#Fluid mask v2 0 trial#
Ideally, a randomized controlled trial would be conducted, but in the absence of such evidence, we can evaluate the ability of masks to block particles under controlled conditions. While there have been numerous studies on the ability of surgical masks and N95 respirators to filter out particles, far less is known about the ability of cloth masks to provide both inward protection to reduce the wearer’s exposure and outward protection for source control. 2020), and lower incidence of COVID-19 by country and between mask mandates and county-level COVID-19 growth rates in the US ( Lyu and Wehby 2020), but a causal relationship has not been confirmed.ĭue to a shortage of medical masks and respirators, some public health agencies have recommended the use of cloth face coverings. There is a correlation between widespread mask wearing ( The Economist 2020), or at least interest in masks ( Wong et al. 2020 Prather, Wang and Schooley 2020), universal masking has emerged as one of a suite of intervention strategies for reducing community transmission of the disease. This combination should produce an overall efficiency of >70% at the most penetrating particle size and >90% for particles 1 μm and larger if the mask fits well.Īmid mounting evidence that COVID-19 is transmitted via inhalation of virus-laden aerosols ( Allen and Marr 2020 Asadi et al.
Based on these findings, we recommend a three-layer mask consisting of outer layers of a flexible, tightly woven fabric and an inner layer consisting of a material designed to filter out particles. We calculated that the particle size most likely to deposit in the respiratory tract when wearing a mask is ∼2 μm. Discrepancies between material filtration efficiency and inward/outward protection efficiency indicated that the fit of the mask was important. Inward protection efficiency and outward protection efficiency were similar for many masks the two efficiencies diverged for stiffer materials and those worn more loosely (e.g., bandana) or more tightly (e.g., wrapped around the head) compared to a standard earloop mask.
The thin acrylic and face shield performed worst. The vacuum bag performed best, with efficiencies of 54-96% for all three metrics, depending on particle size. However, these efficiencies increased rapidly with particle size, and many materials had efficiencies >50% at 2 μm and >75% at 5 μm. At the most penetrating particle size, the vacuum bag, microfiber cloth, and surgical mask had material filtration efficiencies >50%, while the other materials had much lower filtration efficiencies. We evaluated the effectiveness of 11 face coverings for material filtration efficiency, inward protection efficiency on a manikin, and outward protection efficiency on a manikin.
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