COVID-19: How far can a cough really travel?

Coronavirus

BOCA RATON, Fla. (CNN) – As some states start to reopen, the coronavirus is still spreading. U.S. officials still recommend people stand six feet apart from each other, but is that really how far germs can travel from a cough?

Inside a lab at Florida Atlantic University, two engineering professors did an experiment to measure the power of a cough. Using a dummy, they fill its mouth with a mix of glycerin and water, then force the dummy to couch with a pump and measure how far the droplets travel using a green laser light.

“It generates particles on the order of 10-20 microns, which is roughly close to what the smallest droplet sizes are when we cough,” Sid Verma, Assistant Professor of Engineering at FAU said.

The droplets in the experiment traveled a distance of three feet almost immediately. Within five seconds, the droplets were at six feet. Then, in about 10 seconds, the droplets were at nine feet.

Nine feet is three feet beyond the recommended social distancing guidelines.

“It’s already reaching roughly nine feet now, still moving farther, slowly,” Verma said, watching the droplets travel.

The fog of droplets lingered in the air, but kept moving forward, taking another 30 to 40 seconds to float another three feet.

“It’s getting closer to 12 feet now,” Verma said.

Over and over again, the simulated droplets blew past the six foot mark, often doubling that distance.

Manhar Dhanak, Chairman of the Engineering Department at FAU said the droplets could linger at a nine foot distance for two to three minutes. The droplets do become less dense the further they travel, but they still hang in the air with the ability to carry disease.

The professors put a mask on the dummy, and particles still dispersed from the sides, though they did not travel far. They also tested what it would be like if the dummy coughed into a hand. The droplets sprayed in all directions.

The professors found that with a lighter cough, the droplets only traveled about three feet.

Still, Dhanak says, keeping a distance of at least six feet is important.

“Six feet is the minimum distance that you should keep,” Dhanak said. “Further is better.”

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