Pressure drop of filtering facepiece respirators: How low should we go?
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Centers for Disease Control and Prevention, Pittsburgh, Pennsylvania, United States of America (National Institute for Occupational Safety and Health, National Personal Protective Technology Laboratory, Technology Research Branch)
3M Company, St. Paul, Minnesota, United States of America (3M Personal Safety Division)
Raymond J. Roberge   

National Personal Protective Technology Laboratory / NIOSH / CDC, Technology Research Branch, 626 Cochrans Mill Road, Pittsburgh, PA, U.S. 15236
Int J Occup Med Environ Health 2015;28(1):71–80
Introduction: This study was undertaken to determine the mean peak filter resistance to airflow (Rfilter) encountered by subjects while wearing prototype filtering facepiece respirators (PRs) with low Rfilter during nasal and oral breathing at sedentary and low-moderate work rates. Material and methods: In-line pressure transducer measurements of mean Rfilteracross PRs with nominal Rfilter of 29.4 Pa, 58.8 Pa and 88.2 Pa (measured at 85 l/min constant airflow) were obtained during nasal and oral breathing at sedentary and low-moderate work rates for 10 subjects. Results: The mean Rfilter for the 29.4 PR was significantly lower than the other 2 PRs (p < 0.000), but there were no significant differences in mean Rfilter between the PRs with 58.8 and 88.2 Pa filter resistance (p > 0.05). The mean Rfilter was greater for oral versus nasal breathing and for exercise compared to sedentary activity (p < 0.001). Conclusions: Mean oral and nasal Rfilter for all 3 PRs was at, or below, the minimal threshold level for detection of inspiratory resistance (the 58.8–74.5 Pa/l×s–1), which may account for the previously-reported lack of significant subjective or physiological differences when wearing PRs with these low Rfilter. Lowering filtering facepiece respirator Rfilter below 88.2 Pa (measured at 85 l/min constant airflow) may not result in additional subjective or physiological benefit to the wearer.