Respiratory droplets from COVID-19 patients can reach far beyond the current social distancing guidelines of 6 feet, warns a new study.
Saliva droplets can travel large distances, depending on environmental conditions such as wind speed, temperature, pressure and humidity, according to the study published in Physics of Fluids on May 19.
Researchers, Talib Dbouk and Dimitris Drikakis from University of Nicosia in Cyprus, have found that with even a slight breeze of 4 kph, saliva travels 18 feet in 5 seconds.
"The droplet cloud will affect both adults and children of different heights," Drikakis said. "Shorter adults and children could be at higher risk if they are located within the trajectory of the travelling saliva droplets."
Saliva is a complex fluid, and it travels suspended in a bulk of surrounding air released by a cough. Many factors affect how saliva droplets travel, including the size and number of droplets, how they interact with one another and the surrounding air as they disperse and evaporate, how heat and mass are transferred, and the humidity and temperature of the surrounding air.
Previous studies say that potentially infectious cough aerosols remain viable up to 4 m away and for up to 45 minutes.
In order to study how saliva moves through air, Dbouk and Drikakis created a computational fluid dynamics simulation that examines the state of every saliva droplet moving through the air in front of a coughing person. Their simulation considered the effects of humidity, dispersion force, interactions of molecules of saliva and air, and how the droplets change from liquid to vapour and evaporate.
The computational domain in the simulation is a grid representing the space in front of a coughing person. The analysis involved running partial differential equations on 1,008 saliva droplets and solving approximately 3.7 million equations in total.
"Each cell holds information about variables like pressure, fluid velocity, temperature, droplet mass, droplet position, etc.," Dbouk said. "The purpose of the mathematical modelling and simulation is to take into account all the real coupling or interaction mechanisms that may take place between the main bulk fluid flow and the saliva droplets, and between the saliva droplets themselves."
The researchers say that further studies are needed to determine the effect of ground surface temperature on the behaviour of saliva in air and to examine indoor environments, where air conditioning significantly affects the particle movement through air.