Cough droplets can travel beyond six feet, simulation study suggests

A new simulation study suggests that a person coughing can disperse droplets well beyond six feet, and that anyone shorter than the person coughing — such as children — might be at a greater risk of encountering the downward trajectory of those cough droplets.



a person is walking down the street: A Chinese girl wears a protective mask as she tries to catch bubbles blown by her mother while playing at Ritan Park on March 22, in Beijing.


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A Chinese girl wears a protective mask as she tries to catch bubbles blown by her mother while playing at Ritan Park on March 22, in Beijing.

During the coronavirus pandemic, the dispersion of cough droplets has become of great interest among scientists. The new study, published on Tuesday in the journal Physics of Fluids, evaluates the risk of spreading the virus through cough droplets in the air under different tropical outdoor environments.

“Young children may be at greater risk compared to adults based on the typical downward cough trajectory. Teenagers and short adults are advised to maintain a social distance greater than 2 m from taller persons,” the researcher wrote in the study. “Surgical masks are known to be effective at trapping large droplets and therefore recommended for use as necessary.”

The researchers — from Singapore’s Agency of Science, Technology and Research — used numerical models to simulate the trajectory of droplets expelled by a person who suddenly coughs outdoors with someone listening nearby.

The researchers ran the simulation with different droplet sizes, air temperatures, relative humidity, wind speed and varying distances between the cougher and the listener.

The study suggests that at wind speeds of 2 meters per second — or about 4 miles per hour — the travel distances for droplets around the sizes of 100 micrometers and 1,000 micrometers can reach 21.6 feet and 4 feet, respectively, at 86 degrees Fahrenheit.

For a 100-micrometer droplet, the researchers found that the travel distance increases from about 3 feet without wind to about 22 feet at a wind speed of about 6.7 miles per hour.

The study has some limitations, including that the results are based on simulation models — not real-life experiments — and the effects of ambient temperature and humidity on the viability of the coronavirus remains unclear.

This isn’t the first time a model has suggested that a cough can travel farther than six feet. In May, separate research out of Cyprus that also published in the journal Physics of Fluids found that a light breeze could carry some droplets as far as 18 feet.



a group of people walking down the street: People wearing face masks stroll in the old harbour of Marseille, southestern France, on August 26, 2020. - The southern port city of Marseille became the latest to make face coverings compulsory city-wide outdoors, while bars and restaurants will close every day at 11 pm. (Photo by Christophe SIMON / AFP) (Photo by CHRISTOPHE SIMON/AFP via Getty Images)


© CHRISTOPHE SIMON/AFP/AFP via Getty Images
People wearing face masks stroll in the old harbour of Marseille, southestern France, on August 26, 2020. – The southern port city of Marseille became the latest to make face coverings compulsory city-wide outdoors, while bars and restaurants will close every day at 11 pm. (Photo by Christophe SIMON / AFP) (Photo by CHRISTOPHE SIMON/AFP via Getty Images)



a close up of a person talking on a cell phone


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