In-House Filtration Efficiency Assessment of Vapor Hydrogen Peroxide Decontaminated Filtering Facepiece Respirators (FFRs)

Abstract

To cope with the shortage of filtering facepiece respirators (FFRs) caused by the coronavirus disease (COVID-19), healthcare institutions have been forced to reuse FFRs using different decontamination methods, including vapor hydrogen peroxide (VHP). However, most healthcare institutions still struggle with evaluating the effect of VHP on filtration efficiency (FE) of the decontaminated FFRs. We developed a low-cost in-house FE assessment using a novel 3D-printed air duct. Furthermore, we assessed the FE of seven types of FFRs. Following 10 VHP cycles, we evaluated the FE of KN95 and 3M-N95 masks. The 3M-N95 and Benehal-N95 masks showed significant lower FE (80.4-91.8%) at fine particle sizes (0.3-1 µm) compared to other FFRs (FE ≥ 98.1%, p < 0.05). Following 10 VHP cycles, the FE of KN95 masks was almost stable (FE stability > 99.1%) for all particle sizes, while 3M-N95 masks were stable only at 2 and 5 µm (FE stability > 98.0%). Statistically, FE stability of 3M-N95 masks at 0.3, 0.5, and 0.7 µm was significantly lower (p ≤ 0.006) than 2 and 5 µm. The in-house FE assessment may be used as an emergency procedure to validate the decontaminated FFRs, as well as a screening option for production control of FFRs. Following VHP cycles, both masks showed high stability at 5 µm, the size of the most suspected droplets implicated in COVID-19 transmission.

Keywords: COVID-19; FFRs; KN95 masks; N95 masks; decontamination; filtration efficiency; vapor hydrogen peroxide.

Figure 1

Illustration of the 3D-printed specialized air duct used to measure the filtration efficiency (FE) of FFRs. (A–C) are 3D designs from different angles of the air duct. (D) is the actual air duct connected to AeroTrak particle counter (1), through the head (2) of the air duct showing a tested mask (3), bound to the tail (4) of the air duct and the electric fan (5). The overall dimensions of the air ducts are 19-cm-long, 14-cm-wide, and 12-cm-high; the head dimensions are 10-cm-long, 14-cm-wide, and 12-cm, while the tail dimensions are 9-cm-long, 14-cm-wide, and 12-cm.

Figure 2

Filtration efficiency (FE) of different types of FFRs. Seven types of FFRs were applied to FE evaluation for different particle sizes (0.3–5 µm) using AeroTrak particle counter; KN95 (moulded shape, n = 10), 3M-1820 (n = 10), Gerson-1730 (n = 5), Medline (n = 5), Benehal (n = 5), N99/N95 SpectraShield Plus (n = 5), and KN95 (duck shape, n = 5) masks. Symbols represent the mean, and error bars indicate the standard error. Statistically, an overall significant difference (p = 0.001) was observed between the median FE values between the FFRs, with a p-value of 0.001. Pairwise comparison: 3M-N95 vs. N99/N95 SpectraShield: p < 0.05; Benehal-N95 vs. N99/N95 SpectraShield: p < 0.05; no other pairwise comparison significant differences were observed. Raw data are listed in Supplementary Materials 3.

Figure 3

Stability of filtration efficiency (FE) of KN95 and 3M-N95 masks over H2O2 decontamination cycles. Twelve of each KN95 (left panel) and 3M-N95 (right panel) masks were cycled in VHP-STERIS sterilization systems 10 times. The masks were applied to FE stability evaluation after each VHP cycle for different particle sizes (0.3–5 µm) using AeroTrak particle counter. Symbols represent the mean, and error bars indicate the standard error. Statistically, the 3M-N95 masks showed an overall significant (p < 0.001) reduction in FE stability with increased VHP cycles. Pairwise comparison: 0.3 µm vs. 5 µm, p < 0.001; 0.5 µm vs. 5 µm, p < 0.001; 0.7 µm vs. 5 µm, p = 0.006; 0.3 µm vs. 2 µm, p = 0.002; 0.5 µm vs. 2 µm, p = 0.002; no other pairwise comparison significant differences were observed. Raw data are listed in Supplementary Materials 4.