Duke University Medical Center — Science Daily — 11 August 2020
A proof-of-concept study published in Science Advances reports that a simple, low-cost apparatus consisting of a box, a laser, a lens, and a cell phone camera provided visual proof that face masks are effective in reducing droplet emissions during normal wear.
“We confirmed that when people speak, small droplets get expelled, so disease can be spread by talking, without coughing or sneezing. We could also see that some face coverings performed much better than others in blocking expelled particles,” said researcher Martin Fischer, PhD, of Duke University.
The best face coverings were N95 masks without valves — the hospital-grade coverings used by front-line health care workers. Surgical or polypropylene masks also performed well. Hand-made cotton face coverings provided good coverage. However, bandanas and neck fleeces such as balaclavas didn’t block droplets much at all. “Wearing a mask is a simple and easy way to reduce the spread of COVID-19. If everyone wore a mask, we could stop up to 99% of these droplets before they reach someone else,” said Duke physician Eric Westman.