56ºF

How chance of spreading COVID-19 through air changes based on what words are spoken

Experts identify 'P' sound as creating stronger jet stream

Experts have discovered the likelihood of spreading the coronavirus (COVID-19) through aerosols from a person’s mouth changes based on what words that person is saying.

With increasing evidence of COVID-19 spreading through person-to-person contact, one question that often comes up is: How close is too close?

Multiple reports confirm transmission of the SARS-CoV-2 virus indoors from infections aerosols. What’s the risk from ordinary activities, such as speaking or breathing?

In a paper published in the Proceedings of the National Academy of Science, fluid dynamics engineers at Princeton University used high-speed cameras and lasers to study the way ordinary breathing and different types of speech create jets of airflow capable of spreading exhaled aerosols from a person’s mouth.

One video shows that even calm breathing with a slightly open mouth produces a significant jet or air.

Active blowing, as someone would do during an athletic activity, propels the airstream forward with even more speed and distance.

With it comes to ordinary speech, the researchers found that what people say is just as how they say it, in terms of jets of air that are emitted.

When someone said, “sing a song of six pence,” it wasn’t until the word “pence" -- specifically the "P" sound -- that the airflow moved in a forward direction at a higher speed.

During other parts of the phrase, the airstream was directed downward.

Phrases with multiple "P" sounds, such as “Peter Piper picked a peck,” created multiple jets of air that were more similar to breathing or blowing. They pushed air directly forward at a higher speed for a greater distance.

Researchers concluded that depending on the individual sounds, speech creates an exhaled cloud that expands in front of the speaker. Notably, though, the aerosols ejected during speech typically reached the six-foot mark after about 30 seconds, and they were diluted to 3% of their original concentration.

The study didn’t include the change with increasing the volume of speech.


About the Authors: