Researchers at Duke University have created a simple technique to test the effectiveness of various types of masks.
A professor at Duke’s School of Medicine was assisting a local group buy masks in bulk to distribute to community members in need and he wanted to make sure the group purchased masks that were actually effective.
In the study published Friday, researchers with Duke’s physics department demonstrated the use of a simple method that uses a laser beam and cell phone to evaluate the efficiency of masks by studying the transmission of respiratory droplets during regular speech.
Martin Fischer, one of the authors of the study, told CNN,
“We use a black box, a laser, and a camera.
The laser beam is expanded vertically to form a thin sheet of light, which we shine through slits on the left and right of the box.”
In the front of the box is a hole where a speaker can talk into it. A cell phone camera is placed on the back of the box to record light that is scattered in all directions by the respiratory droplets that cut through the laser beam when they talk.
A simple computer algorithm then counts the droplets seen in the video.
When testing their effectiveness, researchers discovered that some masks are literally useless.
Researchers tested 14 commonly available masks. Each mask was tested 10 times.
- Most effective mask was the fitted N95.
- Three-layer surgical masks and cotton masks, which many people have been making at home, also performed well.
- Least effective were neck fleeces, also called gaiter masks and often used by runners.
- Folded bandanas and knitted masks also performed poorly and did not offer much protection.
“We were extremely surprised to find that the number of particles measured with the fleece actually exceeded the number of particles measured without wearing any mask.
We want to emphasize that we really encourage people to wear masks, but we want them to wear masks that actually work.”
This is a very powerful visual tool to raise awareness that a very simple masks, like these homemade cotton masks, do really well to stop the majority of these respiratory droplets.
Companies and manufacturers can set this up and test their mask designs before producing them, which would also be very useful.”
Public health experts have spent months emphasizing that masks are one of the most effective tools to help fight the pandemic, and many US states have now introduced some kind of mask requirement.
But please, no matter what style mask you choose, don’t wear it like this…
(Photos, Duke University; via CNN)