How long and effective does a mask protect you from an infected person who emits virus-laden particles: By implementing one-dimensional physics-based modeling

SARS-CoV-2 spreads via droplets, aerosols, and smear infection. From the beginning of the COVID-19 pandemic, using a facemask in different locations was recommended to slow down the spread of the virus. To evaluate facemasks' performance, masks' filtration efficiency is tested for a range of particle sizes. Although such tests quantify the blockage of the mask for a range of particle sizes, the test does not quantify the cumulative amount of virus-laden particles inhaled or exhaled by its wearer. In this study, we quantify the accumulated viruses that the healthy person inhales as a function of time, activity level, type of mask, and room condition using a physics-based model. We considered different types of masks, such as surgical masks and filtering facepieces (FFPs), and different characteristics of public places such as office rooms, buses, trains, and airplanes. To do such quantification, we implemented a physics-based model of the mask. Our results confirm the importance of both people wearing a mask compared to when only one wears the mask. The protection time for light activity in an office room decreases from 7.8 to 1.4 h with surgical mask IIR. The protection time is further reduced by 85 and 99% if the infected person starts to cough or increases the activity level, respectively. Results show the leakage of the mask can considerably affect the performance of the mask. For the surgical mask, the apparent filtration efficiency reduces by 75% with such a leakage, which cannot provide sufficient protection despite the high filtration efficiency of the mask. The facemask model presented provides key input in order to evaluate the protection of masks for different conditions in public places. The physics-based model of the facemask is provided as an online application.

On the durability of surgical masks after simulated handling and wear.

After the spread of COVID-19, surgical masks became highly recommended to the public. They tend to be handled and used multiple times, which may impact their performance. To evaluate this risk, surgical masks of Type IIR were submitted to four simulated treatments: folding, ageing with artificial saliva or sweat and washing cycles. The air permeability, mechanical integrity, electrostatic potential, and filtration efficiency (FE) of the masks were measured to quantify possible degradation. Overall, air permeability and mechanical integrity were not affected, except after washing, which slightly degraded the filtering layers. Electrostatic potential and FE showed a strong correlation, highlighting the role of electrostatic charges on small particle filtration. A slight decrease in FE for 100 nm particles was found, from 74.4% for the reference masks to 70.6% for the mask treated in saliva for 8 h. A strong effect was observed for washed masks, resulting in FE of 46.9% (± 9.5%), comparable to that of a control group with no electrostatic charges. A dry store and reuse strategy could thus be envisaged for the public if safety in terms of viral and bacterial charge is ensured, whereas washing strongly impacts FE and is not recommended.

Filtration Performance Degradation of In-Use Masks by Vapors from Alcohol-Based Hand Sanitizers and the Mitigation Solutions.

In the current COVID-19 pandemic, wearing masks and hand disinfection are widely adopted hygiene practices. Alcohol-based sanitizers are commonly used for hand disinfection, however, the alcohol vapors can dissipate the charges on electrostatic filters. In the present study, the effects of alcohol vapors from alcohol-based sanitizers during hand disinfection on the in-use masks are studied. The results show that the negative effects are not significant for nonelectrostatic cotton masks or N95 respirators with multiple charged layers, but noticeable for surgical masks. After five rounds of hand disinfection, the filtration efficiencies of the filtering materials of the surgical masks decrease by more than 8% for 400 and 500 nm particles and by 3.7 ± 1.8% for 1 µm particles, the effective filtration efficiency of the surgical masks worn by the volunteers (with leakage considered) decreases by about 5% for ambient aerosol. In another process to imitate intensive disinfection procedures by healthcare workers, a 30 min surface cleaning process using alcohol-based sanitizer is performed, and the effective efficiency of the N95 respirators worn by the volunteers decreases by nearly 9%. The simple practice of avoiding vapor during hand disinfection could mitigate the effects of alcohol vapor, which is demonstrated on two brands of surgical masks.

Evaluation of Regeneration Processes for Filtering Facepiece Respirators in Terms of the Bacteria Inactivation Efficiency and Influences on Filtration Performance.

The regeneration of filtering facepiece respirators (FFRs) is of critical importance because of the severe shortage of FFRs during large-scale outbreaks of respiratory epidemics, such as COVID-19. Comprehensive experiments regarding FFR regeneration were performed in this study with model bacteria to illustrate the decontamination performance of the regeneration processes. The results showed that it is dangerous to use a contaminated FFR without any microbe inactivation treatment because the bacteria can live for more than 8 h. The filtration efficiency and surface electrostatic potential of 75% ethanol-treated FFRs were significantly reduced, and a most penetrating particle size of 200 nm was observed. Steam and microwave irradiation (MWI) showed promising decontamination performances, achieving 100% inactivation in 90 and 30 min, respectively. The filtration efficiencies of steam-treated FFRs for 50 and 100 nm particles decreased from 98.86% and 99.51% to 97.58% and 98.79%, respectively. Ultraviolet irradiation (UVI) effectively inactivated the surface bacteria with a short treatment of 5 min and did not affect the filtration performance. However, the UV dose reaching different layers of the FFP2 mask sample gradually decreased from the outermost layer to the innermost layer, while the model bacteria on the second and third layers could not be killed completely. UVI+MWI and steam were recommended to effectively decontaminate the used respirators and still maintain the respirators' filtration efficiency. The present work provides a comprehensive evaluation for FFR regeneration in terms of the filtration efficiencies for 50-500 nm particles, the electrostatic properties, mechanical properties, and decontamination effects.