PRESSURE DROP OF FILTERING FACEPIECE RESPIRATORS: HOW LOW SHOULD WE GO?

OBJECTIVES: This study was undertaken to determine the mean peak filter resistance to airflow (R(filter)) encountered by subjects while wearing prototype filtering facepiece respirators (PRs) with low R(filter) during nasal and oral breathing at sedentary and low-moderate work rates. MATERIAL AND METHODS: In-line pressure transducer measurements of mean R(filter) across PRs with nominal R(filter) 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 R(filter) for the 29.4 PR was significantly lower than the other 2 PRs (p < 0.000), but there were no significant differences in mean R(filter) between the PRs with 58.8 and 88.2 Pa filter resistance (p > 0.05). The mean R(filter) was greater for oral versus nasal breathing and for exercise compared to sedentary activity (p < 0.001). CONCLUSIONS: Mean oral and nasal R(filter) for all 3 PRs was at, or below, the minimal threshold level for detection of inspiratory resistance (the 58.8–74.5 Pa/1×s(−1)), which may account for the previously-reported lack of significant subjective or physiological differences when wearing PRs with these low R(filter). Lowering filtering facepiece respirator R(filter) below 88.2 Pa (measured at 85 l/min constant airflow) may not result in additional subjective or physiological benefit to the wearer.