Enhanced spread of expiratory droplets by turbulence in a cough jet

Wei, Jianjian; Li, Yuguo

doi:10.1016/j.buildenv.2015.06.018

Cited by 271 publications

(305 citation statements)

References 42 publications

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“…The deposition of medium and large particles occurs throughout the evolution of the cough jet, as also revealed by Bourouiba et al [37]. Wei and Li [40] showed that turbulence can significantly enhance the settling range of particles.…”

Section: Discussionmentioning

confidence: 66%

“…Moreover, only the drag and body forces were considered for the particle motion. Wei and Li [40] demonstrated that evaporation has a significant effect on the spread range of medium-sized droplets in a steady cough jet. Although the effect of evaporation is not considered in this study, it is reasonable to infer this effect is not so important in the transient jet, as particles of all sizes have a similar maximum travel distance.…”

Section: Discussionmentioning

confidence: 99%

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Human Cough as a Two-Stage Jet and Its Role in Particle Transport

Wei

2017

PLoS ONE

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134

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The human cough is a significant vector in the transmission of respiratory diseases in indoor environments. The cough flow is characterized as a two-stage jet; specifically, the starting jet (when the cough starts and flow is released) and interrupted jet (after the source supply is terminated). During the starting-jet stage, the flow rate is a function of time; three temporal profiles of the exit velocity (pulsation, sinusoidal and real-cough) were investigated in this study, and our results showed that the cough flow’s maximum penetration distance was in the range of a 50.6–85.5 opening diameter (D) under our experimental conditions. The real-cough and sinusoidal cases exhibited greater penetration ability than the pulsation cases under the same characteristic Reynolds number (Rec) and normalized cough expired volume (Q/AD, with Q as the cough expired volume and A as the opening area). However, the effects of Rec and Q/AD on the maximum penetration distances proved to be more significant; larger values of Rec and Q/AD reflected cough flows with greater penetration distances. A protocol was developed to scale the particle experiments between the prototype in air, and the model in water. The water tank experiments revealed that although medium and large particles deposit readily, their maximum spread distance is similar to that of small particles. Moreover, the leading vortex plays an important role in enhancing particle transport.

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Section: Discussionmentioning

confidence: 66%

Section: Discussionmentioning

confidence: 99%

Human Cough as a Two-Stage Jet and Its Role in Particle Transport

Wei

2017

PLoS ONE

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134

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“…41 Xie et al 42 found that expired droplets can travel 1.5-2 m. The presence of turbulence greatly enhances droplet spread. 43 Water droplets with sizes on the order of 1 μm evaporate within a few milliseconds, water droplets of 10 μm survive for up to a few tenths of a second, and large droplets of 100 μm can survive for almost a minute. The transient process from a droplet to a droplet nucleus can be ignored when studying the movement of small droplets, 44 whereas evaporation barely affects large droplets because they deposit soon after release.…”

Section: Spread Of Droplets From the Mouth And Nose To The Indoor Envmentioning

confidence: 99%

“…However, medium-sized droplets (eg, 50 μm in diameter) are most sensitive to humidity. 43 Deposition occurs either by gravitational sedimentation, turbulent eddy impaction, or diffusional deposition. Large droplets were first defined as droplets >100 μm by Wells.…”

Section: Spread Of Droplets From the Mouth And Nose To The Indoor Envmentioning

confidence: 99%

Airborne spread of infectious agents in the indoor environment

Wei

2016

American Journal of Infection Control

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435

393

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Key Words:Respiratory droplet indoor air coughing droplet dispersion infection control environmental ventilation Background: Since the 2003 severe acute respiratory syndrome epidemic, scientific exploration of infection control is no longer restricted to microbiologists or medical scientists. Many studies have reported on the release, transport, and exposure of expiratory droplets because of respiratory activities. This review focuses on the airborne spread of infectious agents from mucus to mucus in the indoor environment and their spread as governed by airflows in the respiratory system, around people, and in buildings at different transport stages. Methods: We critically review the literature on the release of respiratory droplets, their transport and dispersion in the indoor environment, and the ultimate exposure of a susceptible host, as influenced by airflows. Results: These droplets or droplet nuclei are transported by expired airflows, which are sometimes affected by the human body plume and use of a face mask, as well as room airflow. Room airflow is affected by human activities such as walking and door opening, and some droplets are eventually captured by a susceptible individual because of his or her inspired flows; such exposure can eventually lead to longrange spread of airborne pathogens. Direct exposure to the expired fine droplets or droplet nuclei results in short-range airborne transmission. Deposition of droplets and direct personal exposure to expired large droplets can lead to the fomite route and the droplet-borne route, respectively. Conclusions: We have shown the opportunities for infection control at different stages of the spread. We propose that the short-range airborne route may be important in close contact, and its control may be achieved by face masks for the source patients and use of personalized ventilation. Our discussion of the effect of thermal stratification and expiratory delivery of droplets leads to the suggestion that displacement ventilation may not be applicable to hospital rooms where respiratory infection is a concern.

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“…Compared to the computational fluid dynamics (CFD) model, the theoretical jet model proposed in this work has a small computational load and provides a crucial tool for predicting the cross‐contamination in indoor environments. The expiratory flow close to the nose or mouth was often treated as a free turbulent jet in the previous studies . Empirical formulas for a non‐isothermal jet have mostly been used to reveal the trajectory of the exhaled flow, but they work well only in a uniform environment and are not appropriate for characterizing the exhaled airflow in a non‐uniform environment, for example, a DV room with thermal stratification …”

Section: Introductionmentioning

confidence: 99%

Direct or indirect exposure of exhaled contaminants in stratified environments using an integral model of an expiratory jet

et al. 2019

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The risk of cross‐infection is high when the susceptible persons are exposed to the pathogen‐laden droplets or droplet nuclei exhaled by infectors. This study proposes a jet integral model to predict the dispersion of exhaled contaminants, evaluating the exposure risk and determining a threshold distance to identify the direct and indirect exposures in both thermally uniform and stratified environments. The results show that the maximum concentration of contaminants exhaled by a bed‐lying infector clearly decreases in a short distance (<1.8 m) in a uniform environment, while it maintains high values in a long distance in a stratified environment. The lock‐up phenomenon largely weakens the decay of the concentration. The direct exposure of the receiver is determined primarily by the impact scope of the exhaled airflow, while the indirect exposure is mainly related to the ventilation rate and air distribution in the room. In particular, the distance of direct exposure is the longest (approximately 2 m) when the receiver's breathing height is at the lock‐up layer in a stratified environment. Our study could be useful for developing effective prevention measures to control cross‐infection in the initial stage of design of indoor layouts and ventilation systems.

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Enhanced spread of expiratory droplets by turbulence in a cough jet

Cited by 271 publications

References 42 publications

Human Cough as a Two-Stage Jet and Its Role in Particle Transport

Human Cough as a Two-Stage Jet and Its Role in Particle Transport

Airborne spread of infectious agents in the indoor environment

Direct or indirect exposure of exhaled contaminants in stratified environments using an integral model of an expiratory jet

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