Restraining respiratory droplets

Wearing face masks to reduce the spread of COVID-19 has become a part of many people’s daily routine. But not all coverings are created equal. To better visualize a mask’s effectiveness, Siddhartha Verma, Manhar Dhanak, and John Frankenfield from Florida Atlantic University in Boca Raton positioned a masked mannequin in front of a camera and pumped bursts of a vaporized liquid mixture through its mouth from a fog machine. They directed a beam from a green laser pointer through a glass rod to create a plane vertical sheet to more easily picture the droplets.

This image shows a mannequin head wearing a stitched mask made of two layers of cotton quilting fabric. The droplets from the simulated cough travel an average distance of 2.5 inches. With a mask made from a single-layer bandana of elastic T-shirt material, droplets travel about 3.5 feet away. More worrisome is the result from the uncovered mouth. In that case, the respiratory droplets travel 2 feet farther on average than the minimum recommended social-distancing guideline of 6 feet. (S. Verma, M. Dhanak, J. Frankenfield, Phys. Fluids 32, 061708, 2020, doi:10.1063/5.0016018 ; picture courtesy of Siddhartha Verma.)