How far droplets can move in indoor environments ? revisiting the Wells evaporation?falling curve

Abstract

Our study reveals that for respiratory exhalation flows, the sizes of the largest droplets that would totally evaporate before falling 2 m away are between 60 and 100 microm, and these expelled large droplets are carried more than 6 m away by exhaled air at a velocity of 50 m/s (sneezing), more than 2 m away at a velocity of 10 m/s (coughing) and less than 1 m away at a velocity of 1 m/s (breathing). These findings are useful for developing effective engineering control methods for infectious diseases, and also for exploring the basic transmission mechanisms of the infectious diseases. There is a need to examine the air distribution systems in hospital wards for controlling both airborne and droplet-borne transmitted diseases.

Risk reduction and management strategies to prevent transmission of infectious disease among dogs at dog shows, sporting events, and other canine group settings

“…In many settings, this can be addressed by establishing distinct areas where the general public is restricted from entering and ensuring adequate space and instructions so dogs from different owners or handlers are housed far enough apart (eg, at least 1 m) to reduce transmission opportunities. 101 Dogs with clinical illness (eg, coughing or sneezing) may exhale droplet particles greater distances (eg, 6 m); therefore, maximization of the distance among dogs when reasonable and prompt removal of dogs with clinical illness are important. 101 It is also important to provide a separate housing location for those dogs that need immediate removal from shared spaces because of a suspected infectious disease but cannot be removed from the premises at that time.…”

“…101 Dogs with clinical illness (eg, coughing or sneezing) may exhale droplet particles greater distances (eg, 6 m); therefore, maximization of the distance among dogs when reasonable and prompt removal of dogs with clinical illness are important. 101 It is also important to provide a separate housing location for those dogs that need immediate removal from shared spaces because of a suspected infectious disease but cannot be removed from the premises at that time.…”

Airborne transmission of disease in hospitals

“…Flugge (1897) showed that droplets from the nose and mouth contained bacteria, but did not travel more than 2 m. Wells (1934) characterized the concepts of airborne transmission and large droplet transmission based on the droplet sizes. In his classical study of airborne transmission, Wells (1934) revealed the relationship between droplet size, evaporation and falling rate by studying the evaporation of falling droplets, and this is referred to as the Wells evaporation-falling curve of droplets by Xie et al (2007). Wells postulated a now widely accepted hypothesis of the distinction between droplet size and airborne transmission routes.…”

Natural Personalised Ventilation - A Novel Approach

“…The RNG k-ε turbulence model (Yakhot and Orszag, 1986) was applied with the Boussinesq approximation for buoyancy. The external air temperature was assumed to be 20 o C. A passive scalar contaminant source (C1) was emitted from an orifice of 0.0025m 2 located at the sitting visitor's mouth and based on Xie et al (2007), the speed of coughing was taken to be 10m/s with a mass flow rate of 0.03kg/s. The temperature of cough was taken as 32 o C with density of particles similar to that of air, consistent with the observed behaviour of passive contaminants such as droplet nuclei (Morawska, 2006;Jiang et al, 2009).…”