Visualization Shows Exactly How Face Masks Stop Covid-19 Transmission

August 15, 2020

A dramatic new visualization shows why it’s a good idea to wear a mask to prevent the spread of a new coronavirus.

Without a mask, droplets produced during coughing can be up to 12 feet (3.7 meters) long, the visualization shows, but with a mask on, that distance is reduced to just a few inches in the best case scenario.

Simulations described today (June 30) in the journal Physics of Fluids also reveal that some cloth masks are better than others at stopping the spread of potentially infectious droplets.

“The visuals used in our study could help communicate to the public the social distance guidelines and the rationale behind the recommendations for mask use,” lead study author Siddhartha Verma, an assistant professor in the College of Engineering and Computer Science at Florida Atlantic University, said in a statement.

To simulate a cough, the researchers attached the head of a mannequin to a fog machine (which generates steam from water and glycerin) and used a pump to expel the steam through the mannequin’s mouth. They then visualized the steam droplets using a “laser sheet” that was created by passing a green laser pointer through a cylindrical rod. In this setup, a simulated cough appeared as glowing green vapor flowing out of the mannequin’s mouth.

The researchers then placed several types of non-medical masks on the mannequin’s head to test their effectiveness in stopping these “coughs.” These masks included homemade masks sewn from two layers of cotton fabric (70 threads per inch), single-ply headbands, loosely folded cotton handkerchiefs, and non-sterile conical masks sold in pharmacies.

They found that a simulated cough could travel up to 12 feet in 50 seconds without the mask covering it.

The homemade stitched cotton mask – which features multiple layers and a snug fit – best reduced the spread of droplets, although there was some leakage at the top of the mask between the nose and the cloth material. When the mannequin wore this mask, droplets moved only about 2.5 inches (6.35 cm) forward from the face. The conical mask also worked well, with the droplets moving only about 8 inches (20 cm) forward from the face.

However, single-ply hoods (made of elastic T-shirt material) and folded handkerchiefs were less effective. Droplets leaked through the mask material, flowing 3.5 feet (1 meter) with the headband and 1 foot (0.3 meter) with the handkerchief.

Still, “although the non-medical masks tested in this study experienced varying degrees of flow leakage, they are likely to be effective in stopping larger respiratory droplets” from dispersing, the authors wrote in the paper.

“Promoting widespread awareness of effective preventive measures [for COVID-19] is critical at this time, as we are observing a significant spike in COVID-19 infections in many states, particularly Florida,” Verma said.