Loose bandanas, handkerchiefs not as effective against COVID-19 as cotton face masks, but still better than nothing at all
A single sneeze can release about 40,000 droplets into the air which can travel at a speed of about 100 m/s.
COVID-19 mainly spreads through the respiratory droplets released when an infected person sneezes or coughs. When these droplets find their way into the mucous linings (eyes, mouth nose) of another person, they can cause infection. Depending on the size of the droplets, they may either fall on surfaces or they may remain airborne for a while.
Face masks and social distancing are said to be two of the most important factors that can help slow down the spread of the COVID-19 causing virus.
According to the World Health Organisation (WHO), everybody (including the healthy and infected) should wear face masks in COVID-19 affected areas. Surgical masks are said to be the best for controlling respiratory droplets in healthcare settings. Three-layer fabric masks may be worn by the general public, especially when social distancing is not as easy.
However, one look outside and you will notice that not a lot of people are following social distancing advice even in areas where it is possible, let alone wearing well-fitted masks. Amongst those who do wear face covers, some use things like handkerchiefs or hold up a piece of cloth to their face.
Now, Dr Siddhartha Verma, an assistant professor at the Florida Atlantic University College of Engineering, and his colleagues say that handkerchiefs and lose clothes may not be as effective as well-fitted masks in stopping the release of respiratory droplets from an infected person.
The findings of the study have been published in the peer-reviewed journal Physics of Fluids.
Every time you sneeze, cough or even talk, you release respiratory droplets into the air. These droplets contain mucus, saliva, various cells from your body and pathogenic microbes like fungi, bacteria and viruses.
The larger droplets usually fall down quickly due to the effect of gravity. However, out of all these droplets, those which have a diameter of less than 5 µm (micrometres) are called droplet nuclei which can remain suspended in air and can even travel over large distance depending on the air pressure in the area.
A single sneeze can release about 40,000 droplets into the air which can travel at a speed of about 100 m/s. Even while talking, a person normally releases around 600 droplets within a minute.
Now imagine what would happen if you are in the path of such an invisible stream of virus or even around it without a face cover or a badly-fitted thin piece of cloth. Conversely, if you are the one infected even with a mild version of the disease, just any covering won’t provide protection to others around you. From what is known right now, about 80% of cases are either mild or asymptomatic. You won’t know who is infected until they show symptoms so it is best to use face masks and maintain social distance at all times.
The right face mask
The WHO suggests that a good face mask should have three layers, a water-resistant outer layer, a water-absorbing inner layer and a filter in between the two.
An ideal mask should snugly fit over the face of a person so there is no space or scope of leakage.
For his study, Verma and his team used a mannequin to simulate a cough or sneeze, a fog/smoke machine and a laser to visualise the jet of respiratory particles released.
Here is what they found:
- When uncovered, the average distance the droplets travelled was about 8 feet.
- A bandana made of elastic t-shirt material with a thread count of about 85 let the respiratory droplets spread between 3 and 7 feet.
- A cotton handkerchief (folded) could let the droplets spread to around 1-3 feet.
- A commercial mask with assorted fabrics allowed droplets to spread up to 8 inches.
- A stitched quilted cotton mask only let the respiratory droplets spread to 2.5 inches.
Explaining the study, Manhar Dhanak, co-author of the study and Department chair at the FAU’s Department of Ocean and Mechanical Engineering said in a press release that unobstructed turbulent jet streams can travel up to 12 feet within 50 seconds though a majority of the droplets fell to the ground by then. This is what social distancing aims at doing.
Adding to this, Verma said that in addition to talking about the efficiency of protective gears against COVID-19, their study can help the general public understand the rationale behind the need for face masks and the social distancing guidelines.
For more information, read our article on COVID-19: What is droplet transmission.
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