Medical-Grade Face Masks Effectively Control Particle Emissions during Expiratory Activities

by | Oct 26, 2020 | 2020, COVID-19

Written by Angeline A. De Leon, Staff Writer. This study demonstrated that wearing surgical masks or KN95 respirators, but not paper or fabric masks, substantially reduced particle emissions even in the absence of testing for proper fitting.

covid-19 maskThe 2020 COVID-19 pandemic has incited a huge demand for face masks and face coverings in order to protect against airborne transmission of virus-laden aerosols and droplets. Although much remains unknown about COVID-19 and the specifics regarding its different modes of transmission 1, the use of face masks has long been relied on as a means to mitigate the spread of infectious respiratory diseases, especially in clinical settings 2. Face masks, when worn properly, appear to significantly protect the wearer 3, as well as bystanders in the general vicinity of infected mask-wearers 4. Epidemiological research suggests that face masks can effectively limit the spread of particles released through coughing 5 and can significantly lower the outward transmission of microorganisms in simulated breathing models 6. Both surgical and homemade cotton masks appear to substantially reduce the spread of virus-containing particles, notably across a wide range of particle sizes 7. Despite promising evidence for the efficacy of mask-wearing, a number of factors still warrant further study. For example, emerging evidence now suggests that masks and personal protective equipment can become potential sources of aerosolized fomites, tiny contaminated dust particles 8. To address the need to better understand the outward particle emission associated with different masks, researchers at the University of California Davis tested the particle emission rates of various types of masks during various expiratory activities.

A total of 10 healthy, non-smoking participants (aged 18-45 years) were enrolled in the experimental study 9. An aerodynamic particle sizer was used to measure the emission rate of micron-scale aerosol particles while study participants completed four distinct expiratory activities (breathing, talking, coughing, and moving their jaws), wearing one of 6 different types of masks/respirators (a surgical mask, an unvented KN95 respirator, a homemade single-layer paper towel mask, a homemade single-layer cotton t-shirt mask, a homemade double-layer cotton t-shirt mask, and a vented N95 respirator). Additional testing was also carried out to assess the friability (tendency of solid material to break into smaller pieces) of each mask via hand-rubbing.

Data revealed that, compared to wearing no mask at all, surgical masks and unvented KN95 respirators were associated with a 90% and 74% average reduction in particle emission rates during speaking and coughing, respectively. For coughing specifically, surgical masks appeared to have significantly greater emission reduction than KN95 respirators (p < 0.05). The majority of emitted particles that were measured across expiratory activities was found to be in the aerosol range (< 5 µm). A notable observation was the substantial shedding of mask fibers in homemade paper and cloth masks due to mechanical action (mask-rubbing), which prevented accurate assessment of their efficacy in reducing outward particle emissions. This manual rubbing of mask fabrics was seen to produce a significant number of particles in the same size range as those detected during expiratory activities (0.3-5 µm).

Collectively, findings from the present study corroborate the critical role of face masks and protective respiratory gear in mitigating the transmission of aerosol particles into the surrounding air. While both surgical masks and KN95 respirators were able to substantially reduce outward particle emission during breathing, talking, and coughing, surgical masks were seen to effect the greatest reductions in particle emission rates, specifically during coughing. In contrast, homemade masks (both paper- and cloth-based) exhibited considerable particle shedding during friability assessments, confirming the potential for some masks to serve as sources of aerosolized particulates. This also highlights the importance of regularly sterilizing homemade masks and handling them with special care during removal to prevent emission of aerosolized fomites. Overall results are consistent with current recommendations for the general public to continue to adhere to mask-wearing protocols during the global pandemic, the efficacy of medical-grade masks being particularly emphasized by study findings. A primary limitation of the current trial is its very limited sample size consisting of only healthy individuals. Future studies are needed to directly measure virus emission, to determine the particle emission rates of used vs. fresh masks, and to test mask performance in test subjects classified as “superemitters” or “superspreaders.”

Source: Asadi S, Cappa CD, Barreda S, et al. Efficacy of masks and face coverings in controlling outward aerosol particle emission from expiratory activities. 2020; 10: 15665. DOI: 10.1038/s41598-020-72798-7.

© The Author(s) 2020 This is an Open Access article licensed under a Creative Commons Attribution 4.0 International License.

Click here to read the full text study.

Posted October 26, 2020.

Angeline A. De Leon, MA, graduated from the University of Illinois at Urbana-Champaign in 2010, completing a bachelor’s degree in psychology, with a concentration in neuroscience. She received her master’s degree from The Ohio State University in 2013, where she studied clinical neuroscience within an integrative health program. Her specialized area of research involves the complementary use of neuroimaging and neuropsychology-based methodologies to examine how lifestyle factors, such as physical activity and meditation, can influence brain plasticity and enhance overall connectivity.

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