Face Mask Safety Study
A new study by Duke University addressing the efficacy of various masks found that the most popular types may in fact be worse than wearing no mask at all.
The study tested a variety of masks and the results for those created of stretch fabric were disturbing. These are primarily neck gaiters and the over-the-ear type made of knitted jersey which stretch to fit the face. Although knits appear solid when at rest, the action of stretching them to fit the face creates large holes in between the fibers, a dangerous choice when trying to prevent droplet transmission.
Martin Fischer, a Duke chemist & physicist and the study's co-author, designed the laser light apparatus used for the tests. They first established a droplet-emission baseline using a no-mask control group. Following that, their conclusions were simple. A professionally fitted N95 mask, which is used most commonly by hospital workers, was the most effective. Right below that followed a multi-layer woven cotton mask preferably containing a non-woven particle filter fabric. Breathable neck gaiters and the popular over-the-ear type made of a stretch fabric ranked worse than the no-mask control group.
The experiment showed that human speech generates droplets which can be caused to linger in the air for more than 8 minutes. "The high droplet count observed in the study could be linked to the porous fabric of the neck gaiter breaking up bigger particles into many little ones that are more likely to hang around longer", Fischer said. "This effect makes wearing some gaiters possibly counterproductive", he added. “It’s not the case that any mask is better than nothing,” he continued. “There are some masks that actually hurt rather than do good.”
The researchers specifically made note of the effectiveness of cotton cloth masks. Experts with the WHO have recommended that cotton fabric masks should ideally have at least three layers.
Peter Tsai, the materials scientist who invented the electrostatic charging technology that N95 masks rely on suggested the use of non-woven fabrics as a component of an effective mask. Non-woven fabrics, which Tsai did years of research on to improve medical masks, are made of individual fibers or filaments that are bound together by various means and act as a barrier to droplet transmission.
Warren S. Warren, professor of physics, chemistry, radiology and biomedical engineering at Duke and co-author of the study said this, “If you can see through it when you put it up to a light and you can blow through it easily, it probably is not protecting anybody.”