While the usefulness of surgical masks, in general, is quite well known (surgeons have been using them for years) there is little-to-no data on many of the DIY face coverings people have been using during the coronavirus pandemic. So, researchers at the Florida Atlantic University’s College of Engineering and Computer Science have done some tests of their own.
The experiment was published in the journal Physics of Fluids and demonstrates the effectiveness of wearing a face covering when you cough using some pretty cool flow visualisation using lasers. Of course, this post isn’t a debate about whether or not you should or shouldn’t wear a mask. You should. This technique just shows that even the simplest of masks helps reduce the risk of infection and it does so using a very cool technique
The demonstration uses an emulated cough from a mannequin. This isn’t quite the same type of flow visualisation as the Schlieren flow visualisation system that NASA uses to test for air turbulence. Instead, a laser lights up a water & glycerin mixture that’s expelled from the mannequin’s mouth which is then recorded by the camera. It’s a similar technique to the one used here on human sneezes.
Using a mannequin allows them to get a consistent strength and speed of “cough” every time – something that humans cannot do naturally.
It shows that small droplets from an unfiltered cough can reach a distance of 12ft in just a minute and a half and linger in still indoor air for several minutes. Aided by a downwind breeze, the droplets dissipate much more quickly.
Our researchers have demonstrated how masks are able to significantly curtail the speed and range of the respiratory droplets and jets. Moreover, they have uncovered how emulated coughs can travel noticeably farther than the currently recommended six-foot distancing guideline.
– Stella Batalama, PhD., dean of FAU’s College of Engineering and Computer Science
When a face covering is applied in the video, the droplets are mitigated substantially, even with something as commonly available as a bandana. When the bandana is swapped out for a homemade stitched fabric mask, very little comes out much beyond the mask at all and what does come out doesn’t spread nearly as far. Even commercially available dust masks from the hardware store have a significant effect on the droplets and particles expelled from a cough.
A very cool technique to demonstrate the principle.
You can read more about the test on the Florida Atlantic University website.