- You don’t need the fanciest mask available to keep yourself and others safe
- Researchers put 11 common fabrics to the test to see how they fared in curbing respiratory drops
- They were all effective, even when sneezing and coughing
As South Africa moved to Level 1 on 21 September 2020, Minister of Health, Zweli Mkhize, called upon citizens to remain vigilant and follow guidelines – including wearing a mask in public spaces.
While there are several studies indicating that homemade fabric masks do help combat the spread of viruses like Covid-19, these studies focused mostly on the transfer of tiny aerosol particles spread through breathing.
Mechanical engineer, professor Taher Saif from the University of Illinois, however, wanted to establish the effectiveness of masks against larger aerosol droplets spread by speaking, coughing and sneezing, as the established research was not comprehensive enough.
The difference between small and large aerosol droplets
According to Saif, aerosol droplets are typically classified as anything less than 5 micrometres and can range from hundreds of nanometres. Larger droplets can be up to 1 millimetre in diameter and are expelled when someone speaks, coughs and sneezes.
These droplets posed a problem because they are able to squeeze through the pores of some fabrics and break into smaller, airborne droplets with momentum.
Breathability and droplet-blocking important
Saif and his team tested 11 common household fabrics for breathability and droplet-blocking, using a medical mask as a benchmark. The results of this experiment were published in the journal Extreme Mechanic Letters.
The fabrics included new and used materials such as garments, quilted cloths, bedsheets, and dishcloth material and the researchers grouped these materials according to their construction, fibre content, weight, thread count, porosity and water-absorption ability.
The researchers tested the materials in the laboratory by using distilled water in the nozzle of an inhaler – the water was seeded with 100-nanometre fluorescent particles – roughly the size of a SARS-CoV-2 particle. When the inhaler was puffed, the water and droplets were ejected out onto the materials covering a plastic dish.
The droplets move from the inhaler at about 17 metres per second. Droplets expelled by sneezing, coughing and talking can move anywhere between 10 and 40 metres per second depending on the force and momentum.
“We found that all of the fabrics tested are considerably effective at blocking the 100-nanometer particles carried by high-velocity droplets similar to those that may be released by speaking, coughing and sneezing, even as a single layer,” Saif said.
“With two or three layers, even the more permeable fabrics, such as T-shirt cloth, achieve droplet-blocking efficiency that is similar to that of a medical mask, while still maintaining comparable or better breathability.
“We count the number of nanoparticles landing on the dish using a high-resolution confocal microscope. We can then use the ratio of the number collected with and without the fabric to give us a measure of droplet-blocking efficiency,” Saif stated.
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