According to a new study published this week in PNAS, thousands of drops of saliva from people who speak loudly can linger in the air for 8 to 14 minutes before disappearing .
The research, conducted by a team from the U.S. National Institutes of Health, could have a significant impact on our understanding of COVID-19 transmission.
Respiratory viruses such as SARS-CoV-2 are transmitted by direct contact or when the virus reaches a place in small droplets released into the air. That is why it is important to cough and sneeze while covering your mouth. However, simple speech can also release thousands of drops of oral fluid into the air, and the researchers were interested in seeing how many were produced and how long they could remain in the air .
In the study, a group of people were asked to repeat phrases and used lasers to visualize the droplets they produced , watching them decay in a closed and stagnant environment.
According to Stokes’ law , the terminal velocity of a falling drop is scaled as the square of its diameter. Once in the air, the droplets generated by speech quickly dehydrate due to evaporation, thus decreasing their size and decreasing their fall.
Based on previous studies of how much viral RNA can be found in oral fluids in the average COVID-19 patient, researchers estimate that a single minute of speaking aloud generates at least 1,000 drops that contain viruses . Their observations suggest that these droplets remain in the air for more than 8 minutes and sometimes up to 14 minutes.