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 4-15 kph can propel saliva droplets 18 feet.

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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. 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.