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. 2022 Jun 11;19(12):7167.
doi: 10.3390/ijerph19127167.

Dry Heat as a Potential Decontamination Method on the Filtration Efficiency of Filtering Facepiece Respirators

Zhixu Jin  1 , Chenchen Sun  1 , Wending Wu  1 , Xiaobing Yang  2   3
Affiliations

Dry Heat as a Potential Decontamination Method on the Filtration Efficiency of Filtering Facepiece Respirators

Zhixu Jin et al. Int J Environ Res Public Health. .

Abstract

Filtering facepiece respirators have been widely used in the fields of occupational health and public hygiene, especially during the COVID-19 pandemic. In particular, disposable respirators have been in high demand, and the waste generated from these disposable products poses a problem for the environment. Here, we aimed to test a practical decontamination method to allow for the reuse of KN95 respirators. In this study, three types of KN95 respirators were heated at 80 °C and 90 °C for different durations (15 min, 30 min, 45 min, 1 h, 2 h, 3 h, 4 h, 6 h, 8 h, 10 h, and 24 h). The filtration efficiencies of the tested KN95 respirators before and after heating were measured, and the changes in microstructure were imaged with a scanning electron microscope (SEM). In addition, a neural network model based on the nonlinear autoregressive with external input (NARX) to predict the filtration efficiency of the KN95 respirator was established. The results show that the temperature and time of dry heating affected particle prevention. The higher the temperature and the longer the heating time, the more obvious the decline in the filtration efficiency of the respirators. When the heating temperature reached 100 °C, the respirator may be no longer suitable for reuse. These results show that a dry heat temperature between 70 °C and 90 °C, and a heating time between 30 min and 2 h is assumed to be a suitable and effective decontamination method for respirators.

Keywords: filtering facepiece respirators; filtration efficiency; heat treatment; neural network.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The three typical KN95 disposable facepiece respirators: (a) CM 8228-1 cup-shaped KN95, (b) CM 6002A head-mounted KN95, (c) 3M 9501+ folding KN95.
Figure 2
Figure 2
The DHG-9070A drying oven.
Figure 3
Figure 3
The sample after treatment.
Figure 4
Figure 4
The schematic of the measuring principle of the TSI 8130 detector. Reprinted with per-mission from Ref. [46]. 2021, TSI Incorporated.
Figure 5
Figure 5
The bidirectional comparison histogram of the filtration efficiency of respirators treated with NaCl particles (blue) and DOP particles (red).
Figure 6
Figure 6
The open-loop structure of the NARX network with external input y(t).
Figure 7
Figure 7
The closed-loop structure of the NARX network with no external input y(t).
Figure 8
Figure 8
The filtration efficiency of DOP particles through (a) 3M KN95, (b) CM 8228-1KN95, and (c) CM 6002A respirators. The filtration efficiency of NaCl particles through (d) 3M KN95, (e) CM 8228-1KN95, and (f) CM 6002A respirators.
Figure 9
Figure 9
(a) The DOP particles and NaCl particles filtration efficiency at 80 °C for 0. 75 h and 24 h, respectively. (b) The DOP and NaCl particle filtration efficiency at 90 °C for 0. 75 h and 24 h, respectively.
Figure 10
Figure 10
The SEM images of the (a) untreated 3M KN95 respirator, (b) 3M KN95 respirator at 80 °C for 24 h, (c) 3M KN95 respirator at 90 °C for 24 h, (d) untreated CM 8228-1 KN95 respirator, (e) CM 8228-1 KN95 respirator at 80 °C for 24 h, (f) CM 8228-1 KN95 respirator at 90 °C for 24 h, (g) untreated of CM 6002A KN95 respirator, (h) CM 6002A KN95 respirator at 80 °C for 24 h, and (i) CM 6002A KN95 respirator at 90 °C for 24 h. The upper left graphs are the fiber diameter distribution histogram.
Figure 10
Figure 10
The SEM images of the (a) untreated 3M KN95 respirator, (b) 3M KN95 respirator at 80 °C for 24 h, (c) 3M KN95 respirator at 90 °C for 24 h, (d) untreated CM 8228-1 KN95 respirator, (e) CM 8228-1 KN95 respirator at 80 °C for 24 h, (f) CM 8228-1 KN95 respirator at 90 °C for 24 h, (g) untreated of CM 6002A KN95 respirator, (h) CM 6002A KN95 respirator at 80 °C for 24 h, and (i) CM 6002A KN95 respirator at 90 °C for 24 h. The upper left graphs are the fiber diameter distribution histogram.
Figure 10
Figure 10
The SEM images of the (a) untreated 3M KN95 respirator, (b) 3M KN95 respirator at 80 °C for 24 h, (c) 3M KN95 respirator at 90 °C for 24 h, (d) untreated CM 8228-1 KN95 respirator, (e) CM 8228-1 KN95 respirator at 80 °C for 24 h, (f) CM 8228-1 KN95 respirator at 90 °C for 24 h, (g) untreated of CM 6002A KN95 respirator, (h) CM 6002A KN95 respirator at 80 °C for 24 h, and (i) CM 6002A KN95 respirator at 90 °C for 24 h. The upper left graphs are the fiber diameter distribution histogram.
Figure 10
Figure 10
The SEM images of the (a) untreated 3M KN95 respirator, (b) 3M KN95 respirator at 80 °C for 24 h, (c) 3M KN95 respirator at 90 °C for 24 h, (d) untreated CM 8228-1 KN95 respirator, (e) CM 8228-1 KN95 respirator at 80 °C for 24 h, (f) CM 8228-1 KN95 respirator at 90 °C for 24 h, (g) untreated of CM 6002A KN95 respirator, (h) CM 6002A KN95 respirator at 80 °C for 24 h, and (i) CM 6002A KN95 respirator at 90 °C for 24 h. The upper left graphs are the fiber diameter distribution histogram.
Figure 11
Figure 11
The time−series response.
Figure 12
Figure 12
A comparison of the neural network prediction results and experimental results.
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