Though face masks can’t stop you from catching Covid-19, their widespread use has become an integral part of slowing the spread of the pandemic. By covering our nose and mouth with some form of mask, we reduce the number of water droplets we release onto surfaces that could potentially contain SARS-CoV-2 virus particles. This keeps others safe, rather than ourselves, but if we all do it then the overall effect is safer public interactions as the pandemic continues.
However, as some photos have shown us, not everyone is up to scratch on how these masks need to be worn in order to be effective. The advice on this has been poorly communicated in some parts of the world, and there have also been unclear guidelines regarding exactly what kind of mask made from which material is best.
To research this, a study published in Physics of Fluids used a hollow manikin head to examine the effectiveness of different mask types when worn covering both the nose and mouth. They padded the hollow cavity so that the internal mouth and nose shapes were similar to that of an adult. The head was mounted at 1.72 meters (5 foot 6 inches) to simulate the average adult male and installed with a pressure impulse that effectively gave a synthetic cough or sneeze from our imaginary Covid-19 patient.
A fog machine was used to emit tracer particles from the respiratory jets that could be picked up on camera to review how the water droplets spread. This was then “lit up” with a green laser to create a rather spooky spital spread effect for which the color green seems all too appropriate.
Without a mask on, the mannequin could fire out droplets much further than the current 2 meters (6 foot) social distancing guideline observed in many countries. The farthest they recorded traveled 3.7 meters (12 feet) and the droplets could remain suspended in midair for up to three minutes.
They then tested how effective simple off-the-shelf masks were looking at single-layer bandana style covering, a homemade cotton mask stitching two bits of fabric together, and a non-sterile cone mask.
The findings revealed that the bandana masks didn’t do much to stop the smallest droplets, which when aerosolized could remain in the air for many days. The most effective in preventing droplet spread were homemade multilayer masks as well as the non-sterile cone masks, which slowed the speed and range of projectile coughs and sneezes. There was still some leakage, but the reduction was far more effective than the bandana mask.
"In addition to providing an initial indication of the effectiveness of protective equipment, the visuals used in our study can help convey to the general public the rationale behind social-distancing guidelines and recommendations for using facemasks," said Siddhartha Verma, PhD, lead author on the study and assistant professor at Florida Atlantic University’s Department of Ocean and Mechanical Engineering, in a statement. "Promoting widespread awareness of effective preventive measures is crucial at this time as we are observing significant spikes in cases of COVID-19 infections in many states, especially Florida."
You can see the full visualization in the video below.