Face masks reduce the distance airborne pathogens can travel by more than half

The effectiveness of face masks has been a hot topic since the rise of COVID-19. However, a new study by researchers at the University of Central Florida offers more evidence that they work.

In a study published today in the Journal of Infectious Diseases, the researchers found that face masks reduce the distance that airborne pathogens can travel when speaking or coughing by more than half compared to not wearing a mask.

The findings are important because airborne viral pathogens, such as SARS-CoV-2, can be encapsulated and transmitted through liquid droplets and aerosols formed during human respiratory functions such as speaking and coughing.

Knowing ways to reduce this transmission distance can help protect people and help manage responses to pandemics, such as COVD-19, which have led to global infection, health care system overload and economic damage.

These responses may include easing some social distancing guidelines when masks are worn.

The study provides clear evidence and guidelines that 3 feet away with face covering is better than 6 feet away without face covering.”

Kareem Ahmed, study co-author, associate professor, UCF’s Department of Mechanical and Aerospace Engineering

Using diagnostic tools commonly used to understand how fluids move through the air, the researchers measured the distance in all directions that droplets and aerosols travel from people who speak and cough, when they wear different types of masks and when they don’t.

Fourteen people took part in the study, 11 men and 3 women, ages 21 to 31.

Each participant recited a phrase and simulated a cough for 5 minutes without a face covering, with a cloth face covering, and with a disposable three-layer surgical mask.

Planar particle imaging was used to measure particle velocity; a phase-doppler interferometer was used to measure droplet size, velocity and volume flux at points within a spray plume; and an aerodynamic particle sizer was used to determine the behavior of particles in the air.

The instruments measured the characteristics, behavior and direction of the airborne particles as they traveled out of the participants’ mouths.

The researchers found that a cloth face that covered emissions in all directions reduced emissions in all directions to about two feet compared to the four feet of emissions produced when coughing or speaking without a mask on.

The reduction was even greater when wearing a surgical mask, reducing the distance cough and speech emissions traveled to only about half a foot.

The researchers got the idea for the study from the jet propulsion research they are doing.

“The principles are the same,” says Ahmed. “Our cough and speech are exhausted propulsion plumes.”

The study is part of the researchers’ larger effort to control airborne disease transmission, including through food ingredients, better understanding factors associated with being a superspreader; and the modeling of airborne disease transmission in classrooms.

Researchers will then expand the study to include more participants. The work is funded in part by the National Science Foundation.

Study co-authors were Jonathan Reyes, lead author and a postdoctoral researcher; Bernhard Stiehl, a postdoctoral researcher; Juanpablo Delgado, a master’s student; and Michael Kinzel, an assistant professor. All are with UCF’s Department of Mechanical and Aerospace Engineering.

Ahmed joined UCF’s Department of Mechanical and Aerospace Engineering in 2014, part of UCF’s College of Engineering and Computer Science. He is also a member of the Center for Advanced Turbomachinery and Energy Research and the Florida Center for Advanced Aero-Propulsion. He served for over three years as a senior aero/thermo engineer with Pratt & Whitney military engines, working on advanced engine programs and technologies. He also served as a faculty member at Old Dominion University and Florida State University.

At UCF, he leads propulsion and energy research with applications to power generation and gas turbine engines, propulsion jet engines, hypersonics and fire safety, as well as research related to supernova science and COVID-19 transmission control.

He received his doctorate in mechanical engineering from the State University of New York at Buffalo. He is an associate fellow of the American Institute of Aeronautics and Astronautics and a fellow of the US Air Force Research Laboratory and Office of Naval Research.

Kinzel received his PhD in aerospace engineering from Pennsylvania State University and joined UCF in 2018. In addition to his membership in UCF’s Department of Mechanical and Aerospace Engineering, part of UCF’s College of Engineering and Computer Science, he also works with UCF’s Center for Advanced Turbomachinery and Energy Research.


University of Central Florida

Reference magazine:

Reyes, J., et al. (2022) Research in humans on the propagation distance of particles from human respiratory function. The Journal of Infectious Diseases. doi.org/10.1093/infdis/jiab609.


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