COVID-19 can be transmitted from asymptomatic but infected people through tiny aerosol droplets in exhaled air. We already know from most research that coughing or sneezing can cause aerosols to fly long distances. However , what happens when we just chat? A new study published in the journal Physics of Fluids has focused precisely on this aspect: how risky is it to talk around another person?
The virus can be expelled simply by speaking
The team of scientists from the University of Tokyo (Japan) used electronic cigarette smoke and laser light to study the flow of expelled breath close to and around two people who were conversing in various positions that we can commonly observe in the service industry, such as in beauty salons, medical exam rooms or long-term care centers and both standing and sitting.
“We analyzed the characteristics of the diffusion of exhalation with and without a mask when a person was standing, sitting, face down or lying on his back,” says Keiko Ishii, leader of the work. “Customer service is inevitably accompanied by speech, which can generate droplets larger than normal breathing. In addition, these can spread through the air and float in the air for a long time, even an hour, ” the authors explain.
For the experiment, carried out in a hair salon at the Yamano College of Aesthetics in Tokyo, artificial cigarette smoke consisted of droplets about one-tenth of a micron in diameter, a size very close to that of a virus particle. The liquid used in these vaping devices, basically a mixture of glycerin and propylene glycol, created a cloud of tiny droplets that scattered light from a laser, allowing airflow patterns to be visualized.
For example, it was perfectly seen how in a situation in a hairdressing salon in which the client was lying on a chair or sofa and the professional was standing and leaning over the client, the exhaled air of a person without a mask who speaks tends to move towards down under the influence of gravity. If a client or patient is below, they could become infected with the coronavirus.
“A significant amount of similar face-to-face contact would occur not only in cosmetology but also in medical and long-term care,” says Ishii.
What if we use a mask?
When wearing a mask while standing or sitting, the vapor cloud tended to adhere to that person’s body, which is warmer than the surrounding air and flowed upward through the body. But if the professional leaned over, still wearing a mask, the aerosol cloud tended to detach from that person’s body and fall on the client just below . Being able, again, to become infected with COVID-19.
The researchers also experimented with protective face shields and found that they can prevent aerosols that seep around the professional’s mask from traveling to the client.
“The face shield promoted increased exhaled breath. Therefore, it is more effective to wear a mask and face shield when offering services to clients,” concludes Ishii.
Referencia: “Relationship between human exhalation diffusion and posture in face-to-face scenario with utterance” Physics of Fluids (2021). DOI: 10.1063/5.0038380
