How Far Can Speech-Induced Airflow Carry Viruses?

  • Author: ChemistryViews.org
  • Published: 29 September 2020
  • Copyright: Wiley-VCH GmbH
  • Source / Publisher: Proceedings of the National Academy of Sciences of the United States of America
thumbnail image: How Far Can Speech-Induced Airflow Carry Viruses?

The COVID-19 pandemic is caused by the coronavirus SARS-CoV-2. To understand and prevent the transmission of this virus, it is important to know how it is transported in the air during breathing, speaking, singing, etc. How these airflows can affect virus transmission is less well understood than for, e.g., sneezing or coughing. However, due to the spread via asymptomatic or presymptomatic individuals, speaking or breathing might be important transmission pathways.


Howard A. Stone, Princeton University, NJ, USA, and colleagues have investigated airflows during breathing and speaking. The team visualized the flow of droplets in air produced by a test subject using a laser sheet and a fog machine and compared the results with numerical simulations of airflow. The airflow was observed during inhalation and exhalation, during blowing, and while the subject spoke different short sentences.


The researchers observed that inhalation draws air from all around the mouth, while exhalation is more directed, and thus, causes faster airflows that can carry aerosols over significant distances. Additionally, speaking changes the flow during exhalation by inducing variations in pressure and speed. The team found that plosive sounds, such as "p", produce directed puffs of air that quickly travel over distances of about 1 m. When several of these sounds are included in the spoken sentence, the sequence of air puffs can produce a jet-like, directed flow that can transport droplets over 2 m in front of the speaker within 30 s of conversation.


According to the researchers, these results indicate that not only the distance from a speaker, but the time spent directly in front of him or her is important for the transmission risk in longer conversations. This insight could be useful to inform guidelines to mitigate the spread of COVID-19.



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