There are the anti-maskers, then there are the considerate types who always wear cloth and store-bought face masks – even when jogging and exercising. But there’s also a third group, one that seems to be increasing in numbers. Do you know who I’m talking about?
They are the people wearing face shields – just face shields, not masks and face shields as is the norm among healthcare workers.
Do they protect the wearer and those in close proximity? A new study has the answer.
Scientists tell us that every time we utter even just a few words, we spray thousands of microscopic aerosol droplets. If we speak loudly or shout or are puffing and panting, then the number of droplets increases enormously. When someone is infected with COVID-19, each aerosol droplet can contain thousands of viral particles, each with the potential to infect others nearby who breathe them in.
To prove the point, scientists at Florida Atlantic University in the US created a visual representation showing why face shields were not effective in preventing the spread of COVID-19.
In their study, published in the journal Physics of Fluids, the researchers simulated coughing by connecting a mannequin’s head to a fog machine, using a pump to expel the vapour through the mannequin’s mouth.
“Using a green laser pointer and cylindrical rod, the simulated cough droplets appear as a glowing green vapour flowing from the mannequin’s mouth,” explained observers.
“During the face shield simulation, the shield initially deflects droplets toward the ground after a cough.
“However, small droplets still hovered at the bottom of the shield and then floated around the sides, eventually spreading about 90 centimetres to the front and back sides of the mannequins.”
The authors said the visuals indicated face shields and masks with exhale valves were not as effective as regular face masks in restricting the spread of droplets.
They said: “The visualisations indicate that although face shields block the initial forward motion of the jet, the expelled droplets can move around the visor with relative ease and spread out over a large area depending on light ambient disturbances.
“Our observations suggest that to minimise the community spread of COVID-19, it may be preferable to use high quality cloth or surgical masks that are of a plain design, instead of face shields and masks equipped with exhale valves.
“Visualisations for a mask equipped with an exhalation port indicate that a large number of droplets pass through the exhale valve unfiltered, which significantly reduces its effectiveness as a means of source control.”
“Professor Brendan Crabb, director and CEO of the Burnet Institute in Melbourne, concurred with those findings, saying face shields did not work unless a surgical mask was worn underneath.
“Bandanas, scarves, those things are not very effective either,” he says.
In other COVID news, Victorian Premier Daniel Andrews announced this morning that cases had risen back above 100 for the first time since last Sunday and that a further 15 people had been added to the state’s death toll. Nine of the 15 deaths were recorded in aged care facilities before yesterday, but were only added to the official death toll today. Eight of the deaths had occurred in a single aged care facility.
The deputy chief health officer says the number of cases is not as low as officials would like and Mr Andrews warns that infections could “explode” if restrictions are opened too quickly.
He will announce a roadmap out of the stage four lockdown in Melbourne on Sunday, pointing out that a “leaked plan” published in the Herald Sun, which proposed keeping stage four restrictions for an additional fortnight with some tweaks, was an “out-of-date draft”.
Are you a conscientious mark-wearer? Do you think face shields should be banned unless there is a medical reason not to do so? And masks with a valve?
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