Respiratory Protection Provided by N95 Filtering Facepiece Respirators Against Airborne Dust and Microorganisms in Agricultural Farms

A new system was used to determine the workplace protection factors (WPF) for dust and bioaerosols in agricultural environments. The field study was performed with a subject wearing an N95 filtering facepiece respirator while performing animal feeding, grain harvesting and unloading, and routine investigation of facilities. As expected, the geometric means (GM) of the WPFs increased with increasing particle size ranging from 21 for 0.7–1 μm particles to 270 for 5–10 μm particles (p < 0.001). The WPF for total culturable fungi (GM = 35) was significantly greater than for total culturable bacteria (GM = 9) (p = 0.01). Among the different microorganism groups, the WPFs of Cladosporium, culturable fungi, and total fungi were significantly correlated with the WPFs of particles of the same sizes. As compared with the WPFs for dust particles, the WPFs for bioaerosols were found more frequently below 10, which is a recommended assigned protection factor (APF) for N95 filtering facepiece respirators. More than 50% of the WPFs for microorganisms (mean aerodynamic diameter < 5 μm) were less than the proposed APF of 10. Even lower WPFs were calculated after correcting for dead space and lung deposition. Thus, the APF of 10 for N95 filtering facepiece respirators seems inadequate against microorganisms (mean aerodynamic size < 5 μm). These results provide useful pilot data to establish guidelines for respiratory protection against airborne dust and microorganisms on agricultural farms. The method is a promising tool for further epidemiological and intervention studies in agricultural and other similar occupational and nonoccupational environments.

Keywords:

• agricultural farms
• airborne dust
• airborne microorganisms
• respirators
• workplace protection factor
• WPF

ACKNOWLEDGMENT

The authors are grateful to farm owners for providing access and help in field measurements.

The authors also thank students and staff members who volunteered to be human subjects in the field testing when needed.

Special thanks go to Mike Brugger and LingYing Zhao (Ohio State University) for helping us find field sites.

This research was supported by the National Institute for Occupational Safety and Health (NIOSH R01 OH04085) and through the Pilot Project Research Training Program of the University of Cincinnati Education and Research Center.

Notes

^A Based on the microscopic analysis.

^B For some microorganism, one observation was lost.

^A GSD_B = between-subject geometric standard deviation.

^B GSD_W = within-subject geometric standard deviation.

^A Mean aerodynamic size is the same as that presented in authors' concurrent paper.14

^B F_dep: fractional deposition of particles in the respiratory tract.18

^C C_full/C_in: ratio of an average concentration measured during the full breathing cycle to that measured during inhalation.16

^D WPF_corr: WPF corrected after accounting for lung deposition and respirator dead volume (WPF_corr = WPF×C_full/C_in)

^E Bias: [WPF-WPF_corr]/[WPF_corr]× 100%, calculated with nonrounded numbers.