Sep 03, 2020

Why face shields are useless if worn without a mask

If you live in Melbourne, or elsewhere in Australia where coronavirus risks have increased, you may well have seen people visiting the supermarket or out for their daily walks wearing clear plastic face shields instead of surgical or cloth face masks. While these are definitely more comfortable to wear, don’t cause foggy glasses and aren’t technically against the law, the question is: are they actually effective in slowing the spread of the virus? 

Unless paired with a face mask, these plastic face shields don’t really do anything to prevent the spread of cough droplets. Professor Brendan Crabb, director and CEO of the Burnet Institute in Melbourne put it bluntly. 

“They don’t work. Face shields don’t work in the absence of a surgical mask underneath,” he said.

“Bandanas, scarves, those things are not very effective either.”

Studies conducted in the United States have further proven their ineffectiveness in the capacity that they are often being used here in Australia. Scientists from Florida Atlantic University published a study in the journal Physics of Fluids, in which they created a visual representation of why these face shields are ineffective in stopping the spread of coronavirus. 

Tracking a simulated cough using a smoke machine and a green laser, scientists were able to track the movement of cough vapours as they are expelled from a mannequin’s mouth, while wearing a face shield. They then compared these vapour movements to the same style of cough while wearing a mask with a ventilator and a surgical mask. 

While the face shield did initially redirect the cough vapour downwards, an amount remained hovering around the base of the plastic shield, floating around the edges. It then travelled and spread approximately 90 centimeters around the mannequin. 

When testing the effectiveness of a mask with a ventilator valve, the results were much the same. While the vapour was initially sent downwards due to the positioning of the mask, the sheer amount of it coming out of the ventilation port did next to nothing in preventing the spread of the vapour.

“Face shields and masks with exhale valves may not be as effective as regular face masks in restricting the spread of aerosolised (sic) droplets,” the authors wrote.

“Thus, despite the increased comfort that these alternatives offer, it may be preferable to use well-constructed plain masks.”

While there was still some leakage of vapour around the edges of a regular surgical face mask, the amount and the range of spread was significantly less than that of the face shield and the ventilated mask. And while wearing any sort of face covering is better than nothing, if we really want to stop the spread effectively, we need to make sure we are wearing the appropriate face coverings.

Image Source: Engin Akyurt at UnSplash

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