- People speaking in close proximity to each other can spread SARS-CoV-2
- Scientists carried out a related experiment in a Japanese hair salon
- They found that wearing a mask underneath a face shield provided the best protection
Speaking while close to other people increases one's risk of spreading Covid-19, new research has revealed.
The study published in Physics of Fluids found that the spread of fluids from the mouth is not limited to coughing or sneezing.
The salon experiment
Researchers used smoke and a laser light to examine the flow of expelled breath near and around two people conversing in various postures as normally seen in hair salons, medical exam rooms or long-term care facilities.
As part of the study, electronic cigarettes were used to produce artificial smoke consisting of droplets about one-tenth micron in diameter, which is similar to the size of a virus particle.
The liquid used in these vaping devices, a mixture of glycerin and propylene glycol, produces a cloud of tiny droplets that scatter light from a laser, which makes airflow patterns visible.
"We analysed, the characteristics of exhalation diffusion with and without a mask, when a person was standing, sitting, facing down, or lying face up," says author Keiko Ishii in a news release.
The experiments were carried out in a hair salon at the Yamano College of Aesthetics in Tokyo, with postures chosen to simulate typical customer service scenarios, including shampooing where a customer is lying back with the technician standing and leaning over the customer.
What the findings revealed
The experiments showed that exhaled air from an unmasked person who is speaking tends to move downward under the influence of gravity. This means that if a customer or patient is lying down, they could become infected.
When a mask is worn while standing or sitting, the vapour cloud tends to attach to that person's body, which is warmer than the surrounding air and flows upward along the body.
If, however, the technician is leaning over the client, the aerosol cloud tends to detach from that person's body and settle onto the client below.
The investigators also experimented with face shields and found they can prevent any aerosols that leak from around the technician's mask from descending to the customer.
"The face shield promoted the rise of the exhaled breath. Hence, it is more effective to wear both a mask and a face shield when providing services to customers," Ishii says.