Six feet may be insufficient for safe social distancing

Researchers have found that the current social distancing guidelines of 6 feet may be insufficient because a mild cough occurring in low wind speeds of 415 kph can propel saliva droplets 18 feet. Airborne transmission of viruses, like the virus causing COVID-19, is not well understood, but a good baseline for the study is a deeper understanding of how particles travel through the air when people cough.

In a paper published in Physics of Fluids, from AIP Publishing, Talib Dbouk and Dimitris Drikakis discovered 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 the bulk of surrounding air released by a cough.

To study how saliva moves through the 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. “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.”

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 the air. –ANI