Talking loudly can leave droplets in the air for 14 minutes and, if inhaled, can cause a new infection, scientists say.
They used very sensitive laser light to demonstrate how a loud voice can emit thousands of airborne droplets per second.
In a confined space, droplets hang around in the air for eight to 14 minutes, according to research, which underscores the importance of wearing masks to prevent the spread of Covid-19.
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The research was carried out by scientists from the University of Pennsylvania and the National Institutes of Health in the United States.
It was published in the Proceedings of the National Academy of Sciences of the United States of America.
In a report, the researchers wrote: “Speech droplets generated by asymptomatic carriers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are increasingly being considered as a likely mode of disease transmission.
“Very sensitive scattering observations of laser light have revealed that loud speech can emit thousands of droplets of oral fluid per second.
“In a closed and stagnant air environment, they disappear from the viewing window with time constants of the order of 8 to 14 min.
“These observations confirm that there is a substantial probability that speaking normally causes transmission of airborne viruses in confined environments. “
The report added: “We estimate that one minute of speaker generates at least 1,000 droplet nuclei containing virions that stay in the air for more than 8 minutes. They could therefore be inhaled by others and … trigger a new SARS-CoV-2 infection. “
During the experiment, the researchers used a laser to observe the spread of droplets when a person repeated the phrase “stay healthy” in a confined space for 25 seconds.
The researchers wrote, “This phrase was chosen because the” th “phonation in the word” healthy “was found to be an effective generator of speech droplets in the oral fluid. “
They concluded in their report: “Our method of scattering laser light not only provides real-time visual evidence of the emission of voice droplets, but also assesses their lifespan in air.
“This direct visualization shows how normal speech generates airborne droplets which can remain suspended for tens of minutes or more and are eminently capable of transmitting diseases in confined spaces. “