COVID Science Update – Face Coverings
A recent study has shown there are more effective types of masks and facial coverings.
Fischer et al., (2020) tested relative droplet counts in the air when subjects spoke while wearing various types of face coverings.
Cite: Fischer et al. (2020). Low-cost measurement of face mask efficacy for filtering expelled droplets during speech. Science Advances, 6(36). https://doi.org/10.1126/sciadv.abd3083
Their data indicated several types of masks and facial coverings were very effective in lowering relative droplet counts. That said, a few were shown to be ineffective.
There were fourteen different face coverings tested.
- Surgical mask (three layers)
- Valved N95 mask (N95 mask with exhalation valve)
- Knitted mask
- Polyproline mask (Two-layer polypropylene apron mask)
- Poly/cotton mask (Cotton-polypropylene-cotton mask)
- MaxAT mask (One-layer Maxima AT mask)
- Cotton2 mask (Two-layer cotton, pleated style mask)
- Cotton4 mask (Two-layer cotton, Olson style mask)
- Cotton3 mask (Two-layer cotton, pleated style mask)
- Cotton1 mask (One-layer cotton, pleated style mask)
- Neck Gaiter (One-layer polyester/spandex, 0.022 g/cm2)
- Bandana (Double-layer bandana, 0.014 g/cm2)
- Cotton5 mask (Two-layer cotton, pleated style mask)
- Fitted N95 (N95 mask, no exhalation valve, fitted)
Each face covering was worn by a speaker who spoke through the mask into the test area with a camera at the other end of the test area. A laser beam was scattered in a plain the speaker and the camera. Droplets were photographed by the camera and then counted. This was repeated 10 times for each face covering. A baseline was taken by the speaker wearing no face covering to see what the droplet count would be. This was set to the “Relative droplet count” of 1.0.
Droplet transmission through face masks Test Results
From the study, “Each solid data point represents the mean and SD over 10 trials for the same mask, normalized to the control trial (no mask), and tested by one speaker. Hollow data points are the mean and SDs of the relative counts over four speakers.”
Test results show that most common masks do a fairly good job at obstructing droplets. However, two very noticeable exceptions are the Bandana (#12) and Neck Gaiter (#11). The material in the Neck Gaiter actually seems to break larger particles apart thus increasing the aerosol spread more than the baseline of no face covering.
These important results indicated several types of masks and face coverings perform better than bandanas and gaiters for protecting people by reducing the spread of respiratory droplets.