Coughs and Sneezes Stay Airborne For Longer Distances Than Previosuly Thought

A team of international researchers discovered that coughs and sneezes stay airborne for longer distances than previously believed.

Researchers at the Massachusetts Institute of Technology found that when one coughs and sneezes virus droplets are expelled at a distance 5 to 200 times greater than if they travel on their own.   

"When you cough or sneeze, you see the droplets, or feel them if someone sneezes on you," co-author John Bush, a professor of applied mathematics at MIT, said in a statement. "But you don't see the cloud, the invisible gas phase. The influence of this gas cloud is to extend the range of the individual droplets, particularly the small ones."

The researchers suggest that engineers and architects should re-examine and reconsider the designs of workplace and hospitals or the air circulation in planes in to order to lower the risk of airborne pathogens being transmitted to people.

Smaller Drops Travel Longer Distance

The novel analysis of coughs and sneezes from a fluid-mechanics perspective was done using high speed imaging of coughs and sneezes including lab simulations and mathematical modeling. 

This new finding knocks previous studies that larger mucus droplets travel much farther than the smaller ones due to the higher momentum. They found that smaller droplets travel farther due to their association with other particles and form a gas puff.

In this paper the researchers call a cough or a sneeze a multiphase turbulent buoyant cloud.

"The cloud entrains ambient air into it and continues to grow and mix," Bourouiba says. "But as the cloud grows, it slows down, and so is less able to suspend the droplets within it. You thus cannot model this as isolated droplets moving ballistically."

Currently, the team plans on developing tools and conducting further studies to get a deeper perspective of this finding.

This study was provided by the National Science Foundation. The finding was documented in the Journal of Fluid Mechanics.