Respiratory performance offered by N95 respirators and surgical masks: human subject evaluation with NaCl aerosol representing bacterial and viral particle size range

Abstract

Objectives: This study aimed at determining the protection factors (PFs) provided by N95 filtering facepiece respirators and surgical masks against particles representing bacterial and viral size ranges (aerodynamic size: 0.04-1.3 mum).

Methods: The protection levels of N95 filtering facepiece respirators (four models) and surgical masks (three models) were investigated while they were donned by 12 subjects performing the OSHA (US Occupational Safety and Health Administration) fit-testing exercises in a test chamber.

Results: About 29% of N95 respirators and approximately 100% of surgical masks had PFs <10, which is the assigned PF designated for this type of respirator by the OSHA. On average, the PFs of N95 respirators were 8-12 times greater than those of surgical masks. The minimum PFs were observed in the size range of 0.04-0.2 mum. No significant difference in PF results was found between N95 respirators with and without an exhalation valve.

Conclusions: The study indicates that N95 filtering facepiece respirators may not achieve the expected protection level against bacteria and viruses. An exhalation valve on the N95 respirator does not affect the respiratory protection; it appears to be an appropriate alternative to reduce the breathing resistance.

Fig. 1.

Schematic presentation of the modified personal sampling system.

Fig. 2.

PF values against particles representing bacterial and viral size range for four models of N95 filtering facepiece respirators: A, B, C and D. The tests were performed when the N95 respirators were donned on human subjects. Total observations are 36 (12 subjects × 3 replicates) for Models A, B and C and 9 (3 subjects × 3 replicates) for Model D. The boxplots show the following: dots (from bottom) represent 5th and 95th percentiles; horizontal lines (from bottom) represent 10th, 25th, 50th, 75th, and 90th percentiles.

Fig. 3.

The comparison of PFs against particles in bacterial and viral size ranges between respirators without (N95 Respirator C) and with (N95 Respirator D) exhalation valves. The tests were performed when the N95 respirators were donned on human subjects. Each data point represents an average and standard deviation of 36 observations for N95 Respirator C and 9 observations for N95 Respirator D.

Fig. 4.

Overall FFs measured for nine models of surgical masks with the PortaCount (with N95-Companion). The mask was donned on a human subject. Each bar represents an average and standard deviation of three replicate measurements performed by one human subject. Each replicate was done with the same type of unused surgical mask.

Fig. 5.

PF values against particles representing bacterial and viral size range for three models of surgical masks: A, B and C. The boxplots show the same as in Fig. 1. The tests were performed when the surgical masks were donned on human subjects. Total observations are 36 (12 subjects × 3 replicates).