Six feet is not far enough for safe social distancing

Six feet is not far enough for safe social distancing. Current social distancing guidelines of staying six feet apart are not sufficient to prevent COVID-19 exposure, according to a new study from the American Institute of Physics. 

The researchers demonstrated that in windy conditions – even with the slightest breeze – saliva can travel 18 feet in five seconds.

The airborne transmission of SARS-CoV-2 and other viruses is not entirely understood. The experts set out to gain a better understanding of how particles travel through the air when a person coughs.

“The droplet cloud will affect both adults and children of different heights,” said study co-author Dimitris Drikakis. “Shorter adults and children could be at higher risk if they are located within the trajectory of the traveling saliva droplets.”

Saliva droplets travel in a bulk of surrounding air released by a cough, but they do not always travel through the air in the same way. The movement of airborne particles is influenced by many factors such as humidity and air temperature.

For their investigation, the researchers 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 model accounted for the effects of humidity, dispersion force, the interactions of saliva molecules and air, and the evaporation process.

Overall, about 3.7 million equations were analyzed with the computer model. The simulation contained a grid that represents the space in front of a coughing person.

“Each cell holds information about variables like pressure, fluid velocity, temperature, droplet mass, droplet position, etc.,” said study co-author Talib Dbouk. 

“The purpose of the mathematical modeling 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 study revealed that a mild cough occurring in wind speeds as low as 4 kilometers per hour, or 2.5 miles per hour, can propel saliva droplets 18 feet.

According to the experts, further research is needed to determine the effect of ground surface temperature on the behavior of saliva in the air.

Additional studies are also needed to examine indoor environments, where air conditioning has a significant impact on particle movement.

“This work is vital, because it concerns health and safety distance guidelines, advances the understanding of spreading and transmission of airborne diseases, and helps form precautionary measures based on scientific results,” said Drikakis.

The research is published in the journal Physics of Fluids.

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By Chrissy Sexton, Earth.com Staff Writer