerosolization of 0.8 μm particles from filtering facepieces without 

exhalation valves was very low (less than 0.002 percent or 1 in every 50,000 particles loaded). 

Reaerosolization was observed to increase by an order of magnitude when the same brands of 

filtering facepieces were tested with exhalation valves. This was attributed to the movement of 

the valve and localized high velocity air that could re-entrain particles collected on the surface of 
v 

the valve or valve housing. Specifically for the 0.8 μm PSL, the number of particles 

reaerosolized was observed to increase with increased loading over the range from 

1 x 104 to 1 x 106 particles/cm2. However, the number of particles did not increase 

proportionally to the increased loading. Increasing the loading by a factor of 10 only increased 

the number of particles reaerosolized by a factor of 5. Further work is recommended to 

determine whether similar trends hold for larger particles. 

 The percent reaerosolization of the biological aerosols was greater than that observed 

for the inert aerosols with a similar AMMD. For example, reaerosolization of the 0.8 μm PSL 

was minimal (~0.002 percent) while reaerosolization of the similarly-sized Bg spores was 

typically 0.05 to 0.1 percent. Similarly, reaerosolization of the 2.2 μm PSL was only 

0.01 percent while reaerosolization of the comparably-sized MS2 "dry" was 0.5 percent. The 

higher reaerosolization for the biological aerosols was attributed to their broader size 

distribution. For example, the MS2 "dry" aerosol had significant mass between 2.5 and 5.0 μm 

that contained viable particles. As described above, the extent of reaerosolization was shown to 

increase with increased particle size. Thus, it is important to consider the entire size distribution 

and not just the nominal particle size when selecting an inert simulant. 

 In conclusion, the performance of NIOSH-approved N95 and P100 cartridges and 

filtering facepieces has been assessed against both inert and biological aerosols under high flow 

conditions representative of ventilation rates during heavy activity. All filters tested were very 

efficient against the bioaerosols tested in this study as measured penetrations were below NIOSH 

requirements for all flow conditions tested. The penetrations of inert particles provided a good 

indication of filter performance against bioaerosols with a similar aerodynamic diameter. When 

comparing penetrations measured under constant and cyclic flow, those measured at a constant 

flow equivalent to the cyclic flow MIF provided a good estimate of performance under cyclic 

flow conditions (i.e., generally within a factor of 2 to 4). Testing at a constant flow equivalent to 

the PIF results in higher penetrations than measured under the cyclic flow condition and, thus, 

would provide a more conservative estimate of performance. All cyclic flow testing performed 

in this task was done using a sinusoidal flow profile. Additional testing is recommended with 

alternative waveforms such as a trapezoidal waveform to assess the effect of flow profile. 

Finally, a method was developed to assess reaerosolization of inert and biological aerosols 

loaded onto a filtering facepiece due to a cough. The extent of reaerosolization was shown to be 

dependent on particle type, particle size, and loading level. Further work is recommended to 

assess the effect of varying the reentrainment flow profile (e.g., sneeze or cough profiles with 

different peak flows) and to assess the effect of loading level of particles greater than 1 μm.
vi 

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vii 

PREFACE 

 

 The work described in this report was authorized under Contract No. 

SP0700-00-D-3180, Task No. 335. This work was started in December 2003 and completed in 

October 2005. 

 Use of either trade or manufacturers’ names in this report does not constitute an 

official endorsement of any commercial products. This report may not be cited for purposes of 

advertisement. 

 This report has been approved for public release. Registered users should request 

additional copies from the Defense Technical Information Center; unregistered users should 

direct such requests to the National Technical Information Service. 

 The text of this contractor report is published as received and was not edited by 

the Technical Releases Office, U.S. Army Edgewood Chemical Biological Center. 

Acknowledgments 

 The authors would like to thank the Office of Law Enforcement Standards, 

National Institute of Standards and Technology, Gaithersburg, MD, and the National Personal 

Protective Technology Laboratory (NPPTL), National Institute for Occupational Safety and 

Health, Pittsburgh, PA, for funding this project. Special appreciation goes to Dr. Samy 

Rengasamy, NPPTL, for his expertise and assistance with planning this study. 
viii 

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ix 

CONTENTS 

 EXECUTIVE SUMMARY ..................................................................................iii 

1.0 INTRODUCTION ................................................................................................ 1 

1.1 Background..................................................................................................... 1 

1.2 Objective......................................................................................................... 1 

1.3 Scope............................................................................................................... 1 

2.0 LITERATURE REVIEW ..................................................................................... 2 

2.1 Search Strategy ............................................................................................... 2 

2.2 Inert Filtration Efficiency ............................................................................... 2 

2.2.1 Aerosol Collection Mechanisms............................................................... 3 

2.2.2 Effect of Particle Size/Flow Rate.............................................................. 4 

2.2.3 Comparison of Constant/Cyclic Flow Penetrations.................................. 7 

2.3 Biological Filtration Efficiency ...................................................................... 8 

2.3.1 Test Methods............................................................................................. 8 

2.3.2 Inert/Biological Penetration Comparison .................................................10 

2.3.3 Effect of Flow Rate...................................................................................13 

2.3.4 Viral Filtration Efficiency.........................................................................13 

2.3.5 Reaerosolization........................................................................................14 

2.4 Summary.........................................................................................................16 

2.4.1 Filter Efficiency Testing ...........................................................................16 

2.4.1.1 Inert Testing........................................................................................16 

2.4.1.2 Biological Testing...............................................................................17 

2.4.1.3 Reaerosolization..................................................................................18 

3.0 INERT PARTICULATE FILTRATION EFFICIENCY TESTING ....................18 

3.1 Test Parameters...............................................................................................18 

3.2 Test Matrix......................................................................................................21 

3.3 Technical Approach........................................................................................22 

3.3.1 Model 3160 Automated Filter Tester........................................................22 

3.3.1.1 System Description .............................................................................22 

3.3.1.2 System Characterization .....................................................................24 

3.3.1.3 Test Procedure ....................................................................................24 

3.3.2 Large Particle Test System .......................................................................25 

3.3.2.1 System Description .............................................................................25 

3.3.2.2 System Characterization .....................................................................26 

3.3.2.3 Test Procedure ....................................................................................27 

3.4 Calculation of Aerosol Penetration.................................................................27 

3.5 Inert Results ....................................................................................................28 

3.5.1 Effect of High Volumetric Flow Rate.......................................................28 

3.5.1.1 Cartridge Filters ..................................................................................28 
x 

3.5.1.2 Filtering Facepieces ............................................................................35 

3.5.2 Constant/Cyclic Flow Comparisons .........................................................41 

3.6 Inert Aerosol Testing Summary......................................................................44 

4.0 BIOAEROSOL FILTRATION EFFICIENCY TESTING...................................45 

4.1 Test Parameters...............................................................................................45 

4.2 Test Matrix......................................................................................................47 

4.3 Technical Approach........................................................................................48 

4.3.1 Test System...............................................................................................48 

4.3.2 Bioaerosol Generation Methods ...............................................................49 

4.3.2.1 Wet......................................................................................................49 

4.3.2.2 Dry ......................................................................................................49 

4.3.3 Aerosol Sampling and Classification........................................................51 

4.3.3.1 Viable Samples ...................................................................................51 

4.3.3.2 Optical Particle Counters ....................................................................52 

4.3.3.3 Cascade Impactor................................................................................52 

4.3.4 System Characterization ...........................................................................53 

4.3.5 Test Procedure ..........................................................................................53 

4.4 Calculation of Aerosol Penetration.................................................................54 

4.5 Bioaerosol Results ..........................................................................................55 

4.5.1 Bg Spore Results.......................................................................................55 

4.5.1.1 Particle Size Distribution ....................................................................55 

4.5.1.2 Bioassay Penetration Results ..............................................................57 

4.5.2 MS2 Phage Results ...................................................................................62 

4.5.2.1 Particle Size Distribution ....................................................................62 

4.5.2.2 MS2 Penetration Results.....................................................................63 

4.5.3 Inert Comparisons.....................................................................................66 

4.5.3.1 Bg Spores............................................................................................66 

4.5.3.2 MS2 Phage..........................................................................................69 

4.6 Summary.........................................................................................................71 

5.0 REAEROSOLIZATION.......................................................................................72 

5.1 Test Parameters...............................................................................................72 

5.2 Test Matrix......................................................................................................74 

5.3 Test Method ....................................................................................................75 

5.3.1 Test System Description ...........................................................................75 

5.3.2 Test Procedure ..........................................................................................76 

5.3.3 Analytical Methods...................................................................................77 

5.3.3.1 Inert Aerosols......................................................................................77 

5.3.3.2 Biological Aerosols.............................................................................78 

5.3.4 System Characterization ...........................................................................78 

5.3.5 Calculation of Reaerosolization................................................................81 

5.4 Results .............................................................................................................82 

5.4.1 Inert Aerosols............................................................................................83 
xi 

5.4.2 Biological Aerosols...................................................................................85 

5.4.2.1 Bg Spores............................................................................................85 

5.4.2.2 MS2 Phage..........................................................................................86 

5.5 Summary and Discussion................................................................................87 

6.0 CONCLUSIONS AND RECOMMENDATIONS ...............................................88 

 LITERATURE CITED .........................................................................................93 

 APPENDIXES 

 A. PHOTOGRAPHS OF CARTRIDGES AND FILTERING 

 FACEPIECES........................................................................................... A-1 

 B. RATIONALE FOR SELECTING FLOW CONDITIONS ......................B-1 

 C. SHAKEDOWN TESTING OF MODEL 3160......................................... C-1 

 D. SHAKEDOWN OF TEST SYSTEM FOR LARGE PARTICLE 

 INERT TESTING ..................................................................................... D-1 

 E. SUMMARY OF MEASURED INERT FILTRATION EFFICIENCIES E-1 

 F. ESTIMATION METHOD FOR CYCLIC FLOW PENETRATIONS .... F-1 

 G. MICROBIOLOGICAL METHODS......................................................... G-1 

 H. SHAKEDOWN TESTING OF THE BIOAEROSOL TEST SYSTEM .. H-1 

 I. SUMMARY OF BIOAEROSOL PENETRATION RESULTS............... I-1 

 J. SUMMARY OF REAEROSOLIZATION RESULTS............................. J-1 
xii 

FIGURES 

1. Four Mechanisms of Particle Capture (DHHS, 2003).......................................... 3 

2. Primary Mechanism of Capture for Various Particle Diameters Indicating 

 MPPS (DHHS, 2003)............................................................................................ 4 

3. Comparison of Sinusoidal Waveforms Used to Assess the Effect 

 of Moderate to High Breather Flows on Filter Performance ................................20 

4. Additional HEPA Filters on Dilution Air Inlet of Model 3160............................23 

5. Lucite Chamber Used to House and Seal Test Filters to the Model 3160............24 

6. Test System Used to Measure Penetration of 0.7, 1.3, and 2.9 μm PSL 

 through the N95 Filters .........................................................................................25 

7. Effect of Particle Size and Constant Flow Rate on Measured Penetration 

 through SEA HE-T P100 Cartridge ......................................................................29 

8. Effect of Particle Size and Cyclic Flow Rate on Measured Penetration 

 through SEA HE-T P100 Cartridge ......................................................................29 

9. Effect of Particle Size and Constant Flow Rate on Measured Penetration 

 through Survivair® 1050 P100 Cartridge..............................................................30 

10. Effect of Particle Size and Cyclic Flow Rate on Measured Penetration 

 through Survivair® 1050 P100 Cartridge ..............................................................30 

11. Penetration of 0.1 μm Particles as Function of Face Velocity for SEA and 

 Survivair® P100 Cartridge Filters ........................................................................31 

12. Effect of Particle Size and Constant Flow Rate on Measured Penetration 

 through North 7506 N95 Cartridge.......................................................................32 

13. Effect of Particle Size and Cyclic Flow Rate on Measured Penetration 

 through North 7506 N95 Cartridge.......................................................................33 

14. Effect of Particle Size and Constant Flow Rate on Measured Penetration 

 through MSA Flexi-Filter N95 Cartridge .............................................................33 

15. Effect of Particle Size and Cyclic Flow Rate on Measured Penetration 

 through MSA Flexi-Filter N95 Cartridge .............................................................34
xiii 

16. Comparison of Ratios of Penetrations Measured through P100 and 

 N95 Cartridges at 180 and 135 L/min...................................................................35 

17. Effect of Particle Size and Flow Rate on Measured Penetration 

 through 3MTM P100 Filtering Facepiece at Constant Flow..................................36 

18. Effect of Particle Size and Flow Rate on Measured Penetration 

 through 3MTM P100 Filtering Facepiece at Cyclic Flow ......................................36 

19. Effect of Particle Size and Flow Rate on Measured Penetration 

 through Moldex P100 Filtering Facepiece at Constant Flow ...............................37 

20. Effect of Particle Size and Flow Rate on Measured Penetration 

 through Moldex P100 Filtering Facepiece at Cyclic Flow ...................................38 

21. Effect of Particle Size and Flow Rate on Measured Penetration 

 through Gerson® N95 Filtering Facepiece at Constant Flow................................39 

22. Effect of Particle Size and Flow Rate on Measured Penetration 

 through Gerson® N95 Filtering Facepiece at Cyclic Flow....................................39 

23. Effect of Particle Size and Flow Rate on Measured Penetration 

 through MSA N95 Filtering Facepiece at Constant Flow ....................................40 

24. Effect of Particle Size and Flow Rate on Measured Penetration 

 through MSA N95 Filtering Facepiece at Cyclic Flow ........................................40 

25. Comparison of Measured Penetrations under Cyclic and Constant Flow 

 Conditions with Minute Volumes of 85 L/min.....................................................42 

26. Comparison of Penetrations Measured under Constant and Cyclic Flow 

 Conditions for Cartridge Filters............................................................................43 

27. Comparison of Penetrations Measured under Constant and Cyclic Flow 

 Conditions for Filtering Facepieces......................................................................43 

28. Comparison of Penetrations Measured under Constant and Cyclic Flow 

 Conditions for P100 Cartridge Filters...................................................................44 

29. Schematic of Test System Used to Measure Bioaerosol Penetration ...................48 

30. Vilnius Aerosol Generator ....................................................................................50 

31. Aerosolization Chamber and Rotary Vane of Vilnius Aerosol Generator ...........51
xiv 

32. Size Distribution of “Wet” and “Dry” Bg Spores Measured Using the 

 Cascade Impactor..................................................................................................56 

33. Size Distribution of Bg Spores Measured Using the Aerosizer............................56 

34. Size Distribution of Bg Spores Measured Using the Aerosizer (Cumulative 

 Number Distribution)............................................................................................57 

35. Comparison of Measured Bg “Wet” Penetrations through N95 Filters................59 

36. Comparison of Measured Bg “Dry” Penetrations through N95 Filters ................59 

37. Comparison of Bg “Wet” and “Dry” Penetrations through Cartridge Filters.......60 

38. Comparison of Bg “Wet” and “Dry” Penetrations through Filtering 

 Facepieces .............................................................................................................60 

39. Comparison of Bg Spore Penetrations Measured Using the Bioassay 

 Method and LAS-X...............................................................................................61 

40. Size Distribution of MS2 “Wet” Measured Using the Sierra Impactor................62 

41. Size Distribution of MS2 “Wet” Measured Using the LAS-X.............................63 

42. Size Distribution of MS2 “Dry” Measured Using the Sierra Impactor 

 and Aerosizer ........................................................................................................63 

43. Comparison of Measured MS2 “Wet” Penetrations through N95 Filters.............65 

44. Comparison of Measured MS2 “Dry” Penetrations through N95 Filters.............65 

45. Comparison of MS2 Phage Penetrations Measured Using the Bioassay 

 Method and LAS-X...............................................................................................66 

46. Comparison of Bg Spore and Inert Penetrations through the North N95 

 7506 Cartridge ......................................................................................................67 

47. Comparison of Measured Inert and Bg Bioaerosol Penetrations 

 Through the North 7506 Cartridge at Constant Flows of 42.5 and 135 L/min.....68 

48. Comparison of Bg Spore and Inert Penetrations through the MSA N95 

 Flexi-Filter Cartridge ............................................................................................68 

49. Comparison of Bg Spore and Inert Penetrations through the MSA N95 

 Affinity Plus Filtering Facepiece..........................................................................69
xv 

50. Comparison of Bg Spore and Inert Penetrations through the Gerson N95 

 1730 Filtering Facepiece.......................................................................................69 

51. Comparison of MS2 “Wet” and Inert Penetrations through the North 

 N95 7506 Cartridge...............................................................................................70 

52. Comparison of MS2 “Wet” and Inert Penetrations through the MSA 

 N95 Flexi-Filter Cartridge ....................................................................................70 

53. Comparison of MS2 “Wet” and Inert Penetrations through the MSA 

 N95 Affinity Plus Filtering Facepiece ..................................................................71 

54. Comparison of MS2 “Wet” and Inert Penetrations through the Gerson 

 N95 1730 Filtering Facepiece...............................................................................71 

55. Cough Profile for Reaerosolization Testing .........................................................74 

56. Schematic of Reaerosolization Test System.........................................................76 

57. Analysis Patterns on 47-mm Collection Filters Used with Fluorescent 

 Microscope to Quantify Loadings of Inert Particles.............................................78 

58. Comparison of Target and Measured Cough Profile Used 

 for Reaerosolization Testing.................................................................................79 

59. Comparison of Number of Particles Collected on Pre- and Post-Cough 

 Filters for Tests Performed with the 0.8 μm PSL .................................................80 

60. Comparison of Number of Particles Collected on Pre- and Post-Cough 

 Filters for Tests Performed with the Biological and Inert Aerosols .....................81 

61. Comparison of Percent Reaerosolization of Inert Particles from MSA and 

 Gerson Filtering Facepieces..................................................................................84 

62. Comparison of Percent Reaerosolization of 0.8 μm PSL from Gerson 

 Respirator with Exhalation Valve Protected during Loading...............................84 

63. Comparison of Percent Reaerosolization of 0.8 μm PSL from Gerson 

 Respirator at Loadings Ranging from 1 x 104

 to 1 x 106 Particles/cm2................85 

64. Comparison of Inert and Bg Spore Reaerosolization Results...............................86 

65. Comparison of Inert and MS2 Phage Reaerosolization Results ...........................87 
xvi 

TABLES 

1. Influence of Filtration Velocity and Aerosol Size on Collection Mechanisms .... 4 

2. Summary of Cartridges and Filtering Facepieces.................................................19 

3. Summary of Challenge Aerosols for Testing N95 and P100 Filters ....................19 

4. Summary of Cyclic Flows Used for Testing with the Inert Aerosol Challenges..20 

5. Test Matrix Completed to Assess the Effect of High Cyclic Flows 

 on Filtration Performance of Cartridge Respirator Filters....................................21 

6. Test Matrix Completed to Assess the Effect of High Cyclic Flows 

 on Filtration Performance of Filtering Facepieces................................................22 

7. Comparison of Face Velocities for P100 and N95 Cartridges..............................34 

8. Test Matrix Completed to Assess Filter Performance under Cyclic Flow 

 Conditions Using a Bioaerosol Challenge ............................................................47 

9. Test Matrix Completed to Assess Filter Performance under Constant Flow 

 Using a Bioaerosol Challenge...............................................................................47 

10. Particle Size Range Six-Stage Cascade Impactor.................................................53 

11. Comparison of “Wet” and “Dry” Bg Size Distributions ......................................55 

12. Comparison of Penetration Measured Using Bioassay Method and Bg Spore 

 “Wet” Aerosol Challenge under Constant and Cyclic Flow Conditions ..............58 

13. Comparison of Penetration Measured Using Bioassay Method and Bg Spore 

 “Dry” Aerosol Challenge under Constant and Cyclic Flow Conditions...............58 

14. Comparison of “Wet” and “Dry” MS2 Aerosol Size Distributions......................62 

15. Comparison of Penetration Measured Using Bioassay Method and MS2 

 “Wet” Aerosol Challenge under Constant and Cyclic Flow Conditions ..............64 

16. Comparison of Penetration Measured Using Bioassay Method and MS2 

 “Dry” Aerosol Challenge under Constant and Cyclic Flow Conditions...............64 

17. Estimated Surface Areas of N95 Filtering Facepieces .........................................73 

18. Test Matrix Completed to Assess Reaerosolization .............................................75 

19. Summary of Reaerosolization Results..................................................................83 
1 

RESPIRATOR FILTER EFFICIENCY TESTING AGAINST PARTICULATE AND 

BIOLOGICAL AEROSOLS UNDER MODERATE TO HIGH FLOW RATES 

1.0 INTRODUCTION 

1.1 Background 

The growing terrorism threat associated with biological and chemical agents presents a 

challenge to emergency responders, healthcare workers, and the civilian population. Currently, 

National Institute for Occupational Safety and Health (NIOSH)-approved respirators are used in 

various workplace settings to provide protection against harmful aerosols. Particulate respirator 

filters are certified using an inert aerosol at a flow rate of 85 L/min. While this is sufficient to 

ensure protection in most situations when used according to recommended practices, it is 

unknown how these filters would perform at higher flow rates or against a biological aerosol that 

could be encountered in an act of terrorism. A rigorous, definitive study assessing respirator 

filter performance challenged with bioaerosols has not yet been conducted to fully address 

particle size dependence. In addition, investigations on the effects of high volumetric and peak 

flow rates on respirator filtration performance associated with high work rates are lacking. 

1.2 Objective 

 

 The primary objective of this task was to evaluate and compare the aerosol filtration 

performance of NIOSH-approved respirator filters with non-biological (inert) and biological test 

aerosols under high breather flow rates. In addition, penetrations measured under constant and 

cyclic flow conditions were compared. Finally, the extent of reaerosolization of surrogate 

biological agents from NIOSH-approved filtering facepiece masks was characterized. 

1.3 Scope 

 The literature review completed to identify previous efforts to assess the effects of 

particle size, particle type, and/or flow condition on the performance of particulate respirator 
2 

filters is described in Section 2.0. Section 3.0 describes the test matrices, methods, and results of 

the inert filtration efficiency testing performed at the U.S. Army's Edgewood Chemical 

Biological Center (ECBC). A similar summary of the bioaerosol testing performed at Battelle 

follows in Section 4.0. The test method developed for reaersolization and the results are 

discussed in Section 5.0. Conclusions and recommendations are provided in Section 6.0. 

2.0 LITERATURE REVIEW

2.1 Search Strategy 

 A literature search was completed to identify previous efforts to assess the effects of 

particle size, particle type, and/or flow condition on the performance of particulate respirator 

filters. The purpose of the search was to help define the test parameters and matrices for this 

task. The search included the open literature, test standards, and the Chemical Biological 

Information Analysis Center (CBIAC) and Defense Technical Information Center (DTIC) 

databases. A partial list of search terms included: filter, respirator, efficiency, penetration, 

cyclic, breather, aerosol, and biological. In addition, a search of the open literature was 

completed to identify previous work assessing reaerosolization of biological aerosols from 

filtering facepieces. A partial list of key words used in the search included: filter, respirator, 

bioaerosol, reaerosolization, and reentrainment. Limited information was identified on the 

reaerosolization of particles from filter materials. The title, author, and abstract of each record 

were reviewed to identify the potentially relevant articles. 

2.2 Inert Filtration Efficiency 

 The most relevant studies are summarized below following a brief overview of the 

primary mechanisms for aerosol collection and the influence of filtration velocity and aerosol 

size on each mechanism (Section 2.2.1). A number of studies that assessed the effect of both 

particle size and constant flow rate on measured penetration are reviewed in Section 2.2.2. Two 

studies that compare penetrations measured under constant and cyclic flow are reviewed in 

Section 2.2.3. 
3 

2.2.1 Aerosol Collection Mechanisms 

Particle penetration is dependent on several parameters including the aerosol particle size, 

filtration velocity (based on flow rate and available surface area), and several filter parameters 

including the thickness, fiber diameter, and solidity or fiber packing density (i.e., ratio of solid 

fiber volume to gross filter volume). The four primary collection mechanisms, illustrated in 

Figure 1, for aerosol filtration are: (1) inertial impaction, (2) interception, (3) diffusion, and 

(4) electrostatic (Hinds, 1999). The general trends regarding the influence of filtration velocity 

and aerosol size on the mechanisms are summarized in Table 1. Particles less than 0.1 μm are 

most effectively collected by the diffusion mechanism. Diffusion occurs when the random 

(Brownian) motion of a particle causes that particle to contact a fiber. As velocity is increased, 

collection by diffusion is reduced. Interception occurs when a particle does not deviate from the 

stream line but is intercepted by the fiber (i.e., streamline passes within one particle radius of 

fiber). Interception is the most important collection mechanism for particles in the most 

penetrating particle size (MPPS) and is independent of velocity. Inertial impaction occurs when 

a particle deviates from the streamline around the fiber and collides with the fiber. This 

mechanism is most effective for larger particles and is enhanced by higher particle velocities. 

The electrostatic mechanism is an enhancement to mechanical filtration. Electret media are 

made of dielectric materials that have a significant microscopic bipolar charge on the fibers with 

a low net macroscopic charge. Charged particles are attracted to oppositely charged fibers by the 

Coulombic force. Neutral particles are collected by the polarization force induced by local 

electric fields within the filter media. 

Figure 1. Four Mechanisms of Particle Capture (DHHS, 2003) 
4 

Table 1. Influence of Filtration Velocity and Aerosol Size on Collection Mechanisms 

Mechanism Increased Filtration Velocity Increased Aerosol Size 

Inertial Impaction Collection Increased Collection Increased 

Interception Independent of Velocity Collection Increased 

Diffusion Collection Reduced Collection Reduced 

Electrostatic Collection Reduced Collection Reduced 

 The three primary collection mechanisms, diffusion, interception, and impaction, are 

effective over different particle sizes. The MPP through a filter exists where none of the 

mechanisms is dominant. This generally occurs between 0.05 and 0.5 μm depending on the filter 

properties and filtration velocity (Hinds, 1999). A generic illustration of the effect of particle 

size on filtration efficiency is provided in Figure 2. The figure also indicates where each 

collection mechanism is predominant over the particle size range. Penetration generally 

increases with increased flow rate or velocity in the region of the MPPS because the diffusion 

collection mechanism is reduced. This also generally leads to a shift in the MPPS toward 

smaller particles. Collection efficiency of larger particles can actually increase with increased 

velocity as the inertial impaction mechanism is enhanced. 

Figure 2. Primary Mechanism of Capture for Various Particle Diameters 

Indicating MPPS (DHHS, 2003)

2.2.2 Effect of Particle Size/Flow Rate 

 Several published studies have assessed the effect of particle size and/or flow rate on 

the measured efficiency of respirator filters including: Ruuskanen et al. (1988), Brosseau et al. 
5 

(1989); Stevens and Moyer (1989), Fardi and Lui (1991), Chen et al. (1992), Qian et al. (1998), 

Hanley and Foarde (2003). The challenge aerosols employed consisted mainly of chargeneutralized dioctyl phthalate (DOP), sodium chloride (NaCl), corn oil, or polystyrene latex (PSL) 

spheres. The aerosol concentrations upstream and downstream of the filter were typically 

analyzed using a laser aerosol spectrometer (LAS) or condensation nucleus counter (CNC) for 

particle sizes in the submicrometer range. For particles larger than 1 μm, researchers frequently 

used an aerodynamic particle sizer (APS, TSI Inc., Shoreview, MN) or aerodynamic size 

spectrometer (Aerosizer®, Amherst Process Instruments Inc., Hadley, MA). In general, the 

studies were conducted at constant flow rates ranging from 16 to 85 L/min using a variety of 

disposable dust-mist (DM), dust-fume-mist (DFM), and high-efficiency particulate air (HEPA) 

respirator filters. These respirator filters were certified under the requirements of 30 CFR 11 

(1972), which has since been replaced by 42 CFR 84 (1995). 

Stevens and Moyer (1989) evaluated the effect of a “worst-case” aerosol on the filtration 

efficiency of a variety of DM, DFM, and high-efficiency respirator filters. The most penetrating 

particle sizes were determined as a function of test flow rate. Filters were challenged with either 

solid NaCl aerosol or liquid DOP aerosol with numerical median diameters (NMDs) ranging 

from 0.03 to 0.3 μm and constant flow rates ranging from 16 to 85 L/min. The particle size of 

maximum penetration varied with filter type and flow rate, and was less than 0.25 μm NMD in 

all cases. As the flow rate was increased, the magnitude of penetration increased and a shift 

towards a smaller particle size for maximum penetration was observed. This is consistent with 

the mechanisms described above. At the most penetrating conditions, the high-efficiency filters 

provided greater than 99.97 percent efficiency, while the DM and DFM respirators had 

efficiencies ranging from 67 to 89 percent and 85 to 99 percent, respectively. 

Brosseau et al. (1989) evaluated electrostatic DM respirators from ten manufacturers 

challenged with monodisperse PSL particles ranging in size from 0.102 to 2.02 μm. Filter 

penetration was greatest for particles 0.1 μm in diameter, which was consistent with the results 

of Stevens and Moyer (1989). In addition, appreciable differences were found in the 

performances of filters distributed by the ten different manufacturers, where filter penetration 

ranged from about 5 to 15 percent for the most penetrating particle sizes. 

Fardi and Liu (1991) challenged DM and DFM respirators composed of charged and 

uncharged fibers using monodisperse NaCl and DOP particles with diameters in the range of 
6 

0.035 to 0.4 μm. Tests were conducted at constant flow rates ranging from 16 to 48 L/min, and 

aerosol penetration measurements were made using a condensation nucleus counter, 

aerodynamic particle sizer, and laser optical particle counter for purposes of comparison. 

Results obtained by these instruments were in agreement with each other in the overlapping size 

range of the instruments. The most penetrating particle size was found to be approximately 

0.1 μm for filters containing charged fibers and 0.3 to 0.4 μm for mechanical filters. Consistent 

with Stevens and Moyer (1989), for all filters tested there was an increase in penetration with 

increasing particle size for small particles until a maximum was reached, and then penetration 

decreased with particle size for larger particles. For the range of respirator filters tested, the peak 

penetration varied from 1.2 to 30 percent at 16 L/min, 3.5 to 37 percent at 28 L/min, and 6 to 

45 percent at 48 L/min. There was no significant difference in penetration between solid NaCl 

and liquid DOP particles of the same size. 

Chen et al. (1992) assessed aerosol penetration as a function of particle size for several 

filtering facepieces and DM, DFM, and HEPA respirator cartridges using corn oil particles over 

a size range of 0.1 to 15 μm. Tests were conducted at constant flow rates ranging from 5 to 

100 L/min. The respirators were sealed to a mannequin head form during testing. Results 

showed an increase in aerosol penetration with increasing flow rate in the submicrometer size 

range, leading the authors to concede that the primary removal mechanisms are diffusion and 

electrostatic attraction within this size range. The penetration of supermicrometer-sized aerosol 

particles decreased with mask flow, indicating removal of large particles by impaction. 

Only a limited number of recent studies were identified that have evaluated N-, R-, and 

P-type respirators certified under 42 CFR 84. Qian et al. (1998) compared the measured 

filtration efficiency of NIOSH-approved N95 respirators with that of DM and DFM respirators 

using challenge aerosols of NaCl and PSL particles with sizes ranging from 0.1 to 5.10 μm. 

Tests were conducted at constant flow rates of 32 and 85 L/min. N95 respirators were found to 

have higher filtration efficiencies than DM and DFM respirators, showing at least 95 percent 

efficiency against particles at the most penetrating particle size (0.1 to 0.3 μm). The filtration 

efficiency increased with size, reaching approximately 99.5 percent or higher at about 0.75 μm. 

In a more recent study, Hanley and Foarde (2003) assessed the filtration efficiency 

provided by the C2A1 canister against an inert potassium chloride aerosol (0.3 to 10 μm) over a 

range of constant flow rates (30, 50, and 80 L/min). The results demonstrated that the 
7 

penetration rapidly decreased as the particle size increased above 0.3 μm, and penetration of 

particles ranging from 0.3 to 0.7 μm increased with higher flow rate. Penetrations could not be 

accurately measured for particles greater than 0.7 μm as the downstream aerosol concentrations 

were below the detection limit of the aerosol particle counter, demonstrating the difficulty in 

generating sufficient challenge concentrations of the larger particles to accurately measure 

penetrations of high-efficiency filters. 

Martin and Moyer (2000) evaluated several N95, N99, R95 and P100 electrostatic 

respirator filters to determine filter efficiency and most penetrating particle size. Challenge 

aerosols included NaCl (0.075 μm NMD, 1.86 GSD) and DOP (0.185 μm NMD, 1.60 GSD), and 

a constant flow rate of 85 L/min was used for N95 filters and 42.5 L/min for N99, R95, and P100 

filters. Tests involved comparing “as received” filters to those dipped in isopropanol to remove 

the electrical charge associated with the filter fibers. All of the filters tested which had the 

electrostatic charge removed showed a dramatic increase in filter penetration. For the NaCl 

aerosol, N-series filters increased in maximum penetration from less than 5 percent up to 35 to 

55 percent. Similarly, the maximum penetration increase with the R95 filters was from 0.03 

percent up to 50 percent and for the P100 filters from 0.001 to 4 percent. In addition, there was a 

shift in the most penetrating particle size from approximately 0.05 to 0.10 μm for the new filters 

toward larger sizes in the 0.25 to 0.35 μm range once the electrostatic charge was removed. 

2.2.3 Comparison of Constant/Cyclic Flow Penetrations 

A limited number of studies were identified that assessed the effect of cyclic flow on 

filter performance. The two most relevant studies were by Stafford et al. (1973) and 

Brosseau et al. (1990). 

Stafford et al. (1973) measured the penetration of monodisperse PSL (0.176 to 2.02 μm) 

and DOP (0.3 μm) aerosols through respirator filter cartridges at three cyclic flows with mean 

flow rates of 30, 35, and 53 L/min. These flows were selected to correspond to work rates of 

415, 622, and 830 kg-m/min. Tests were also conducted at a constant flow rate of 16 L/min 

(equivalent to 32 L/min through a pair of cartridges). At steady-flow conditions, the maximum 

penetration occurred at a particle size of 0.3 μm, which is consistent with theoretical single-fiber 

predictions. However, during cyclic flow the particle size that produced maximum penetration 
8 

varied between filters, in one case less then 0.3 μm and in the other approximately 0.5 μm. Also, 

the maximum penetration was considerably higher than corresponding steady-flow values, 

suggesting that tests conducted under steady-flow conditions may provide a considerable 

overestimate of filter performance. 

Brosseau et al. (1990) compared the collection of silica and asbestos aerosols by DM 

respirators under breathing and constant flows. The cyclic flow was sinusoidal with a mean flow 

of 76 L/min and a peak flow of 100 L/min, and represented a work rate of 622 kg-m/min. The 

constant flow rate was 32 L/min. In general, the silica penetration under cyclic flow conditions 

was about one and a half times as great as that measured under steady flow conditions, which is 

consistent with the results of Stafford et al. (1973). The asbestos results were inconclusive as the 

results varied by filter. 

2.3 Biological Filtration Efficiency 

The majority of research published in the open literature has focused on evaluation of 

surgical masks and a variety of disposable dust-mist (DM), dust-fume-mist (DFM), and highefficiency particulate air (HEPA) respirator filters for protection against bacterial aerosols 

(Brosseau et al., 1994; Chen et al., 1994; Johnson et al., 1994; Willeke et al., 1996; 

Brosseau et al., 1997; McCullough et al., 1997; Wake et al., 1997; Qian et al., 1998). 

2.3.1 Test Methods 

Previous studies were largely conducted to assess use of respirators in controlling 

healthcare-worker exposures to infectious biological aerosols, namely Mycobacterium 

tuberculosis, the organism which causes tuberculosis. The studies used bacterial test aerosols 

including M. chelonae, M. abscessus, Bacillus subtilis, B. megatherium, B. alcalophilus, 

Streptococcus salivarius, Staphylococcus epidermidis, Pseudomonas fluorescens, P. alcaligenes, 

and Micrococcus luteus to simulate pathogenic organisms such as M. tuberculosis. No studies 

were identified in the open literature that assessed viral aerosol penetration through respirator 

filters. 
9 

Test system designs and methodologies employed for evaluating mask and respirator 

filter efficiency against biological aerosols varied between different research groups. 

Brousseau et al. (1994) used a column apparatus with vertical airflow to minimize aerosol losses 

to the duct walls by sedimentation. The mask or respirator filter was sealed with wax onto a 

metal plate within the duct. Measurements upstream and downstream of the filter were 

corroborated with Andersen cascade impactors and an aerodynamic particle sizer (APS, 

TSI Inc.), which measures the aerosol concentrations of viable and total particles, respectively. 

By comparison, Willeke et al. (1996) conducted tests using a rectangular test chamber with 

perforated metal sheets at the top and bottom of the chamber to ensure a uniform aerosol 

concentration in the vicinity of the test mannequin. The mask or respirator was sealed to the 

mannequin head form with silicone adhesive or petroleum jelly. Upstream and downstream 

particle concentrations were measured with an aerodynamic size spectrometer (Aerosizer®, 

Amherst Process Instruments Inc.) Finally, Wake et al. (1997) designed a test system which was 

comprised of two aerodynamically identical flow lines, one of which contained the mask or 

respirator filter while the other served as a reference line. The mask or filter was sealed with 

PVC tape or hot-melt adhesive within the flow line, and the downstream aerosol concentrations 

were measured using all glass impingers (AGI) for both the filtered and reference lines. The 

penetration through the filter was obtained from the ratio of the filtered and reference lines. 

The bacterial aerosols were typically aerosolized using a 6-jet Collison nebulizer 

(BGI Inc.) operated at pressures ranging from 7 to 15 psi. McCullough et al. (1998) found that 

reducing the nebulizer operating pressure to 3 psi increased the percentage of culturable particles 

of M. abscessus from 15 to 45 percent. Generated challenge concentrations, if reported, were 

generally in the range of 104

 to 106 colony forming units (CFU)/m3 air, the higher concentration 

being used to provide a sufficient downstream concentration when testing the most efficient 

filters. Most studies were conducted under constant airflow rates ranging from 16 to 85 L/min. 

As alluded to above, a variety of techniques have been used to measure the challenge and filtered 

aerosol concentrations. Total particle analyzers used include the APS, Aerosizer®, and LAS. 

Viable particle samplers include the Andersen six-stage impactor, membrane filters, and AGIs. 

Viable sampling involves collecting and transferring the sampled organisms onto growth media 

to allow the organism to replicate for enumeration. Organism viability can be reduced due to 

aerosolization, transport, and sampling. Total particle analyzers measure both viable and 
10 

non-viable particles, therefore aerosol concentration measurements are higher than those 

determined by viable samplers. Strong correlation of filter penetration measured by viable 

samplers and the APS has been reported (Brousseau et al., 1994; Chen et al., 1994; McCullough 

et al., 1997; Johnson and Andersen, 1996). In some cases, it was noted that the filter 

penetrations were slightly lower for the Andersen impactor (Chen et al., 1994) and AGI (Johnson 

and Andersen, 1996) compared to the APS. However, because of the strong correlation, 

researchers suggest that a total particle analyzer may be used in place of more labor-intensive 

viable sampling techniques for determining bioaerosol penetration. 

A single test standard was identified for evaluating the filtration efficiency of medical 

face mask materials using a biological aerosol (ASTM F 2101-01, 2001). A bacterial aerosol of 

S. aureus is generated from a suspension using a nebulizer, with a target mean particle size of 

3.0 μm. Tests are conducted under a constant flow rate of 28.3 L/min. A six-stage Cascade 

impactor is used to measure the aerosol penetration downstream of the filter. The reported 

maximum filtration efficiency that can be measured using this method is 99.9 percent. 

2.3.2 Inert/Biological Penetration Comparison 

 

 Several studies have compared measured penetrations of inert and biological aerosols 

through masks and respirator filters. Qian et al. (1998) evaluated the unloaded filtration 

efficiency of NIOSH-approved N95 respirators using challenge aerosols of polydisperse NaCl 

particles (0.1 to 0.7 μm), monodisperse polystyrene latex (PSL) spheres (0.60, 1.02, 2.94, 3.96, 

and 5.10 μm), and two bioaerosols, B. subtilis (mean aerodynamic diameter 0.8 μm) and 

B. megatherium (mean aerodynamic diameter 1.2 μm). Tests were conducted at a constant flow 

rate of 85 L/min. For both bacteria, the filtration efficiency of the N95 respirator was 

99.5 percent or higher, equivalent to the data for the inert particles of the same aerodynamic 

diameter. 

Brousseau et al. (1994) compared filtration efficiencies of the bioaerosol M. chelonae

(0.78 μm NMAD, 1.2 GSD) to inert aerosols containing either monodisperse PSL particles 

(0.804 μm) or dioctyl phthalate (DOP) particles (0.12 μm NMAD, 1.5 GSD) for various layers 

of fiberglass flatsheet filter media. Tests were conducted at a steady flow rate of 46 L/min. 

Results indicated no significant difference in penetration through flatsheet fiberglass filter media 
11 

when challenged with M. chelonae and PSL particles of the same aerodynamic size. In addition, 

penetration of DOP particles as measured with an optical particle counter were closely correlated 

with the penetration of M. chelonae measured by the Andersen impactor and APS, as well as 

PSL particles measured by the APS. Based on their results, Brousseau et al. suggest that an inert 

aerosol with aerodynamic particle size similar to a bioaerosol of interest is an appropriate test 

aerosol to predict bioaerosol filter collection. 

Under equivalent test conditions, Chen et al. (1994) report this same conclusion for 

experiments with a surgical mask and several disposable DM, DFM, and HEPA respirators 

against challenge aerosols of M. chelonae and PSL particles. Mean efficiencies for viable 

M. chelonae ranged from 97 percent for the surgical mask and DM respirator to more than 

99.99 percent for the HEPA respirator. Mean efficiencies for the PSL particles were slightly 

lower in some cases, ranging from 96 percent for the surgical mask and DM respirator to more 

than 99.99 percent for the HEPA respirator. Chen et al. raised the question about practical 

significance of the measured differences between the filters tested in their study (less than 3 

percent), when it has been estimated that at least 10 to 20 percent leakage occurs in masks not 

properly fitted to the wearer’s face. 

Wake et al. (1997) evaluated the filter efficiency of several respirator filters, disposable 

dust masks, and surgical masks against the bioaerosols B. globigii, M. luteus, and P. alcaligenes, 

monodisperse urea aerosols (1.5, 3, 5, 7, and 9 μm), and a NaCl aerosol (0.6 μm MMAD, 

2.3 GSD). Bacterial penetration generally corresponded to those of non-biological aerosols of 

similar size, but no direct comparisons were made. Bacterial penetration ranged from less than 

0.01 percent to 0.88 percent for various glass fiber and wool resin respirator filters, compared to 

up to 1.56 percent for the 1.5 μm urea particles and up to 0.31 percent for the NaCl particles. 

Hanley and Foarde (2003) assessed the filtration efficiency provided by the C2A1 

canister against a bioaerosol of B. globigii (Bg) spores over a range of constant flow rates (30, 

50, and 80 L/min). For comparison, tests were also completed with a polydisperse potassium 

chloride aerosol with particles ranging in size from 0.3 to 10.0 μm. Samples of the challenge 

and downstream aerosol were collected on polycarbonate membrane filters with a pore size of 

0.4 μm. Downstream samples were collected on filters with a diameter of 142 mm to allow the 

full canister flow to be passed through the filter without excessive pressure drop. All measured 

efficiencies with the bioaerosol challenge exceeded 99.99997 percent. In 31 of 33 tests, no Bg 
12 

spores were detected downstream of the C2A1 canister. The results demonstrated that inert 

aerosol penetration in the 0.7 to 1.0 μm size range were consistent with those measured using the 

Bg spore challenge. 

Previous reports on filter performance against particles of various sizes, shapes and 

aspect ratios contain conflicting results. Willeke et al. (1996) compared penetrations through 

surgical masks and DM respirators of several rod-shaped bacteria (B. megatherium, 

P. fluorescens, B. alcalophilus) of varying aspect ratios with that of spherical S. salivarius and 

inert corn oil particles. Results indicate the penetration of spherical S. salivarius bacteria were 

approximately the same as spherical corn oil particles in the aerodynamic size range from 0.9 to 

1.7 μm. The penetration of rod-shaped bacteria was lower than S. salivarius, and decreased with 

increase of aspect ratio showing that filter penetration of bacteria is a strong function of their 

shape. As an example, Pseudomonas fluorescens, with an average aspect ratio of 3, was found to 

penetrate 50 to 60 percent less than spherical particles of the same aerodynamic diameter. 

Willeke et al. postulated that due to greater surface area of non-spherical particles compared to 

spherical ones, interception and electrostatic attraction cause greater removal (i.e., less 

penetration) for rod-shaped bacteria compared to spherical particles of the same aerodynamic 

size. 

In comparison, McCullough et al. (1997) evaluated the penetration of M. abscessus

(mean aerodynamic diameter 0.69 μm), B. subtilis (mean aerodynamic diameter 0.88 μm), and 

S. epidermidis (mean aerodynamic diameter 0.87 μm) bioaerosols, along with a monodisperse 

PSL aerosol (0.55 μm) through a variety of DM and DFM respirator filters and surgical masks. 

In all cases, penetration of the PSL aerosol was greater than any of the biological aerosols due to 

its smaller aerodynamic diameter. However, the penetration of B. subtilis (a rod) was found 

greater than S. epidermidis (a sphere) at approximately the same aerodynamic diameter. 

Contrary to Willeke et al. (1996), the authors suggested that the aerodynamic diameter of the 

bacteria may not be an accurate predictor of aerosol penetration for non-spherical particles in 

these filters, particularly when electrostatic forces are dominant. 

Particle shape was also found to influence penetration through fibrous filters. Tuinman 

and Steeenweg (1998) compared aerosols with several shapes including rod-shaped caffeine 

particles, angular urea particles, plate-like eicosanoic acid particles, and needle-shaped arachidic 

acid particles to spherical oil particles with an equivalent particle size distribution 
13 

(approximately 0.04 to 0.8 μm). The penetration decreased from spherical particles to angular 

particles and rods to the lowest penetration for plates. The reduction in penetration for 

rod-shaped particles compared to spherical particles was consistent with the findings of 

Willeke et al. (1996) for rod-shaped bacteria with aspect ratio similar to the caffeine particles. 

2.3.3 Effect of Flow Rate 

Several studies have been conducted assessing the effects of flow rate on filter efficiency 

of biological aerosols. Willeke et al. (1996) evaluated constant air flow rates ranging from 16 to 

80 L/min to simulate breathing rates representative of conditions ranging from rest to strenuous 

work. Increasing the flow to 50 and 80 L/min resulted in increased penetrations of P. 

fluorescens through a DM respirator of 6 and 8 percent, respectively. The effect was most 

significant for particles less than 1 μm in aerodynamic diameter. Brosseau et al. (1997) assessed 

the effect of flow rate (45 and 85 L/min) and relative humidity (30 and 70 percent) on the 

penetration of M. abscessus aerosol through 16 respirator filters and 5 surgical masks. The 

median penetration of M. abscessus at 45 L/min was 2, 0.4, and 0.02 percent for DM, DFM, and 

HEPA filters, respectively. Increasing the flow rate to 85 L/min resulted in greater penetration, 

and changes in relative humidity caused minimal effects on bioaerosol collection. McCullough 

et al. (1997) reported similar results for a variety of respirator filters and surgical masks against 

three bacterial aerosols (M. abscessus, S. epidermidis, B. subtilis) under the same flow rate and 

relative humidity conditions. Only one study, conducted by Johnson et al. (1994), was identified 

in the open literature that tested a biological aerosol using cyclic rather than constant flow 

conditions. Johnson et al. simulated normal breathing during light exertion using an automated 

breathing simulator (TSI Inc.) operated at a breathing rate of 15 breaths/min, tidal volume of 1.5 

L/breath, and minute volume of 22.5 L/min. 

2.3.4 Viral Filtration Efficiency 

Research efforts on respirator filter efficiency have largely focused on bacterial aerosols, 

thus limited information on viral aerosols was found. Harstad and Filler (1969) evaluated the 

performance of ultra-high-efficiency filter papers against the submicron viral aerosol of T1 
14 

bacteriophage (0.12 μm NMD) and the bacterial aerosol of B. globigii spores (1.0 μm NMD). 

Submicron phage aerosols were generated using a Dautrebande aerosol generator, Bg spore 

aerosols using a vaponefrin nebulizer, and aerosol concentration was measured upstream and 

downstream of the test filter using AGIs. Phage penetration through filters averaged 0.00095 

percent, and increased markedly (up to 0.39 percent) with an increase in velocity up to 

150 ft/min and neutralizing with bipolar air ions. Penetration of bacterial spore aerosols through 

the filter papers was essentially zero. 

Hofacre et al. (1996) measured the penetration of a viral aerosol of MS2 phage and a 

monodisperse PSL aerosol (0.173 μm) through a HEPA filter used for collective protection. The 

MS2 phage aerosol concentrations upstream and downstream of the filter were measured using 

both a bioassay enumeration technique and a light scattering instrument. The inert aerosol 

concentrations were measured using the light scattering instrument. Aerosol penetration 

measured using the light scattering technique was statistically equivalent for both the MS2 phage 

and PSL particles, while the penetration of MS2 phage measured using the bioassay method was 

consistently lower. The study concluded that inert aerosols of similar size provided a 

conservative indication of HEPA filter performance against a bioaerosol. 

2.3.5 Reaerosolization 

 Qian et al. (1997a) evaluated the reaerosolization of inert and biological aerosols from 

three different models of N95 half-mask respirators at velocities up to 300 cm/sec, intended to 

represent violent sneezing or coughing. The filters were loaded with aerosols of either NaCl 

(0.15 to 1.0 μm), PSL (0.60, 1.02, 2.94, 3.96, and 5.10 μm), or the bacterium B. subtilis or B. 

megatherium. The flow rate during loading was a constant 85 L/min and the environmental 

conditions were ambient (T=25oC, RH=22%). The particle loading (1x105 particles/cm2

) was the 

same for both the inert and biological aerosols. A quick release valve was used to pulse the 

airflow in the opposite direction of loading to simulate the cough or sneeze. An aerosol size 

spectrometer (Aerosizer®, Amherst Process Instruments, Hadley, MA) was used to measure the 

concentration up- and downstream of the filter. For each filter model, NaCl particle penetration 

was less than 5 percent, thus satisfying the certification requirement of 95 percent or more 

collection efficiency. Reaerosolization was found insignificant for particles less than 1.0 μm, 
15 

with less than 0.025 percent becoming reentrained. For the condition of violent sneezing or 

coughing, only larger particles were reaerosolized in significant amounts, with about 1 percent of 

3 μm and 6 percent of 5 μm PSL particles. This is of importance as single bacteria may 

aggregate or attach to inert particles to form larger clusters, increasing their risk of potential 

reaerosolization. In addition, results indicate that bacteria become reentrained at high air 

velocities more easily than the NaCl particles of similar size, which the authors reason may 

signify a weaker bond to the filter fibers or more surface area exposed to the airflow. Finally, no 

reaerosolization of particles was observed when the relative humidity was increased to 

35 percent, which the authors attribute to liquid bridging between particles and filter fibers that 

increases the adhesion force. 

In a related study, Qian et al. (1997b) assessed the effects of particle size, inert particle 

type, filter type, and reentrainment velocity on reaerosolization of inert aerosols including NaCl, 

PSL, corn oil, and dust. Similar test methods were used as described above. Flat sheets of three 

types of fibrous filter media used in half-mask respirators were evaluated. The collection 

efficiency of the filters ranged from approximately 93 percent for 0.6 μm particles to 

99.8 percent for 5.1 μm particles. Reaerosolization trends were in agreement with the previous 

study as reaerosolization of 0.6 to 5.1 μm particles increased approximately with the square of 

particle size and the square of reentrainment velocity, and decreased with relative humidity. 

Reaerosolization was also found to be a function of the particle type as dust was found to have 

the highest reentrainment, while corn oil was not reentrained at any of the test conditions. This 

was attributed to differences in interaction with the filter fibers of oily particles compared to 

solid, irregularly shaped particles. Consistent with previous studies, electrostatic charges on the 

filter fibers significantly increased the collection of submicrometer particles; however, particle 

reaerosolization was only slightly impeded by the embedded charges. Finally, filter properties 

were found to significantly affect particle reaerosolization. The number of reaerosolized 

particles decreased slightly with filter thickness, which supports the concept that most of the 

particles are reentrained from the front layer of the filter. Essentially no particle reentrainment 

was observed from charged felt, compared with up to 5 to 15 percent from glass fiber HEPA and 

polypropylene filters. 

Reentrainment of bioaerosols from air ventilation filters has also recently been studied. 

Jankowska et al. (2000) compared the collection efficiency and reentrainment rate of the fungal 
16 

spores Penicillium brevicompactum and P. melinii against that of inert potassium chloride (KCl) 

particles using a medium prefilter and a higher efficiency fine filter. The fungal spores were 

aerosolized from an agar surface, simulating dry spore dispersion. Solid KCl particles were 

aerosolized from an aqueous solution using a Collison nebulizer. The aerosol concentrations upand downstream of the filter were measured using an Aerosizer®. Filter loading ranged from 

approximately 105

 to 106 particles/cm2. The collection efficiency was found to be slightly lower 

for fungal spores than for KCl particles of the equivalent aerodynamic size. Reaerosolization 

increased with reentrainment velocity for all test particles. When the reentrainment velocity was 

the same as the loading velocity, the reaerosolization was less than 0.4 percent. When the 

reentrainment velocity was increased to 3.0 m/s, the reaerosolization of fungal spores was higher 

than that of KCl particles, ranging from 2 to 6 percent for P. brevicompactum, 5 to 12 percent for 

P. melinii, and 0.2 to 0.6 percent for KCl particles. The higher reentrainment of fungal spores 

was attributed to the presence of aggregated spores, such that the reentrainment velocity may 

become sufficient to break up the aggregates and reentrain the spores. The differences between 

fungal spores were attributed to surface structure, where P. melinii spores have a spiny surface 

imparting weaker contact with the filter fibers. 

2.4 Summary 

This section provides a brief summary of the trends observed in the literature and the 

impact on the current study. In addition, it identifies the data gaps in the literature and how they 

pertain to goals of the current study. 

2.4.1 Filter Efficiency Testing 

2.4.1.1 Inert Testing. Numerous studies were identified in the literature review that 

assessed the effect of flow rate and particle size on the measured aerosol penetration through 

particulate respirator filters. However, no studies were identified that assess the effect of high 

volumetric flow rates that may be encountered during heavy work rates on filter performance. 

Few studies in the literature assessed filtration performance above 85 L/min constant flow and 

none above 100 L/min. The results have shown that penetration of submicron particles, 
17 

specifically those in the MPPS range, tend to increase with increased flow rate. The MPPS is 

generally in the range of 0.1 to 0.3 μm depending on the type of filter. Particles larger than 1 μm 

have been shown to be collected more efficiently at higher flow rates as inertial impaction is 

enhanced. Previous studies have also demonstrated that even N95 filters are very efficient 

(>99.5%) at removing particles above 0.7 μm. To this end, the particle sizes tested in this study 

were focused on those in the MPPS region. Five particle sizes were tested over the range from 

0.02 to 0.3 μm and only three particle sizes greater than 0.3 μm. 

 Few studies were identified that assessed aerosol filtration performance under cyclic 

flow conditions. The studies that were reviewed concluded that higher penetrations were 

measured under cyclic flow conditions, corresponding to various work rates, than measured 

under constant flow rates used in test standards (i.e., 32 or 85 L/min). There is considerable 

debate regarding the impact of the peak inhalation flow on filter performance, both from an 

aerosol and gas/vapor filtration perspective. No conclusions could be drawn from the literature 

as to the impact of peak flow or what an appropriate constant flow rate is to provide an estimate 

of performance under cyclic flow. As this is an important objective of the current study, the 

constant flows were matched to the cyclic flow minute volume, mean inhalation flow, or peak 

inhalation flow to permit comparisons. 

2.4.1.2 Biological Testing. In summary, appreciable differences were found in the 

performance of respirator filters when challenged with biological aerosols. Overall, studies have 

confirmed that N95 and HEPA respirators are substantially more efficient than DM and DFM 

respirators and surgical masks against biological aerosols. Consistently, no significant difference 

in filter penetration was found between spherical inert and spherical bioaerosol particles of 

similar aerodynamic diameter, suggesting that inert particles of the same size may be used to 

predict bioaerosol efficiency. In some cases, the penetration of rod-shaped bacteria was lower 

than that of spherical organisms of the same aerodynamic diameter, indicating that in addition to 

particle size, particle shape may also affect penetration through respirator filters. Finally, 

increases in flow rates to levels representative of heavy working conditions were found to 

increase biological aerosol penetration, particularly for submicrometer particles. This becomes 

critically important when considering that a certain number of pathogenic organisms of 
18 

submicrometer size may be sufficient to cause a serious health risk. No studies were identified 

in the literature that assessed viral penetration through particulate respirator filters. 

 2.4.1.3 Reaerosolization. Particle size, shape and composition, air velocity, humidity, 

and filter properties were all factors found to significantly affect particle reentrainment from 

filter materials. Large particles of approximately 5.0 μm diameter and greater were found to be 

most susceptible to reaerosolization. Biological particles were found to become reentrained 

more easily than inert particles of comparable size, which is suspected to result from weaker 

contact with filter fibers due to irregular shapes and surface characteristics. In addition, 

aggregation of bacteria and fungal spores to form larger clusters was determined to also increase 

potential reaerosolization. 

3.0 INERT PARTICULATE FILTRATION EFFICIENCY TESTING 

 Currently, NIOSH-approved particulate air purifying respirator filters are tested against 

salt or oil aerosols at a constant flow rate of 85 L/min for certification per 42 CFR Part 84 

(1995). However, measurements of physiological parameters of workers show peak inhalation 

flow rates from 300 to 400 L/min for short durations during certain high work load activities 

(Caretti et al., 2004). As discussed in Section 2.0, studies to determine the effect of high breather 

flows on the filtration efficiency of NIOSH-approved particulate filters are lacking in the open 

literature. This section describes the testing completed to assess the effect of particle size, flow 

rate, and flow condition (i.e., cyclic versus constant) on filtration of inert aerosols. The two 

primary objectives of the inert testing were: (1) assess the effect of high volumetric flow 

conditions on the performance of NIOSH-approved particulate respirator filters and (2) compare 

performance under constant and cyclic flow conditions. 

3.1 Test Parameters 

 The filters, summarized in Table 2, were selected in consultation with NIOSH and 

included two N95 filtering facepieces, two P100 filtering facepieces, two N95 cartridges, and 

two P100 cartridges. The two brands of commercial P100 filtering facepieces used in the study 
19 

had exhalation valves. The valves were not sealed during the inert filtration efficiency testing. 

Photographs of each filter are provided in Appendix A. The filters were not preconditioned prior 

to testing (i.e., tested as-received). The environmental conditions during testing were maintained 

at ambient temperature (25 ± 3°C) and relative humidity (40 ± 10%). Table 3 summarizes the 

challenge aerosols and the target particle sizes. Solid aerosols (i.e, salt and PSL) were used with 

the N95 filters and oil aerosols (i.e., Emery 3004 and DOP) were used with the P100 filters. This 

approach is consistent with how certification testing is performed by NIOSH (42 CFR 84, 1995). 

For each particle size, the challenge aerosol concentration was adequate to measure efficiencies 

of at least 99.97 percent. 

Table 2. Summary of Cartridges and Filtering Facepieces 

Filter Type Rating Model Manufacturer 

N95 Flexi-Filter MSA (Pittsburgh, PA) 

N95 7506 North Safety Products (Cranston, RI) 

P100 HE-T SEA (Branford, CT) Cartridge 

P100 1050 Survivair (Santa Ana, CA) 

N95 1730 Louis M. Gerson, Co., Inc. (Middleboro, MA) 

N95 Affinity Plus MSA (Pittsburgh, PA) 

P100 8293 3M (St. Paul, MN) 

Filtering 

Facepiece 

P100 2360 Moldex-Metric, Inc. (Culver City, CA) 

Table 3. Summary of Challenge Aerosols for Testing N95 and P100 Filters 

Filter Type N95 P100 

Target NMAD (μm) Challenge Aerosol 

0.02, 0.05, 0.1, 0.2, 0.3 NaCl DOP 

0.7, 1.3, 2.9 PSL Emery 3004 

Tests were performed over a range of constant and cyclic flow conditions. The rationale 

for selection of the flow conditions is provided in Appendix B. As noted in the appendix, the 

cyclic flow conditions were selected to simulate work intensities ranging from moderate to 

exhaustive. The selected flow conditions are based on studies performed with unmasked 

subjects and, thus, are likely extreme under conditions of respirator wear. The breathing 

machine used in this study produced a sinusoidal waveform. The cyclic flow conditions with 

corresponding peak inhalation flow (PIF) and mean inhalation flow (MIF) are summarized in 

Table 4 and compared graphically in Figure 3. The MIF is the average flow rate over the 
20 

inhalation portion of the breathing cycle. The PIF represents the maximum flow rate obtained 

over the inhalation cycle. For a sinusoidal waveform, the PIF is π times the minute volume. The 

constant flow rates were selected to match a cyclic flow minute volume, MIF, or PIF for 

comparison purposes. These were 85 ± 5, 270 ± 15, and 360 ± 20 L/min. For example, the 85 

L/min constant flow matches a cyclic flow minute volume (2.3 L tidal volume, 37 breaths/min) 

and a MIF (1.6 L tidal volume, 25 breaths/min). Since all single cartridges were from dualcartridge respirators, they were tested at half of the tidal volume or constant flow rate stated 

previously. 

Table 4. Summary of Cyclic Flows Used for Testing with the Inert Aerosol Challenges 

Breathing Rate 

(breaths/min) 

Tidal Volume 

(L) 

Minute Volume 

(L/min) 

PIF(a)

(L/min) 

MIF(b) 

(L/min) 

25 1.6 40 130 85(c)

37 2.3 85 270(c) 175 

42 2.7 115 360(c) 230 

44 3.1 135 430 270(c)

(a) Peak inspiratory flow rate assuming ideal sinusoidal waveform 

(b) Mean inspiratory flow rate assuming ideal sinusoidal waveform 

(c) Selected for constant flow testing 

-500

-400

-300

-200

-100

0

100

200

300

400

500

0 0.5 1 1.5 2 2.5

Time (sec)

Flow Rate (L/min)

1.6 L Tidal Vol, 25 BPM

2.3 L Tidal Vol, 37 BPM

2.7 L Tidal Vol, 42 BPM

3.1 L Tidal Vol, 44 BPM

Figure 3. Comparison of Sinusoidal Waveforms Used to Assess the Effect of Moderate 

to High Breather Flows on Filter Performance 
21 

3.2 Test Matrix 

The test matrices for the cartridges and filtering facepieces are provided in Tables 5 

and 6, respectively. The tables indicate the number of tests performed at each combination of 

filter, particle size, and flow condition. The 0.02 to 0.3 μm aerosol challenges have been 

grouped since the efficiencies were measured sequentially using the same cartridge or filtering 

facepiece, as will be described in Section 2.3.1. Similarly, the 0.7 and 1.3 μm particle sizes have 

been grouped. Only two replicates were performed with the 2.9 μm challenge at each flow 

condition due to the high efficiency of the filters. The results demonstrated that the penetration 

of 2.9 μm particles was less than 0.001 percent for all conditions tested. Tests were not 

performed with the filtering facepieces at the highest cyclic flow condition for particle sizes 

ranging from 0.02 to 0.3 μm due to problems generating a stable challenge with the proper 

aerosol size distribution at this flow condition. 

Table 5. Test Matrix Completed to Assess the Effect of High Cyclic Flows on Filtration 

Performance of Cartridge Respirator Filters

Constant Flow 

(L/min) Cyclic Flow (L/min) 

42.5 135 180 20 42.5 57.5 67.5 

Filter 

 Target NMAD 

(μm) # Tests Completed 

0.02, 0.05, 0.1, 0.2, 0.3 3 3 3 3 3 3 3 

North N95 0.7, 1.3 3 3 3 3 3 3 3 

2.9 2 2 2 2 2 2 2 

0.02, 0.05, 0.1, 0.2, 0.3 3 3 3 3 3 4 3 

MSA N95 0.7, 1.3 3 3 3 3 3 3 3 

2.9 2 2 2 2 2 2 2 

0.02, 0.05, 0.1, 0.2, 0.3 3 3 3 3 3 3 3 

SEA P100 0.7, 1.3 3 4 3 3 3 4 3 

2.9 2 2 3 2 2 2 2 

0.02, 0.05, 0.1, 0.2, 0.3 3 3 3 3 3 3 3 

Survivair P100 0.7, 1.3 3 3 3 3 3 3 3 

2.9 2 2 2 2 2 3 3 
22 

Table 6. Test Matrix Completed to Assess the Effect of High Cyclic Flows 

on Filtration Performance of Filtering Facepieces 

Constant Flow 

(L/min) Cyclic Flow (L/min) 

85 270 360 40 85 115 135 

Filter 

 Target NMAD 

(μm) # Tests Completed 

0.02, 0.05, 0.1, 0.2, 0.3 3 5 6 3 3 3 0(a)

MSA N95 0.7, 1.3 3 3 3 3 3 3 3 

2.9 2 2 2 2 2 2 2 

0.02, 0.05, 0.1, 0.2, 0.3 3 3 3 3 3 3 0(a)

Gerson N95 0.7, 1.3 3 3 3 3 3 3 3 

2.9 2 2 2 2 2 2 2 

0.02, 0.05, 0.1, 0.2, 0.3 3 3 3 3 1 3 0(a)

3M P100 0.7, 1.3 3 3 3 3 3 3 3 

2.9 3 3 3 3 3 3 3 

0.02, 0.05, 0.1, 0.2, 0.3 3 3 3 3 3 0(a) 0(a)

Moldex P100 0.7, 1.3 3 3 3 3 3 3 3 

2.9 3 4 4 4 3 3 3 

(a) Stable challenge could not be generated using TSI Model 3160 Automated Filter Tester. 

3.3 Technical Approach 

This section describes the test systems and procedures that were used to measure the inert 

filtration efficiencies. A modified Model 3160 Automated Filter Tester (TSI, Shoreview, MN) 

was used for testing with the 0.02 to 0.3 μm aerosols, and is described in Section 3.3.1. Due to 

limitations with the Model 3160, a separate test system was used for the 0.7, 1.3, and 2.9 μm 

aerosols, and is described in Section 3.3.2. 

3.3.1 Model 3160 Automated Filter Tester 

3.3.1.1 System Description. The Model 3160 consisted of four primary components: 

(1) aerosol generation system, (2) aerosol sensing devices, (3) filter holder, and (4) vacuum 

pump or breathing machine. The aerosol generation system consisted of an atomizer and 

electrostatic classifier (EC). The atomizer generated a polydisperse oil or salt aerosol that was 

passed through the EC to generate the desired monodisperse aerosol at the desired particle size. 

The aerosol exiting the EC was diluted with HEPA-filtered room air. The aerosol number 

concentrations up- and downstream of the test filter were measured simultaneously using two 

condensation particle counters (CPCs). The upstream CPC (Model 3760A, TSI, Shoreview, 
23 

MN) sampled at 1.5 L/min and the downstream CPC (Model 3762, TSI, Shoreview, MN) 

sampled at 3.0 L/min. The higher sample flow rate on the downstream CPC increased the 

sensitivity of the Model 3160 and allowed shorter sample durations. The upstream sample was 

diluted by a factor of approximately 100 prior to measurement using a diluter (Model 3302A, 

TSI). The dilution factor was adjustable based on the expected challenge concentration. A 

vacuum pump was used to pull the desired constant flow rate through the test filter. The flow 

rate was measured using a mass flow meter (Series 4000, TSI, Shoreview, MN). 

 Several modifications were made to the Model 3160 to permit efficiency measurements 

over the range of flow conditions. First, additional HEPA filters were installed at the dilution air 

inlet, as shown in Figure 4. Second, a 1.5 hp vacuum pump was added for testing at constant 

flows in excess of 150 L/min, and a breathing machine was adapted for cyclic flow testing. 

Finally, the test filters were housed in a Lucite® chamber, measuring approximately 

22x18x10 cm, that was sealed between the filter chucks as shown in Figure 5. The aerosol 

entered the chamber through a 7.5-cm hole on top of the chamber. The filtering facepieces were 

placed over a similar sized hole in the bottom of the chamber and sealed using an adhesive. 

Threaded fittings were machined to mate with the cartridges. 

Figure 4. Additional HEPA Filters on Dilution Air Inlet of Model 3160 

Added 

HEPA 

Filters 
24 

Figure 5. Lucite® Chamber Used to House and Seal Test Filters to the Model 3160 

3.3.1.2 System Characterization. Shakedown tests were conducted to characterize the 

test system and establish the proper operating conditions. This included assessing the effect of 

non-isokinetic sampling, flow calibrations, and characterization of the challenge particle size 

distribution. The shakedown testing is detailed in Appendix C. 

3.3.1.3 Test Procedure. Prior to testing a filter, the dilution ratio on the upstream CPC 

was verified at a specific particle size and flow condition. This was done without a test filter 

(i.e., cartridge or filtering facepiece) to ensure no sampling bias between the up and downstream 

samples (i.e., measured penetration was 100 percent indicating agreement between the up- and 

downstream CPCs). The sample bias test results are provided in Appendix C. With the dilution 

ratio set, the cartridge or filtering facepiece was mounted to the Lucite® chamber and the 

chamber sealed to the Model 3160. The vacuum pump or breathing machine was connected to 

the test system and set to the proper conditions. The Model 3160 was programmed to 

sequentially measure efficiencies at the following particle sizes: 0.02, 0.05, 0.1, 0.2, and 0.3 μm. 

The Model 3160 was started and automatically stepped through the particle sizes and measured 

the efficiencies. When complete, the vacuum pump or breathing machine was stopped and the 

filter removed from the test system and discarded. 
25 

3.3.2 Large Particle Test System 

The Model 3160 was unable to produce particles greater than 0.4 μm under high flow 

conditions due to limitations of the system. This section describes the test system and approach 

used to measure filter efficiencies with challenge aerosols ranging from 0.7 to 2.9 μm. 

3.3.2.1 System Description. The test system, pictured in Figure 6, consisted of an 

aerosol generation system, exposure chamber, filter holder, breathing machine (or vacuum 

pump), and aerosol sampling/classification system. For the N95 filters, a Collison nebulizer was 

Figure 6. Test System Used to Measure Penetration of 0.7, 1.3, and 2.9 μm 

PSL through the N95 Filters 

used to aerosolize PSL particles suspended in distilled water. A 24-jet Collison (BGI Inc., 

Waltham, MA) was used to aerosolize the 2.9 μm PSL and a 6-jet Collison (BGI Inc., Waltham, 

MA) was used to aerosolize the 0.7 and 1.3 μm PSL. For the P100 filters, a 6-jet Collison 

nebulizer was used to aerosolize Emery 3004 oil. The nebulizer produced a polydisperse oil 

aerosol with sufficient numbers of 0.7, 1.3, and 2.9 μm particles to measure efficiencies of at 

least 99.97 percent. The aerosol exiting the nebulizer was mixed with filtered house air before 

passing through a neutralizer (Model 3012, TSI, Shoreview, MN). The generator continuously 

delivered aerosol-laden air to the exposure chamber to ensure a stable aerosol challenge was 
26 

maintained. Additional dilution air was pulled, as needed, through two HEPA filters located on 

top of the chamber. The chamber contained mixing fans to ensure a well-mixed challenge 

atmosphere. Chamber pressure was measured using a magnehelic® pressure gauge. Excess 

challenge was vented through HEPA filters and exhausted into the room. 

 The filter holder was mounted on the bottom of the chamber. The design of the filter 

holder was specific to the filter being tested. For the filtering facepieces, the holder consisted of 

a cone with a flat plate at the top. The filtering facepiece was sealed to the flat plate using rope 

caulk. For the cartridges, threaded fittings were machined. The filter holder was mounted to a 

2.5-cm OD stainless steel bulkhead fitting that passed through the bottom of the chamber. The 

filter holder was connected to the breathing machine with large diameter (~2.5 cm OD) flexible 

tubing. The breathing machine allowed for the adjustment of the tidal volume and breathing 

rate. The challenge-laden atmosphere was pulled through the test filter during inhalation. The 

breathing machine was equipped with a check valve such that the exhaled air was exhausted into 

the room after being filtered. The test system was also set up such that the test filter (i.e., 

cartridge or filtering facepiece) was bypassed during system startup to minimize loading since 

the objective of this effort was to measure the initial penetration. 

 The aerodynamic particle sizer (APS, Model 3321, TSI, Shoreview, MN) and diluter 

(Model 3302A, TSI, Shoreview, MN) were used to measure the challenge and downstream 

aerosol concentrations. The chamber contained a stainless steel probe that extended 10 cm 

beyond the chamber wall for collecting samples of the challenge atmosphere. The downstream 

aerosol concentration was sampled from a small chamber (cylindrical in shape with 15 cm 

diameter and 25 cm length) equipped with a stainless steel sample probe that extended 

approximately 7.5 cm into the chamber. Testing without a filter in the holder was completed to 

assess potential sampling bias on the measured penetrations due to the non-isokinetic sampling 

downstream. 

3.3.2.2 System Characterization. Shakedown tests were completed to verify the proper 

operating conditions of the system. This included no-filter testing to identify any potential 

sampling bias between the up- and downstream samples and characterizing the challenge 

aerosol. The shakedown testing is detailed in Appendix D. 
27 

 3.3.2.3 Test Procedure. The filter was mounted to the test fixture. The outlet valves 

on the P100 filtering facepieces were not sealed during testing. The test chamber was sealed and 

the breathing or vacuum pump, as appropriate, was started. The challenge generation system 

was started and permitted to operate for 10 to 20 minutes depending on the flow condition to 

allow the aerosol to reach a steady state concentration. During this time, the cartridge or filtering 

facepiece was bypassed to minimize filter loading. When steady state was reached, the valves 

were adjusted such that flow was pulled through the test filter. A sample of the challenge aerosol 

was collected with the APS for two minutes. Next, the sampling line was switched to sample 

downstream of the filter and adequate time was given for the instrument to stabilize. The 

downstream sample duration was varied to provide adequate time to permit efficiency 

measurements of at least 99.97 percent based on the challenge concentration. For the N95 filters, 

the sample duration was five minutes when testing 0.7 and 1.3 μm particles and 

15 minutes during testing with the 2.9 μm particles. The longer sample duration was needed 

with the 2.9 μm PSL particles because the challenge concentration was lower. The P100 filters 

required 15 minutes of downstream sampling when testing with the 0.7, 1.3, and 2.9 μm oil 

challenge particles. After sampling downstream was complete, the sample line was switched to 

the upstream and a second two minute sample of the challenge concentration was collected. If 

the two challenge samples (i.e., before and after downstream sampling) were not within 20 

percent of each other, the test was repeated as the challenge aerosol was not stable. After the 

challenge sample was collected, the aerosol generation system was stopped and the chamber 

flushed. The filter was removed from the test system and discarded, and a new filter was tested. 

3.4 Calculation of Aerosol Penetration 

 The percent aerosol penetration (P) was defined as the ratio of the downstream aerosol 

concentration (CDown) to the challenge aerosol concentration (CChal): 

(%) = ×100

Chal

Down

C

C P

Alternatively, the filtration efficiency (η) was defined as: 

(%) 100 1 ×100 ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = − = −

Chal

Down

C

C

η P
28 

The concentrations were the average number concentrations measured by the aerosol 

sensing instrument (i.e., APS or CPC). The challenge concentration was the average of the 

challenge measurements made before and after the downstream sample. 

3.5 Inert Results 

The inert testing had two primary objectives: (1) assess the effect of high volumetric 

flow rates on performance of NIOSH-approved respirator filters over a range of particle sizes 

and (2) compare performance under constant and cyclic flow conditions. The results that address 

each objective are discussed in Sections 3.5.1 and 3.5.2, respectively. 

3.5.1 Effect of High Volumetric Flow Rate 

This section summarizes the results of the inert testing. Penetrations were measured as a 

function of both flow rate and particle size. The cartridge results are summarized in Section 

3.5.1.1 and the filtering facepieces follow in Section 3.5.1.2. A complete summary of the 

measured penetrations for each trial is provided in Appendix E. 

 3.5.1.1 Cartridge Filters. The effects of particle size and flow condition on measured 

penetrations for the SEA HE-T and the Survivair® P100 cartridges are shown in Figures 7 

through 10. The constant and cyclic flow conditions are provided in separate figures. The 

horizontal red line identifies the maximum allowable penetration based on the NIOSH P100 

requirement (0.03%). Each data point represents the mean penetration and the error bars 

represent the 95 percent confidence intervals. The solid lines represent the best fit regressions. 

Both filters were extremely efficient for particles between 0.7 and 2.9 μm as penetrations were 

typically less than the minimum detection limit of 0.0001 percent at all flow conditions. Thus, 

the regressions provided are based on the particle sizes ranging from 0.02 to 0.3 μm. The most 

penetrating particle size (MPPS) was between 0.1 to 0.2 μm for both filters under both constant 

and cyclic flow. The MPPS shifted toward the lower end of this range as the flow rate increased. 

This observation is consistent with the literature (Stevens and Moyer, 1989). The primary 

collection mechanisms for particles in this range are interception and diffusion. The diffusion 
29 

mechanism becomes less efficient as the filtration velocity increases leading to a decrease in the 

MPPS. 

0.0001

0.001

0.01

0.1

1

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

42.5 L/min

135 L/min

180 L/min

Figure 7. Effect of Particle Size and Constant Flow Rate on Measured 

Penetration through SEA HE-T P100 Cartridge 

0.0001

0.001

0.01

0.1

1

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

20 L/min [MIF = 42.5 L/min]

42.5 L/min [PIF = 135 L/min]

57 L/min [PIF =180 L/min]

68 L/min [MIF = 135 L/min]

Figure 8. Effect of Particle Size and Cyclic Flow Rate on Measured 

Penetration through SEA HE-T P100 Cartridge 
30 

0.0001

0.001

0.01

0.1

1

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

42.5 L/min

135 L/min

180 L/min

Figure 9. Effect of Particle Size and Constant Flow Rate on Measured 

Penetration through Survivair® 1050 P100 Cartridge 

0.0001

0.001

0.01

0.1

1

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

20 L/min [MIF = 42.5 L/min]

42.5 L/min [PIF = 135 L/min]

57 L/min [PIF =180 L/min]

68 L/min [MIF = 135 L/min]

Figure 10. Effect of Particle Size and Cyclic Flow Rate on Measured 

Penetration through Survivair® 1050 P100 Cartridge 
31 

 The SEA HE-T filter met the requirement for a P100 filter across all particle sizes at all 

flow conditions tested. Penetrations in excess of 0.03 percent were measured for the Survivair®

filter. This is potentially due to differences in surface areas between the two filters. The SEA 

filter has approximately double the surface area and, thus, the filtration velocity would be half 

that of the Survivair filter at an equivalent flow rate. The measured penetrations of 0.1 μm 

particles (approximately the MPPS) under constant flow conditions are plotted as a function of 

filtration velocity in Figure 11. Note that the measured penetrations are similar at equivalent 

face velocities. Based on Figure 11, the filters exceed 0.03 percent penetration when the face 

velocity exceeds approximately 3.3 cm/sec. 

0.0001

0.001

0.01

0.1

1

0.1 1 10

Face Velocity (cm/s)

Penetration (%)

0.1 um - SEA P100

0.1 um - Survivair P100

Figure 11. Penetration of 0.1 μm Particles as Function of Face Velocity 

for SEA and Survivair® P100 Cartridge Filters 

 The effects of particle size and flow condition on measured penetrations through the 

North 7506 and MSA Flexi-Filter N95 cartridges are shown in Figures 12 through 15. Both 

filters efficiently removed particles greater than 1 μm as penetrations were less than 0.1 percent 

regardless of flow condition. As observed for the P100 cartridges, the penetration of submicron 

particles tended to increase with increased flow rate. For both N95 cartridge filters, the MPPS 

was approximately 0.05 μm and generally independent of flow rate. This MPPS was smaller as 
32 

compared to that observed for the P100 filters. This could be due to higher filtration velocities as 

compared to the P100 cartridges that contained pleated media. The estimated surface areas and 

corresponding face velocities at the three constant flow rates are compared in Table 7. Recall, 

the MPPS is expected to decrease as the face velocity increases. The smaller MPPS could also 

be attributed to differences in the media type (i.e., electrostatic property, fiber diameter, solidity, 

thickness). However, evaluation of these properties was beyond the scope of this effort. 

Penetrations of 0.02 and 0.05 μm particles through the North cartridge exceeded 10 percent at 

the highest flow conditions. Based on its small size and low surface area, it is not suitable for 

use under the high flow conditions evaluated in this study. 

0.0001

0.001

0.01

0.1

1

10

100

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

42.5 L/min

135 L/min

180 L/min

Figure 12. Effect of Particle Size and Constant Flow Rate on Measured 

Penetration through North 7506 N95 Cartridge 
33 

0.0001

0.001

0.01

0.1

1

10

100

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

20 L/min[MIF = 42.5 L/min]

42.5 L/min [PIF = 135 L/min]

57 L/min [PIF = 180L/min]

68 L/min [MIF = 135 L/min]

Figure 13. Effect of Particle Size and Cyclic Flow Rate on Measured 

Penetration through North 7506 N95 Cartridge 

0.0001

0.001

0.01

0.1

1

10

100

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

42.5 L/min

135 L/min

180 L/min

Figure 14. Effect of Particle Size and Constant Flow Rate on Measured 

Penetration through MSA Flexi-Filter N95 Cartridge
34 

0.001

0.01

0.1

1

10

100

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

20 L/min [MIF = 42.5 L/min]

42.5 L/min [PIF = 135 L/min]

57 L/min [PIF = 180 L/min]

68 L/min [MIF =135 L/min]

Figure 15. Effect of Particle Size and Cyclic Flow Rate on Measured Penetration 

through MSA Flexi-Filter N95 Cartridge 

Table 7. Comparison of Face Velocities for P100 and N95 Cartridges 

Flow Rate (L/min) 

42.5 135 180 

Filter 

Estimated 

Surface Area 

(cm2) Face Velocity (cm/s) 

SEA P100 1,000 0.7 2.2 2.9 

Survivair P100 400 1.7 5.5 7.3 

MSA N95 100 7.1 23 30 

North N95 50 14 45 60 

 As discussed above, the penetration through both the P100 and N95 cartridges tended to 

increase with increased flow rate. However, the magnitude of this increase was dependent on 

filter type and particle size. For example, Figure 16 compares the ratios of penetrations at 180 

and 135 L/min for each cartridge. For the P100, the largest increases were seen with the 0.02 μm 

particles. It should be noted that both P100 filters effectively filtered the 0.02 μm particles even 

at the highest flow rates as penetrations were less than the 0.03 percent requirement. In contrast, 

increases in penetration across the particle sizes shown was fairly uniform for the N95 filter but 

the highest increases in penetration were observed for the 0.3 μm particles. 
35 

0.1

1

10

100

0.01 0.1 1 10

Particle Size (μm)

Ratio (P180 L/min:P135 L/min)

SEA P100

Survivair P100

MSA N95

North N95

Figure 16. Comparison of Ratios of Penetrations Measured through P100 and N95 

Cartridges at 180 and 135 L/min 

 3.5.1.2 Filtering Facepieces. The effects of particle size and flow condition on 

measured penetration through the 3MTM P100 filtering facepiece are shown in Figures 17 and 18. 

Regressions were not provided due to the extremely poor fit to the data. The MPPS was 0.02 to 

0.05 μm. As seen with the cartridges, the 3M filter was very efficient against the 1.3 and 2.9 μm 

challenges as penetrations were less than 0.001 percent. The penetration of submicron particles 

was highly dependent on flow conditions. Similar trends were observed for the constant and 

cyclic flow conditions. Penetrations of 0.02 to 0.01 μm particles increased by more than an 

order of magnitude between the lowest and highest flow rates. 
36 

0.0001

0.001

0.01

0.1

1

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

85 L/min

270 L/min

360 L/min

Figure 17. Effect of Particle Size and Flow Rate on Measured Penetration 

through 3MTM P100 Filtering Facepiece at Constant Flow 

0.0001

0.001

0.01

0.1

1

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

40 L/min (cyclic) [MIF = 85

L/min. PIF = 130 L/min]

85 L/min (cyclic) [MIF = 175

L/min, PIF = 270 L/min]

115 L/min (cyclic) [MIF = 230

L/min, PIF = 360 L/min]

Figure 18. Effect of Particle Size and Flow Rate on Measured Penetration 

through 3MTM P100 Filtering Facepiece at Cyclic Flow 

 
37 

 The effects of particle size and flow condition on measured penetration through the 

Moldex® P100 filtering facepiece are shown in Figures 19 and 20. For the constant flow testing 

the penetrations increased more than an order-of-magnitude as the flow increased from 85 to 

270 L/min. Penetrations did not increase significantly when tested at 360 L/min. The MPPS at 

85 L/min was 0.05 μm and penetrations clearly declined as particle size increased or decreased. 

In fact, the penetrations measured between 0.05 and 0.3 μm particles varied by more than an 

order of magnitude. In comparison, the penetrations measured over the same particle size range 

at 270 and 360 L/min varied by less than a factor of two. 

0.0001

0.001

0.01

0.1

1

10

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

85 L/min

270 L/min

360 L/min

Figure 19. Effect of Particle Size and Flow Rate on Measured Penetration 

through Moldex P100 Filtering Facepiece at Constant Flow 
38 

0.0001

0.001

0.01

0.1

1

10

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

40 L/min [MIF = 85 L/min]

85 L/min [PIF = 270 L/min]

Figure 20. Effect of Particle Size and Flow Rate on Measured Penetration 

through Moldex P100 Filtering Facepiece at Cyclic Flow 

 

 The effects of particle size and flow conditions on measured penetrations through the 

Gerson® and MSA N95 filtering facepieces are shown in Figures 21 through 24. Penetrations of 

1.3 and 2.9 μm particles were less than 1 percent under all flow conditions. Penetration of 

submicron particles increased significantly between 85 and 270 L/min constant flow. The 

penetrations for each particle size at 270 and 360 L/min were similar. Penetrations of particles 

between 0.02 and 0.3 μm were greater than 5 percent at the highest flow conditions tested. 
39 

0.01

0.1

1

10

100

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

85 L/min

270 L/min

360 L/min

Figure 21. Effect of Particle Size and Flow Rate on Measured Penetration 

through Gerson® N95 Filtering Facepiece at Constant Flow 

0.01

0.1

1

10

100

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

40 L/min [MIF = 85 L/min]

85 L/min [PIF = 270 L/min]

115 L/min [PIF = 360 L/min]

Figure 22. Effect of Particle Size and Flow Rate on Measured Penetration 

 through Gerson® N95 Filtering Facepiece at Cyclic Flow 
40 

0.01

0.1

1

10

100

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

85 L/min

270 L/min

360 L/min

Figure 23. Effect of Particle Size and Flow Rate on Measured Penetration 

through MSA N95 Filtering Facepiece at Constant Flow 

0.01

0.1

1

10

100

0.01 0.1 1 10

Particle Size (μm)

Penetration (%)

40 L/min [MIF = 85 L/min]

85 L/min [PIF = 270 L/min]

115 L/min [PIF = 360 L/min]

Figure 24. Effect of Particle Size and Flow Rate on Measured Penetration 

through MSA N95 Filtering Facepiece at Cyclic Flow 

 

 
41 

3.5.2 Constant/Cyclic Flow Comparisons 

An important aspect of this task was to compare penetrations measured under constant 

and cyclic flow conditions. NIOSH certification testing of particulate filters is performed at a 

constant flow rate of 85 L/min (42 CFR 84, 1995) to demonstrate that filters meet a minimum 

requirement under controlled laboratory conditions. However, measurements of physiological 

parameters of workers show peak inhalation flow rates in excess of 300 L/min for short durations 

during high work load activities (Caretti et al., 2004; Kaufman and Hastings, 2005). As 

described in Section 2.1, few studies have been completed to correlate performance measured 

under constant and cyclic flow. Thus, there is concern that current certification test flow 

conditions may underestimate performance under actual use conditions. 

The cyclic and constant flow conditions for this task were selected to allow comparisons 

based on cyclic flow: (1) minute volume, (2) MIF, and (3) PIF. Recall, the MIF is the average 

flow rate over the inhalation portion of the breathing cycle and the PIF is the maximum flow rate 

obtained. The flow conditions used to make these comparisons where noted in Table 3. For 

example, the 85 L/min constant flow matches a cyclic flow minute volume (2.3 L tidal volume, 

37 breaths/min) and a MIF (1.6 L tidal volume, 25 breaths/min). 

 Figure 25 compares the penetrations measured under 85 L/min cyclic (based on minute 

volume) and constant flows. Although not explicitly shown, the data points correspond to the 

measured penetrations over the range of particle sizes tested (i.e., 0.02 to 2.9 μm). The black 

line is the 1-to-1 line and represents perfect agreement between the penetrations measured under 

the different flow conditions. The red and blue solid lines represent the best fit regressions of the 

cartridge and filtering facepiece data, respectively. The dashed lines represent 95 percent 

confidence intervals. The regression lines are both above the 1-to-1 line by a factor of 5 to 10 

indicating higher penetrations were measured under cyclic flow for a given minute volume or 

constant flow of 85 L/min. The regressions for the cartridges and filtering facepieces were nearly 

identical indicating that the trend is not dependent on filter type (i.e., cartridge versus filtering 

facepiece). Higher penetrations under cyclic flow were expected and are in agreement with the 

literature (Brosseau et al., 1990). For the sinusoidal flow used in this task (2.3 L and 37 

breaths/min), over 95 percent of the inhalation volume passes through the filter at a rate in excess 
42 

of the minute volume. The peak flow reaches 270 L/min. As discussed above, penetration tends 

to increase with increased flow rate. 

Constant Flow

Average Penetration (%)

0.0001 0.001 0.01 0.1 1 10 100

Cyclic Flow

Average Penetration (%)

0.0001

0.001

0.01

0.1

1

10

100

Cartridge Data

Cartridge Regression

95% Confidence Interval

1:1 Line

Filtering Facepiece Data

Filtering Facepiece Regression

95% Confidence Interval

Figure 25. Comparison of Measured Penetrations under Cyclic and Constant Flow 

Conditions with Minute Volumes of 85 L/min 

 Figure 26 and 27 compare the measured penetrations under constant flow with those 

measured under cyclic flow with an equivalent MIF or PIF for the cartridges and filtering 

facepieces, respectively. The trends were nearly identical for both filter types. The MIF data 

points tend to lie above the 1-to-1 line indicating the penetrations measured under constant flow 

equivalent to the MIF were lower (40 percent lower on average) than the corresponding cyclic 

flow penetration. The converse was observed for the PIF comparison indicating that testing at a 

constant flow equivalent to the PIF provides a conservative estimate of filter performance under 

cyclic flow. The regression line for the PIF comparison nears the 1-to-1 line at the higher 

penetrations (>1%) where the data is for the N95 filters. Thus, it may be more important to 

consider the PIF when testing N95 filters, especially at the high volumetric flow rates that can be 

experienced during heavy work loads. As stated earlier, the N95 cartridges and both types of 

filtering facepieces are not well-suited for the high flow rates due their lower surface area as 

compared to the P100 cartridge filters evaluated in this study. A similar plot containing only 

P100 cartridge data is provided in Figure 28. Good agreement (within a factor of two) is 

observed between the constant flow penetrations and those measured at a cyclic flow with an 
43 

equivalent MIF. A method to estimate the cyclic flow penetration based on measured constant 

flow is provided in Appendix F. Good agreement is shown between the predicted and measured 

cyclic flow penetrations from this study. 

Constant Flow

Average Penetration (%)

0.0001 0.001 0.01 0.1 1 10 100

Cyclic Flow

Average Penetration (%)

0.0001

0.001

0.01

0.1

1

10

100

MIF Regression

95% Confidence Interval

PIF Regression

95% Confidence Interval

North N95 [MIF] 

MSA N95 [MIF] 

SEA P100 [MIF] 

Survivair P100 [MIF] 

North N95 [PIF] 

MSA N95 [PIF] 

SEA P100 [PIF] 

Survivair P100 [PIF] 

: log [ ] 1.1 log [ ] 0.15; 0.985

: log [ ] 0.98 log [ ] 0.20; 0.964

2

10 10

2

10 10

= × − =

= × + =

PIF P P r

MIF P P r

Cyclic Const

Cyclic Const

Figure 26. Comparison of Penetrations Measured under Constant and Cyclic Flow 

Conditions for Cartridge Filters 

Constant Flow

Average Penetration (%)

0.0001 0.001 0.01 0.1 1 10 100

Cyclic Flow

Average Penetration (%)

0.0001

0.001

0.01

0.1

1

10

100

MIF Regression

95% Confidence Interval

PIF Regression

95% Confidence Interval

MSA N95 [MIF]

Gerson N95 [MIF] 

3M P100 [MIF] 

Moldex P100 [MIF] 

MSA N95 [PIF]

Gerson N95 [PIF]

3M P100 [PIF]

Moldex P100 [PIF] 

:log [ ] 1.2 log [ ] 0.10; 0.947

:log [ ] 0.95 log [ ] 0.17; 0.944

2

10 10

2

10 10

= × − =

= × + =

PIF P P r

MIF P P r

Cyclic Const

Cyclic Const

Figure 27. Comparison of Penetrations Measured under Constant and Cyclic Flow 

Conditions for Filtering Facepieces
44 

Constant Flow

Average Penetration (%)

0.0001 0.001 0.01 0.1 1

Cyclic Flow

Average Penetration (%)

0.0001

0.001

0.01

0.1

1

MIF Regression

95% Confidence Interval

PIF Regression

95% Confidence Interval

SEA P100 [MIF] 

Survivair P100 [MIF] 

SEA P100 [PIF] 

Survivair P100 [PIF] 

: log [ ] 0.96 log [ ] 0.42; 0.947

: log [ ] 0.96 log [ ] 0.04; 0.923

2

10 10

2

10 10

= × − =

= × + =

PIF P P r

MIF P P r

Cyclic Const

Cyclic Const

Figure 28. Comparison of Penetrations Measured under Constant and Cyclic Flow 

Conditions for P100 Cartridge Filters 

3.6 Inert Aerosol Testing Summary

 Filter efficiency testing was completed to assess the effect of particle size and flow 

condition on measured penetration. The following trends were observed: 

• Penetration of submicron particles tended to increase with increased volumetric flow 

rate. The magnitude of increase was dependent on the filter type and particle size. 

• The MPPS for P100 cartridges was generally between 0.1 to 0.2 μm and shifted toward 

the lower end of this range with increased flow. 

• The MPPS for the N95 cartridges was generally 0.05 to 0.1 μm for all flow conditions. 

• The MPPS for both P100 and N95 filtering facepieces was 0.05 to 0.1 μm. 

• All filters efficiently removed the 0.7, 1.3, and 2.9 μm particles. Penetrations through 

P100 and N95 filters were less than 0.03 and 5 percent respectively, at all flow 

conditions and, thus, met the NIOSH requirement. 

• Penetrations of submicron particles were in excess of the NIOSH requirements under 

the high flow conditions for all filters except the SEA HE-T P100 cartridge. The 
45 

Assigned Protection Factor (APF) of the mask and workplace breathing rates must be 

taken into account to determine if the increase in penetration is significant. 

 The following trends were observed regarding the comparison of penetrations measured 

under constant and cyclic flow conditions: 

• Higher penetrations were measured under cyclic flow conditions as compared to a 

constant flow with an equivalent minute volume. 

• Testing at a constant flow equivalent to the cyclic flow PIF provided a conservative 

estimate of filter performance under cyclic conditions. 

• For the P100 cartridges, penetrations measured under constant flow and cyclic flow 

with an equivalent MIF were within a factor of two. 

4.0 BIOAEROSOL FILTRATION EFFICIENCY TESTING

 NIOSH-approved N, R, and P series particulate respirator filters have been shown to be 

effective against inert test aerosols in the most penetrating size range. However, it has not been 

well established that these filters provide comparable protection against biological aerosols 

especially with regard to high breather flow rates. This section describes the test methods and 

matrices that were used to characterize the performance of NIOSH-approved N95 and P100 

filters using bacterial and viral aerosols under high breathing flows. The flow conditions and 

filter types were the same as described in Section 3.0 to allow direct comparison to the inert 

aerosol results. The two primary objectives were to: (1) assess respirator performance against 

bioaerosols, both bacterial and viral, under high flow conditions and (2) compare the measured 

aerosol penetrations to those of the inert aerosols. 

4.1 Test Parameters 

 The filters tested included two N95 filtering facepieces, two P100 filtering facepieces, 

two N95 cartridges, and two P100 cartridges. They were the same brands and models as 

described in Table 2 of Section 3.1 and once again the exhalation valves were not sealed. The 

environmental conditions during testing were maintained at ambient temperature (25 ± 3°C) and 
46 

relative humidity (40 ± 10%). The filters were not preconditioned prior to testing (i.e., tested asreceived). Tests were performed at two cyclic and two constant flow rates. The cyclic flow 

conditions had minute volumes of 85 and 135 L/min. Refer to Table 4 for the tidal volumes and 

breathing rates. The constant flow rates were 85 and 270 L/min. The 85 L/min was selected as 

it is the NIOSH certification flow rate. The 270 L/min provided an equivalent PIF and MIF to 

the cyclic flow conditions. Again, cartridges were tested at half the flow rate. 

 The biological aerosols consisted of bacterial Bg spores and viral MS2 phage. Both 

were generated using two different methods referred to as "wet" and "dry". Wet denotes 

dispersion of organisms in an effort such that the primary organism is achieved from a liquid 

suspension using a nebulizer. Dry denotes generation from a powder with a special carrier 

material or as agglomerates. Preparation and aerosol generation methods are described in 

Section 4.3. Bg spores were selected as the test aerosol due to their robustness. Thus, they have 

a high probability of remaining viable during the test. Bg spores are also a simulant commonly 

used for anthrax spores. Bg spores are rod-shaped with an approximate diameter of 0.7 to 0.8 

μm and a length of 1.5 to 1.8 μm (Johnson et al., 1994). The aerodynamic diameter is typically 

0.8 to 1.0 μm when suspended in water and aerosolized using a collison nebulizer (McCullough 

et al., 1997; Hanley and Foarde, 2003; Hofacre and Forney, 1996). 

 MS2 was selected as a representative viral aerosol as its viability after aerosolization 

has been demonstrated in a previous study (Hofacre et al., 1996). Viruses range in size from 

0.02 to 0.3 μm and are generally found airborne as part of a droplet nuclei or attached to inert 

particles (Hinds, 1999). MS2 phage is icosahedron-shaped measuring approximately 20 nm in 

diameter. It is a bacteriophage that replicates inside host E. coli cells. Bacteriophages are nonpathogenic to humans and thus are safe to use for testing with limited engineering controls. As 

described earlier, Hofacre et al. (1996) aerosolized MS2 phage using a three-jet Collison 

nebulizer and measured the particle size distribution using a high-sensitivity laser aerosol 

spectrometer (HS-LAS, Particle Measuring Systems, Boulder, CO). The MS2 was present over 

a wide range of particle sizes likely as aggregates. The number distribution mode was 

approximately 0.1 μm and the mass distribution mode was 0.3 to 0.4 μm. 

 The bioaerosol challenge concentration was dependent on the target particle size and 

generation method. During characterization, suitable operating parameters were determined to 

permit measurement of aerosol penetrations of at least 0.03 percent, the NIOSH P100 
47 

requirement. Estimates of the minimum measurable penetration were made based on the 

challenge concentration, downstream sampling duration, and minimum detection limit of the 

aerosol sensing instrument. The minimum measurable penetration was generally 0.003, an 

order-of-magnitude lower than the NIOSH P100 requirement. 

4.2 Test Matrix 

 The test matrices completed with the bioaerosol challenges are provided in Tables 8 

and 9 for cyclic and constant flows, respectively. Three replicates were completed for each cell 

in the test matrix with the exception of the MS2 "dry" testing where only two replicates were 

performed due to the high efficiency of the filters. Each test included measurement of the 

aerosol penetration using both a bioassay method for viable organisms and an aerosol sensing 

instrument to measure total particle penetration. 

Table 8. Test Matrix Completed to Assess Filter Performance under 

Cyclic Flow Conditions Using a Bioaerosol Challenge 

Minute Filtering Facepiece Cartridges 

Volume 

(L/min) 

Challenge 

Aerosol 

MSA 

N95 

Gerson 

N95 

3M 

P100 

Moldex 

P100 

North 

N95 

MSA 

N95 

SEA 

P100 

Survivair 

P100 

Bg "wet" 3 3 3 3 3 3 3 3 

Bg "dry" 3 3 3 3 3 3 3 3 

MS2 "wet" 3 3 3 3 3 3 3 3 85(a)

MS2 "dry" 2 2 2 2 2 2 2 2

Bg "wet" 3 3 3 3 3 3 3 3 

Bg "dry" 3 3 3 3 3 3 3 3 

MS2 "wet" 3 3 3 3 3 3 3 3 135(a)

MS2 "dry" 2 2 2 2 2 2 2 2

(a) Cartridges were tested at half the minute volume. 

Table 9. Test Matrix Completed to Assess Filter Performance under 

Constant Flow Using a Bioaerosol Challenge 

Flow Filtering Facepiece Cartridges 

Rate 

(L/min) 

Challenge 

Aerosol 

MSA 

N95 

Gerson 

N95 

3M 

P100 

Moldex 

P100 

North 

N95 

MSA 

N95 

SEA 

P100 

Survivair 

P100 

Bg "wet" 3 3 3 3 3 3 3 3 

Bg "dry" 3 3 3 3 3 3 3 3 

MS2 "wet" 3 3 3 3 3 3 3 3 85(a)

MS2 "dry" 2 2 2 2 2 2 2 2

Bg "wet" 3 3 3 3 3 3 3 3 

Bg "dry" 3 3 3 3 3 3 3 3 

MS2 "wet" 3 3 3 3 3 3 3 3 270(a)

MS2 "dry" 2 2 2 2 2 2 2 2

(a) Cartrdiges were tested at half the flow rate. 
48 

4.3 Technical Approach 

4.3.1 Test System 

 The test system used for biological testing was very similar to that used at ECBC for the 

inert testing with the large particle challenges (i.e., 0.7 to 2.9 μm). The test system, illustrated in 

Figure 29 for generating with a nebulizer, included an aerosol generator, exposure chamber with 

filter holder, aerosol classifier/sampler, and breathing machine. The aerosol generation and 

sampling systems varied depending on the biological aerosol being generated and are described 

in Sections 4.3.2 and 4.3.3. 

Figure 29. Schematic of Test System Used to Measure Bioaerosol Penetration 

The aerosol generation systems delivered a continuous flow of aerosol laden air to the 

chamber to ensure a fresh, stable challenge aerosol was maintained. The challenge laden air 

exiting the generator was mixed with HEPA filtered dilution air. When generating from a liquid 
49 

solution, this mixing promoted the drying of the aerosol. The aerosol was then passed through a 

charge neutralizer (Model 3012, TSI, Shoreview, MN) and introduced into the test chamber 

where it was dispersed by small mixing fans. Excess challenge was vented through a HEPA 

filter and exhausted into the hood. The HEPA filters also allowed additional dilution air to be 

pulled into the chamber upon demand. The mask filter (filtering facepiece or cartridge) was 

mounted onto a holder and sealed inside the chamber. The holder was connected to the 

breathing machine (cyclic flow) or vacuum pump (constant flow) by flexible tubing. Similar to 

the approach used at ECBC for the inert testing, the downstream aerosol was sampled from a 

small chamber equipped with a stainless steel sample probe. The downstream chamber was also 

fitted with a port for sampling with the aerosol sensing instruments. 

4.3.2 Bioerosol Generation Methods 

 Biological aerosols were generated using two different methods: (1) from an aqueous 

solution and (2) from a dry powder. This section describes both of these aerosol generation 

methods. For details regarding the preparation of the Bg spores and MS2 phage, refer to 

Appendix G. 

4.3.2.1 Wet. The aerosol generation system for the wet technique consisted of a 

nebulizer, dryer, and charge neutralizer. The Bg spores or MS2 were suspended in filtered, 

deionized water and aerosolized using a 24-jet Collison nebulizer. Typical suspension 

concentrations were 1 x 108

 colony forming units (cfu)/ml for the Bg spores and 1 x 1011 plaque 

forming units (pfu)/ml for MS2 phage. The aerosol was diluted with filtered house air and then 

pass through a Kr-85 charge neutralizer (Model 3012, TSI, Shoreview, MN) prior to delivery to 

the test chamber. Typical viable challenge concentrations were 1 x 105

 cfu or pfu/L air. The 

charge neutralizer had to be removed from the test system when challenged with MS2 "wet" to 

obtain the target concentration. 

4.3.2.2 Dry. The preparation of the dry powders is described in Appendix G. The dry 

powders were aerosolized using the Vilnius Aerosol Generator (VAG, CH Technologies, 

Westwood, NJ) shown in Figure 30. The VAG consists of three primary components: 
50 

(1) disperser, (2) aerosol monitor, and (3) output controller. The dry powder is placed on a 

membrane in the aerosolization chamber. Compressed air is used to vibrate the membrane to 

aerosolize the powder and also activate a rotary turbovane which deaglommerates the particles. 

The aerosolization chamber and turbovane are shown in Figure 31. The Microdust 880 (Casella, 

Bedford, UK) is used to continuously monitor the aerosol output. The controller processes the 

signal from the Microdust 880 and adjusts the frequency of vibration to maintain a steady aerosol 

output. Typical viable aerosol concentrations were generally 1 x 104

 to 1 x 105 cfu or pfu/L air. 

Figure 30. Vilnius Aerosol Generator 
51 

Figure 31. Aerosolization Chamber and Rotary Vane of Vilnius Aerosol Generator 

4.3.3 Aerosol Sampling and Classification

Samples to assess penetration of viable organisms were collected on 47-mm filters as 

described in Section 4.3.3.1. In addition, two types of light scattering instruments, described in 

Section 4.3.3.2 were used to measure total-particle efficiencies. 

 4.3.3.1 Viable Samples. Viable samples were collected on 47-mm filters for 

subsequent bioassay. Bg spores were collected on mixed cellulose ester filters and the MS2 

phage was collected on water soluble gelatin filters. The mixed cellulose ester filters were not 

used with the MS2 due to poor collection efficiency at the smaller particle size. The challenge 

sample was collected through a sampling probe that extended away from the chamber wall. The 

47-mm filter was housed in a 47 mm filter holder and a sample pump was used to pull 4 L/min 

through the filter. A critical orifice was used to control the flow rate. The filters were analyzed 

as described in Appendix G to determine the number of colony forming units (cfu) or plaque 

forming units (pfu) per liter of air sampled. 

 
52 

4.3.3.2 Optical Particle Counters. The Aerosizer® (Amherst Proscess Instruments, 

Hadley, MA) classifies particles based on their aerodynamic behavior. The instrument measures 

the time-of-flight as particles are accelerated through the sensing zone of the instrument. The 

time-of-flight is proportional to particle size and density. The density of the aerosol material is 

used to determine the particle size distribution either on a number, surface, or volume (mass) 

basis. The Aerosizer® can classify particles ranging from 0.5 to 200 μm. Data reducing software 

that accompanies the instrument permits user selected size ranges to be analyzed. Thus, 

polydisperse aerosols could be analyzed within a selected size range. The sample flow rate is 

1.5 L/min. 

 The laser aerosol spectrometer (LAS-X, Particle Measuring Systems, Boulder, CO) is a 

laser aerosol spectrometer capable of classifying particles between 0.1 and 3.0 μm in diameter 

into 16 size discrete bins. The LAS provides a measure of the particle size based on the light 

scattering properties of the aerosol. Particles are focused into the sensing region by the 

pneumatic system such that particles pass through one at a time. The light from the He-Ne laser 

is scattered by the particle, which is then collected by receiving optics. The signal intensity 

produced is proportional to the particle size and the number of signals is a measure of the 

number of particles counted. Thus, the LAS gives a number distribution of the aerosol and size 

specific channels of interest which can be selected for data analysis. The sample flow rate is 

approximately 100 cm3

/min. 

4.3.3.3. Cascade Impactor. A cascade impactor (Model 266 Marple Impactor, Sierra 

Instruments, Carmel Valley, CA) was used to characterize the aerodynamic particle size 

distribution of the viable biological aerosols. The impactor was operated at 2.4 L/min. Particles 

of sufficient size and inertia cross the flow streamline and are impacted on slides and collected. 

Smaller particles are able to remain in the flow streamlines and pass on to the next stage. Each 

stage has an associated diameter cut-point equivalent to particle size (diameter). A calculation of 

the loaded mass of the impactor slide and the volumetric flow rate, in conjunction with volumedensity relationship, reveals the number of particles with a given size bin. Characteristics of the 

impactor are listed in Table 10 with ranges of aerodynamic particle diameters highlighted. The 

number of viable particles collected on each stage was determined by bioassay. 
53 

Table 10. Particle Size Range Six-Stage Cascade Impactor 

Impactor Stage Aerodynamic Diameter Range (μm) 

Backup filter d ≤ 0.29 

Stage 1R 0.29 < d ≤ 0.78 

Stage 6 0.78 < d ≤ 1.5 

Stage 5 1.5 < d ≤ 3.2 

Stage 4 3.2 < d ≤ 6.8 

Stage 3 6.8 < d ≤ 12 

Stage 2 12 < d ≤ 19 

Stage 1 d > 19 

4.3.4 System Characterization 

 Prior to efficiency testing, shakedown testing was performed to establish proper 

operating conditions. This included comparison of the Battelle and ECBC test systems, 

characterization of the aerosol generators, measurement of bioaerosol particle size distributions, 

and characterization of the viable particle samplers. The shakedown testing is described in 

Appendix H. 

4.3.5 Test Procedure 

 The mask filter was mounted to the test fixture and the exposure chamber sealed. The 

breathing machine and bioaerosol generation system were started and allowed to operate for 

approximately 10 minutes to reach a steady state challenge concentration. The mask filter and 

downstream bioaerosol sampler were bypassed during system startup. After approximately 10 

minutes, sampling with the viable particle samplers began by directing the flow through the 

mask filter. The upstream and downstream 47-mm filters were collected simultaneously. 

Sample duration depended on the expected aerosol concentration and was typically 2 minutes for 

the challenge aerosol and 10 minutes for the downstream. Two sets of 47 mm filters were 

collected in sequence. The average measured concentrations were used to determine the 

penetration. 

 Sampling with the HS-LAS or Aerosizer® was performed simultaneously with the 

viable particle samplers. First, the challenge was sampled for approximately two minutes. The 

sampling line was then switched to downstream of the filter and adequate time was given for the 
54 

instrument response to stabilize. The downstream sample duration ranged from five to fifteen 

minutes to provide sufficient time to count a statistically significant number of particles. A 

second sample of the challenge was then recorded. If the two challenge samples (before and 

after downstream sampling) were not within 20 percent of each other, the test was repeated. 

After sampling was complete, the aerosol generation system was stopped and the chamber 

flushed with clean air. The viable particle samplers were removed from the test system for 

analysis. 

4.4 Calculation of Aerosol Penetration 

 The aerosol penetration was defined in Section 3.4 for the inert aerosols. Efficiencies 

were measured based on both total and viable particle concentrations. For the total particle 

analyzers, the size specific channels of interest were selected for the analysis. The challenge 

concentration was the average of the measurements made before and after the downstream 

sample. The aerosol number concentration used was determined by summing the number of 

particles in the selected size range and dividing by the volume of air sampled (product of 

sampling flow rate and sampling duration). The viable particle concentration was determined 

from the bioassay of the 47-mm filters. Two upstream and two downstream samples were 

collected during each test. The number of particles, after correcting for dilution factors during 

bioassay, was divided by the volume of air sampled to obtain the number concentration. The 

average values were used to calculate the penetration. 

 As described in Section 4.1, the challenge concentration was maintained at a level to 

measure penetrations of at least 0.03 percent. Minimum detection limits were established for 

both the Bg spore and MS2 phage enumeration methods. The limits were 2 cfu or pfu/L air 

sampled. The typical challenge concentration for the Bg spore testing was 1 x 105

 cfu/L 

resulting in a minimum measurable penetration of 0.002 percent. Likewise, depending on flow 

condition, the challenge concentration of MS2 phage ranged between 1 x 104

 and 1 x105 leading 

to minimum penetrations of 0.02 to 0.002 percent. The actual minimum penetration varied from 

trial to trial depending on the measured challenge concentration. 
55 

4.5 Bioaerosol Results 

 This section summarizes the results of testing with biological aerosols. Section 4.5.1 

discusses the measured Bg spore particle size distributions and the measured penetrations. A 

similar discussion follows in Section 4.5.2 for the MS2 phage. Section 4.5.3 compares the 

penetrations measured using the biological aerosols to those measured with the inert aerosols. 

4.5.1 Bg Spore Results 

 4.5.1.1. Particle Size Distribution. The aerosol size distributions of the Bg spores 

generated using the "wet" and "dry" methods were characterized using the cascade impactor and 

Aerosizer. The results are summarized in Table 11 and are compared graphically in Figures 32 

through 34 as measured by the impactor and Aerosizer. Note that the lower limit for the 

Aerosizer is 0.5 μm. Both instruments indicated that aerosolization from the dry powder led to a 

slightly larger median diameter and broader distribution. The particle size distributions were 

consistent with the literature which indicated an aerodynamic diameter ranging from 0.8 to 1.0 

μm (McCullough et al., 1997; Hanley and Foarde, 2003; Hofacre and Forney, 1996). 

Table 11. Comparison of "Wet" and "Dry" Bg Size Distributions 

Generation Aerosizer Impactor 

Method NMD (μm) σg

(a) AMMD (μm) σg

Bg "wet" 1.1 1.1 0.7 2.5 

Bg "dry" 1.3 1.6 0.9 2.7 

(a) σg = Geometric standard deviation.
56 

Aerodynamic Diameter, μm

0.5 1 2 3 4 5 6 7 8 910 20

Probability

1

10

16

50

84

90

99

70

95

30

5 Bg "Wet"

Bg "Wet" Regression

Bg "Dry"

Bg "Dry" Regression

Figure 32. Size Distribution of "Wet" and "Dry" Bg Spores Measured 

Using the Cascade Impactor 

0

500

1000

1500

2000

2500

3000

3500

4000

0.1 1 10

Particle Diameter (um)

Number Concentration (#/cc)

Bg (Wet)

Bg (Dry)

Figure 33. Size Distribution of Bg Spores Measured Using the Aerosizer 
57 

Aerodynamic Diameter, μm

0.5 1 2 3 4 5 6 7 8 9 10

Probability

1

10

16

50

84

90

99

70

95

30

5

Bg "wet" 

Bg "dry" 

Figure 34. Size Distribution of Bg Spores Measured Using the Aerosizer 

(Cumulative Number Distribution) 

4.5.1.2 Bioassay Penetration Results. The penetrations measured using the Bg spore 

aerosol challenge and bioassay method are summarized in Tables 12 and 13 for the "wet" and 

"dry" generation techniques. The penetrations generally represent the average of at least three 

trials. Average penetrations with at least one trial below the minimum detection limit (~0.002%) 

are noted and standard deviations are not provided. The results from the individual trials are 

summarized in Appendix I. Both the P100 cartridges and filtering facepieces were very efficient 

against the Bg spore challenge as all penetrations were less than the 0.03 percent requirement, 

generally by at least an order-of-magnitude. The N95 filters were less efficient as compared to 

the P100 filters but still had penetrations generally less than 0.5 percent. As shown in Figures 35 

and 36, the penetrations increased with increased flow rate with exception of the MSA Affinity 

Plus® filtering facepiece and the "wet" Bg challenge. The cause of this anomaly was not 

identified and repeated tests provided similar results. This trend was not observed for the Bg 

"dry" aerosol. 
58 

Table 12. Comparison of Penetration Measured Using Bioassay Method and Bg Spore 

"Wet" Aerosol Challenge under Constant and Cyclic Flow Conditions 

Flow Rate(a) (L/min) 

Constant Cyclic 

85 270 85 135 Filter Type Filter 

Average Penetration (%) 

MSA N95 0.002(b) 0.005±0.001 0.003(b) 0.034±0.041 

North N95 0.005 0.009(b) 0.006±0.004 0.014±0.007 

Survivair® P100 0.003(b) 0.004(b) 0.001(b) 0.006 Cartridge (b)

SEA P100 0.004(b) 0.004(b) 0.002(b) 0.002(b)

MSA N95 0.13±0.12 0.13±0.10 0.35±0.18 0.047±0.024 

Gerson® N95 0.036±0.23 0.40±0.18 0.21±0.08 0.26±0.07 

3M® P100 0.003(b) 0.010(b) 0.005(b) 0.005(b)

Filtering 

Facepiece 

Moldex P100 0.023(b) 0.012(b) 0.006±0.002 0.009±0.002 

(a) Cartridge testing performed at half the flow rate 

(b) At least one trial resulted in penetration below detectable limit 

Table 13. Comparison of Penetration Measured Using Bioassay Method and Bg Spore 

"Dry" Aerosol Challenge under Constant and Cyclic Flow Conditions 

Flow Rate(a) (L/min) 

Constant Cyclic 

85 270 85 135 Filter Type Filter 

Average Penetration (%) 

MSA N95 0.005(b) 0.014±0.004 0.013±0.002 0.030±0.011 

North N95 0.006±0.005 0.074±0.075 0.055±0.047 0.032±0.001 

Survivair® P100 0.003(b) 0.030(b) 0.002(b) 0.003 Cartridge (b)

SEA P100 0.001(b) 0.003(b) 0.003(b) 0.002(b)

MSA N95 0.035±0.030 0.042±0.016 0.13±0.048 0.64±0.59 

Gerson® N95 0.028±0.007 0.20±0.064 0.20±0.14 2.4±2.5 

3M® P100 0.008(b) 0.03(b) 0.001(b) 0.003(b)

Filtering 

Facepiece 

Moldex P100 0.017±0.015 0.004(b) 0.003(b) 0.003(b)

(a) Cartridge testing performed at half flow rate 

(b) At least one trial resulted in penetration below detectable limit 
59 

0.001

0.01

0.1

1

10

MSA Flexi-Filter

(Cartridge)

North 7506

(Cartridge)

MSA Affinity Plus

(Filtering

Facepiece)

Gerson 1730

(Filtering

Facepiece)

Penetration (%)

85 L/min (constant)

270 L/min (constant)

85 L/min (cyclic)

135 L/min (cyclic)

Figure 35. Comparison of Measured Bg "Wet" Penetrations through N95 Filters 

0.001

0.01

0.1

1

10

MSA Flexi-Filter

(Cartridge)

North 7506

(Cartridge)

MSA Affinity Plus

(Filtering

Facepiece)

Gerson 1730

(Filtering

Facepiece)

Penetration (%)

85 L/min (constant)

270 L/min (constant)

85 L/min (cyclic)

135 L/min (cyclic)

Figure 36. Comparison of Measured Bg "Dry" Penetrations through N95 Filters 

 The penetrations measured using the "wet" and "dry" Bg challenges with the bioassay 

method are compared in Figures 37 and 38 for the cartridges and filtering facepieces, 

respectively. The black diagonal line is the 1-to-1 line and represents perfect agreement. The 
60 

error bars represent one standard deviation about the mean. In general, the penetrations 

measured with each challenge for each filter were within a factor of four. From a practical 

perspective, the differences in the penetrations were not significant. 

0.0001

0.001

0.01

0.1

1

10

0.0001 0.001 0.01 0.1 1 10

Bg "Wet" Penetration (%)

Bg "Dry" Penetration (%)

MSA N95

North N95

SEA P100

Survivair P100

Figure 37. Comparison of Bg "Wet" and "Dry" Penetrations through Cartridge Filters

0.0001

0.001

0.01

0.1

1

10

0.0001 0.001 0.01 0.1 1 10

Bg "Wet" Penetration (%)

Bg "Dry" Penetration (%)

Gerson N95

MSA N95

Moldex P100

3M P100

Figure 38. Comparison of Bg "Wet" and "Dry" Penetrations through Filtering Facepieces 
61 

 Figure 39 compares the penetrations measured using the bioassay method with that 

using the LAS-X. Again, the black diagonal line represents the 1-to-1 line. During each trial, 

the penetration was measured using both techniques creating paired data. For the LAS-X, the 

penetration was calculated based on size specific channels ranging from 0.65 to 1.25 μm 

(Channels 9, 10, and 11). The results from each trial are plotted in Figure 39. Higher 

penetrations tended to be measured using the LAS as compared to the bioassay method as 

evidenced by the majority of the data points lying below the 1-to-1 line. This is likely because 

the LAS measured total particle penetration while the bioassay method measured only the viable 

particle penetration. These results demonstrate that using an optical light scattering instrument 

such as the LAS to measure bacterial aerosol penetration provides a conservative estimate of 

filter performance. This conclusion is consistent with the literature (Brosseau et al., 1994) and is 

notable since the LAS-X method is much less labor intensive compared to the bioassay method. 

Penetration, LAS-X (%)

0.0001 0.001 0.01 0.1 1

Penetration, Bioassay (%)

0.0001

0.001

0.01

0.1

1

"Wet" Bg Cartridges

"Wet" Bg Filtering Facepieces

"Dry" Bg Cartrdiges

"Dry" Bg Filtering Facepieces

Figure 39. Comparison of Bg Spore Penetrations Measured Using the Bioassay 

Method and LAS-X 
62 

4.5.2 MS2 Phage Results 

 4.5.2.1. Particle Size Distribution. The aerosol size distributions of the MS2 phage 

generated using the "wet" and "dry" aerosolization methods were characterized using the cascade 

impactor, LAS, and Aerosizer. The results are summarized in Table 14 and are compared 

graphically in Figures 40 through 42. Note that the lower limit for the Aerosizer is 0.5 μm and 

the LAS is 0.1 μm. 

Table 14. Comparison of "Wet" and "Dry" MS2 Aerosol Size Distributions 

Generation LAS/Aerosizer Impactor 

Method NMD (μm) σg AMMD (μm) σg

MS2 "wet" 0.2(a) 1.4 0.5 1.3 

MS2 "dry" 2.3(b) 1.3 2.5 2.0 

(a) Size distribution measured using LAS-X only. 

(b) Size distribution measured using Aerosizer only. 

Aerodynamic Diameter, μm

0.5 1 2 3 4 5 6 7 8 910 20

Probability

1

10

16

50

84

90

99

70

95

30

5

Figure 40. Size Distribution of MS2 "Wet" Measured Using the Sierra Impactor
63 

Figure 41. Size Distribution of MS2 "Wet" Measured Using the LAS-X

Aerodynamic Diameter, μm

0.5 1 2 3 4 5 6 7 8 910 20

Probability

1

10

16

50

84

90

99

70

95

30

5

Cascade Impactor

Aerosizer

Figure 42. Size Distribution of MS2 "Dry" Measured Using the Sierra 

Impactor and Aerosizer

 4.5.2.2 MS2 Penetration Results. The penetrations measured using the MS2 phage 

aerosol challenge and bioassay method are summarized in Tables 15 and 16 for the "wet" and 

"dry" aerosol generation techniques. The results from the individual trials are summarized in 

Appendix I. The P100 and N95 filters both met their respective penetration requirements 

(i.e., maximum 0.03 and 5 percent penetration) at all flow conditions tested. This is significant 

because the MS2 "wet" aerosol is near the MPPS for both types of filters. As shown in Figure 

43, mean penetration of the "wet" MS2 aerosol tended to increase with increased flow rate. All 

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2

Particle Diameter (μm)

Δni/nTΔlog di
64 

filters were highly efficient at removing the MS2 "dry" aerosol challenge as expected since it had 

a count median diameter above 1 μm. Flow rate did not have as significant an effect on MS2 

“dry” aerosol penetrations as with the smaller MS2 "wet" as shown in Figure 44. The P100 

filters are not included in Figures 43 and 44 as the measured penetrations were generally below 

detectable limits. Assuming that inertial impaction is the primary mechanism for collection of 

the MS2 "dry" aerosol, penetration would not be expected to change significantly with increased 

flow. 

Table 15. Comparison of Penetration Measured Using Bioassay Method and MS2 "Wet" 

Aerosol Challenge under Constant and Cyclic Flow Conditions 

Flow Rate(a) (L/min) 

Constant Cyclic 

85 270 85 135 Filter Type Filter 

Average Penetration (%) 

MSA N95 0.55±0.75 1.3±1.2 1.1±1.0 0.54±0.36 

North N95 0.30±0.10 1.9±1.1 1.7±2.0 2.5±1.7 

Survivair® P100 0.022±0.015 0.018(b) 0.012(b) 0.030 Cartridge (b)

SEA P100 0.002(b) 0.009(b) 0.007(b) 0.015(b)

MSA N95 0.51±0.37 1.7±1.8 0.93±0.60 1.1±0.61 

Gerson® N95 0.51±0.30 1.8±0.55 0.48±0.07 0.89±0.43 

3M® P100 0.001(b) 0.014(b) 0.002(b) 0.003(b)

Filtering 

Facepiece 

Moldex P100 0.005±0.003 0.050±0.007 0.001(b) 0.010±0.006 

(a) Cartridge testing performed at half the flow rate 

(b) At least one trial resulted in penetration below detectable limit 

Table 16. Comparison of Penetration Measured Using Bioassay Method and MS2 "Dry" 

Aerosol Challenge under Constant and Cyclic Flow Conditions 

Flow Rate(a) (L/min) 

Constant Cyclic 

85 270 85 135 Filter Type Filter 

Average Penetration (%) 

MSA N95 0.009(b) 0.007±0.004 0.003(b) 0.025±0.005 

North N95 0.001(b) 0.022±0.001 0.005±0.002 0.012±0.009 

Survivair® P100 0.002(b) 0.002(b) 0.005(b) 0.012 Cartridge (b)

SEA P100 0.001(b) 0.002(b) 0.001(b) 0.004(b)

MSA N95 0.007 0.009±0.004 0.022±0.009 0.082±0.030 

Gerson® N95 0.22±0.27 0.52±0.69 0.60 0.075±0.034 

3M® P100 0.002(b) 0.004(b) 0.009(b) 0.003(b)

Filtering 

Facepiece 

Moldex P100 0.004(b) 0.004(b) 0.014(b) 0.004(b)

(a) Cartridge testing performed at half flow rate 

(b) At least one trial resulted in penetration below detectable limit 
65 

0.1

1

10

MSA Flexi-Filter

(Cartridge)

North 7506

(Cartridge)

MSA Affinity Plus

(Filtering

Facepiece)

Gerson 1730

(Filtering

Facepiece)

Penetration (%)

85 L/min (constant) 270 L/min (constant) 85 L/min (cyclic) 135 L/min (cyclic)

Figure 43. Comparison of Measured MS2 "Wet" Penetrations through N95 Filters

0.001

0.01

0.1

1

10

MSA Flexi-Filter

(Cartridge)

North 7506

(Cartridge)

MSA Affinity Plus

(Filtering

Facepiece)

Gerson 1730

(Filtering

Facepiece)

Penetration (%)

85 L/min (constant)

270 L/min (constant)

85 L/min (cyclic)

135 L/min (cyclic)

Figure 44. Comparison of Measured MS2 "Dry" Penetrations through N95 Filters 

 Figure 45 compares the penetrations measured using the bioassay method with that 

using the LAS-X for the MS2 "wet" aerosol challenge. The "dry" aerosol results are not 
66 

included as the majority of the penetrations measured using the bioassay method were below 

detectable limts. For the LAS-X, the penetration was calculated based on size specific channels 

ranging from 0.13 to 0.25 μm (Channels 2, 3, and 4). As observed for the Bg spores, higher 

penetrations tended to be measured using the LAS as compared to the bioassay method. 

Penetration, LAS-X (%)

0.0001 0.001 0.01 0.1 1

Penetration, Bioassay (%)

0.0001

0.001

0.01

0.1

1

"Wet" MS2 Cartridges

Figure 45. Comparison of MS2 Phage Penetrations Measured Using the 

Bioassay Method and LAS-X 

4.5.3 Inert Comparisons 

 This section compares the penetrations measured using the biological aerosols with 

those measured using the inert aerosols as described in Section 3.0. The Bg spore comparisons 

are provided in Section 4.5.4.1 and the MS2 comparisons follow in Section 4.5.4.2. The 

comparisons were performed only on the N95 filters as they generally had measurable 

penetrations. The biological penetrations through the P100 filters were generally below 

detectable limits. 

4.5.3.1 Bg Spores. Figure 46 compares the "wet" and "dry" aerosol penetrations through 

the North 7506 cartridge with the 0.7 and 1.3 μm PSL. As shown, similar penetrations were 

measured with the 1.3 μm PSL as with the Bg aerosols. The penetration of 0.7 μm PSL was 

typically an order-of-magnitude higher. Figure 47 also demonstrates the agreement with a 
67 

micron sized particle. The red and blue horizontal lines represent the average penetrations 

measured using the Bg challenge at 42.5 and 135 L/min constant flow, respectively. The 

intersection of these lines with the inert results is an indication of the inert particle size that 

provides an equivalent penetration. For example, measured bioaerosol and inert penetrations 

intersect at a particle size of approximately 1.7 μm for the North 7506 cartridge at a 135 L/min 

flow rate. This intersection is designated by the blue circle. The Bg spores had an AMMD of 

approximately 1.2 μm as measured by the Aerosizer. Similar trends were observed for the other 

N95 filters in Figures 48 through 50. In most cases, the 1.3 μm PSL provided the best agreement 

as inert and Bg penetrations were generally within a factor of five. 

0.001

0.01

0.1

1

10

42.5 L/min Constant 135 L/min Constant 42.5 L/min Cyclic 68 L/min Cyclic

Flow Condition

Penetration (%)

Bg "Wet"

Bg "Dry"

0.7 um PSL

1.3 um PSL

Figure 46. Comparison of Bg Spore and Inert Penetrations through 

the North N95 7506 Cartridge 
68 

0.00001

0.0001

0.001

0.01

0.1

1

10

100

0.01 0.1 1 10

Particle Size (um)

Penetration (%)

Inert Data - 42.5 L/min

Inert Data - 135 L/min

 Bg Penetration - 42.5 L/min

Bg Penetration - 135 L/min

Figure 47. Comparison of Measured Inert and Bg Bioaerosol Penetrations through the 

North 7506 Cartridge at Constant Flows of 42.5 and 135 L/min 

0.0001

0.001

0.01

0.1

1

10

42.5 L/min Constant 135 L/min Constant 42.5 L/min Cyclic 68 L/min Cyclic

Flow Condition

Penetration (%)

Bg "Wet"

Bg "Dry"

0.7 um PSL

1.3 um PSL

Figure 48. Comparison of Bg Spore and Inert Penetrations through the 

MSA N95 Flexi-Filter Cartridge 
69 

0.01

0.1

1

10

85 L/min Constant 270 L/min Constant 85 L/min Cyclic 135 L/min Cyclic

Flow Condition

Penetration (%)

Bg "Wet"

Bg "Dry"

0.7 um PSL

1.3 um PSL

Figure 49. Comparison of Bg Spore and Inert Penetrations through the MSA N95 Affinity 

Plus Filtering Facepiece 

0.01

0.1

1

10

85 L/min Constant 270 L/min Constant 85 L/min Cyclic 135 L/min Cyclic

Flow Condition

Penetration (%)

Bg "Wet"

Bg "Dry"

0.7 um PSL

1.3 um PSL

Figure 50. Comparison of Bg Spore and Inert Penetrations through the Gerson N95 1730 

Filtering Facepiece 

 4.5.3.2 MS2 Phage. Similar comparisons are provided in Figures 51 through 54 for the 

MS2 phage aerosol and 0.1, 0.3, and 0.7 μm PSL penetrations through the N95 filters. The 

comparisons are not as well-defined for the MS2 phage. For the N95 cartridges, penetrations of 

0.1 and 0.3 μm PSL were generally higher than that of the MS2 "wet" aerosol and, thus, would 

provide a conservative estimate of filter performance. Due to its smaller size, the MS2 “wet” 
70 

aerosol penetration tended to be slightly higher than the 0.7 μm PSL. For the N95 filtering 

facepieces, the MS2 “wet” aerosol penetrations tended to be lower than those measured with the 

0.1, 0.3, and 0.7 μm PSL. The penetration of the MS2 “dry” aerosol was typically below 

detectable limits. This was consistent with the penetrations measured for an inert aerosol of 

similar size (i.e., 2.9 μm PSL). 

0.1

1

10

100

42.5 L/min Constant 135 L/min Constant 42.5 L/min Cyclic 68 L/min Cyclic

Flow Condition

Penetration (%)

MS2 "Wet"

0.1 um PSL

0.3 um PSL

0.7 um PSL

Figure 51. Comparison of MS2 "Wet" and Inert Penetrations through the 

North N95 7506 Cartridge 

0.001

0.01

0.1

1

10

100

42.5 L/min Constant 135 L/min Constant 42.5 L/min Cyclic 68 L/min Cyclic

Flow Condition

Penetration (%)

MS2 "Wet"

0.1 um PSL

0.3 um PSL

0.7 um PSL

Figure 52. Comparison of MS2 "Wet" and Inert Penetrations through 

the MSA N95 Flexi-Filter Cartridge 
71 

0.1

1

10

100

85 L/min Constant 270 L/min Constant 85 L/min Cyclic 135 L/min Cyclic

Flow Condition

Penetration (%)

MS2 "Wet"

0.1 um PSL

0.3 um PSL

0.7 um PSL

Figure 53. Comparison of MS2 "Wet" and Inert Penetrations through the 

MSA N95 Affinity Plus Filtering Facepiece 

0.1

1

10

100

85 L/min Constant 270 L/min Constant 85 L/min Cyclic 135 L/min Cyclic

Flow Condition

Penetration (%)

MS2 "Wet"

0.1 um PSL

0.3 um PSL

0.7 um PSL

Figure 54. Comparison of MS2 "Wet" and Inert Penetrations through the 

Gerson N95 1730 Filtering Facepiece 

4.6 Summary 

 The performance of NIOSH-approved N95 and P100 respirator filters has been assessed 

against bioaerosol challenges under high volumetric flow conditions. Mean penetrations were 

below the penetration requirements for the respective filter types (i.e., penetration less than 5 

percent for N95 and less than 0.03 percent for P100 filters) under all flow conditions tested. 

Penetrations of Bg spores through the P100 filters were typically below detectable limits and, 

thus, had penetrations at least an order-of-magnitude below the P100 requirement. The N95 

filters also were very efficient at removing the bacterial aerosol challenges as average 

penetrations were less than 0.5 percent. There were not significant differences in the 
72 

penetrations measured using the "wet" and "dry" Bg spore aerosolization methods. The most 

penetrating of the biological aerosols tested was the "wet" MS2 phage as the particle size was 

closest to the MPPS. Average penetrations through the N95 and P100 filters were less than 2 

and 0.03 percent, respectively, under all flow conditions. An inert aerosol of similar 

aerodynamic diameter was shown to provide a reasonable estimate of performance against 

biological aerosols as measured penetrations were generally within a factor of five. The Bg 

spore "wet" and "dry" aerosol penetrations agreed favorably with the 1.3 μm PSL results. In 

magnitude, the MS2 "wet" penetrations through the cartridges were typically between 

penetrations measured using the 0.3 and 0.7 μm PSL. Comparisons were not made with the MS2 

"dry" as penetrations were typically below detectable limits. However, this is in agreement with 

the penetrations measured for the 2.9 μm PSL. The results demonstrated that testing with inert 

particles in the MPPS range provides a conservative estimate against the biological aerosols 

assessed in this study. Finally, the results demonstrated that using an optical light scattering 

instrument such as the LAS to measure bacterial aerosol penetration provides a conservative 

estimate of filter performance. This is significant due to the labor intensive nature of the 

bioassay method. 

5.0 REAEROSOLIZATION 

 Reaerosolization of biological agents from previously bio-contaminated filtering 

facepieces is a potential concern for emergency responders and health care workers. The 

objective of this subtask was to assess the significance of reaerosolization of biological aerosols 

during simulated coughing through loaded filtering facepieces. The results were also compared 

to those measured using inert particles of similar size to the bioaerosols. 

5.1 Test Parameters 

 Particle reaerosolization from two brands of N95 filtering facepieces was assessed, the 

MSA Affinity Plus and the Gerson 1730 and 1740. Within each brand, tests were performed on 

filtering facepieces with and without exhalation valves. The Gerson 1730 and 1740 models are 

identical with the exception that the1740 has an exhalation valve. The exhalation valves were 
73 

not sealed during the loading or reaerosolization tests. The estimated surface areas of the 

filtration media for each of the filtering facepieces are summarized in Table 17. The filtering 

facepeices were loaded at a cyclic flow rate of 85 L/min (2.3 L tidal volume, 37 breaths/min). 

The filters were not preconditioned with humidified air prior to loading. The loading and 

reaerosolization tests were performed under ambient laboratory temperature (25 ± 5°C) and the 

relative humidity was measured (40 ± 10%). Fluorescent PSL (Duke Scientific, Palo Alto, CA) 

with nominal diameters of 0.8 and 2.2 μm were used as the inert aerosol challenge. Four 

biological aerosols, the same as described in Section 4.0, were used and included Bg "wet", Bg 

"dry", MS2 "wet", and MS2 "dry." One reaersolization flow profile was assessed that 

represented a cough. This profile, shown in Figure 55, was provided by ECBC and is based on 

measurements made during human subject testing. The peak flow rate was approximately 370 

L/min which corresponded to a superficial velocity of approximately 40 cm/s assuming that the 

flow is evenly distributed over the entire facepiece (~170 cm2

). The cough profile was repeated 

three times in succession during each reaersolization test over a period of approximately 30 

seconds. 

Table 17. Estimated Surface Areas of N95 Filtering Facepieces 

Filtering Facepiece Surface Area (cm2

) 

MSA Affinity Plus 175 

MSA Affinity Plus (w/exhalation valve) 160 

Gerson 1730 170 

Gerson 1740 (w/exhalation valve) 150 
74 

0

50

100

150

200

250

300

350

400

0 0.1 0.2 0.3 0.4 0.5 0.6

Time (sec)

Flow Rate (L/min)

Figure 55. Cough Profile for Reaersolization Testing 

 

The target loading level was 1x104

 particles/cm2 based on modeling by Stuempfle et al. 

(2004) who estimated the respirable concentration-time profile in ventilated enclosures 

(buildings) immediately following an intentional bio-agent release. The model was used to 

estimate resuspension of respirable pathogens by human activity after delayed entry into a 

contaminated area. This represents a "worst case" scenario for users of filtering facepiece 

respirators. Based on the model results and assuming a breathing rate of 40 L/min, an 8-hour 

exposure, and a filter surface area of approximately 200 cm2

, a loading of 1x104 particles/cm2

represents a threat-based level. A limited set of tests were performed with the 0.8 μm inert 

aerosol to assess the effect of higher particle loading. Tests were performed at loading levels of 

1x105

 and 1x106 particles/cm2 with the MSA Affinity Plus. The loading of 1x105 particles/cm2

is consistent with Qian et al. (1997a).

5.2 Test Matrix 

 The test matrix completed to assess the extent of reaerosolization from the N95 filtering 

facepieces is provided in Table 18. Factors investigated included filter type, particle size, 

particle type, and loading level. The inert aerosols selected for testing were fluorescent PSL with 

nominal diameters of 0.8 and 2.2 μm. The 0.8 μm PSL had a similar diameter as the Bg spores 

and the 2.2 μm PSL had a similar diameter as the MS2 phage aerosolized as a dry powder.
75 

Table 18. Test Matrix Completed to Assess Reaerosolization

Target Load = 1 x 104 1 x 105 1 x 106

Loading 

Flow 

(L/min) Aerosol 

Gerson 

1730 

No Ex. Valve 

Gerson 

1740 

Ex. Valve 

MSA 

Affinity Plus 

No Ex. Valve 

MSA 

Affinity Plus 

Ex. Valve 

MSA 

Affinity Plus 

No Ex. Valve 

MSA 

Affinity Plus 

No Ex. Valve 

Bg "wet" 3 2 2 3 0 0 

Bg "dry" 1 1 0 0 0 0 

MS2 "wet" 3 1 3 3 0 0 

MS2 "dry" 3 3 0 0 0 0 

0.8 μm PSL 3 2 2 3 3 3 

85 Cyclic 

2.2 μm PSL 3 3 0 0 0 0 

5.3 Test Method 

5.3.1 Test System Description 

 

 The test system used to load the filtering facepieces with the inert or biological particles 

was the same as described in Section 4.3.1. The bioaerosol generation system was as described 

in Section 4.3.2. The inert aerosol challenge was generated from aqueous suspension using a 

6-jet Collison nebulizer. The flow from the nebulizer was diluted with filtered, house air and 

passed through a Kr-85 charge neutralizer (Model 3012, TSI, Shoreview, MN). Samples of the 

challenge aerosol were collected on 47-mm filters to quantify the challenge concentration. The 

inert particles were collected on membrane filters (Type HA, Millipore, Bedford, MA) with a 

rated pore size of 0.45 μm. Membrane filters were used such that the particles would be 

collected on the surface of the filter and not embedded within the fibers. This was important as a 

counting method using a fluorescent microscope was used to quantify the number of particles 

collected. The bioaerosol samples were collected on either mixed cellulose ester or 

water-soluble filters for subsequent bioassay. 

A separate test system, illustrated in Figure 56, was used to measure the percent 

reaersolization. It consisted of the breathing machine, filtering facepeice holder, reaerosolization 

chamber, and aerosol sampling/classification system. The breathing machine used to simulate 

the cough was connected to the filter holder using 2.5-cm OD flexible tubing. The inlet air to the 

breathing machine was HEPA filtered such that the exhaled air was particulate free. The holder 

for the filtering facepiece consisted of a flat plate with a 7.5 cm hole centrally located to permit 
76 

airflow. This plate was welded onto a cone that allowed the flow from the breathing machine to 

expand and distribute over the entire area of the filter. The filter holder sealed to the top of the 

reaerosolization chamber. The chamber was cylindrical with a 0.7 m diameter and 0.6 m height. 

The bottom of the chamber tapered down to the 47-mm collection filter. The internal volume of 

the chamber was approximately 300 L. A vacuum pump was used to pull a continuous, constant 

flow through the chamber and collection filter. Make-up air was drawn through the HEPA filters 

located at the top of the chamber as needed. 

MFM

Carbon

Filter

Regulator

House

 Air

HEPA

Filter

HEPA

Filter

MFM

Pump

HEPA Filtered Purge

P

MFM MFM

Carbon

Filter

Regulator

House

 Air

HEPA

Filter

HEPA

Filter

MFM

Pump

HEPA Filtered Purge

P

MFM

Figure 56. Schematic of Reaerosolization Test System 

5.3.2 Test Procedure 

 The filtering facepeice was sealed to the holder and placed in the exposure chamber 

described in Section 4.3.1 for loading. The breathing machine was started and pulled 85 L/min 

(2.3-L tidal volume, 37 breaths/min) through the filtering facepeice. The aerosol generation 

system was started to begin loading the filtering facepiece. For both inert and biological aerosol, 

samples were also collected on 47-mm reference filters. The required loading duration was 

Filtering Facepiece 

Collection Filter 
77 

estimated based on the challenge concentration, flow rate, and filter surface area. It was assumed 

that the filtering facepieces were 100 percent efficient against all challenge aerosols. At the 

desired loading level, the aerosol generation system and breathing machine were stopped and the 

chamber flushed with HEPA filtered air. 

 The filtering facepeice and holder were removed from the exposure chamber and sealed 

to the reaerosolization chamber shown in Figure 56. The sample pump was started to flush the 

chamber with HEPA filtered air and sampling began with a pre-cough collection filter. Sample 

duration was sufficient to exchange the air within the chamber three times (typically 15 to 

25 minutes depending on sample flow rate). The sample pump was then stopped and the 47-mm 

collection filter replaced. The sample pump was started again and the breathing machine was 

used to simulate the cough. The cough profile was repeated three times. A valve was used such 

that the inhaled air between coughs was HEPA filtered room air. The chamber was again 

sampled for sufficient time to exchange the chamber volume three times. The sample pump was 

stopped and the filter removed from the system for analysis. Polonium-210 static eliminators 

were used to minimize particle loss during transport to laboratory for analysis. 

5.3.3 Analytical Methods 

Filtering facepiece loadings (#/cm2

) were estimated based on the loading of a 47-mm 

reference filter loaded simultaneously. The loading on the reference filter was transformed to the 

loading on the filtering facepiece by taking into account the relative collection flow rates, 

durations, and surface areas (refer to Section 5.3.5). The methods used to quantify the loading 

on the reference filters are described in Sections 5.3.2.1 and 5.3.2.2 for the inert and biological 

aerosols, respectively. 

5.3.3.1 Inert Aerosols. The number concentrations of inert aerosols collected on the 

membrane filters were quantified using a fluorescent microscope (Model SZX12, Olympus, 

Melville, NY) to count the particles collected on selected regions of the filter. The area of the 

field-of-view was known based on the magnification and allowed the number of particles/cm2

 to 

be determined. The method assumed that particles were evenly distributed over the surface of 

the filter as only a percentage of the surface area was analyzed. The selected areas ranged from 
78 

the center to the edge to identify any potential bias in the radial direction. As shown in Figure 

57, five areas were analyzed for the loading filters and 20 areas were analyzed for the collection 

filters. More areas were analyzed for the collection filter due to the expected lower loading 

levels. Magnification for analysis of the loading filters was 45x resulting in a field of view that 

was 1 mm in diameter. Less magnification (12x) was used for the collection filter to increase the 

viewing area to 5 mm and maximize potential to locate particles. This permitted approximately 

25 percent of the collection filter to be analyzed. 

Figure 57. Analysis Patterns on 47-mm Collection Filters Used with Fluorescent 

Microscope to Quantify Loadings of Inert Particles 

 5.3.3.2. Biological Aerosols. The biological samples were collected on 47-mm filters 

for subsequent bioassay using the methods that were described in Section 4.3.3.1. 

5.3.4 System Characterization 

 Shakedown tests were initially conducted to characterize the test system and establish 

the proper operating conditions. Significant effort went into the design of the test chamber and 

several iterations were explored. The initial test chamber was cylindrical with an internal 

volume of only 10 L. The advantage of the relatively small chamber was the short time required 

to flush the chamber when sampling at 40 L/min. However, the small chamber provided too 

much resistance for the breathing machine during the cough such that the 360 L/min peak flow 

could not be reached. Efforts to reduce pressure within the chamber were unsuccessful. It was 
79 

not feasible to increase the sample flow rate enough to adsorb the high peak flow. The highest 

flow rate that could be pulled through the membrane filter was 40 L/min. Using multiple 

collection filters or increasing the surface area would have been disadvantageous from the 

analytical perspective (i.e., low numbers of particles spread across a larger surface area). Thus, 

the chamber was scaled up to the final volume of 300 L/min. The cough profile was verified by 

measuring the flow rate using a rapid response mass flow meter (Model 4000, TSI) that is 

capable of measuring and data logging the flow rate at 10 ms intervals. The measured cough 

profile is compared with the target profile in Figure 58 and demonstrates the 360 L/min peak 

flow was obtained. 

0

50

100

150

200

250

300

350

400

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Time (Sec)

FLow Rate (L/min)

0.8GERSON1740REP2

0.8GERSON1740REP3

0.8GERSON1740REP1

Target Cough Profile

Figure 58. Comparison of Target and Measured Cough Profile Used 

for Reaerosolization Testing 

The larger chamber was disadvantageous from a sample collection perspective as longer 

sample durations were required and there was more surface area for particles to adhere. The 

chamber was designed to create an airflow pattern directed downward toward the collection filter 

to reduce particle loss to the chamber walls, dead spots, or circulating air flow. In addition, the 

system was oriented such that gravity would enhance particle collection due to settling. A series 

of shakedown tests using the 0.8 μm PSL challenge were performed to assess the sampling 

approach. Initially three 47-mm filters were collected during each reaerosolization test: (1) a 

pre-cough filter to determine if particles were shed during the attachment of the loaded filter to 

the system, (2) a post-cough filter to collect particles displaced by the cough, and (3) a post-test filter 
80 

to verify the chamber was flushed. Particles were consistently collected on the pre-cough filter. The 

counts were not attributed to contamination within the test system as the post-test filters were 

generally found to have zero counts indicating minimal carryover between tests. Thus, the particles 

collected on the pre-cough filter were attributed to the physical process of connecting the loaded 

filter to the chamber. 

Following the shakedown testing, only the pre- and post- cough samples were collected. The 

particle counts on the pre- and post-cough 47-mm filters are compared in Figure 59 for each of the 

trials completed with the 0.8 μm PSL. The trials are shown in the order of completion. The postcough filters had higher counts in 15 of the 18 trials. The highest pre-cough counts were observed in 

trials 2 and 6 and both had higher counts than the post-cough filter from the previous test. Thus, the 

high counts were attributed to the process of connecting the filter to the test system. Unfortunately, 

no samples were collected between the pre- and post-cough filters to demonstrate the chamber had 

been completely flushed before the cough. However, even if the pre-cough filter is treated as a 

system background, the results demonstrate that particles were reaerosolized from the filtering 

facepieces as particle counts were generally higher post-cough. This trend was consistent throughout 

all challenge aerosols. The average particle counts pre- and post- cough are compared for each of the 

inert and biological challenges in Figure 60. 

0

200

400

600

800

1000

1200

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Trial #

Number of Particles Collected (#)

Pre-Cough

Post-Cough

Figure 59. Comparison of Number of Particles Collected on Pre- and Post-Cough Filters 

for Tests Performed with the 0.8 μm PSL 
81 

0.1

1

10

100

1000

10000

100000

MS2 "Wet" MS2 "Dry" Bg "Wet" 0.8 um PSL 2.2 um PSL

Average Number Particles Collected (#)

Pre-Cough

Post-Cough

Figure 60. Comparison of Number of Particles Collected on Pre- and Post-Cough Filters 

for Tests Performed with the Biological and Inert Aerosols 

5.3.5 Calculation of Reaerosolization 

 The challenge aerosol concentration (CChal) was derived from the results of the 

reference filter analysis using the following relationship: 

R L

R R

Chal Q t

P A

C L

×

×

(# / ) =

where PR is the loading density determined for the reference filter (#/cm2

), AR is the area of the 

reference filter (cm2

), QR is the flow rate through the reference filter (L/min), and tL is the 

loading duration (min). The number of particles loaded (PFF) onto the filtering facepiece was 

then determined using the following equation: 
82 

FF Chal FF L P (# ) = C ×Q ×t

where QFF is the flow rate through the filtering facepiece (L/min). It was assumed that the filters 

were 100 percent efficient for all challenge aerosols. 

 The number of particles reaerosolized (PC) was based on the bioassay or fluorescence 

analysis of the collection filter. The percent of particles reaerosolized (fR) was then the ratio of 

the number of particles reaerosolized (PC) to the number of particles loaded on the filtering 

facepiece (PFF): 

(%) x100

P

P f

FF

C

R =

5.4 Results 

Table 19 summarizes the results of the reaerosolization testing with both the inert and 

biological aerosols. Results from individual trials are summarized in Appendix J. The target 

loading level was 1 x 104

 particles/cm2 for all challenge aerosols with the exception of the higher 

loading tests performed with the 0.8 μm PSL. The average measured loadings for each challenge 

type are also summarized in Table 19. Note that tests with the 2.2 μm PSL and Bg "wet" 

aerosols had loading levels approximately an order-of-magnitude less than the target due to 

lower than expected challenge concentrations. In all cases, the percent reaerosolization was less 

than one percent of the number of particles loaded onto the filtering facepiece. The inert aerosol 

results are further discussed in Section 5.4.1 and the biological results in Section 5.4.2. 
83 

Table 19. Summary of Reaerosolization Results 

(a) No tests performed at test condition 

5.4.1 Inert Aerosols 

 Figure 61 compares the percent reaerosolization of inert particles measured from the 

MSA and Gerson respirators. All reaersolizations were less than 0.1 percent. The percent 

reaerosolization tended to increase with increased particle size and was not significantly different 

between the two brands of filtering facepieces. Higher percent reaerosolizations were measured 

for the respirators that contained exhalation valves. The increase was more significant for the 

smaller particles that were not reaersolized as easily from the filter media. Reaerosolization 

increased by a factor of 2 for the 2.2 μm PSL and a factor of 4 to 8 for the 0.8 μm PSL. The 

extent of reaerosolization was expected to be lower from the filters with exhalation valves as 

velocity through the aerosol media was likely lower due to the flow through the valve. However, 

the mechanical movement of the valve and localized high velocity flow may have re-entrained 

particles collected on the surface of the valve or valve housing. To further investigate the higher 

reaerosolization, Gerson filtering facepieces with the exhalation valve covered with tape were 

loaded with 0.8 μm PSL. This prevented loading on the valve and housing. The tape was then 

removed prior to the reaerosolization test. Figure 62 compares these results with those from the 

Filter Type 

Gerson 

1730 

(No Ex. Valve) 

Gerson 

1740 

(Ex. Valve) 

MSA 

Affinity Plus 

(No Ex. Valve) 

MSA 

Affinity Plus 

(Ex. Valve) 

Reaerosolization (%) 

Challenge 

Aerosol 

Average 

Loading 

(#/cm2) Average 95% CI Average 95% CI Average 95% CI Average 95% CI 

0.8 μm 

PSL 2.2 x 104 0.002 0.0003 0.008 0.0005 0.0008 0.0003 0.007 0.0007 

0.8 μm 

PSL 1.7 x 105 -

(a) - - - 0.0006 0.00005 - - 

0.8 μm 

PSL 9.4 x 105 - - - - 0.0004 0.00001 - - 

2.2 μm 

PSL 2.0x103 0.03 0.005 0.04 0.006 - - - - 

Bg "wet" 1.0 x103 0.06 0.01 0.07 0.1 0.03 0.003 0.05 0.02 

Bg "dry" 1.4x104 0.1 0.2 - - - - - 

MS2 "wet" 3.1 x104 0.07 0.08 0.1 - 0.07 0.08 0.1 0.1 

MS2 "dry" 4.5 x104 0.5 0.2 0.7 0.2 - - - - 
84 

Gerson respirators with no or unprotected valves. The percent reaerosolization decreased by a 

factor of 2 as compared to tests with the unprotected valves. 

0.0001

0.001

0.01

0.1

MSA (w/o valve) MSA (w/valve) Gerson (w/o

valve)

Gerson (w/valve)

% Reaerosolized

0.8 um PSL

2.2 um PSL

Figure 61. Comparison of Percent Reaerosolization of Inert Particles from MSA 

and Gerson Filtering Facepieces 

0.0001

0.001

0.01

0.1

Gerson (w/o valve) Gerson (w/valve,

protected)

Gerson (w/valve)

% Reaerosolized

Figure 62. Comparison of Percent Reaerosolization of 0.8 μm PSL from Gerson Respirator 

with Exhalation Valve Protected during Loading
85 

 The effect of loading on the percent reaerosolization of 0.8 μm PSL is shown in Figure 

63. Although averages were less than 0.002 percent for all loadings, the percent reaerosolization 

tended to decrease as the loading increased. However, more particles were reaerosolized at the 

higher loading levels. The average numbers of particles reaerosolized for the different loading 

levels were 35, 180, and 740 particles. Thus, as loading increased by an order-of-magnitude, the 

average number of particles reaerosolized increased only by a factor of approximately 5. 

0.0001

0.001

0.01

0.1

Normal (1E4/cm2) High (1E5/cm2) Ultra (1E6/cm2)

% Reaerosolized

Figure 63. Comparison of Percent Reaerosolization of 0.8 μm PSL from Gerson Respirator 

at Loadings Ranging from 1 x 104 to 1 x 106 Particles/cm2

5.4.2 Biological Aerosols 

This section summarizes the results of the reaerosolization testing completed with the 

biological aerosols. The results are also compared to the inert results described above. The Bg 

spore results are provided in Section 5.4.2.1 and the MS2 phage results follow in Section 5.4.2.2. 

 5.4.2.1 Bg Spores. Figure 64 compares the measured reaersolization of the Bg "wet" 

and Bg "dry" aerosols to that measured for the inert 0.8 μm PSL. Recall from Section 4.0, the 

AMMDs for both the "wet" and "dry" Bg were approximately 1.0 μm. The mean 
86 

reaerosolization of the Bg spores tended to be higher for the respirators with exhalation valves 

but the effect was not as significant as observed with the 0.8 μm PSL. The percent 

reaerosolization of the Bg spores was generally an order-of-magnitude higher than the inert PSL. 

0.0001

0.001

0.01

0.1

1

MSA (w/o valve) MSA (w/valve) Gerson (w/o valve) Gerson (w/valve)

% Reaerosolized

0.8 um PSL

Bg wet

Bg Dry

Figure 64. Comparison of Inert and Bg Spore Reaerosolization Results 

 5.4.2.2 MS2 Phage. Figure 65 compares the extent of reaerosolization of MS2 "wet" 

and "dry" aerosols with the 2.2 μm PSL. The NMD of the MS2 "dry" aerosol was 2.3 μm while 

the "wet" was 0.2 μm. Significant differences in reaerosolization were observed between the 

inert and biological aerosols. Of particular interest was the extent of reaerosolization of 

MS2 "wet" aerosol as it was approximately an order-of-magnitude higher than that observed for 

the 2.2 μm PSL. This was contrary to the inert results shown previously that indicated percent 

reaersolization increased with particle size. The highest reaerosolization percentages were 

observed for the MS2 "dry" aerosol with a mean of approximately 0.5 percent, nearly two ordersof-magnitude higher than the 2.2 μm PSL results. This difference was attributed to polydisperse 

size distribution of the MS2. Although both had similar NMDs, the PSL was monodisperse 

while the MS2 was polydisperse with significant mass between 2 and 5 μm containing viable 

particles. Higher percent reaerosolization is expected as the particle size approaches 5 μm as 
87 

was demonstrated by Qian et al. (1997a) who showed reaerosolization increased from 0.05 to 6 

percent as the particle size increased from 1.5 to 5.0 μm. 

0.0001

0.001

0.01

0.1

1

MSA (w/o valve) MSA (w/valve) Gerson (w/o valve) Gerson (w/valve)

% Reaerosolize

d

2.2 um PSL

MS2 Wet

MS2 Dry

Figure 65. Comparison of Inert and MS2 Phage Reaerosolization Results 

5.5 Summary and Discussion 

 A test method was developed to quantify the extent of reaerosolization from a filtering 

facepiece loaded with either an inert or biological aerosol. Tests were performed to assess the 

effect of particle size, particle type, and loading level. Two brands of filtering facepieces were 

tested, the MSA Affinity Plus and Gerson 1730. The levels and trends of reaerosolization were 

similar for both brands. For the inert aerosols, reaerosolization was observed to increase with 

increased particle size over the range tested (0.8 to 2.2 μm). This trend was consistent with that 

observed by Qian et al. (1997a) who attributed this to increased drag force on the larger particles. 

The extent of reaerosolization of 0.8 μm particles from filtering facepieces without exhalation 

valves was very low (less than 0.002 percent or 1 in every 50,000 particles loaded). The percent 

reaerosolization increased by an order of magnitude when filtering facepieces with exhalation 

valves were tested. This was attributed to the movement of the valve and localized high velocity 

air that could re-entrain particles collected on the surface of the valve or valve housing. 
88 

 Specifically for the 0.8 μm PSL, the number of particles reaerosolized was observed to 

increase with increased loading over the range from 1 x 104

 to 1 x 106 particles/cm2. However, 

the number of particles did not increase proportionally to the increased loading. Increasing the 

loading by a factor of 10 only increased the number of particles reaerosolized by a factor of 5. 

Further work is recommended to determine if similar trends hold for larger particles. 

 The extent of reaerosolization of the biological aerosols was greater than that observed 

for the inert aerosols with a similar diameter. For example, reaerosolization of the 0.8 μm PSL 

was very low (~0.002%) while reaerosolization of the Bg spores was typically 0.05 to 0.1 

percent. Similarly, reaerosolization of the 2.2 μm PSL was only 0.01 percent while 

reaerosolization of the MS2 "dry" aerosol was 0.5 percent. The higher reaerosolization for the 

biological aerosols was attributed to their broader size distribution. For example, the MS2 "dry" 

aerosol had significant mass between 2.5 and 5.0 μm that contained viable particles. As 

described above, the extent of reaerosolization has been shown to increase with increased 

particle size. Thus, it is important to consider the entire size distribution and not just the nominal 

particle size when selecting an inert simulant for characterizing reaerosolization. 

6.0 CONCLUSIONS AND RECOMMENDATIONS 

The performance of NIOSH-approved N95 and P100 filtering facepieces has been 

assessed against both inert and biological aerosols under high flow conditions representative of 

ventilation rates during heavy activity. For the inert particles, the most penetrating particle size 

(MPPS) was generally between 0.1 and 0.2 μm for the P100 cartridges and 0.05 and 0.10 μm for 

the filtering facepieces and N95 cartridges. The penetration of submicron particles tended to 

increase with flow rate and penetrations in excess of the NIOSH N95 and P100 requirements 

were measured. However, the intended use, type and size distribution of the particulate hazard, 

APF, and other factors must be considered to determine if this increase in penetration is 

significant with regard to the overall protective capability of the respirator. 

 As was discussed in Section 2.0, the primary factors that influence penetration are 

filtration velocity, particle size, and the properties of the filter media. This task strictly focused 

on the effect of filtration velocity and particle size. The properties of the media from the various 

filters were not compared to identify those that could account for differences in performance. It 
89 

is recommended to characterize the media properties including fiber diameter, solidity, and 

thickness. These values could then be used to model the penetrations using the single fiber 

theory developed by Lee and Liu (1980) and compared to the measured values contained in this 

report. Electret media are commonly used in N95 filters and filtering facepieces to lower 

inhalation resistance. Electret media may be more susceptible to the high flow conditions as the 

collection mechanism is less efficient. Thus, further testing to compare performance of electret 

and mechanical media is recommended. 

 In comparing penetrations measured under constant and cyclic flow conditions, the MIF 

and PIF were determined to be important parameters. For the P100 cartridges, similar 

penetrations were measured under constant and cyclic flow if the constant flow was equivalent to 

the MIF. However, it may be more important to consider the PIF when testing filtering 

facepieces or N95 cartridges, especially at the high volumetric flow rates that can be experienced 

during heavy work loads. These filters are not well-suited for the high volumetric flow rate 

applications due to their lower surface areas as compared to the P100 cartridges. Selecting a 

constant flow equivalent to the peak inhalation flow generally provides a conservative estimate 

of filter performance under cyclic flow conditions. All cyclic flow testing performed in this task 

used a sinusoidal flow profile. Additional testing is recommended with alternative waveforms 

such as a trapezoidal that may be more realistic during periods of heavy exertion (Kaufman and 

Hastings, 2005). 

 A method was developed to predict cyclic flow penetrations based on measured 

penetrations over a range of constant flows. The method was applied to the inert data generated 

in this task. Good agreement was observed between the predicted cyclic flow penetrations and 

those measured in this study. Similar to the recommendation above, measured cyclic flow 

penetrations under different types of waveforms are needed to further validate the predictive 

method. 

 The performance of NIOSH-approved N95 and P100 respirator filters has been assessed 

against bioaerosol challenges under high volumetric flow conditions. Mean penetrations were 

below the penetration requirements for the respective filter types (i.e., penetration less than 5 

percent for N95 and less than 0.03 percent for P100 filters) under all flow conditions tested. 

Penetrations of Bg spore aerosols through the P100 filters were typically below detectable limits 

and, thus, had penetrations at least an order-of-magnitude below the P100 requirement. The N95 
90 

filters also were very efficient at removing the bacterial aerosol challenges as average 

penetrations were less than 0.5 percent. There were not significant differences in the 

penetrations measured using the Bg spore aerosols generated from liquid suspension and dry 

powder. The most penetrating of the biological aerosols tested was the "wet" MS2 phage as the 

particle size was closest to the MPPS. Penetrations through the N95 and P100 filters were 

typically less than 2 and 0.03 percent, respectively, under all flow conditions. 

 An inert aerosol of similar aerodynamic diameter was shown to provide a good estimate 

of performance against biological aerosols (i.e., measured penetrations within a factor of five). 

The Bg spore "wet" and "dry" penetrations agreed favorably with the 1.3 μm PSL results. In 

magnitude, the MS2 "wet" penetrations through the cartridges were typically between 

penetrations measured using the 0.3 and 0.7 μm PSL challenges. Comparisons were not made 

with the MS2 "dry" as penetrations were typically below detectable limits. This was consistent 

with the penetrations measured using a similar sized inert aerosol (i.e., 2.9 μm PSL). The results 

demonstrated that testing with inert particles in the MPPS range provides a conservative estimate 

against the biological aerosols assessed in the study. Finally, the results demonstrated that higher 

penetrations tended to be measured using an optical light scattering instrument such as the LAS 

to measure bacterial aerosol penetration as compared to the bioassay approach. Thus, it provides 

a worst case penetration measurement. This is significant due to the labor intensive nature of the 

bioassay method. 

 A test method was developed to quantify the extent of reaerosolization from a filtering 

facepiece loaded with either an inert or biological aerosol. All tests were performed with a 

cough profile that had a peak flow of 360 L/min. Further work is recommended to assess the 

effect of cough profile and increased peak flow. Tests were performed to assess the effect of 

particle size, particle type, and loading level. For the inert aerosols, reaerosolization was 

observed to increase with increased particle size over the range tested (0.8 to 2.2 μm). The 

extent of reaerosolization of 0.8 μm PSL particles from filtering facepieces without exhalation 

valves was very low (less than 0.002 percent or 1 in every 50,000 particles loaded). For the 

0.8 μm PSL particles, percent reaerosolization from filters with an exhalation value increased by 

an order-of-magnitude. The number of particles reaersolized was shown to increase with 

increased loading for the 0.8 μm PSL particles. Further work is recommended to assess the 
91 

effect of loading on reaerosolization of particles larger than 1 μm since they are easier to 

reaerosolize. 

 The extent of reaerosolization of the biological aerosols was greater than that observed 

for the inert aerosols with a similar AMMD. For example, reaerosolization of the 0.8 μm PSL 

was very low (~0.002%) while reaerosolization of the Bg spores was typically 0.05 to 0.1 

percent. Similarly, reaerosolization of the 2.2 μm PSL was only 0.01 percent while 

reaerosolization of the MS2 "dry" was 0.5 percent. The higher reaerosolization for the biological 

aerosols was attributed to their broader size distribution. For example, the MS2 "dry" aerosol 

had significant mass between 2.5 and 5.0 μm that contained viable particles. As described 

above, the extent of reaerosolization increases with increased particle size. Thus, it is important 

to consider the entire size distribution and not just the nominal particle size when selecting an 

inert simulant for reaerosolization experiments. 
92 

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93 

LITERATURE CITED 

ASTM F 2101-01, "Standard Test Method for Evaluating the Bacterial Filtration Efficiency 

(BFE) of Medical Face Mask Materials, Using a Biological Aerosol of Staphylococcus aureus." 

American Society for Testing and Materials, West Conshohocken, Pennsylvania (June 2001). 

Brosseau, L.M., Evans, J.S., Ellenbecker, M.J., and Feldstein, M.L., "Collection Efficiency of 

Respirator Filters Challenged with Monodisperse Latex Aerosols." Am. Ind. Hyg. Assoc. J. 

50(10): pp 544-549 (1989). 

Brosseau, L.M., Chen, S.K., Vesley, D., and Vincent, J.H., "System Design and Test Method for 

Measuring Respirator Filter Efficiency Using Mycobacterium Aerosols." J. Aerosol Sci. 25(8): 

pp 1567-1577 (1994). 

Brosseau, L.M., Ellenbecker, M.J., and Evans, J.S., "Collection of Silica and Asbestos Aerosols 

by Respirators at Steady and Cyclic Flow." Am. Ind. Hyg. Assoc. J. 51(8): pp 420-426 (1990). 

Brosseau, L.M., McCullough, N, and Vesley, D., "Mycobacterial Aerosol collection Efficiency 

of Respirator and Surgical Mask Filters Under Varying Conditions of Flow and Humidity" Appl. 

Occup. Environ. Hyg. 12(6): pp 435-445 (1997). 

Caretti, D.M., Gardner, P.D., and Coyne, K.M., "Workplace Breathing Rates: Defining 

Anticipated Values and Ranges for Respirator Certification Testing", U.S. Army Edgewood 

Chemical Biological Center Technical Report, ECBC – TR-316 (2004). 

Chen, C.C., Lehtimaki, M., and Willeke, K., "Aerosol Penetration through Filtering Facepieces 

and Respirator Cartridges" Am. Ind. Hyg. Assoc. J. 53(9): pp 566-574 (1992). 

Chen, S.K., Vesley, D., Brosseau, L.M., and Vincent, J.H., "Evaluation of Single-Use Masks and 

Respirators for Protection of Health Care Workers Against Mycobacterial Aerosols." Am. J. 

Infection Control 22(2): pp 65-74 (April 1994). 

Code of Federal Regulations. Respiratory protection. Title 30, CFR, Part 11. Washington, DC: 

U.S. Government Printing Office, Office of the Federal Register (1972). 

Code of Federal Regulations. Respiratory protection. Title 42, CFR, Part 84. Washington, DC: 

U.S. Government Printing Office, Office of the Federal Register (1995). 

42 CFR Part 84. Respiratory Protection; Final Rule. Federal Register, Washington, D.C. 

Vol. 60, No. 110 (1995). 

Department of Health and Human Services (DHHS) Publication 2003-136, "Guidance for 

Filtration and Air-Cleaning Systems to Protect Building Environments from Airborne Chemical, 

Biological, and Radiological Attacks," (April 2003). 
94 

Fardi, B., and Liu, B.Y.H., "Performance of Disposable Respirators." Part. Part. Syst. Charact. 

8: pp 308-314 (1991). 

Hanley, J.T., and Foarde, K.K., "Validation of Respirator Filter Efficacy." Report by RTI 

International, Research Triangle Park, N.C., RTI Contract No. DAAD 19-02-C-0097, Project 

No. 08621 (March 30, 2003). 

Harstad, B.J. and Filler, M.E., “Evaluatin of Air Filters with Submicron Viral Aerosols and 

Bacterial Aerosols,” Am. Ind. Hyg. Assoc. J. pp. 280-290, May-June (1969). 

Hinds, W.C., Aerosol Technology; Properties, Behavior, and Measurement of Airborne 

Particles. John Wiley & Sons, New York, New York: 1999. 

Hofacre, K., Schumacher, P., Hecker, R., Forney, T., "Filtration Efficiency Assessment of HEPA 

Filters Against a Bioaerosol Challenge." Battelle Memorial Institute Report to U.S. 

Army/ERDEC Armored Systems Modernization Team, Contract No. SP0900-94-D-0002, Task 

No. 39, Delivery Order 19 (May 15, 1996). 

Hofacre, K.C. and Forney, T.L., “Test Method for Measuring Mask Protection Factors Using a 

Bioaerosol Challenge.” Battelle Memorial Institute Final Report, February (1996) 

Johnson, B., Martin, D.D., and Resnick, I.G., "Efficacy of Selected Respiratory Protective 

Equipment Challenged with Bacillus subtilis subps. niger" Applied and Environmental 

Microbiology, 60(6): pp 2184-2186 (1994). 

Jankowska, E., Reponen, T., Willeke, K., Grinshpun, S., and Choi, K., "Collection of Fungal 

Spores on Air Filters and Spore Reentrainment from Filters into Air" J. Aerosol Science, 31(8): 

pp 968-978 (2000). 

Kaufman, J.W. and Hastings, S.,"Respiratory Demand During Rigorous Physical Work in a 

Chemical Protective Ensemble," J. of Occup. and Env. Hyg., 2:pp 98-110 (2005) 

Martin, S.B. and Moyer, E. S., “Electrostatic Respirator Filter Media : Filter Efficiency and Most 

Penetrating Particle Size Effects,” Appl. Occup. Env. Hyg. 15(8) pp. 609-617 (2000). 

McCollough, N.V., Brosseau, L.M., and Vesley, D., "Collection of Three Bacterial Aerosols by 

Respirator and Surgical Mask Filters Under Varying Conditions of Flow and Relative 

Humidity." Ann. Occup. Hyg. 41(6): pp 677-690 (1997). 

McCullough, N.V., Brosseau, L.M., Vesley, D., and Vinent. J.H., “Improved Methods for 

Generation, Sampling, and Recovery of Biological Aerosols in Filter Challenge Tests,” Am. Ind. 

Hyg. Assoc. J. 59: pp 234-241 (1998). 

Qian, Y., Willeke, K., Grinshpun, S.A., and Donnelly, J., "Performance of N95 Respirators: 

Reaerosolization of Bacteria and Solid Particles." Am. Ind. Hyg. Assoc. J. 58: pp 876-880 

(1997a). 
95 

Qian, Y., Willeke, K., Ulevicious, V., and Grinshpun, S., "Particle Reentrainment from Fibrous 

Filters." Aerosol Sci. and Tech. 27: pp 394-404 (1997b). 

Qian, Y., Willeke, K., Grinshpun, S.A., Donnelly, J., and Coffey, C.C., "Performance of N95 

Respirators: Filtration Efficiency for Airborne Microbial and Inert Particles." Am. Ind. Hyg. 

Assoc. J. 59: pp 128-132 (1998). 

Ruuskanen, J., Chen, C.-C., Carpenter, D.R., Sherman, A., and Willeke, K., "Aerosol Penetration 

Characteristics for Disposable Respirator Facepieces." J. Aerosol Sci. 19(7): pp 1445-1448 

(1988). 

Stafford, R.G., Ettinger, H.J., and Rowland, T.J., “Respirator Cartridge Filter Efficiency under 

Cyclic- and Steady-Flow Conditions.” Am. Ind. Hyg. Assoc. J. May: pp 182-192 (1973). 

Stevens, G.A. and Moyer, E.S., "Worst Case' Aerosol Testing Parameters: I. Sodium Chloride 

and Dioctyl Phthalate Aerosol Filter Efficiency as a Function of Particle Size and Flow Rate." 

Am. Ind. Hyg. Assoc. J. 50(5): pp 257-264 (1989). 

Stuempfle, A. K, and Fischer, B.W., “Biological Aerosol Hazard Assessments of Emergency 

Responders in Specific Scenarios: Summary Report”, OMI-762, prepared by OptiMetrics, Inc. 

under Contract No: DAAD13-02-F-0028 for US Army Edgewood Chemical Biological Center, 

Aberdeen Proving Ground, MD, 15 January 2004. 

Tui man, I.L. and Steenweg, L., “The Influence of Particle Shape on the Penetration through 

Fibrous Filters,” J. Aerosol Science, 29: pp S1163-S1164 (1998). 

Wake, D., Bowry, A.C., Crook, B., and Brown, R.C., "Performance of Respirator Filters and 

Surgical Masks Against Bacterial Aerosols." J. Aerosol Sci. 28(7): pp 1311-1329 (1997). 

Willeke, K., Qian, Y., Donnelly, J., Ginshpun, S., and Ulevicius, V., "Penetration of Airborne 

Microorganisms Through a Surgical Mask and a Dust/Mist Respirator." Am. Ind. Hyg. Assoc. J. 

57: pp 348-355 (1996). 
96 

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A-1 

APPENDIX A 

PHOTOGRAPHS OF CARTRIDGES AND FILTERING FACEPIECES 
A-2 

Figure A-1. SEA HE-T P100 Cartridge 

Figure A-2. Survivair 1050 P100 Cartridge
A-3 

Figure A-3. North 7506 N95 Cartridge 

Figure A-4. MSA Flexi-Filter N95 Cartridge 
A-4 

Figure A-5. 3M 8293 P100 Filtering Facepiece 

Figure A-6. Moldex 2360 P100 Filtering Facepiece
A-5 

Figure A-7. MSA Affinity Plus N95 Filtering Facepiece 

Figure A-8. Gerson 1730 N95 Filtering Facepiece 
A-6 

Blank
B-1 

APPENDIX B 

RATIONALE FOR SELECTING FLOW CONDITIONS 
B-2 

B.1 Introduction 

The cyclic flow conditions were selected based on an analysis of data completed by the 

U.S. Army's Edgewood Chemical Biological Center (ECBC) to assess the relationship between 

workload and ventilation rate (Caretti et al., 2004). A brief review of literature regarding 

unencumbered ventilation is provided in Section B.2. For a complete review, refer to Caretti et 

al. (2004). Section B.3 presents the data compiled by ECBC illustrating the effect of breathing 

resistance from an APR on ventilation at different work intensities. The rationale for the selected 

flow conditions is provided in Section B.4. 

B.2 Unencumbered Ventilation 

 Incremental exercise testing permits a rapid, yet thorough assessment of an individual’s 

cardiorespiratory responses to exercise, including the level of the subject’s exercise limitation. 

Typically, such testing spans a tolerable work rate range from low to high levels, during which, 

large amounts of respiratory and cardiovascular data are collected up to and including the 

voluntary endpoint of testing. Many published reports have documented breathing patterns 

adopted by healthy humans during incremental exercise [Blackie et al. (1991); Gallagher et 

al. (1987); Neder et al. (2001); Wasserman et al. (1987)]. In general, it has been demonstrated in 

subjects with various fitness levels that increasing minute volumes are due to increases in both 

tidal volume and breathing frequency at low exercise intensities. At high exercise intensities, 

increases in minute volume are accomplished mainly by increasing breathing frequency, with 

tidal volume showing a plateau [Gallagher et al. (1987)]. 

 Normal values and ranges of ventilation at maximal exercise with respect to age, sex, 

and body anthropometrics have also been established using incremental testing. Blackie et 

al. (1991) exposed 231 subjects (120 women; 111 men) to a symptom-limited maximal 

progressive incremental cycle ergometer exercise test. All subjects underwent a medical 

screening and physical examination, including spirometry for those who had a history of 

smoking. Competitive athletes were excluded. The test subject population was dispersed in 

equal numbers (n =20) in ten-year age categories of 20-29 years, 30-39 years, 40-49 years, 

50-59 years, 60-69 years, and 70-79 years for each sex, with the exception of men over 70 years
B-3 

 of age (n = 11). Measurements of minute volume (V&E ), tidal volume (VT), and breathing 

frequency ( f ) were obtained at the end of each subject’s exercise test when maximal 

performance had been attained. The mean values at maximal exercise (V&E max, VT max, and f max) 

are presented in Table B-1 for each age group for both sexes. Average V&E max was 97 ± 25 

L·min-1 for all male subjects and ranged from 66 ± 12 to 114 ± 23 L·min-1. For females, average 

V&E max was 69 ± 22 L·min-1 and ranged from 48 ± 12 to 87 ± 17 L·min-1. Independent of age, 

V&E max, and VT max were significantly greater (p<0.001) for males compared to females. There 

was no difference in f max between men and women. 

Table B-1. Mean Values for Ventilation at the End of Maximum Exercise 

(Blackie et al., 1991) 

Group and Age 

(yr) 

VE, max 

(L/min) 

Fmax

(breaths/min) 

VT, max

(L) 

Men 20-29 114 ± 23 42 ± 8 2.7 ± 0.4 

Men 30-39 105 ± 30 40 ± 15 2.7 ± 0.6 

Men 40-49 102 ± 23 36 ± 7 2.9 ± 0.6 

Men 50-59 97 ± 15 36 ± 6 2.8 ± 0.3 

Men 60-69 83 ± 14 33 ± 6 2.6 ± 0.4 

Men 70-79 66 ± 12 30 ± 6 2.3 ± 0.4 

Men Mean 97 ± 25 36 ± 9 2.7 ± 0.5 

Women 20-29 87 ± 17 41 ± 7 2.2 ± 0.5 

Women 30-39 88 ± 19 44 ± 8 2.0 ± 0.3 

Women 40-49 74 ± 19 35 ± 8 2.1 ± 0.4 

Women 50-59 60 ± 15 32 ± 8 1.9 ± 0.4 

Women 60-69 56 ± 14 33 ± 9 1.7 ± 0.2 

Women 70-79 48 ± 12 31 ± 7 1.6 ± 0.3 

Women Mean 69 ± 22 36 ± 9 1.9 ± 0.4 

 Sue and Hansen (1984) reported values similar to Blackie et. al. (1991) for VT 

(2.28 ± 0.43 L) and f (41.6 ± 9.6 min-1) at maximum exercise in a population of middle-aged 

men (mean age = 54 years, range 34 to 74 years). Comparable values ofV&E have also been 

reported for specific age and gender groups and individual subjects at maximum efforts of 

incremental cycling exercise. Wasserman et al. (1987) measured V&E max values of 107 L·min-1

for a 55-year-old male executive, 89 L·min-1 for a 59 year old retired male shipyard worker, 

70 L·min-1 for a 45-year-old female homemaker, and 90 L·min-1 for a 37 year old male shipyard 

machinist, all values that fall within age-specific data reported by Blackie et al. (1991).
B-4 

In a study of similar design to that of Blackie et al. (1991), Neder et al. (2001) assessed 

breathing patterns during incremental exercise of 120 normal, healthy, sedentary individuals 

(60 males, 60 females) evenly distributed in age groups of 20-39 years, 40-59 years, and 

60-80 years. Although these investigators were primarily interested in developing normative 

ventilatory data at selected submaximal ventilatory stresses, maximal V&E data were reported for 

each age group by sex. For females, Neder et al. (2001) recorded average V&E max values of 

approximately 76 ± 14 L·min-1, 67 ± 11 L·min-1, and 50 ± 10 L·min-1 for the age groups of 

20-39 years, 40-59 years, and 60-80 years. Maximal V&E averaged 120 ± 28 L·min-1, 

99 ± 22 L·min-1, and 77 ± 12 L·min-1 for the three ascending male age groups. Again, these 

values reflect the data reported by Blackie et al. (1991) for a similar subject population. 

Therefore, the data presented in Table A-1 serve as a reasonable representation of normal 

maximal ventilatory responses to exhaustive incremental exercise for a wide range of ages in 

both males and females. 

B.3 Preliminary ECBC Data Compilation 

 The data in Table B-2 represent analysis of breath-by-breath ventilation data from three 

studies [Caretti et al. (2004); Coyne (2001); Johnson et al. (1999)], and provide a preliminary 

assessment of the impact of resistance breathing on ventilation at different work rates. The effect 

of breathing resistance and exercise intensity on measured breathing frequency and tidal volume 

are graphically illustrated in Figures B-1 and B-2. The 0.7 cm H2O/L/s resistance condition 

represents a “no mask” condition. The three other resistance conditions correspond to those 

imposed while wearing various air-purifying respirators (APRs). For reference, the resistance of 

the M40 military mask is approximately 2.7 cm H2O/L/s at 85 L/min. Both the mean tidal 

volume and breathing frequency tended to increase with increased work rate for each inhalation 

group. The breathing frequency tended to increase in higher proportions at the lower resistances. 

For example, the frequency increased by 65% as the exercise intensity increased from 30 to 85% 

at a resistance of 0.7 cm H2O/L/s. In comparison, the mean frequency only increased by 50% at 

an inhalation resistance of 5.73 cm H2O/L/s. There was not a significant difference in the tidal 

volumes measured for specific exercise intensities with inhalation resistances between 1.84 and 
B-5 

5.73 cm H2O/L/s. In several cases including the 85% exercise intensity, the tidal volume tends 

to decrease with increased inhalation resistance. 

Table B-2. Preliminary Data Compiled by ECBC to Assess Impact of Breathing Resistance 

and Work Intensity on Ventilation 

VE (L/min) VT (L) FR (min-1) PIF (L/min)

Estimated 

Work 

Intensity 

(% VO2 max) 

Inhalation 

Resistance 

(cm H2O/L/s) x S.D. x S.D. x S.D. x S.D. 

30 0.7 26.1 1.4 1.0 0.2 31.5 18.0 128.3 20.0 

 1.84 22.8 5.8 1.1 0.2 22.6 6.9 140.6 62.4 

 3.2 21.0 7.3 1.1 0.2 19.1 4.9 128.4 26.5 

 5.73 19.5 5.9 0.9 0.2 26.6 16.9 116.9 37.7 

40 0.7 26.9 7.6 1.1 0.2 29.7 10.4 159.3 24.4 

 1.84 30.1 7.1 1.4 0.4 22.4 3.6 179.6 96.4 

 3.2 30.0 7.9 1.4 0.3 22.9 4.7 170.4 43.8 

 5.73 26.9 8.2 1.2 0.3 27.2 10.9 177.5 77.8 

50 0.7 31.1 10.5 1.1 0.4 41.1 22.3 182.2 33.8 

 1.84 43.4 16.5 1.7 0.5 26.7 3.5 211.1 58.1 

 3.2 37.1 8.6 1.5 0.4 31.1 15.1 189.3 38.8 

 5.73 36.6 8.7 1.4 0.4 30.1 9.5 232.7 87.7 

70 0.7 46.2 14.1 1.4 0.5 52.4 28.2 264.6 52.3 

 1.84 53.4 13.1 1.9 0.6 32.4 10.6 239.1 54.4 

 3.2 57.2 14.8 1.8 0.4 35.0 9.9 295.5 144.9 

 5.73 51.4 15.7 1.7 0.6 36.6 11.7 349.7 94.0 

85 0.7 67.4 32.1 1.7 0.5 52.0 23.8 354.8 135.8 

 1.84 73.9 21.4 2.2 0.6 35.7 11.5 305.6 95.8 

 3.2 75.5 23.6 2.1 0.7 38.6 9.0 349.6 117.9 

 5.73 60.5 19.0 1.8 0.5 40.1 14.4 395.4 103.4 
B-6 

0

10

20

30

40

50

60

70

80

90

0.7 1.84 3.2 5.73

Inhalation resistance (cmH2O/L/s)

Fr (min-1)

30%

40%

50%

70%

85%

Figure B-1. Average (±SD) Breathing Frequency (Fr) at Exercise Intensities of about 30%, 

40%, 50%, 70%, and 85% of Maximal Oxygen Consumption (VO2 max) for Four 

Inhalation Resistance Conditions 

0

0.5

1

1.5

2

2.5

3

0.7 1.84 3.2 5.73

Inhalation resistance (cmH2O/L/s)

VT (L)

30%

40%

50%

70%

85%

Figure B-2. Average (±SD) Tidal Volume (VT) at Exercise Intensities of 30%, 40%, 50%, 

70%, and 85% of Maximal Oxygen Consumption (VO2 max) for Four Inhalation Resistance 

Conditions
B-7 

B.4 Rationale for Selected Flow Conditions 

 The cyclic flow conditions, summarized in Table B-3, were selected based on the 

analysis described previously. The 40 L/min minute volume represents a moderate breathing 

condition to allow comparison with the penetrations measured at higher flows. The 85 L/minute 

volume corresponded to a work intensity of approximately 85 percent VO2 max, respectively, as 

shown in Figures B-1 and B-2. The minute volume of 114 L/min corresponded to the average 

tidal volume and frequency during exhaustive incremental exercise of 20 to 29-year-old males as 

measured by Blackie et al. (1991). Adding one standard deviation to this minute volume 

provides the final flow condition. It is noted that the measurements made by Blackie et al. were 

unencumbered and, thus, provide a conservative estimate of breathing during maximal exercise 

under conditions of respirator wear. 

Table B-3. Summary of Selected Cyclic Flow Conditions 

Rate 

(breaths/min) 

Tidal Volume 

(L) 

Minute Volume 

(L/min) 

PIF(a)

(L/min) 

MIF(b)

(L/min) 

25 1.6 40 130 85 

37 2.3 85 270 175 

42 2.7 115 360 230 

44 3.1 135 430 275 

(a) Peak inspiratory flow rate assuming ideal sinusoidal waveform 

(b) Mean inspiratory flow rate assuming ideal sinusoidal waveform 

B.5 Constant Flow Conditions 

 Three constant flows were selected for testing: 85, 270, and 360 L/min. The 85 L/min 

represented the constant flow rate used in NIOSH certification of N95 and P100 particulate 

respirator filters. The 270 and 360 L/min represented the peak inspiratory flow rates of the 

cyclic flows with minute volumes of 85 and 115 L/min, respectively. In addition, the 270 L/min 

was approximately the mean inspiratory flow of the 135 L/min cyclic flow condition. 
B-8 

B.6 References 

Blackie, S.P., M.S. Fairbarn, N.G. McElvaney, P.G. Wilcox, N.J. Morrison, and R.L. Pardy. 

"Normal Values and Ranges for Ventilation and Breathing Pattern at Maximal Exercise." Chest 

100: 136-142 (1991). 

Caretti, D.M., P.D. Gardner, and K.M. Coyne, "Workplace Breathing Rates: Defining 

Anticipated Values and Ranges for Respirator Certification Testing," U.S. Army Edgewood 

Chemical Biological Center Technical Report, ECBC-TR-316, September (2004). 

Coyne, K. “Modeling the Pulmonary Effects of Respiratory Protective Masks During Physical 

Activity.” University of Maryland College Park (2001). 

Gallagher, C.G., E. Brown, and M. Younes. "Breathing Pattern During Maximal Exercise and 

During Submaximal Exercise with Hypercapnia." J. Appl. Physiol. 63: 238-244 (1987).

Johnson, A.T., W.H. Scott, C.G. Lausted, M.B. Benjamin, K.M. Coyne, M.S. Sahota, and M.M. 

Johnson. "Effect of Respirator Inspiratory Resistance Level on Constant Load Treadmill Work 

Performance." Am. Ind. Hyg. Assoc. J. 60: 474-479 (1999). 

Neder, J.A., L.E. Nery, C. Peres, and B.J. Whipp. "Reference Values for Dynamic Responses to 

Incremental Cycle Ergometry in Males and Females Aged 20 to 80." Am. J. Respir. Crit. Care 

Med. 164: 1481-1486 (2001). 

Sue, D.Y. and J.E. Hansen. "Normal Values in Adults During Exercise Testing." Clin. Chest 

Med. 5: 89-98 (1984). 

Wasserman, K., J.E. Hansen, D.Y. Sue, and B.J. Whipp. “Principals of Exercise Testing and 

Interpretation.” Philadelphia: Lea & Febiger, 1987. 
C-1 

APPENDIX C 

SHAKEDOWN TESTING OF MODEL 3160 
C-2 

C.1 Model 3160 Shakedown Testing 

Shakedown tests were conducted to characterize the test system and establish proper 

operating conditions. This included assessing the effect of non-isokinetic sampling, flow 

calibrations, and characterization of the challenge particle size distribution. 

C.2 No Filter Testing 

 Due to the range of flow conditions, it was not practical to sample isokinetically. 

However, non-isokinetic sampling is not expected to have a large effect for the small particle 

sizes (0.02 to 0.3 μm). To confirm this, tests were initially conducted without a test filter in the 

exposure chamber (i.e., Lucite® box). A penetration of 100 percent would indicate agreement 

between the measured upstream and downstream concentrations. Figures C-1 and C-2 compare 

the measured penetrations at the constant and cyclic flow conditions for the cartridge testing. 

Figure C-3 compares the no-filter penetrations measured at the filtering facepiece cyclic flow 

conditions. Data were not collected under the constant flow conditions. The data represents the 

means of three independent trials and the error bars represent one standard deviation. The 

measured penetrations were typically in the 90 to 110 percent range. From a practical 

perspective, the differences are not expected to have a significant impact on measured 

penetrations. 

10

100

1000

0.02 0.05 0.1 0.2 0.3

Particle Size (um)

Penetration (%)

42.5 L/min

135 L/min

180 L/min

Figure C-1. Penetrations Measured Without Test Filter at Constant 

Flow Conditions for Cartridge Testing 
C-3 

10

100

1000

0.02 0.05 0.1 0.2 0.3

Particle Size (um)

Penetration (%)

0.8 L, 25 bpm

1.2 L, 37 bpm

1.4 L, 42 bpm

1.6 L, 44 bpm

Figure C-2. Penetrations Measured Without Test Filter at Cyclic 

Flow Conditions for Cartridge Testing 

10

100

1000

0.02 0.05 0.1 0.2 0.3

Particle Size (um)

Penetration (%)

1.6 L, 25 bpm

2.3 L, 37 bpm

2.7 L, 42 bpm

3.1 L, 44 bpm

Figure C-3. Penetrations Measured Without Test Filter at Cyclic 

Flow Conditions for Filtering Facepiece Testing 

C.3 Challenge Characterization 

 Shakedown tests were performed to characterize the particle size distributions of the 

challenge aerosols. The particle size distribution is important since the Model 3160 uses a CPC 

that does not classify particles into discrete size ranges. Thus, all particles are assumed to be the 

particle size of interest. The Model 3160 was used to sequentially generate challenge aerosols 

with target mean particle sizes of 0.02, 0.05, 0.1, 0.2, and 0.3 μm. An electrostatic classifier and 
C-4 

CPC were used to measure the particle size distributions. The measured size distributions 

generated by the Model 3160 at a constant flow rate of 85 L/min are shown in Figures C-4 and 

C-5 for the salt and oil aerosols, respectively. Recall that a salt aerosol was used for testing the 

N95 filters and a dioctyl phthalate (DOP) aerosol for testing the P100 filters. Distinct peaks are 

observed for both aerosol types at target mean particle sizes of 0.05, 0.1, and 0.2 μm. However, 

a significant portion of the 0.3 μm challenge is below the target particle size. In addition, the 

particle concentration is approximately an order of magnitude lower than the other challenges. 

1

10

100

1000

10 100 1000

Size (nm)

Concentration (#/cc)

0.05 um

0.1 um

0.2 um

0.3 um

Figure C-4. Measured Particle Size Distributions of Salt Aerosol 

Used to Challenge N95 Filters 

10

100

1000

10000

100000

10 100 1000

Size (nm)

Concentration (#/cc)

0.05 um

0.1 um

0.2 um

0.3 um

Figure C-5. Measured Particle Size Distributions of DOP Aerosol 

Used to Challenge P100 Filters 

Figures C-6 and C-7 compare the measured size distributions of the 0.2, 0.3, and 0.4 μm 

aerosols at constant flow rates of 85 and 360 L/min, respectively. Note the similarity between 

the distributions of the 0.3 and 0.4 μm aerosols. Both distributions tend to shift toward smaller
C-5 

 particles as the flow rate is increased from 85 to 360 L/min. This is potentially due to 

increased evaporation caused by the additional dilution air, and could account for the increase in 

penetration observed with increasing particle size over 0.2 μm for the P100 filtering facepiece as 

discussed in Section 3.5.2.1 of the report. Figures C-8 and C-9 compare the up- and downstream 

distributions measured for the 0.4 μm aerosol at 85 and 360 L/min. Note that only a small 

fraction of the particles penetrating are greater than 0.3 μm. This shift in particle size could 

account for the increase in penetration with increased particle size observed for the filtering 

facepieces. 

1

10

100

1000

10000

100000

19.5

23.3

27.9

33.4

40

47.8

57.3

68.5

82

98.2

118

141

168

202

241

289

346

414

496

594

710

851

Size (nm)

Concentration (#/cc)

0.2 um

0.3 um

0.4 um

Figure C-6. Measured Size Distributions of the 0.2, 0.3, and 0.4 μm DOP 

Challenges at Flow Rate of 85 L/min 
C-6 

1

10

100

1000

10000

100000

19.5

23.3

27.9

33.4

40

47.8

57.3

68.5

82

98.2

118

141

168

202

241

289

346

414

496

594

710

851

Size (nm)

Concentration (#/cc)

0.2 um

0.3 um

0.4 um

Figure C-7. Measured Size Distributions of the 0.2, 0.3, and 0.4 μm DOP Challenges at 

Flow Rate of 360 L/min 

0.1

1

10

100

1000

10000

19.5

22.5

25.9

30

34.6

40

46.1

53.3

61.5

71

82

94.7

109

126

146

168

195

225

259

300

346

400

461

533

615

710

820

947

Size (nm)

Concentration (#/cc)

0.4 um Upstream

0.4 um Downstream

Figure C-8. Comparison of Measured Size Distributions Upstream and Downstream of 

Moldex P100 Filter at a Flow Rate of 85 L/min
C-7 

0.1

1

10

100

1000

10000

19.522.525.9

30

34.6

40

46.153.361.5

7182

94.7

109126146168195225259300346400461533615710820947

Size (nm)

Concentration (#/cc)

0.4 um Upstream

0.4 um Downstream

Figure C-9. Comparison of Measured Size Distributions Upstream and Downstream of 

Moldex P100 Filter at a Flow Rate of 360 L/min
C-8 

Blank
D-1 

APPENDIX D 

SHAKEDOWN OF TEST SYSTEM FOR LARGE PARTICLE INERT TESTING 
D-2 

D.1 Large Particle Shakedown Testing 

 Shakedown tests were completed to verify the proper operating conditions of the 

system. This included both no-filter testing to identify any potential sampling bias between the 

up- and downstream samples, and characterizing the challenge aerosol. 

D.2 No Filter Testing 

 Shakedown tests without a filtering facepiece or cartridge in the system were completed 

to identify any potential sampling bias between the up- and downstream measurements. The 

PSL with nominal diameters of 0.7, 1.3 and 2.9 μm were generated at three different constant 

flow rates. The measured no-filter penetrations are provided in Figure D-1. The results are 

based on the average of three independent trials at each test condition. The error bars represent 

one standard deviation. A penetration of 100 percent would represent agreement between the 

upstream and downstream measurements and no sampling bias. For the 0.7 and 1.3 μm particles, 

the measured penetrations ranged between 90 and 110 percent. However, the measured 

penetration of the 2.9 μm particle tended to decrease with increased flow rate indicating a 

sampling bias downstream for this particle size. Similar trends are observed under the cyclic 

flow conditions as shown in Figure D-2. 

10.00

100.00

1000.00

42.5 180 360

Flow (L/min)

% Penetration

0.67 um

1.3 um

2.9 um

Figure D-1. Penetrations Measured Without Test Filter at Constant Flow Conditions 
D-3 

10.00

100.00

1000.00

20 67.5 135

Minute Volum (L)

Penetration (%)

0.67 um

1.3 um

2.9 um

Figure D-2. Penetrations Measured Without Test Filter at Cyclic Flow Conditions 

 The no-filter penetrations with the 2.9 μm PSL are also shown in Figure D-3 as a 

function of flow rate. Each data point represents the mean of at least two trials and the error bars 

represent one standard deviation. The data points are connected by lines to emphasize the trends. 

These results were used to generate correction factors that could be applied to the 2.9 μm PSL 

results specific to each flow condition. However, the measured penetrations were below 

detectable limits in all cases (<0.001%), so it was not necessary to correct the data. 

40.00

50.00

60.00

70.00

80.00

90.00

100.00

110.00

0 50 100 150 200 250 300 350 400

Flow (L/min)

% Penetration

Constant Flow

Cyclic Flow

Figure D-3. 2.9 μm PSL No Filter Penetration for Cyclic and Constant Flows 
D-4 

Further experiments were performed to characterize the sampling technique for the 

2.9 μm aerosol. The downstream expansion chamber was removed and replaced with a tee 

fitting (with an approximate diameter of 2.5 cm) that allowed the insertion of isokenetic 

sampling probes with various inlet diameters, as summarized in Table D-1. Each probe was used 

to sample downstream during no-filter testing at a constant flow rate of 360 L/min. The results, 

shown in Figure D-4, indicated that the measured penetration tended to increase as the probe 

inlet diameter increased. Penetrations ranging from 90 to 95 percent were measured using 

probes 6 through 8. 

Table D-1. Summary of Isokinetic Probe Inlet Dimensions 

Probe Number Inlet ID (in) Inlet ID (cm) 

2 1/16 0.16 

4 1/8 0.32 

5 5/32 0.40 

6 3/16 0.48 

7 7/32 0.56 

8 1/4 0.64 

10

100

1000

45678

Probe Diameter (#/32 in.)

% Penetration

Figure D-4. Penetrations Measured Without a Test Filter at 360 L/min 

With Probes of Various Inlet Diameters 

 Probe 6 and a 0.3 cm ID probe located near the inlet of the downstream tubing, directly 

underneath the filter holder, were used to sample a 2.9 μm challenge downstream at different 

flow rates. The results are shown in Figure D-5. The percent penetration measured at each 
D-5 

sample location and flow rate represents a single trial. The measurements were all between 85 

and 115 percent. From a practical perspective, the differences are not expected to have a 

significant impact on measured penetrations. 

10

100

1000

42.5 180 360

Flow (L/min)

% Penetration

Downstream Inlet Probe

Probe # 6 Inline

Figure D-5. Comparison of Measured Penetrations Made 

Using Two Different Sampling Probes 

 

D.3 Challenge Aerosol Characterization 

Shakedown testing was also completed to assess the stability of the challenge 

concentration, which is required to sequentially make aerosol measurements between up- and 

downstream. Figure D-6 illustrates the length of time required for the challenge to reach steady 

state at various constant flow conditions. The challenge aerosol was 1.3 μm PSL generated using 

a 6-jet Collison nebulizer. As expected, the required duration to reach steady state increased 

with decreased flow rate. The challenge concentration reached steady-state within 5 minutes at 

the 180 and 360 L/min flow conditions. It took approximately 10 minutes at 135 L/min and 

20 minutes at 42.5 L/min. These times are consistent with those expected based on the flow rate 

and test chamber volume. Recall, the test filter is bypassed during startup to prevent loading of 

the filter. Note that the aerosol concentration decreased as the flow rate increased, due to the 

additional dilution air. 
D-6 

0

200

400

600

800

1000

1200

1400

0.0 5.0 10.0 15.0 20.0 25.0 30.0

Time (min)

Challenge Concentration (#/cc)

42.5 L/min

135 L/min

180 L/min

360 L/min

Figure D-6. Challenge Aerosol Concentration During System Startup 

 The same test was also performed with the 2.9 μm PSL at a flow rate of 135 L/min. 

The measured challenge concentration as a function of time is shown in Figure D-7. It took 

approximately 5 minutes for the chamber to reach steady state. Figure D-7 also compares 

concentration measurements made using the APS with and without the diluter (Model 3302A, 

TSI). Measurements made without the diluter were more consistent and, thus, the 2.9 μm 

challenge tests were not diluted prior to measurement. Note that the challenge concentration was 

only 20 particles/cc. The challenge concentration was increased by using a 24-jet Collison 

nebulizer and removing the charge neutralizer (Model 3012, TSI) from the test system. Figure 

D-8 shows the challenge concentration as a function of time at a flow rate of 135 L/min after the 

modifications. The concentration reached approximately 160 particles/cc after 

5 minutes.
D-7 

0

5

10

15

20

25

30

0 2 4 6 8 10 12 14 16

Time (min)

Challenge Concentration (#/cc)

No Diluter

Diluter

Figure D-7. Comparison of 2.9 μm Challenge Aerosol Concentration Measured Using the 

APS With and Without the Diluter 

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20 25

Time (min)

Challenge Concentration (#/cc)

Figure D-8. Measured Challenge Concentration of 2.9 μm PSL During System Startup at a 

Flow Rate of 135 L/min 

 Due to the large test matrix, conducting 0.67 and 1.3 μm PSL tests simultaneously was 

considered advantageous. The mixture was aerosolized using the 6-jet Collison nebulizer. 

Figure D-9 illustrates the challenge concentration as a function of time for both particle sizes. 

The size distribution measured using the APS is shown in Figure D-10 and indicates two distinct 

peaks at the desired particle sizes. Aerosol penetrations through the MSA Flexi-Filter® were 

made using each particle size individually and as a mixture. Similar penetrations were measured 
D-8 

with both approaches, as shown in Table D-2. Thus, testing 0.67 and 1.3 μm PSL 

simultaneously was performed to reduce the number of tests. The 2.9 μm particles could not be 

included in the mixture since the diluter was required to measure the 0.67 and 1.3 μm challenge 

concentrations. 

0

500

1000

1500

2000

2500

0 5 10 15 20 25

Time (min)

Challenge Concentration (#/cc)

0.67 um PSL

1.3 um PSL

Figure D-9. Challenge Concentration of 0.67 and 1.3 μm PSL 

Generated from a Mixture Using Collison Nebulizer 

0

100

200

300

400

500

600

700

800

<0.523

0.5830.6730.7770.8981.0371.1971.3821.5961.8432.1292.4582.8393.2783.7864.3715.048

Size (μm)

Concentration (#/cc)

Figure D-10. Particle Size Distribution Measured Using APS of 0.67 and 1.3 μm PSL 

Mixture Generated Using Collison Nebulizer
D-9 

Table D-2. Comparison of Measured Penetrations through MSA Flexi-Filter Using 

0.67 and 1.3 μm PSL Aerosolized Individually and as Mixture 

As mentioned previously, it would be beneficial to conduct 0.7, 1.3, and 2.9 μm filter 

tests simultaneously. A 6-jet Collison nebulizer was used to aerosolize Emery 3004 oil. The 

size distribution based on number concentration as measured using the APS is shown in Figure 

D-11. Adequate concentrations of 0.7, 1.3, and 2.9 μm particles were generated to measure oil 

efficiencies with all three particle sizes during a single trial. Thus, the 0.7, 1.3, and 2.9 μm oil 

tests were performed simultaneously.

0

200

400

600

800

1000

1200

0.542

0.673

0.835

1.037

1.286

1.596

1.981

2.458

3.051

3.786

4.698

5.829

7.234

8.977

Size (um)

Concentration (#/cc)

Figure D-11. Distribution of Emery 3004 Aerosol Generated Using Collison Nebulizer 

 Shakedown testing was performed to verify the assumption that the supermicron test 

system was well mixed. An oil challenge was generated with a 6-jet Collison Nebulizer. The 

aerosol exiting the nebulizer mixed with dry, filtered house air and passed through a charge 

neutralizer (Model 3012, TSI) before entering the chamber. An exhaust flow of 180 L/min was

Measured Penetration (%) Challenge 0.67 μm 1.3 μm 

0.67 μm PSL 0.358 - 

0.67 μm PSL 0.289 - 

1.3 μm PSL - 0.0263 

1.3 μm PSL - 0.0254 

Mixed (0.67 and 1.3 μm PSL) 0.378 0.0263 

Mixed (0.67 and 1.3 μm PSL) 0.351 0.0284 
D-10 

drawn through a filter mounted in a filter holder. A significant amount of 0.67 and 1.3 μm oil 

particles was generated. Two tests were completed using two different probes. The first test 

used a long straight sample probe to sample from the left side of the chamber, center of the 

chamber, and right side of the chamber. The second test used a curved probe to sample from the 

front of the chamber, the center of the chamber, and the back of the chamber. Both probes were 

inserted through the center of the chamber’s left side panel. The combined results of both tests 

showed a slight concentration increase from right to left and little difference from front to back 

for both particle sizes tested. A top view of the chamber, with a comparison of the 1.3 μm 

concentrations, is shown in Figure D-12. The percentages shown were calculated by dividing the 

concentration found from each section by the concentration found in the center and multiplying 

by 100 percent. 

 106 % 

113 % 100 % 86 % 

 107 % 

Front 

Figure D-12. Top View of Supermicron Test System with 1.3 μm Concentrations Shown as 

a Percentage of the Center Concentration 
E-1 

APPENDIX E 

SUMMARY OF MEASURED INERT FILTRATION EFFICIENCIES 
E-2 

Table E-1. Summary of Measured Penetrations through SEA HE-T Cartridge 

Particle Size (μm) 

0.02 0.05 0.1 0.2 0.3 0.7 1.3 2.9 

Flow 

Rate 

(L/min) Trial Penetration (%) 

1 <0.0001 <0.0001 0.0002 0.0004 0.0003 <0.0001 <0.0001 <0.0001 

2 <0.0001 <0.0001 0.0003 0.0006 0.0003 <0.0001 <0.0001 <0.0001 

3 <0.0001 <0.0001 0.0002 0.0003 0.0002 <0.0001 <0.0001 (a) 

x <0.0001 <0.0001 0.0002 0.0004 0.0003 <0.0001 <0.0001 <0.0001 

42.5 

σ - - 0.0000 0.0001 0.0001 - - - 

1 0.0001 0.002 0.009 0.012 0.006 <0.0001 <0.0001 <0.0001 

2 0.0001 0.002 0.008 0.011 0.005 <0.0001 <0.0001 <0.0001 

3 0.0001 0.002 0.010 0.012 0.006 <0.0001 <0.0001 (a) 

4 (b) (b) (b) (b) (b) <0.0001 <0.0001 (b) 

x 0.0001 0.002 0.0091 0.012 0.006 <0.0001 <0.0001 <0.0001 

135 

σ 0.0000 0.0004 0.0010 0.0009 0.0008 - - - 

1 0.005 0.008 0.029 0.030 0.019 <0.0001 <0.0001 <0.0001 

2 0.002 0.009 0.027 0.021 0.012 <0.0001 <0.0001 <0.0001 

3 0.001 0.005 0.030 0.018 0.010 <0.0001 <0.0001 <0.0001 

x 0.003 0.007 0.029 0.023 0.014 <0.0001 <0.0001 <0.0001 

180 

σ 0.002 0.002 0.001 0.006 0.005 - - - 

1 <0.0001 <0.0001 0.0002 0.0003 0.0002 <0.0001 <0.0001 <0.0001 

2 0.0001 <0.0001 0.0001 0.0003 0.0002 <0.0001 <0.0001 <0.0001 

3 <0.0001 <0.0001 0.0002 0.0003 0.0002 <0.0001 <0.0001 (a) 

x 0.0001 <0.0001 0.0001 0.0003 0.0002 <0.0001 <0.0001 <0.0001 

20(c)

σ - - 0.0000 0.0000 0.0000 - - - 

1 0.0002 0.001 0.006 0.009 0.003 0.0001 <0.0001 <0.0001 

2 0.0001 0.0009 0.005 0.007 0.005 <0.0001 <0.0001 <0.0001 

3 0.0001 0.0003 0.002 0.002 0.002 <0.0001 <0.0001 (a) 

x 0.0001 0.0008 0.004 0.006 0.003 0.0001 <0.0001 <0.0001 

42.5(c)

σ 0.0000 0.0004 0.002 0.003 0.002 - - - 

1 0.0004 0.002 0.010 0.013 0.007 0.0012 <0.0001 <0.0001 

2 0.0005 0.001 0.005 0.006 0.004 <0.0001 <0.0001 <0.0001 

3 0.0006 0.001 0.005 0.006 0.006 <0.0001 <0.0001 (a) 

4 (b) (b) (b) (b) (b) <0.0001 <0.0001 (b) 

x 0.0005 0.002 0.006 0.008 0.006 0.0004 <0.0001 <0.0001 

57.5(c)

σ 0.0001 0.0007 0.003 0.004 0.002 - - - 

1 0.001 0.004 0.016 0.018 0.010 <0.0001 <0.0001 <0.0001 

2 0.001 0.002 0.007 0.009 0.008 <0.0001 <0.0001 <0.0001 

3 0.002 0.002 0.008 0.010 0.010 <0.0001 <0.0001 (a) 

x 0.001 0.003 0.010 0.012 0.010 <0.0001 <0.0001 <0.0001 

67.5(c)

σ 0.0003 0.001 0.005 0.005 0.001 - - - 

(a) Only two tests planned 

(b) Test not planned 

(c) Cyclic flow minute volume 
E-3 

Table E-2. Summary of Measured Penetrations through Survivair 1050 Cartridge 

Particle Size (μm) 

0.02 0.05 0.1 0.2 0.3 0.7 1.3 2.9 

Flow 

Rate 

(L/min) Trial Penetration (%)

1 0.0003 0.003 0.008 0.009 0.006 <0.0001 <0.0001 <0.0001 

2 0.0001 0.002 0.006 0.008 0.004 <0.0001 <0.0001 <0.0001 

3 0.0001 0.002 0.007 0.008 0.004 <0.0001 <0.0001 (a) 

x 0.0002 0.002 0.007 0.008 0.005 <0.0001 <0.0001 <0.0001 

42.5 

σ 0.0001 0.0005 0.0007 0.0010 0.001 - - - 

1 0.003 0.037 0.093 0.059 0.035 <0.0001 <0.0001 <0.0001 

2 0.004 0.043 0.10 0.064 0.038 <0.0001 <0.0001 <0.0001 

3 0.005 0.048 0.10 0.063 0.039 <0.0001 <0.0001 (a) 

x 0.004 0.043 0.098 0.062 0.037 <0.0001 <0.0001 <0.0001 

135 

σ 0.001 0.005 0.005 0.003 0.002 - - - 

1 0.025 0.12 0.23 0.12 0.086 0.0001 <0.0001 <0.0001 

2 0.021 0.097 0.19 0.10 0.068 0.0001 <0.0001 <0.0001 

3 0.008 0.029 0.046 0.030 0.034 <0.0001 <0.0001 (a) 

x 0.018 0.084 0.16 0.086 0.063 0.0001 <0.0001 <0.0001 

180 

σ 0.009 0.050 0.097 0.049 0.027 0.0000 - - 

1 0.0002 0.002 0.016 0.010 0.008 0.0001 <0.0001 <0.0001 

2 0.0002 0.002 0.008 0.010 0.006 <0.0001 <0.0001 <0.0001 

3 0.0003 0.003 0.010 0.013 0.007 0.0011 <0.0001 (a) 

x 0.0002 0.003 0.011 0.011 0.007 0.0006 <0.0001 <0.0001 

20(b)

σ 0.0001 0.0005 0.004 0.002 0.0008 0.0008 - - 

1 0.003 0.019 0.049 0.036 0.018 <0.0001 <0.0001 <0.0001 

2 0.003 0.019 0.046 0.036 0.014 <0.0001 <0.0001 <0.0001 

3 0.003 0.021 0.049 0.033 0.016 <0.0001 <0.0001 (a) 

x 0.003 0.020 0.048 0.035 0.016 <0.0001 <0.0001 <0.0001 

42.5(b)

σ 0.0003 0.001 0.001 0.002 0.002 - - - 

1 0.005 0.029 0.066 0.041 0.020 <0.0001 <0.0001 <0.0001 

2 0.004 0.030 0.076 0.051 0.022 <0.0001 <0.0001 <0.0001 

3 0.010 0.044 0.097 0.072 0.035 <0.0001 <0.0001 <0.0001 

x 0.006 0.034 0.080 0.055 0.026 <0.0001 <0.0001 <0.0001 

57.5(b)

σ 0.004 0.008 0.016 0.016 0.008 - - - 

1 0.013 0.064 0.13 0.078 0.032 <0.0001 <0.0001 <0.0001 

2 0.009 0.047 0.097 0.059 0.041 <0.0001 <0.0001 <0.0001 

3 0.016 0.063 0.12 0.083 0.044 <0.0001 <0.0001 <0.0001 

x 0.013 0.058 0.12 0.074 0.039 <0.0001 <0.0001 <0.0001 

67.5(b)

σ 0.003 0.010 0.018 0.013 0.007 - - - 

(a) Only two tests planned 

(b) Cyclic flow minute volume 
E-4 

Table E-3. Summary of Measured Penetrations through North 7506 Cartridge 

Particle Size (μm) 

0.02 0.05 0.1 0.2 0.3 0.7 1.3 2.9 

Flow 

Rate 

(L/min) Trial Penetration (%)

1 4.9 8.5 3.2 1.9 1.0 0.0 0.00 0.0001 

2 5.9 9.0 3.3 1.8 1.0 0.2 0.03 <0.0001 

3 5.8 9.0 3.5 1.9 1.1 0.2 0.03 (a) 

x 5.5 8.8 3.4 1.9 1.0 0.2 0.02 0.0000 

42.5 

σ 0.6 0.3 0.2 0.1 0.0 0.1 0.01 0.0000 

1 16.3 18.6 9.9 8.4 5.9 2.7 0.07 0.0002 

2 14.6 17.9 9.7 8.8 5.9 2.4 0.08 <0.0001 

3 9.8 14.7 9.1 5.9 3.8 2.8 0.09 (a) 

x 13.6 17.1 9.6 7.7 5.2 2.6 0.08 0.0001 

135 

σ 3.4 2.0 0.4 1.5 1.2 0.2 0.01 0.0001 

1 17.6 21.5 14.2 13.8 9.9 3.7 0.07 0.0002 

2 20.5 21.6 14.9 14.2 9.8 1.8 0.06 0.0004 

3 16.8 19.5 11.9 14.2 9.8 2.9 0.05 (a) 

x 18.3 20.8 13.7 14.1 9.9 2.8 0.06 0.0003 

180 

σ 1.9 1.2 1.6 0.2 0.0 1.3 0.01 0.0002 

1 6.8 6.1 2.9 2.2 1.5 0.4 0.04 <0.0001 

2 6.6 6.4 2.7 2.2 1.9 0.7 0.07 <0.0001 

3 7.4 8.6 2.9 2.2 1.2 0.6 0.06 (a) 

x 6.9 7.0 2.9 2.2 1.5 0.5 0.06 <0.0001 

20(b)

σ 0.5 1.3 0.1 0.0 0.4 0.1 0.02 - 

1 11.3 13.0 6.0 5.4 3.7 2.0 0.09 <0.0001 

2 12.4 14.3 7.9 7.0 5.0 1.7 0.08 <0.0001 

3 8.1 9.2 4.3 3.0 1.7 0.5 0.01 (a) 

x 10.6 12.2 6.1 5.1 3.5 1.4 0.06 <0.0001 

42.5(b)

σ 2.2 2.6 1.8 2.0 1.6 0.8 0.05 - 

1 15.5 18.3 9.4 8.2 5.8 3.5 0.13 <0.0001 

2 15.3 17.0 9.5 8.7 7.4 2.6 0.09 0.0004 

3 14.1 16.5 9.4 8.4 7.1 2.7 0.09 (a) 

x 15.0 17.3 9.4 8.5 6.8 2.9 0.10 0.0003 

57.5(b)

σ 0.7 0.9 0.1 0.3 0.8 0.5 0.03 - 

1 18.4 21.7 12.3 11.0 7.9 0.9 0.01 0.0028 

2 19.2 15.9 10.2 11.0 6.4 2.6 0.07 0.0005 

3 18.8 18.8 10.9 11.0 8.3 2.6 0.07 (a) 

x 18.8 18.8 11.2 11.0 7.5 2.0 0.05 0.0016 

67.5(b)

σ 0.4 2.9 1.1 0.0 1.0 1.0 0.03 0.0016 

(a) Only two tests planned 

(b) Cyclic flow minute volume 
E-5 

Table E-4. Summary of Measured Penetrations through MSA Flexi-Filter 

Particle Size (μm) 

0.02 0.05 0.1 0.2 0.3 0.7 1.3 2.9 

Flow 

Rate 

(L/min) Trial Penetration (%)

1 0.2 0.4 0.1 0.0 0.0 0.00 0.00 <0.0001 

2 0.2 0.8 0.3 0.1 0.0 0.01 0.00 <0.0001 

3 0.2 0.8 0.4 0.1 0.1 0.00 0.00 (a) 

x 0.2 0.7 0.3 0.1 0.0 0.00 0.00 <0.0001 

42.5 

σ 0.0 0.2 0.1 0.1 0.0 0.00 0.00 - 

1 2.2 5.3 2.7 1.8 1.0 0.25 0.03 <0.0001 

2 2.1 3.1 1.7 1.0 0.5 0.29 0.02 <0.0001 

3 2.0 5.2 2.8 1.9 1.2 0.40 0.02 (a) 

x 2.1 4.6 2.4 1.6 0.9 0.31 0.02 <0.0001 

135 

σ 0.1 1.2 0.6 0.5 0.4 0.08 0.00 - 

1 2.6 2.8 2.1 1.7 1.1 0.65 0.04 <0.0001 

2 3.7 5.7 4.2 3.4 2.9 0.90 0.03 <0.0001 

3 4.6 9.4 6.9 5.2 3.3 0.53 0.03 (a) 

x 3.7 6.0 4.4 3.4 2.4 0.69 0.03 <0.0001 

180 

σ 2.6 2.8 2.1 1.7 1.1 0.26 0.00 - 

1 0.5 0.9 0.5 0.3 0.2 0.01 0.00 <0.0001 

2 0.8 1.2 0.6 0.6 0.6 0.02 0.00 <0.0001 

3 0.7 1.0 0.6 0.6 0.8 0.01 0.00 (a) 

x 0.7 1.0 0.6 0.5 0.6 0.01 0.00 <0.0001 

20(c)

σ 0.1 0.2 0.1 0.2 0.3 0.01 0.00 - 

1 2.0 2.0 1.1 0.8 0.7 0.14 0.01 <0.0001 

2 3.3 3.8 2.0 1.4 1.3 0.09 0.01 <0.0001 

3 2.9 4.2 2.5 2.4 2.9 0.15 0.01 (a) 

x 2.7 3.3 1.9 1.5 1.6 0.13 0.01 <0.0001 

42.5(c)

σ 0.7 1.2 0.7 0.8 1.2 0.03 0.00 - 

1 5.5 7.9 5.8 5.1 4.5 0.27 0.02 <0.0001 

2 2.0 4.2 2.1 1.4 0.8 0.26 0.02 <0.0001 

3 7.8 10.5 8.2 8.0 7.4 0.22 0.02 (a) 

4 3.6 7.2 3.9 2.7 1.9 (b) (b) (b) 

x 4.7 7.5 5.0 4.3 3.6 0.25 0.02 <0.0001 

57.5(c)

σ 2.5 2.6 2.6 2.9 3.0 0.03 0.00 - 

1 4.3 8.0 4.8 3.8 3.1 0.52 0.05 <0.0001 

2 4.6 7.0 4.8 5.0 5.9 0.29 0.02 <0.0001 

3 4.4 9.2 6.4 5.0 3.8 0.48 0.03 (a) 

x 4.4 8.1 5.3 4.6 4.3 0.43 0.03 <0.0001 

67.5(c)

σ 3.2 2.4 2.7 2.9 2.9 0.12 0.01 - 

(a) Only two tests planned 

(b) Test not planned 

(c) Cyclic flow minute volume 
E-6 

Table E-5. Summary of Measured Penetrations through 3M 8293 

Particle Size (μm) 

0.02 0.05 0.1 0.2 0.3 0.7 1.3 2.9 

Flow 

Rate 

(L/min) Trial Penetration (%)

1 0.006 0.009 0.004 0.004 0.004 <0.0001 <0.0001 <0.0001 

2 0.007 0.008 0.002 0.001 0.0008 0.0011 0.0004 <0.0001 

3 0.011 0.014 0.005 0.005 0.006 <0.0001 <0.0001 <0.0001 

x 0.008 0.010 0.004 0.003 0.004 0.0004 0.0002 <0.0001 

85 

σ 0.003 0.003 0.002 0.002 0.002 - - - 

1 0.17 0.20 0.041 0.019 0.045 0.002 0.0001 0.0002 

2 0.23 0.21 0.039 0.012 0.035 0.004 0.001 <0.0001 

3 0.26 0.26 0.049 0.012 0.033 0.001 0.0002 <0.0001 

x 0.22 0.22 0.043 0.014 0.038 0.002 0.0005 0.0001 

270 

σ 0.047 0.035 0.005 0.004 0.007 0.001 0.0005 - 

1 0.61 0.52 0.17 0.12 0.30 0.002 0.0001 0.0001 

2 0.43 0.33 0.11 0.19 0.37 0.002 0.0002 0.0001 

3 0.58 0.31 0.17 0.11 0.27 0.002 <0.0001 0.0001 

x 0.54 0.39 0.15 0.14 0.31 0.002 0.0001 0.0001 

360 

σ 0.098 0.12 0.035 0.04 0.055 0.0002 0.0001 0.0000 

1 0.014 0.030 0.004 0.0003 0.0003 0.002 0.001 0.0006 

2 0.010 0.025 0.003 0.0004 0.0004 0.0004 0.0003 0.0003 

3 0.021 0.028 0.006 0.003 0.003 0.001 0.0008 0.0001 

x 0.015 0.028 0.005 0.001 0.001 0.001 0.0008 0.0003 

40(b)

σ 0.005 0.003 0.001 0.002 0.002 0.0006 0.0005 0.0003 

1 0.21 0.30 0.051 0.006 0.007 0.0001 <0.0001 <0.0001 

2 (a) (a) (a) (a) (a) 0.0008 0.0005 0.0001 

3 (a) (a) (a) (a) (a) 0.0006 0.0003 0.0001 

x 0.21 0.30 0.051 0.006 0.007 0.0008 0.0005 0.0001 

85(b)

σ - - - - - 0.0003 0.0001 0.0000 

1 0.45 0.43 0.086 0.012 0.018 0.0003 <0.0001 <0.0001 

2 0.41 0.44 0.081 0.013 0.021 0.0002 <0.0001 <0.0001 

3 0.42 0.52 0.094 0.017 0.021 0.0005 0.0002 0.0001 

x 0.42 0.47 0.087 0.014 0.020 0.0003 0.0002 0.0001 

115(b)

σ 0.022 0.045 0.007 0.003 0.002 0.0002 - - 

1 (a) (a) (a) (a) (a) 0.004 0.001 0.0003 

2 (a) (a) (a) (a) (a) 0.001 0.0004 <0.0001 

3 (a) (a) (a) (a) (a) 0.003 0.001 0.0001 

x - - - - - 0.002 0.0009 0.0002 

135(b)

σ - - - - - 0.001 0.0005 0.0001 

(a) Test not planned 

(b) Cyclic flow minute volume 
E-7 

Table E-6. Summary of Measured Penetrations through Moldex 2360 

Particle Size (μm) 

0.02 0.05 0.1 0.2 0.3 0.7 1.3 2.9 

Flow 

Rate 

(L/min) Trial Penetration (%)

1 0.014 0.061 0.035 0.004 0.002 0.0002 <0.0001 <0.0001 

2 0.007 0.026 0.010 0.0006 0.0002 0.0001 <0.0001 <0.0001 

3 0.012 0.058 0.022 0.006 0.002 <0.0001 <0.0001 <0.0001 

x 0.011 0.048 0.022 0.003 0.001 0.0002 <0.0001 <0.0001 

85 

σ 0.004 0.019 0.012 0.003 0.001 0.0001 - - 

1 1.5 1.3 0.67 0.52 0.72 0.037 0.0003 0.0002 

2 0.36 0.61 0.33 0.42 0.58 0.063 0.0001 0.0005 

3 0.36 0.91 0.54 0.37 0.20 0.025 0.0017 0.0001 

4 (a) (a) (a) (a) (a) 0.022 (a) 0.0001 

x 0.75 0.94 0.51 0.43 0.50 0.037 0.0007 0.0002 

270 

σ 0.67 0.35 0.17 0.075 0.27 0.016 0.0009 0.0002 

1 0.33 0.64 1.1 0.17 0.29 0.056 0.019 0.001 

2 0.38 0.70 0.34 0.15 0.24 0.047 0.0001 0.004 

3 1.9 2.2 1.6 1.4 1.6 0.04 0.0002 0.0006 

4 (a) (a) (a) (a) (a) (a) (a) 0.0004 

x 0.86 1.2 1.0 0.57 0.71 0.0490 0.0064 0.0014 

360 

σ 1.1 1.0 0.89 0.89 0.96 0.0023 0.0001 0.0015 

1 0.009 0.081 0.032 0.004 0.059 0.0008 0.0005 0.0001 

2 0.026 0.11 0.053 0.018 0.014 0.0005 0.0003 <0.0001 

3 0.014 0.10 0.047 0.015 0.004 0.0002 <0.0001 <0.0001 

4 (a) (a) (a) (a) (a) (a) (a) 0.0002 

x 0.016 0.096 0.044 0.013 0.026 0.0005 0.0004 0.0001 

40(b)

σ 0.009 0.013 0.011 0.007 0.029 0.0003 0.0001 0.0000 

1 0.18 0.70 0.30 0.047 0.016 0.009 0.0009 <0.0001 

2 0.16 0.69 0.32 0.055 0.020 0.003 <0.0001 <0.0001 

3 0.14 0.79 0.37 0.059 0.029 0.003 0.0001 <0.0001 

x 0.16 0.73 0.33 0.054 0.022 0.005 0.0005 <0.0001 

85(b)

σ 0.023 0.057 0.037 0.006 0.007 0.003 0.0006 - 

1 (a) (a) (a) (a) (a) 0.020 0.006 0.001 

2 (a) (a) (a) (a) (a) 0.028 0.005 0.0001 

3 (a) (a) (a) (a) (a) 0.013 0.0003 <0.0001 

4 (a) (a) (a) (a) (a) 0.031 (a) (a) 

x - - - - - 0.023 0.004 0.0007 

115(b)

σ - - - - - 0.008 0.003 0.0008 

1 (a) (a) (a) (a) (a) 0.016 0.001 0.0007 

2 (a) (a) (a) (a) (a) 0.026 <0.0001 0.0001 

3 (a) (a) (a) (a) (a) 0.014 <0.0001 <0.0001 

x - - - - - 0.019 0.001 0.0004 

135(b)

σ - - - - - 0.007 - 0.0005 

(a) Test not planned 

(b) Cyclic flow minute volume 
E-8 

Table E-7. Summary of Measured Penetrations through MSA Affinity Plus 

Particle Size (μm) 

0.02 0.05 0.1 0.2 0.3 0.7 1.3 2.9 

Flow 

Rate 

(L/min) Trial Penetration (%)

1 1.0 2.7 1.9 1.3 0.9 0.86 0.20 0.0006 

2 1.3 3.3 2.4 1.8 1.4 1.1 0.21 <0.0001 

3 0.6 2.4 1.6 1.2 1.0 0.81 0.19 (a) 

x 1.0 2.8 2.0 1.4 1.1 0.92 0.20 0.0004 

85 

σ 0.4 0.5 0.4 0.3 0.3 0.16 0.01 - 

1 1.8 5.1 3.8 3.4 2.5 5.9 0.18 0.0026 

2 5.4 9.1 8.3 7.8 6.0 2.0 0.04 0.0017 

3 2.2 5.5 4.2 3.5 2.5 3.7 0.17 (a) 

4 4.2 9.7 8.5 7.7 5.5 (b) (b) (b) 

5 4.8 8.8 7.2 5.7 4.0 (b) (b) (b) 

x 3.7 7.6 6.4 5.6 4.1 3.8 0.13 0.0022 

270 

σ 1.6 2.2 2.2 2.2 1.6 2.0 0.08 0.0006 

1 4.8 7.9 7.6 7.1 5.6 3.82 0.13 0.0013 

2 3.4 6.1 6.4 6.2 5.0 3.39 0.08 0.0007 

3 3.1 6.8 6.8 6.4 5.2 5.86 0.15 (a) 

4 6.0 10.7 10.1 9.1 7.1 (b) (b) (b) 

5 5.9 10.4 10.4 9.2 7.4 (b) (b) (b) 

6 5.1 9.6 8.7 8.0 6.3 (b) (b) (b) 

x 4.7 8.6 8.3 7.7 6.1 4.36 0.12 0.0010 

360 

σ 1.2 1.9 1.7 1.3 1.0 1.32 0.04 0.0004 

1 1.3 3.1 2.0 1.6 1.1 1.04 0.16 0.0004 

2 1.3 2.8 1.9 1.7 1.0 1.42 0.23 0.0004 

3 1.7 3.4 2.6 2.3 1.8 2.07 0.28 (a) 

x 1.4 3.1 2.2 1.8 1.3 1.51 0.22 0.0004 

40(c)

σ 0.2 0.3 0.4 0.4 0.5 0.52 0.06 0.0000 

1 3.3 7.8 5.1 4.2 3.0 1.02 0.13 0.0001 

2 4.6 7.6 6.1 5.4 3.7 2.14 0.16 0.0014 

3 4.7 10.7 9.1 8.2 5.9 2.47 0.19 (a) 

x 4.2 8.7 6.7 5.9 4.2 1.87 0.16 0.0008 

85(c)

σ 0.8 1.7 2.1 2.0 1.5 0.76 0.03 0.0009 

1 7.2 14.1 13.1 12.5 8.6 1.45 0.02 0.0002 

2 8.5 13.3 12.5 11.2 8.5 3.67 0.15 <0.0001 

3 6.5 12.8 11.9 10.3 7.2 4.32 0.24 (a) 

x 7.4 13.4 12.5 11.3 8.1 3.14 0.14 0.0002 

115(c)

σ 1.0 0.7 0.6 1.1 0.7 1.51 0.11 - 

1 (b) (b) (b) (b) (b) 3.28 0.09 0.0006 

2 (b) (b) (b) (b) (b) 2.64 0.07 0.0004 

3 (b) (b) (b) (b) (b) 2.52 0.05 (a) 

x - - - - - 2.81 0.07 0.0005 

135(c)

σ - - - - - 0.41 0.02 0.0001 

(a) Only two tests planned 

(b) Test not planned 

(c) Cyclic flow minute volume 
E-9 

Table E-8. Summary of Measured Penetrations through Gerson 1730 

Particle Size (μm) 

0.02 0.05 0.1 0.2 0.3 0.7 1.3 2.9 

Flow 

Rate 

(L/min) Trial Penetration (%)

1 2.2 4.2 3.0 2.5 1.7 0.47 0.12 0.0059 

2 2.0 4.1 2.7 2.0 1.4 0.39 0.07 0.0036 

3 2.3 4.4 3.0 2.1 1.4 0.38 0.07 (a) 

x 2.1 4.2 2.9 2.2 1.5 0.41 0.09 0.0048 

85 

σ 0.2 0.2 0.2 0.2 0.2 0.05 0.03 0.0016 

1 7.2 10.9 10.1 9.1 7.8 2.78 0.09 0.0003 

2 4.4 8.4 8.4 7.2 4.8 2.77 0.27 0.0050 

3 5.4 9.9 8.7 7.1 5.3 3.27 0.18 (a) 

x 5.6 9.7 9.1 7.8 6.0 2.94 0.18 0.0027 

270 

σ 1.4 1.3 0.9 1.1 1.6 0.29 0.09 0.0033 

1 6.8 8.9 9.0 7.9 6.0 3.46 0.11 0.0014 

2 6.0 8.9 9.1 7.7 6.6 3.37 0.10 0.0010 

3 4.9 7.5 7.7 6.5 5.2 3.29 0.09 (a) 

x 5.9 8.4 8.6 7.4 5.9 3.37 0.10 0.0012 

360 

σ 1.0 0.8 0.8 0.8 0.7 0.08 0.01 0.0003 

1 4.4 8.7 6.3 5.9 5.1 0.58 0.11 0.0013 

2 3.4 7.2 4.8 4.0 3.1 0.57 0.11 0.0016 

3 4.0 7.7 5.5 5.6 5.1 0.58 0.14 (a) 

x 3.9 7.9 5.5 5.2 4.4 0.58 0.12 0.0015 

40(c)

σ 0.5 0.8 0.8 1.0 1.1 0.01 0.02 0.0002 

1 7.5 13.6 11.3 9.5 6.5 1.63 0.16 0.0010 

2 9.9 15.9 14.6 11.9 8.0 2.18 0.22 0.0026 

3 7.7 13.7 11.4 10.2 7.4 1.89 0.37 (a) 

x 8.4 14.4 12.5 10.5 7.3 1.90 0.25 0.0018 

85(c)

σ 1.4 1.3 1.9 1.2 0.7 0.28 0.11 0.0011 

1 12.6 18.7 16.8 14.6 10.1 1.99 0.11 0.0015 

2 9.1 15.1 14.3 12.1 8.2 1.74 0.16 0.0021 

3 11.4 15.3 15.5 13.1 8.8 2.42 0.08 (a) 

x 11.0 16.4 15.5 13.2 9.0 2.05 0.11 0.0018 

115(c)

σ 1.8 2.0 1.3 1.2 1.0 0.34 0.04 0.0004 

1 (b) (b) (b) (b) (b) 2.70 0.10 <0.0001 

2 (b) (b) (b) (b) (b) 2.43 0.15 0.0021 

3 (b) (b) (b) (b) (b) 2.29 0.08 (a) 

x - - - - - 2.47 0.11 0.0011 

135(c)

σ - - - - - 0.21 0.03 - 

(a) Only two tests planned 

(b) Test not planned 

(c) Cyclic flow minute volume 
E-10 

Blank 
F-1 

APPENDIX F 

ESTIMATION METHOD FOR CYCLIC FLOW PENETRATIONS 
F-2 

F.1 Introduction 

 

 The results summarized in Section 3.5 demonstrated that the mean inhalation flow is a 

key parameter when comparing penetrations measured under constant and cyclic flow 

conditions. To further understand the relationship, a method was developed to predict cyclic 

flow penetrations based on penetrations measured over a range of constant flow rates. The 

method is described in Section F.2 and compared to the experimental results that were discussed 

in Section 3.0. 

F.2 Approach 

 Initially, the effect of flow rate on penetration for a specific particle size must be 

determined experimentally. A regression analysis of this data provides the penetration as a 

function of flow rate: 

B ( ) Pi FC = A× FC

where Pi is the penetration of the specific particle size (%), FC the constant flow rate (L/sec), and 

A and B the regression coefficients. An example is provided in Figure F-1 for the SEA P100 

cartridge tested against a 0.2 μm particle at flow rates of 42.5, 135, and 180 L/min. For cyclic 

flow, the flow rate through the filter is time dependent and, thus, the penetration will also be time 

dependent. Assuming sinusoidal flow, the time dependent flow rate F(t) is given by: 

⎟

⎠

⎞ ⎜

⎝

⎛ F t = F t Peak

ω

2π ( ) sin

where FPeak is the peak inhalation flow rate (L/sec), ω is the breathing flow cycle time (sec), and t 

is the time (sec). The flow rate over the inhalation cycle is provided in Figure F-2 for the four 

cyclic flow conditions used in cartridge testing. Combining the above expressions gives the 

penetration as a function of time over the inhalation cycle: 

B

2 ( ( )) sin ⎥

⎦

⎤ ⎢

⎣

⎡ ⎟

⎠

⎞ ⎜

⎝

⎛ P F t = A× F t i Peak

ω

π

which is shown in Figure F-3 for each of the four flow conditions.
F-3 

y = 0.0011x2.8267

R2 = 0.9989

0.0001

0.001

0.01

0.1

1

0.1 1 10

Flow Rate (L/sec)

Penetration (%)

0.2 um

Figure F-1. Effect of Flow Rate and Particle Size on Measured Penetration 

Through the Survivair® P100 Cartridge 

0

50

100

150

200

250

0 0.2 0.4 0.6 0.8 1 1.2 1.4

T ime ( sec)

0.8 L, 25 breaths/min

1.15 L, 37 breaths/min

1.35 L, 42 breaths/min

1.55 L, 44 breaths/min

Figure F-2. Instantaneous Flow Rates During Inhalation Cycle 

Assuming Ideal Sinusoidal Waveform

B P(F(t)) A F (t) i = × i
F-4 

0.E+00

1.E-02

2.E-02

3.E-02

4.E-02

5.E-02

6.E-02

7.E-02

8.E-02

9.E-02

1.E-01

0 0.2 0.4 0.6 0.8 1 1.2 1.4

T ime ( sec)

0.8 L, 25 bpm

1.15 L, 37 bpm

1.35 L, 42 bpm

1.55 L, 44 bpm

Figure F-3. Predicted Instantaneous Penetrations During Inhalation Cycle Based on 

Measured Constant Flow Penetrations for the SEA Cartridge 

 The average penetration over the inhalation cycle was then determined for each cyclic 

flow condition using the following expression: 

∫

∫ = 2

0

2

0

( ( ))

π

π

dt

P F t dt

P

i

Avg

The integral was estimated using a numerical technique. The predicted cyclic flow penetrations 

using this method are compared with the measured cyclic flow penetrations measured for the 

cartridges and filtering facepieces in Figures F-4 and F-5. The figures include a variety of 

particle sizes and flow conditions. The flow rates in the legend represent cyclic flow minute 

volumes. The dashed line is the one-to-one line, and represents agreement between the predicted 

and measured penetrations. The results show that the penetration measured during breathing 

flow conditions can be accurately estimated from the constant flow conditions, as all data points 

tend to lie on the one-to-one line. 
F-5 

0.0001

0.001

0.01

0.1

1

10

100

0.0001 0.001 0.01 0.1 1 10 100

Predicted Penetration (%)

Measured Penetration (%)

SEA P100 (0.1, 0.2, 0.3 um)

Survivair P100 (0.1, 0.2, 0.3 um)

North N95 (0.1, 0.3, 0.7 um)

MSA N95 (0.1, 0.3, 0.7 um)

1:1 Line

Figure F-4. Comparison of Measured and Predicted Cyclic Flow Penetrations 

Through Cartridges 

 

0.001

0.01

0.1

1

10

100

0.001 0.01 0.1 1 10 100

Predicted Penetration (%)

Measured Penetration (%)

MSA N95 (0.02 to 0.3 um)

Gerson N95 (0.02 to 0.3 um)

Moldex P100 (0.02 to 0.3 um)

3M P100 (0.02 to 0.3 um)

Figure F-5. Comparison of Measured and Predicted Cyclic Flow Penetrations 

Through Filtering Facepieces 
F-6 

Blank
G-1 

APPENDIX G 

MICROBIOLOGICAL METHODS 
G-2 

G.1 Bg Spores 

G.1.1 Growth/Harvest of Bg 

The Bg spores were purchased from the U.S. Army's Dugway Proving Ground 

(Dugway, UT) in powder form. 

G.1.2 Quantification of Bg Spores 

The concentration of Bg spores was determined by the standard plate and count method. 

Samples collected on mixed cellulose ester filters were removed from their respective filter 

holders using decontaminated forceps and placed in 50 mL conical tubes containing 10 mL 

pH=7.4 phosphate buffered saline (PBS). Extraction was then performed by vortexing each tube 

at the maximum setting for 30 seconds each. Bg samples were serially diluted in PBS per 

standard microbiological protocols. Samples were then plated in triplicate on Tryptic Soy Agar 

(TSA) using the Spiral Biotech Autoplate® 4000 (Figure G-1). The plates were incubated 

overnight at 30°C. Colony forming units per mL (cfu/mL) were determined by counting the 

resulting colonies with the Spiral Biotech QCount® colony counter Figure G-2. 

Figure G-1. Spiral Biotech Autoplate 4000®
G-3 

Figure G-2. Spiral Biotech QCount® Colony Counter 

G.2 MS2 Phage 

G.2.1 Growth of E. coli 

 

E. coli serves as the host for MS2 replication and was needed for the MS2 

quantification assay. Before culturing, the E. coli (American Type Culture Collection [ATCC] 

No. 15597, Rockville, MD) stock was tested for purity by streaking on a tryptic soy agar (TSA) 

plate, incubating at 37°C for 12 hours, and examining the plate for contaminating colonies. 

After verifying the stock was pure, a working solution of E. coli was prepared by inoculating 

nutrient broth (NB) media and incubating in a shaking incubator at 37°C and 150 revolutions per 

minute (rpm).

G.2.2 Growth/Harvest of MS2 

MS2 was prepared according to the U.S. Army Dugway Proving Ground Draft SOP: 

MS2 Growth and Purification (March, 1996). Two 50 mL overnight cultures of Escherichia coli

A/λ in LB-Miller broth were prepared by inoculating each 50 mL aliquot of LB-Miller in 

250 mL flasks with one colony each of E. coli A/λ. The cultures were incubated approximately 
G-4 

12 hours at 37 °C with shaking at 200 rpm. After the incubation period was complete, each 

50 mL culture was used to inoculate 500 mL of LB-Miller broth in 2800 mL fernbach flasks. 

The cultures were incubated at 37°C until a cellular density of 108

 to 109 cells was achieved 

indicated by an optical density at 600 nm of 0.2 to 0.3. Once this density was achieved, each 

culture was inoculated with 3 mL of a 5.0E+11 pfu/mL MS2 suspension to achieve a multiplicity 

of infection of approximately 0.5. The cultures were incubated at 37°C with shaking at 200 rpm 

until lysis occurred, which was indicated by a drop in optical density. To aid in release of phage 

from the cells, 500 μL of 0.05 g lysozyme/mL was added to each culture and incubated at 37°C 

with shaking at 200 rpm for 30 minutes. After the incubation, 1.0 mL of 0.5 M EDTA and 

1.0 mL of chloroform were added to each culture and incubated at 37°C with shaking at 200 rpm 

for 30 minutes. The suspensions were then centrifuged at 8000 rpm at 4°C for 30 minutes in 

250 mL centrifuge bottles to remove cell debris. The supernatant was filtered through a 0.22 μm 

cellulose acetate filter. This crude preparation was stored at 2 - 8°C. 

The MS2 phage stock solution was from the ATCC (No. 15597-B1). MS2 was grown by 

adding 0.1 mL of the MS2 stock and 0.2 mL of the E. coli working solution to 3 mL of molten 

top agar and then pouring the mixture onto a TSA plate. Plates were incubated for 24 hours at a 

temperature of 37°C to allow virus growth. After incubation, 3 mL of filtered, de-ionized water 

was added to plates which had 103

 to 104 plaques and the surface of the plate agitated for five 

minutes to facilitate transfer of MS2 from the agar to the water. The liquid was removed from 

the plates, centrifuged at 8000 rpm for 15 minutes and filtered through a 0.2 μm filter to remove 

any cellular debris. MS2 remained in suspension throughout centrifugation and filtration. This 

clarified virus suspension became the working solution for bioaerosol generation and its 

infectivity was determined as described in section G.2.4. Previous experience has shown that 

this working solution will have > 109

 infectious virus particles per mL of solution. 

 A precipitation procedure was used to further purify the crude MS2 preparations. The 

crude MS2 suspensions were added to a sterile 2000 mL flask containing a sterile stir bar. 

Sodium chloride was added to a final concentration of 0.5 M (29.2 g/L). Polyethylene glycol 

8000 was added to a final concentration of 10% (100 g /L). The suspension was stirred at the 

lowest setting for 12 hours while incubating at 4°C. The precipitation suspension was then 

centrifuged in 250 mL centrifuge bottles at 10,000 rpm for 30 minutes at 4°C. The resulting
G-5 

supernatant was discarded and the pellets were resuspended in one liter of 0.22 μm-filtered 

distilled water. This purified suspension was the stored at 2 – 8°C. 

G.2.3 Dry MS2 Preparation 

Dry MS2 was prepared by adding 500 mL of the purified MS2 suspension to 500 mL of 

20% skim milk solids. The resulting suspension was mixed thoroughly and divided equally 

among three 500 mL bottles. The MS2 suspensions were then frozen at -70°C for three hours. 

The surface area of the MS2 was maximized by incubating the bottles at a slant during freezing. 

The frozen MS2 suspensions were then placed uncapped in freeze flasks and connected to a 

Labconco Lyph-Lok 6 freeze dry system. The samples were dried for 6 days. After the samples 

were completely dry, they were removed from the lyophilizer and large pieces were broken up 

with a spatula. Particle size was further reduced by light grinding with a mortar and pestle. The 

dry MS2 was then placed in a US Stoneware milling jar with 16 pieces of 0.5 inch milling media. 

The milling jar was placed on an automated roller and the MS2 was milled for three hours. The 

dry MS2 was removed from the milling jar and stored in a sterile Nalgene bottle. Final particle 

size reduction was achieved using a jet mill (Model 00 Jet-O-Mizer, Fluid Energy Processing 

and Equipment Company, Telford, PA) operated at 120 psig. The crude MS2 was fed to the jet 

mill using an electromagnetic vibrating feeder (Model F-TO-C, FMC Technologies, Homer City, 

PA). The feed material to the jet mill is entrained by the stream of circulation fluid within the jet 

mill. The violent jet action breaks up individual particles through particle to particle impaction. 

The jet mill is shown in Figures G-3 and G-4. After milling, the dry MS2 was mixed with 

10 percent Aerosil by weight. 
G-6 

Figure G-3. Jet Mill Used for Processing Dry MS2 

Figure G-4. Jet Mill and Vibrating Feeder Used for Processing Dry MS2 

G.2.4 Enumeration of MS2 

The number of infective virus particles was determined by plaque assay. Plaque assays 

are done by infecting a monolayer of host cells. When light is passed through a Petri dish 

containing a monolayer of cells the dish appears cloudy. As the virus grows and lyses the host, 

the area where cells are dying becomes clear. This is called a plaque. Ideally, the virus sample 
G-7 

is diluted so that each plaque is made by a single virus particle and the concentration of 

infectious virus in a sample is given as the number of pfu per mL of solution.

 Sampled gelatin filters were removed from their respective filter holders using 

decontaminated forceps and placed in 50 mL conical tubes containing 10 mL pH=7.4 phosphate 

buffered saline (PBS). The filters were then solubilized by incubating at 37°C with shaking at 

200 rpm for 15 minutes. MS2 samples were then serially diluted in PBS per standard 

microbiological protocols and plated following the method described by U.S. Army Dugway 

Proving Ground Draft SOP: MS2 Growth and Purification (March, 1996). Using this method, a 

0.1 mL aliquot of diluted MS2 suspension was transferred to an empty Petri dish, along with a 

0.2 mL aliquot of Escherichia coli A/λ host cells in the logarithmic phase of growth. 

Approximately 20 mL of TSA with a decreased percentage of agar (0.75%) was then poured into 

each dish and the contents were thoroughly mixed. Each sample was plated in triplicate and the 

plates were incubated overnight at 37°C. Plaques, areas of clearing caused by lysis of the E.coli

host cell lawn, were counted and used to calculate the plaque forming units per mL (pfu/mL). 
G-8 

Blank 
H-1 

APPENDIX H 

SHAKEDOWN TESTING OF THE BIOAEROSOL TEST SYSTEM 
H-2 

H.1 Bioaerosol Test System Shakedown

 Prior to efficiency testing, shakedown testing was performed to establish proper 

operating conditions. This included inert testing to compare with the ECBC test system, 

characterization of the challenge aerosol, flow calibrations, and characterization of the viable 

particle samplers. The system shakedown results are provided in this Appendix. 

H.2 Comparison with ECBC Test System 

An objective of this task is to compare efficiencies measured using the inert and 

biological aerosols. Since the inert testing was performed at ECBC and the biological testing at 

Battelle, shakedown tests were performed with inert aerosols to compare the two test systems. 

Inert testing was completed at Battelle with the North N95 cartridge filter and challenge aerosols 

of 0.3 and 1.0 μm PSL. The upstream and downstream concentrations were measured using the 

LAS-X. The results are provided in Table H-1 and graphically compared in Figure H-1. In 

general, the measured penetrations at both facilities were similar with the exception of the 

1.3 μm results at a constant flow of 180 L/min. The penetration measured at Battelle under these 

conditions was approximately an order of magnitude higher than that measured at ECBC. The 

trends in measured penetration are similar for both facilities. 

 

Table G-1. Comparison of Inert Filtration Efficiencies Measured at Battelle and ECBC 

Filter 

Particle 

Size 

(μm) 

Flow 

Condition 

Flow Rate 

(L/min) 

Average 

Penetration 

(%) 

ECBC 

Penetration 

(%) 

North N95 0.3 Constant 42.5 1.6 ± 0.04 1.0 ± 0.02 

North N95 0.3 Constant 180 13 ± 2.8 10 ± 0.02 

North N95 1.3(a) Constant 42.5 0.03 ± 0.04 0.03 ± 0.01 

North N95 1.3(a) Constant 180 0.3 ± 0.06 0.06 ± 0.01 

North N95 0.3 Cyclic 42.5(b) 3.9 ± 2.7 3.5 ± 1.7 

North N95 0.3 Cyclic 68(c) 4.3 ± 6.2 7.5 ± 1.0 

North N95 1.3(a) Cyclic 42.5 0.08 ± 0.02 0.06 ± 0.05 

North N95 1.3(a) Cyclic 68 0.05 0.05 ± 0.03 

(a) 1.0 um PSL used in Battelle testing 

(b) 1.15 L tidal volume, 37 breaths/min 

(c) 1.55 L tidal volume, 44 breaths/min
H-3 

0.001

0.01

0.1

1

10

100

Constant - 42.5 L/min Constant - 180 L/min Cyclic - 42.5 L/min Cyclic - 68 L/min

Penetration (%)

ECBC - 0.3 um

Battelle - 0.3 um

ECBC - 1 um

Battelle - 1 um

Figure H-1. Comparison of Inert Filtration Efficiencies 

 Measured at Battelle and ECBC 

H.3 Challenge Aerosol Characterization 

Shakedown testing was completed to measure the size distribution of the Bg spores and 

to verify the generator maintained a stable output. The aerosol concentration as a function of test 

duration as measured by the Aerosizer is shown in Figure H-2. The bioaerosol particle size 

distributions were measured using either a laser aerosol spectrometer, Aerosizer, or cascade 

impactor as was described in the report. Attempts to measure the particle size distributions of 

the bioaerosols using the Andersen impactor were unsuccessful due to the high challenge 

concentration which resulted in overloading of the stages.
H-4 

1.00E+07

1.00E+08

1.00E+09

1.00E+10

0 5 10 15 20 25 30 35 40 45

Time (min)

Concentration (#/m3

)

Figure H-2. Concentration of Bg Spore Aerosol Challenge as a Function of Test Time 

H.4 Bioaerosol Sampling 

Tests were completed to characterize the collection efficiencies of the cellulose ester 

filters. The collection efficiencies were measured by collecting samples with two filters operated 

in series and performing a bioassay on each. The initial filter typically collected over 

99.99 percent of the total spores collected. 

 Tests were also completed without a respirator filter to compare samples collected upand downstream. Tests were performed at constant flow rates of 42.5 and 180 L/min and 

resulted in measured penetrations of 97.3 and 93.3 percent, respectively. Similar tests at cyclic 

flows with minute volumes of 40 and 135 L/min resulted in penetrations of 93 and 103 percent. 

Thus, the upstream and downstream measurements were within 10 percent for all tests. 

 Following a test with a Bg spore challenge, the test system was flushed with HEPA 

filtered air and a negative control test was performed. Samples were collected from the 

downstream chamber and bioassayed. No viable particles were detected. This demonstrated the 

procedure for sterilization of the system and 47-mm filter holders was successful and there was 

no carryover between tests. The minimum detection limit of the bioassay technique was set at 20 

cfu or pfu/L air sampled. A typical challenge concentration was 1 x 105

 cfu/L air sampled. 

Thus, the minimum measurable penetration was typically 0.005 percent. This was nearly an 

order-of-magnitude lower than the P100 penetration requirement (<0.03 percent). 
I-1 

APPENDIX I 

SUMMARY OF BIOAEROSOL PENETRATION RESULTS 
I-2 

Table I-1. Summary of Measured Penetrations through SEA HE-T 

Bioaerosol Challenge 

Bg "Wet" Bg "Dry" MS2 "Wet" MS2 "Dry" 

Flow 

Rate 

(L/min) Trial Penetration (%) 

1 <0.005 <0.001 <0.002 <0.001 

2 <0.003 <0.001 <0.004 <0.001 

3 <0004 <0.001 <0.001 - 

x 0.004 0.001 0.002 0.001 

42.5 

Constant 

σ 0.001 - 0.002 - 

1 <0.004 <0.002 <0.013 <0.001 

2 <0.004 <0.003 <0.008 <0.002 

3 <0.004 <0.003 <0.005 - 

x 0.004 0.003 0.009 0.002 

135 

Constant 

σ - 0.001 0.004 0.001 

1 <0.001 <0.005 <0.001 <0.001 

2 <0.001 <0.002 <0.013 <0.001 

3 <0.003 <0.001 <0.006 - 

x 0.002 0.003 0.007 0.001 

42.5 

Cyclic(a)

σ 0.001 0.002 0.006 - 

1 <0.001 <0.001 0.015 <0.002 

2 <0.002 <0.002 <0.010 <0.005 

3 <0.003 <0.002 <0.020 - 

x 0.002 0.002 0.015 0.004 

67.5 

Cyclic(a)

σ 0.001 0.001 0.005 0.002 

(a) Cyclic flow minute volume 

Table I-2. Summary of Measured Penetrations through Survivair 1050 

Bioaerosol Challenge 

Bg "Wet" Bg "Dry" MS2 "Wet" MS2 "Dry" 

Flow 

Rate 

(L/min) Trial Penetration (%) 

1 <0.004 0.008 0.059 <0.030 (b)

2 <0.003 <0.001 0.005 <0.002 

3 <0.002 <0.001 0.002 - 

x 0.003 0.003 0.022 0.002 

42.5 

Constant 

σ 0.001 0.004 0.032 - 

1 <0.005 0.086 <0.008 <0.001 

2 <0.004 <0.002 0.035 <0.002 

3 <0.004 <0.002 <0.012 - 

x 0.004 0.030 0.018 0.002 

135 

Constant 

σ 0.001 0.048 0.016 0.001 

1 0.001 <0.002 0.017 <0.008 

2 0.002 <0.003 <0.007 <0.001 

3 0.001 <0.001 <0.012 - 

x 0.001 0.002 0.012 0.005 

42.5 

Cyclic(a)

σ 0.001 0.001 0.005 0.005 

1 <0.001 <0.003 <0.047 <0.015 

2 0.006 <0.003 0.013 <0.009 

3 0.013 <0003 <0.32 (b) - 

x 0.006 0.003 0.030 0.012 

67.5 

Cyclic(a)

σ 0.006 - 0.024 0.004 

(a) Cyclic flow minute volume 

(b) Not included in average due to low challenge concentration 
I-3 

Table I-3. Summary of Measured Penetrations through MSA Flexi-Filter 

Bioaerosol Challenge 

Bg "Wet" Bg "Dry" MS2 "Wet" MS2 "Dry" 

Flow 

Rate 

(L/min) Trial Penetration (%) 

1 <0.002 <0.001 1.4 <0.001 

2 <0.002 0.012 0.24 <0.016 

3 <0.002 <0.001 0.012 - 

x 0.002 0.005 0.55 0.009 

42.5 

Constant 

σ - 0.007 0.75 0.010 

1 <0.004 0.013 2.7 0.010 

2 0.006 0.018 0.80 0.004 

3 0.005 0.011 0.43 - 

x 0.005 0.014 1.3 0.007 

135 

Constant 

σ 0.001 0.004 1.2 0.004 

1 0.003 0.014 1.0 <0.002 

2 <0.002 0.010 0.16 <0.004 

3 <0.003 0.014 2.1 - 

x 0.003 0.013 1.1 0.003 

42.5 

Cyclic(a)

σ 0.001 0.002 1.0 0.002 

1 0.003 0.036 0.68 0.022 

2 0.080 0.017 0.81 0.029 

3 0.019 0.037 0.13 - 

x 0.034 0.030 0.54 0.025 

67.5 

Cyclic(a)

σ 0.041 0.011 0.36 0.005 

(a) Cyclic flow minute volume 

(b) Low challenge, not included in average 

Table I-4. Summary of Measured Penetrations through North 7506 

Bioaerosol Challenge 

Bg "Wet" Bg "Dry" MS2 "Wet" MS2 "Dry" 

Flow 

Rate 

(L/min) Trial Penetration (%) 

1 0.008 0.003 0.39 0.001 

2 <0.004 0.003 0.32 0.002 

3 <0.003 0.012 0.19 - 

x 0.005 0.006 0.30 0.001 

42.5 

Constant 

σ 0.003 0.005 0.10 0.001 

1 0.009 0.16 0.78 0.022 

2 <0.005 0.018 2.1 0.021 

3 0.013 0.042 2.9 - 

x 0.009 0.074 1.9 0.022 

135 

Constant 

σ 0.004 0.075 1.1 0.001 

1 0.004 0.030 0.53 0.004 

2 0.010 0.026 4.0 0.007 

3 0.004 0.110 0.54 - 

x 0.006 0.055 1.7 0.005 

42.5 

Cyclic(a)

σ 0.004 0.047 2.0 0.002 

1 0.021 0.039 1.0 0.006 

2 0.013 0.023 4.3 0.018 

3 0.008 0.035 2.1 - 

x 0.014 0.032 2.5 0.012 

67.5 

Cyclic(a)

σ 0.007 0.001 1.7 0.009 

(a) Cyclic flow minute volume 
I-4 

Table I-5. Summary of Measured Penetrations through 3M 8293 

Bioaerosol Challenge 

Bg "Wet" Bg "Dry" MS2 "Wet" MS2 "Dry" 

Flow 

Rate 

(L/min) Trial Penetration (%) 

1 <0.003 0.018 <0.001 <0.002 

2 <0.003 <0.003 <0.001 <0.002 

3 <0.003 <0.001 <0.001 - 

x 0.003 0.008 0.001 0.002 

85 

σ - 0.009 - - 

1 <0.008 <0.002 <0.012 <0.004 

2 <0.012 <0.003 <0.014 <0.004 

3 <0.009 <0.004 <0.015 - 

x 0.010 0.003 0.014 0.004 

270 

σ 0.002 0.001 0.002 - 

1 <0.009 <0.002 <0.004 <0.005 

2 <0.004 <0.001 <0.001 0.014 

3 <0.003 <0.001 <0.001 - 

x 0.005 0.001 0.002 0.009 

85(a)

σ 0.003 0.001 0.002 0.006 

1 <0.005 <0.001 <0.001 <0.003 

2 <0.007 <0.001 <0.001 <0.002 

3 <0.003 0.008 <0.008 - 

x 0.005 0.003 0.003 0.003 

135(a)

σ 0.002 0.004 0.004 0.001 

(a) Cyclic flow minute volume 

(b) Low challenge, not included in average 

Table I-6. Summary of Measured Penetrations through Moldex 2396 

Bioaerosol Challenge 

Bg "Wet" Bg "Dry" MS2 "Wet" MS2 "Dry" 

Flow 

Rate 

(L/min) Trial Penetration (%) 

1 0.056 0.034 0.008 <0.004 

2 <0.008 0.004 <0.002 <0.004 

3 <0.004 0.015 0.006 - 

x 0.023 0.017 0.005 0.004 

85 

Constant 

σ 0.029 0.015 0.003 - 

1 <0.007 <0.004 0.057 <0.005 

2 0.015 0.004 0.043 <0.003 

3 <0.014 <0.005 0.051 - 

x 0.012 0.004 0.050 0.004 

270 

Constant 

σ 0.004 0.001 0.007 0.001 

1 0.008 <0.001 <0.002 <0.002 

2 0.005 <0.001 <0.001 0.026 

3 0.007 0.006 0.001 - 

x 0.006 0.003 0.001 0.014 

85 

Cyclic(a)

σ 0.002 0.003 0.001 0.017 

1 0.010 <0.002 0.014 <0.007 

2 <0.006 0.001 0.013 <0.002 

3 0.010 0.007 <0.003 - 

x 0.009 0.003 0.010 0.004 

135 

Cyclic(a)

σ 0.002 0.003 0.006 0.04 

(a) Cyclic flow minute volume 
I-5 

Table I-7. Summary of Measured Penetrations through MSA Affinity Plus 

Bioaerosol Challenge 

Bg "Wet" Bg "Dry" MS2 "Wet" MS2 "Dry" 

Flow 

Rate 

(L/min) Trial Penetration (%) 

1 0.25 0.016 0.64 0.010 

2 0.12 0.069 0.10 <0.004 

3 0.008 0.019 0.80 - 

x 0.13 0.035 0.51 0.007 

85 

Constant 

σ 0.12 0.030 0.37 0.004 

1 0.071 0.029 3.0 0.011 

2 0.11 0.059 0.35 0.006 

3 0.28 0.038 0.34 - 

4 0.075 - - - 

x 0.13 0.042 1.7 0.009 

270 

Constant 

σ 0.099 0.016 1.8 0.004 

1 0.19 0.087 0.18 0.028 

2 0.52 0.18 0.89 0.016 

3 0.48 0.13 1.6 - 

4 0.19 - 1.1 - 

x 0.35 0.13 0.93 0.022 

85 

Cyclic(a)

σ 0.18 0.048 0.60 0.009 

1 0.032 0.13 1.2 0.060 

2 0.021 0.52 0.31 0.10 

3 0.069 1.28 1.1 - 

4 0.065 - 1.8 - 

x 0.047 0.64 1.1 0.082 

135 

Cyclic(a)

σ 0.024 0.59 0.61 0.030 

(a) Cyclic flow minute volume 

(b) Low challenge, not included in average 

Table I-8. Summary of Measured Penetrations through Gerson 1730 

Bioaerosol Challenge 

Bg "Wet" Bg "Dry" MS2 "Wet" MS2 "Dry" 

Flow 

Rate 

(L/min) Trial Penetration (%) 

1 0.062 0.034 0.30 0.028 

2 0.022 0.030 0.72 0.40 

3 0.024 0.020 - - 

x 0.036 0.028 0.51 0.22 

85 

Constant 

σ 0.023 0.007 0.30 0.27 

1 0.39 0.25 1.6 1.0 

2 0.22 0.22 1.3 0.037 

3 0.60 0.12 2.4 - 

x 0.40 0.20 1.8 0.52 

270 

Constant 

σ 0.18 0.064 0.55 0.69 

1 0.28 0.096 0.43 0.60 

2 0.13 0.13 0.77 6.8(b)

3 0.24 0.36 0.53 - 

x 0.21 0.20 0.48 0.60 

85 

Cyclic(a)

σ 0.077 0.14 0.07 - 

1 0.17 0.32 0.90 0.099 

2 0.30 1.6 0.35 0.051 

3 0.30 5.2 1.4 - 

4 - - 0.89 - 

x 0.26 2.4 0.89 0.075 

135 

Cyclic(a)

σ 0.074 2.5 0.43 0.034 

(a) Cyclic flow minute volume 

(b) Probable leak in seal to system, not included in average
I-6 

Blank
J-1 

APPENDIX J 

SUMMARY OF REAEROSOLIZATION RESULTS 
J-2 

Table J-1. Summary of Reaerosolization Trials with 0.8 μm PSL Aerosol 

Filtering Facepiece 

Loading Collection Filter 

Filter Type Trial 

Density 

(#/cm2

) 

Number 

(#) 

PreCough 

(#) 

PostCough 

(#) 

Reaerosolization 

(%) 

Average 

(%) St Dev 

1 1.3x104 2.2 x106 0 3 0.0001 

2 1.7x104 3.0 x106 12 66 0.002 MSA Affinity Plus 

(No Valve) 3 - - - - - 

0.001 0.001 

 

1 1.4x105 2.4 x107 350 200 0.0008 

2 1.4x105 2.5 x107 95 205 0.0008 MSA Affinity Plus 

(No Valve) 3 1.6x105

 2.8 x107 0 75 0.0003 

0.0006 0.0003 

1 8.2x105 1.4 x108 20 175 0.0001 

2 8.2x105 1.4 x108 50 700 0.0005 MSA Affinity Plus 

(No Valve) 3 8.2x105 1.4 x108 145 1070 0.0007 

0.0005 0.0003 

1 1.8x104 2.8 x106 35 200 0.007 

2 2.5x104 3.9 x106 50 362 0.009 MSA Affinity Plus 

(With Valve) 3 1.7x104

 2.6 x106 58 150 0.006 

0.007 0.002 

1 1.4x104 2.4 x106 25 65 0.003 

2 1.5x104 2.6 x106 100 70 0.003 Gerson 1730 

(No Valve) 3 2.4x104

 4.1 x106 25 85 0.002 

0.003 0.0003 

1 3.3x104 4.9 x106 410 600 0.012 

2 4.6x104 7.0 x106 30 775 0.011 Gerson 1740 

(With Valve) 3 2.9x104

 4.3 x106 15 120 0.003 

0.009 0.005 

1 2.2x104 3.4 x106 15 145 0.004 

2 2.5x104 3.8 x106 25 155 0.004 

Gerson 1740 

(Valve Protected During 

Loading) 3 2.2x104

 3.3 x106 165 130 0.004 

0.004 0.0002 

Table J-2. Summary of Reaerosolization Trials with 2.2 μm PSL Aerosol 

Filtering Facepiece 

Loading Collection Filter 

Filter Type Trial 

Density 

(#/cm2

) 

Number 

(#) 

PreCough 

(#) 

PostCough 

(#) 

Reaerosolization 

(%) 

Average 

(%) St Dev 

1 1.7x103 2.9 x105 85 20 0.006 

2 2.7x103 4.6 x105 35 35 0.008 Gerson 1730 

(No Valve) 3 2.1x103

 3.6 x105 30 50 0.015 

0.009 0.005 

1 1.9x103 2.9 x105 130 20 0.006 

2 1.7x103 2.5 x105 80 35 0.014 Gerson 1740 

(With Valve) 3 2.1x103

 3.2 x105 35 52 0.016 

0.012 0.005 
J-3 

Table J-3. Summary of Reaerosolization Trials with Bg Spore Aerosol 

Filtering Facepiece 

Loading Collection Filter 

Filter Type Wet/Dry 

Tria

l 

Density 

(#/cm2

) 

Number 

(#) 

PreCough 

(#) 

PostCough 

(#) 

Reaerosolization 

(%) 

Average 

(%) St Dev 

1 9.2x102 1.6x105 100 55 0.034 

2 9.0x102 1.6x105 262 60 0.037 MSA Affinity Plus 

(No Valve) Wet 

3 - - - - - 

0.035 0.002 

 

1 6.8x102 1.2x105 20 55 0.046 

2 6.8x102 1.2x105 10 25 0.019 MSA Affinity Plus 

(With Valve) Wet 

3 6.5x102

 1.1x105 10 60 0.054 

0.040 0.018 

1 1.2x103 2.1x105 30 140 0.065 

2 2.2x103 3.8x105 30 170 0.045 Gerson 1730 

(No Valve) Wet 

3 1.0x103

 1.8x105 35 105 0.058 

0.056 0.012 

1 3.8x102 2.4 x106 8 115 0.18 

2 8.0x102 2.6 x106 0 20 0.012 Gerson 1740 

(With Valve) Wet 

3 - - - - - 

0.094 0.13 

1 1.2x104 2.1 x106 - 2670 0.13 

2 - - - - - Gerson 1730 

(No Valve) Dry 

3 - - - - - 

0.13 - 

1 1.5x104 2.3 x106 - 3550 0.16 

2 - - - - - Gerson 1740 

(With Valve) Dry 

3 - - - - - 

0.16 - 

Table J-4. Summary of Reaerosolization Trials with MS2 Phage Aerosol 

Filtering Facepiece 

Loading Collection Filter 

Filter Type Wet/Dry 

Tria

l 

Density 

(#/cm2

) 

Number 

(#) 

PreCough 

(#) 

PostCough 

(#) 

Reaerosolization 

(%) 

Average 

(%) St Dev 

1 1.1x104 2.0 x106 1090 765 0.038 

2 1.7x104 2.9 x106 35 3610 0.124 MSA Affinity Plus 

(No Valve) Wet 

3 1.7x104

 2.9 x106 175 1050 0.035 

0.066 0.050 

 

1 9.3x103 1.5 x106 1300 890 0.06 

2 8.9x103 1.5 x106 0 300 0.02 MSA Affinity Plus 

(With Valve) Wet 

3 1.1x104

 1.7 x106 610 4300 0.3 

0.11 0.12 

1 1.8x104 1.3 x106 35 200 0.007 

2 2.5x104 1.6 x106 50 362 0.009 Gerson 1730 

(No Valve) Wet 

3 1.7x104

 2.2 x106 58 150 0.006 

0.007 0.002 

1 7.8x104 1.3x107 730 42,000 0.32 

2 6.8x104 1.1x107 0 61,000 0.53 Gerson 1730 

(No Valve) Dry 

3 6.4x104

 1.0x107 60 59,000 0.54 

0.46 0.13 

1 4.1x104 6.2x106 1900 43,000 0.69 

2 1.3x104 2.0x106 960 9,700 0.49 Gerson 1740 

(With Valve) Dry 

3 8.9x103

 1.3x106 880 4,500 0.30 

0.51 0.18 


FIRST CLASS

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