Documentary Research of Human Respiratory Droplet Characteristics

Zhang, Hualing; Li, Dan; Xie, Ling; Xiao, Yimin

doi:10.1016/j.proeng.2015.09.023

Cited by 66 publications

(70 citation statements)

References 79 publications

(96 reference statements)

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“…Respiratory droplets can be of various sizes 17,18 and are commonly classified as aerosols (made of droplets that are <5 μm) and droplets that are greater than 5 μm. 3 Although the fate of these droplets largely depends on environmental factors such as humidity, temperature, etc., in general, the larger droplets settle due to gravity and do not travel distances more than 1−2 m. 19 However, aerosols remain suspended in the air for longer durations due to their small size and play a key role in spreading infection.…”

mentioning

confidence: 99%

Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks

et al. 2020

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The emergence of a pandemic affecting the respiratory system can result in a significant demand for face masks. This includes the use of cloth masks by large sections of the public, as can be seen during the current global spread of COVID-19. However, there is limited knowledge available on the performance of various commonly available fabrics used in cloth masks. Importantly, there is a need to evaluate filtration efficiencies as a function of aerosol particulate sizes in the 10 nm to 10 μm range, which is particularly relevant for respiratory virus transmission. We have carried out these studies for several common fabrics including cotton, silk, chiffon, flannel, various synthetics, and their combinations. Although the filtration efficiencies for various fabrics when a single layer was used ranged from 5 to 80% and 5 to 95% for particle sizes of <300 nm and >300 nm, respectively, the efficiencies improved when multiple layers were used and when using a specific combination of different fabrics. Filtration efficiencies of the hybrids (such as cotton−silk, cotton−chiffon, cotton−flannel) was >80% (for particles <300 nm) and >90% (for particles >300 nm). We speculate that the enhanced performance of the hybrids is likely due to the combined effect of mechanical and electrostatic-based filtration. Cotton, the most widely used material for cloth masks performs better at higher weave densities (i.e., thread count) and can make a significant difference in filtration efficiencies. Our studies also imply that gaps (as caused by an improper fit of the mask) can result in over a 60% decrease in the filtration efficiency, implying the need for future cloth mask design studies to take into account issues of "fit" and leakage, while allowing the exhaled air to vent efficiently. Overall, we find that combinations of various commonly available fabrics used in cloth masks can potentially provide significant protection against the transmission of aerosol particles.

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confidence: 99%

Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks

et al. 2020

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“…Some studies did work with particles. Relatively small particles in the range 0‐10 μm in diameter were usually investigated, mainly because this is the dominant range of expiratory droplet nuclei for almost all breathing activities …”

Section: Thermofluid Boundary Conditions For Thermal Manikinsmentioning

confidence: 99%

“…Relatively small particles in the range 0-10 μm in diameter were usually investigated, mainly because this is the dominant range of expiratory droplet nuclei for almost all breathing activities. 36,163 Most studies defined the concentration of expiratory media, but few explained the reasoning behind their particular definition (eg, 2.7% of N 2 O). Generally, in mouth exhalation, nose exhalation, coughing and talking, coughing produces the largest droplet concentrations 164,165 and nose exhalation the least.…”

Section: Breathing Temperature (°)mentioning

confidence: 99%

Airborne spread of expiratory droplet nuclei between the occupants of indoor environments: A review

2018

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This article reviews past studies of airborne transmission between occupants in indoor environments, focusing on the spread of expiratory droplet nuclei from mouth/nose to mouth/nose for non-specific diseases. Special attention is paid to summarizing what is known about the influential factors, the inappropriate simplifications of the thermofluid boundary conditions of thermal manikins, the challenges facing the available experimental techniques, and the limitations of available evaluation methods. Secondary issues are highlighted, and some new ways to improve our understanding of airborne transmission indoors are provided. The characteristics of airborne spread of expiratory droplet nuclei between occupants, which are influenced correlatively by both environmental and personal factors, were widely revealed under steady-state conditions. Owing to the different boundary conditions used, some inconsistent findings on specific influential factors have been published. The available instrumentation was too slow to provide accurate concentration profiles for time-dependent evaluations of events with obvious time characteristics, while computational fluid dynamics (CFD) studies were mainly performed in the framework of inherently steady Reynolds-averaged Navier-Stokes modeling. Future research needs in 3 areas are identified: the importance of the direction of indoor airflow patterns, the dynamics of airborne transmission, and the application of CFD simulations.

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“…Studies in European hospitals [1] indicate that nosocomial infections contribute significantly to morbidity and mortality rates and that many of these infections are transmitted by airborne pathogens [2]. Everyday pulmonary activities, like breathing [3], coughing [4,5], sneezing [6], talking [3], are sources of bio-aerosols [7] that may be laden with the pathogens responsible for infectious disease transmission. Once the bio-aerosols leave the infected person their fate depends on multiple and complex factors [7–10].…”

Section: Introductionmentioning

confidence: 99%

Assessment of displacement ventilation systems in airborne infection risk in hospital rooms

et al. 2019

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Efficient ventilation in hospital airborne isolation rooms is important vis-à-vis decreasing the risk of cross infection and reducing energy consumption. This paper analyses the suitability of using a displacement ventilation strategy in airborne infection isolation rooms, focusing on health care worker exposure to pathogens exhaled by infected patients. The analysis is mainly based on numerical simulation results obtained with the support of a 3-D transient numerical model validated using experimental data. A thermal breathing manikin lying on a bed represents the source patient and another thermal breathing manikin represents the exposed individual standing beside the bed and facing the patient. A radiant wall represents an external wall exposed to solar radiation. The air change efficiency index and contaminant removal effectiveness indices and inhalation by the health care worker of contaminants exhaled by the patient are considered in a typical airborne infection isolation room set up with three air renewal rates (6 h-1, 9 h-1 and 12 h-1), two exhaust opening positions and two health care worker positions. Results show that the radiant wall significantly affects the air flow pattern and contaminant dispersion. The lockup phenomenon occurs at the inhalation height of the standing manikin. Displacement ventilation renews the air of the airborne isolation room and eliminates the exhaled pollutants efficiently, but is at a disadvantage compared to other ventilation strategies when the risk of exposure is taken into account.

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Documentary Research of Human Respiratory Droplet Characteristics

Cited by 66 publications

References 79 publications

Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks

Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks

Airborne spread of expiratory droplet nuclei between the occupants of indoor environments: A review

Assessment of displacement ventilation systems in airborne infection risk in hospital rooms

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