The study looked at the breathability and the droplet-blocking capability of 11 common fabrics, and for this, medical masks were taken as a benchmark.
Saif said that the established knowledge was not enough to determine whether homemade masks actually were effective. (Image: Graphic by Michael Vincent)
Coronavirus pandemic homemade masks: Homemade masks effective in battling coronavirus even for larger droplets, finds study! Studies have previously indicated that homemade masks, when paired with physical distancing and frequent hand washing, are effective in containing the spread of the novel coronavirus that causes COVID-19. Several of these studies have, however, focused on studying the tiny aerosol particles to see if the spread could be contained. On the other hand, larger droplets are generated when a person speaks, sneezes or coughs. Now, a study, led by University of Illinois professor Tahel Saif, has determined how effectively common household fabrics can contain the spread of the virus particles carried in larger droplets.
COVID-19 homemade masks: Aim of the study
Saif said that the established knowledge was not enough to determine whether homemade masks actually were effective and hence, led this study, the findings of which have been published in Extreme Mechanics Letters journal and accessed by Financial Express Online. Typically, aerosol particles are classified to be less than 5 micrometres, and they lie in the range of hundreds of nanometres. Larger droplets, on the other hand, have a diameter of up to 1 mm, and they can be expelled when a person sneezes, coughs or even speaks. These are the expulsions that are worrisome, because if they gain sufficient momentum, they are capable of escaping from the pores of some fabrics, and break into smaller droplets, becoming airborne. However, it is also important that masks are comfortable and breathable so that people are compelled to wear them, researchers said.
A statement by the University quoted Said as saying that a mask that is made of a low-breathability fabric is uncomfortable and also prone to leakages, as the air is forced out from around the contours of the face. This, Saif said, defeated the very purpose of masks and only provided a false sense of protection. Saif added the team of researchers aimed to prove with the help of their study that there were several common household fabrics that could provide breathability as well as efficiently block small as well as large droplets.
COVID-19: How was the study conducted?
The study looked at the breathability and the droplet-blocking capability of 11 common fabrics, and for this, medical masks were taken as a benchmark. These common household fabrics included new garments as well as used ones, bedsheets, material used in dishcloths and quilted cloths. The fabrics were then characterised by the researchers as per their construction, their weight, the fibre content, porosity, rate of water absorption as well as the thread count.
Said said that breathability was easy to test for these fabrics, as they simply had to measure the airflow rate through the fabric. The complicated aspect was testing the ability to block droplets, Saif added.
To test that, researchers filled an inhaler’s nozzle with distilled water that was seeded with 100-nanometre diameter fluorescent particles. This is also the size of a particle of the novel coronavirus. When puffed, the inhaler forcefully expelled water through the nozzle, generating high-momentum droplets that were collected on a plastic dish placed in front of the inhaler. The fabrics were tested by repeating this test, with several materials being placed over the dishes that collected the droplets.
Saif said that the team then counted the number of nanoparticles that landed on the dish with the help of a high-resolution confocal microscope. Then, the efficiency in blocking the droplets was measured by using the ratio of the number of nanoparticles collected with and without the fabric. Apart from that, the velocity as well as the size of the particles that the inhaler expelled were also measured through a high-speed video.
The team found that the droplets left the inhaler at a velocity of 17 metres a second, while the velocities of droplets that humans expel while speaking, sneezing and coughing range between 10 and 40 metres per second.
As far as the size was concerned, it was detected that the inhaler-expelled droplets’ diameters ranged between 0.1 to 1 mm, and this matched the size of the larger droplets that are generated while speaking, coughing and sneezing.
Saif said that the team found that all of the tested fabrics were considerably effective when it came to blocking 100 nanometre particles that were carried by the larger droplets, even if there was only one layer. Saif added that if the fabric was double or triple-layered, even fabrics like T-shirt cloth, which are more permeable, achieved the same efficiency as a medical mask, all the while maintaining better or comparable breathability.
Notably, the Centre for Disease Control and Prevention (CDC), the nodal healthy agency of the US government, has also encouraged people to make masks at home and wear them, even giving instructions on how to make a mask.