Coughing visualization illustrates the benefits of wearing a good mask

// Mechanical Engineering

Visualization of testing different mask styles

UW–Madison Mechanical Engineering Professor Scott Sanders’ team modified a mannequin so that the mouth releases a puff of air containing fog, in order to see how well different mask styles perform under regular and laser light.

Coupling function with fashion, home-sewn face masks today are widely available in a variety of forms and fabrics.

But while national experts underscore that wearing a mask is effective in helping to prevent the spread of COVID-19, not all masks—or the materials with which they’re made—contain virus particles equally.

In a new video, University of Wisconsin-Madison engineer Scott Sanders demonstrates how droplets from a single cough escape from or remain inside of varying mask styles and materials.

Photo of Scott Sanders
Scott Sanders

A mechanical engineering professor who conducts much of his research through the world-renowned UW-Madison Engine Research Center, Sanders is an expert in using lasers to characterize the way gases and particles behave in combustion engines.

As a result, pivoting to study mask materials, construction, fit and filtration as the COVID-19 pandemic emerged was a natural next step—especially since a cough or sneeze can spray particles in a size range that Sanders could study with the tools he already uses in his combustion systems research.

In his video, Sanders used a mannequin to produce a simulated cough (adding more droplets than are in an actual cough, to make the cough easier to see). While the visualization doesn’t directly track the spread of virus particles, Sanders believes it will help people see a risk that is otherwise invisible. With no mask, droplets travel more than 3 feet in front of the mannequin. Masks with valves allow many particles to escape. Cloth masks do a better job of containing the particles; however, cloth masks with a loose weave don’t perform as well as those made with tightly woven cloth. And, masks without fitted nose pieces allow particles to escape through gaps in the top, under the wearer’s eyes. Other mask styles, including flat-fold masks, can leak particles out the sides near the ears.

In his tests, Sanders found that in general, the homemade mask shape most effective at containing droplets is a neck-gaiter-style mask that combines a nose piece with an elastic cord that wearers can toggle to snug the mask to their face. The extra effectiveness of the neck-gaiter mask does come at a cost: It is a larger mask, and it isn’t as easily removed. “That said, wearers can quickly and easily slide the gaiter down around their neck and back up to their face as needed,” he says.

Additionally, the neck-gaiter mask can be a good alternative for small children or others for whom traditional masks might be difficult to fit, and it may be more tolerable for people who are sensitive to wearing other mask styles because of underlying respiratory or other concerns.

Sanders believes his visualization enables people to see a risk that is otherwise mostly invisible. “I hope that research like this will enable people to make informed decisions about distancing and mask-wearing,” he says.

He also has created a video that shows a simple way to sew the neck-gaiter mask using a rectangle of tightly woven fabric, a toggle, cord and metal nose piece. “There are two aspects to masks: Personal protection, or reducing the amount of airborne droplets the wearer inhales, and source control, which is containing the wearer’s own respiratory droplets. The ideal mask would do an excellent job at both aspects, and work whether wearers are talking, yelling, coughing, or sneezing,” he says. “That is a tall order—even for medical-grade respirators, let alone homemade masks; however, as the video shows, a homemade cloth mask with a nose piece can provide significant source control, which in turn could improve public health.”

Sanders emphasizes that home-sewn masks aren’t designed to replace medical-grade personal protective equipment—and should be used in conjunction with other recommended measures, including physical distancing and frequent hand-washing, among others.

Sanders received funding to conduct this research and produce the videos through the Wisconsin Partnership Program in the UW School of Medicine and Public Health. He is part of a larger team of collaborators within the UW-Madison College of Engineering and across campus that is focused on masks and mask material screening.

 

Author: Renee Meiller