NIDDK finds speech droplets last 8 minutes in air, suggesting COVID-19 risk

Normal speech generates airborne droplets that can remain suspended for 8 minutes or longer and are eminently capable of transmitting disease in confined spaces, according to a study by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) that could have implications for managing COVID-19 risk.

The researchers created a closed, stagnant air environment and measured the suspension of droplets into the enclosed space as an individual repeated the phrase "stay healthy" in a loud voice for 25 seconds. The droplet patterns were monitored for 80 minutes.

At the relative humidity (27%) and temperature (23 °C) of the experiment, the researchers expected the droplets to dehydrate within a few seconds; instead, the droplets remained suspended for 8 to 14 minutes. Factoring in the average COVID-19 virus RNA load per droplet that has been reported in earlier studies, the NIDDK team estimated that 1 minute of loud speaking would generate at least 1,000 virus-containing droplets that would remain airborne for more than 8 minutes—long enough to be inhaled by others.

The findings were published on May 13 by the Proceedings of the National Academy of Sciences (PNAS). The research team included three NIDDK representatives and one coauthor from the University of Pennsylvania.

Read the study: https://www.pnas.org/content/early/2020/05/12/2006874117