![]() 10 emulated coughs using the vaporized liquid mixture to visualize the effectiveness of different mask materials and designs. The results showed that N95 respirators, surgical, and cotton masks strongly reduce the respiratory droplet count, whereas the bandana did not show the same effectiveness. 9 designed a low-cost experimental method to probe the respiratory droplet transmission of regular speech through different facial masks. Studies are also emerging, seeking to quantify the effect of facial masks as a means to limit the transport of pathogen-bearing droplets. 14 investigated the dynamics of various sized individual droplet dispersion in a source–sink pair flow field using a simplified numerical model and showed that unlike the large droplets, the intermediate-sized droplets have a minimal dispersion range. 8–11 Dbouk and Drikakis 12,13 employed a statistically stationary Reynolds-averaged Navier–Stokes (RANS) computational fluid dynamics (CFD) model to simulate droplet transport during coughing and showed that while saliva droplets from coughing travel less than 2 m under stagnant ambient air, they could travel very fast and for several meters downwind when a mild ambient breeze is present as a result of turbulence transport. 5 and 7 for excellent recent reviews).Įxperimental studies have suggested, for instance, that under certain conditions, pathogen-bearing droplets emitted during violent expiratory events (coughing and sneezing) can travel up to 7 m–8 m. 6–14 Several experimental and computational studies are now beginning to emerge, seeking to fill this major knowledge gap and yield improved science-based physical distancing guidelines (see Refs. 5 There is now mounting evidence that such guidelines are based on outdated scientific studies carried out decades ago, 6 which, among others, have overlooked the physics of respiratory emissions, the range of droplet size distribution such emissions produce, the turbulent flow processes that transport respiratory droplets, and the potential effects of ambient wind conditions on such transport. 1–5 However, recommended social distancing guidelines vary considerably, with the WHO recommending at least 1 m while the CDC recommending at least 1.8 m of separation. The World Health Organization (WHO), the United States Centers for Disease Control (CDC), and other public health organizations are recommending social distancing and the use of facial coverings as two of the most important weapons to curb the spread of the pandemic. ![]() Under outdoor conditions with a unidirectional mild breeze, however, leakage flow through the mask can cause saliva particulates to be entrained into the energetic shear layers around the body and transported very fast at large distances by the turbulent flow, thus limiting the effectiveness of facial masks.Īs the coronavirus disease of 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is spreading around the globe, it causes devastating loss of life, threatens to topple national health care systems, and wreaks havoc on the global economy. Thus, in indoor environments, either medical or non-medical grade facial masks can successfully limit the spreading of saliva particulates to others. ![]() We show that during indoor coughing some saliva particulates could travel up to 0.48 m, 0.73 m, and 2.62 m for the cases with medical grade, non-medical grade, and without facial masks, respectively. Our simulations (a) are carried out under both a stagnant ambient flow (indoor) and a mild unidirectional breeze (outdoor), (b) incorporate the effect of human anatomy on the flow, (c) account for both medical and non-medical grade masks, and (d) consider a wide spectrum of particulate sizes, ranging from 10 µm to 300 µm. To expand the scientific underpinnings of such recommendations, we carry out high-fidelity computational fluid dynamics simulations of unprecedented resolution and realism to elucidate the underlying physics of saliva particulate transport during human cough with and without facial masks. ![]() Social distancing and face masks are widely recommended around the globe to protect others and prevent the spread of the virus through breathing, coughing, and sneezing. The coronavirus disease outbreak of 2019 has been causing significant loss of life and unprecedented economic loss throughout the world.
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