Conversation spreads droplets more than six feet indoors

By John Sullivan

Tiled images of exhaled air
Image courtesy of Stone lab

With implications for the transmission of diseases like COVID-19, researchers have found that ordinary conversation creates a conical, “jet-like” airflow that carries a spray of tiny droplets from a speaker’s mouth across meters of an interior space.

Howard Stone, the Donald R. Dixon ’69 and Elizabeth W. Dixon Professor of Mechanical and Aerospace Engineering, and co-lead researcher Manouk Abkarian, a senior scientist at the University of Montpellier in France, led experiments to learn how widely and quickly exhaled material could spread.

In an article published Sept. 25, 2020, in the Proceedings of the National Academy of Sciences, the researchers concluded that normal conversations can spread exhaled material at least far as, if not beyond, the social distancing guideline of six feet. The research was funded by a National Science Foundation Rapid Response Research grant.

The researchers also said that while masks do not completely block the flow of aerosols, they play a critical role in disruption of the spray of droplets from a speaker’s mouth. This identifies why [most] masks play a big role,” Stone said. “They cut everything off.”