Normal Conversation Spreads Virus-Laden Droplets Beyond 6 Feet

Ordinary conversation releases airborne droplets that can spread widely through indoor spaces, a finding with big implications for transmission of the new coronavirus, researchers say.

Their experiments showed that everyday talk can expel droplets farther than the typical “social distancing” limit of 6 feet.

“People should recognize that they have an effect around them,” said Howard Stone, a professor of mechanical and aerospace engineering at Princeton University in New Jersey. “It’s not just around your head, it is at the scale of meters.” One meter equals just over 3 feet.

How COVID-19 spreads is not fully understood, but it’s believed that people without symptoms could infect others through tiny droplets created when they speak, sing or laugh.

“Lots of people have written about coughs and sneezes and the kinds of things you worry about with the flu,” Stone said in a university news release. “But those features are associated with visible symptoms, and with this disease we are seeing a lot of spread by people without symptoms.”

Stone and his colleagues conducted tests to determine how far and fast exhaled droplets from normal speaking could spread in an interior space without good ventilation.

In such settings, normal conversation can spread droplets at least as far as, and even beyond, social distancing guidelines recommended by U.S. officials (6.5 feet) and the World Health Organization (3.2 feet), according to the study published online recently in the journal Proceedings of the National Academy of Sciences.

“It certainly highlights the importance of ventilation,” Stone said. “Especially if you have an extended conversation.”

While masks do not completely block the flow of exhaled droplets, researchers said they significantly reduce it.

“Masks really cut this flow off tremendously,” Stone said. “This identifies why [most] masks play a big role. They cut everything off.”

The study didn’t account for movement of a speaker’s head or body, and background air movement created by ventilation and other speakers, Stone noted. Analyzing those factors would require more investigation.

Want to see just how far those “conversation droplets” spread? Princeton supplied this video, illustrating the movement of a cloud of tiny droplets, illuminated by a laser sheet placed in front of the person speaking:

More information

The U.S. Centers for Disease Control and Prevention has more on COVID-19.