Science- Talking expels viral particles that gravity could carry from person to person, a new study found.
- Employees standing or leaning over clients could infect them.
Masks reduce the risk, but infection is possible if the mask is loose and air escapes through gaps.
Most people know by now to wear a mask in public settings to slow the spread of the novel
But speaking at a normal volume also expels viral particles, and these could transfer to another person even, in some cases, when you're wearing a mask, according to a study published February 23 in Physics of Fluids.
Japanese researchers found that in scenarios where a customer is sitting or lying below an employee (or vice versa), airflow could carry viral particles from person to person. That could be a problem for settings such as a hair salon, a spa, or a medical or care facility.
Previous research has found that talking can produce a huge amount of viral particles in a short time, so understanding how this works may be important to protecting people from infection in medical and customer service settings.
Gravity pulls contagious particles downward if you lean or stand over another person
The researchers, from Aoyama Gakuin University and Yamano College of Aesthetics, used e-cigarettes to generate a vapor cloud with particle sizes similar to those that carry the coronavirus. They then used laser light to study the airflow pattern of the particles in different settings. Participants spoke the same word ("onegaishimasu," a common Japanese greeting) while sitting, standing, and lying down in different positions, with and without masks.
When a person speaks without a mask, the particles they exhale are carried downward by gravity, so someone sitting or lying below them might be infected.
With a mask, those particles are more contained in a vapor cloud by warm air surrounding the person's body, and are less likely to travel toward other people. That significantly reduces the risk, the researchers found.
If a person leans over, however, exhaled particles are pulled downward, the study found. If the mask is loose, and viral particles escape, this could present an infection risk.
That could be a problem in situations such as table massage, other spa services, or medical care in which a patient is lying on a bed.
The researchers used surgical-style, non-woven masks, and found particles weren't likely to escape through the sides or bottom of the mask, but the top, through gaps around the nose. It's not clear from this study how a tighter-fitting or woven mask might fare, or if double-masking might help.
Wearing a face shield helped prevent particles from being carried by gravity, though.
"The face shield promoted the rise of the exhaled breath," study author Keiko Ishii, professor of mechanical engineering at Aoyama Gakuin University, said in a press release.. "Hence, it is more effective to wear both a mask and a face shield when providing services to customers."