Type of construction and materials used, the two key factors for a mask to be effective

In recent months, masks and social distancing have quickly established themselves as the main means of combating COVID-19. Although the use of facial protection is a standard weapon in the fight against epidemics in epidemiology, the effectiveness of these means has not yet been the subject of detailed studies in the case of coronaviruses. According to the WHO, wearing masks and social distancing reduce the risk of transmission and infection for everyone by more than 80%. But what about masks, which types are most effective? Which fabrics allow increased efficiency? At present, there are no specific guidelines on the most effective materials and designs for face masks. However, a new study has shown in more detail how important the type of construction of the mask as well as the materials used are if one wishes to minimize the spread of droplets or sneezing in order to reduce the spread and transmission. coronavirus.

Admittedly, there have already been studies on the performance of medical grade masks, but data on masks made from tissue used by the vast majority of the population remains scarce. Research by scientists at the College of Engineering and Computer Science at Florida Atlantic University has just been published and demonstrates, through the visualization of emulated coughs and sneezes, a method to assess the effectiveness of face masks in clogging of droplets.

The rationale for the recommendation to use masks or other face covers is to reduce the risk of cross-infection through the transmission of respiratory droplets from infected individuals to healthy individuals.

The researchers used visualization of the flow in a laboratory environment with a sheet and a laser beam, as well as a mixture of distilled water and glycerin to generate the synthetic cloud that formed the content of a cough stream. . They visualized droplets expelled from a manikin’s mouth while simulating coughing and sneezing. Thus, they tested masks easily accessible to the general public (and which are not part of medical grade masks).

Researchers tested a single layer mask designed with a tissue, a homemade mask and sewn using two layers of cotton, and a non-sterile conical style mask, available in most pharmacies. It was then by placing these different masks on the mannequin that they were able to trace the path of the droplets and demonstrate the differences in the functioning of these masks.

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With a folded cotton handkerchief forming a mask, the droplets traveled approximately 38 centimeters apart. Credits: Florida Atlantic University / College of Engineering and Computer Science

The results showed that the folded tissue face masks (see image above) offer minimal stopping capacity for the smallest aerosol respiratory droplets.

However, well-fitting homemade masks with multiple layers of fabric, and standard conical-style masks, have been shown to be the most effective in reducing the dispersion of droplets. Indeed, these masks were able to reduce the speed and range of the respiratory jets significantly, although there were some leaks through the mask materials, as well as along the small spaces at the edges.

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With the cotton mask sewn by hand, the droplets traveled a distance of 5 centimeters. Credits: Florida Atlantic University / College of Engineering and Computer Science

The researchers also tested the range of droplets when a person is not wearing a mask, and it is important to note that, these droplets from coughing, could have moved much further than the two meters distancing currently requested.

Indeed, without a mask, the droplets traveled more than 2 meters and 43 centimeters; with a bandana, they made a little over a meter (109 centimeters); with a folded cotton handkerchief, they covered 37 centimeters; with the hand-sewn quilted cotton mask, the droplets were propelled to 5 centimeters; and with the cone-shaped mask, the droplets traveled about 20 centimeters.

conical cone folded mask-cotton-coronavirus

With the conical style mask, the droplets traveled about 20 centimeters. Credits: Florida Atlantic University / College of Engineering and Computer Science

« In addition to providing a first indication of the effectiveness of protective equipment, the visuals used in our study can help to make the general public understand the reasons behind the guidelines and recommendations relating to social distancing for use of face masks “Said Siddhartha Verma, lead researcher and assistant professor who co-authored the article with Manhar Dhanak, department director, professor and director of SeaTech and with John Frakenfeld, technical paraprofessional. ” Promoting widespread awareness of effective preventive measures is crucial at this time, as we observe significant peaks of COVID-19 infections in many states, particularly in Florida “, he added.

When the mannequin was not equipped with a mask, it projected droplets much further than the social distance guidelines of two meters (1m80 in the case of the United States). Researchers observed droplets moving up to more than three and a half meters in about 50 seconds. In addition, the droplets were suspended in the air for up to three minutes.

These observations, combined with other recent studies, suggest that current guidelines for social distancing should be updated to account for aerosol transmission of the pathogen. « We found that, although the unobstructed turbulent jets moved up to 365 centimeters, a large majority of the ejected droplets fell to the ground at this point », And declared Dhanak. « It is important to note that the number and concentration of droplets will decrease with increasing distance, which is the fundamental reason for social estrangement »added Dhanak.

On the same theme: Coronavirus: the mechanism of loss of smell finally explained

The pathogen responsible for COVID-19 is mainly found in respiratory droplets which are expelled by infected people during coughing, sneezing or even talking and breathing.

In addition to COVID-19, respiratory droplets are also the primary means of transmission for various other viral and bacterial diseases, such as colds, flu, tuberculosis, SARS (severe acute respiratory syndrome) and MERS (middle respiratory syndrome -Orient), to name a few. These pathogens are wrapped in respiratory droplets, which can land on healthy individuals and cause direct transmission, or on inanimate objects, which can then lead to infection when a healthy individual comes into contact with them. .

« Our researchers have demonstrated how masks can significantly reduce the speed and range of droplets and respiratory jets. In addition, they discovered how the emulated cough can travel significantly further than the currently recommended course of action. “Said Stella Batalama, Ph.D., dean of the FAU College of Engineering and Computer Science. ” Their research describes the procedure for setting up simple visualization experiments using readily available materials, which can help healthcare professionals, medical researchers and manufacturers to qualitatively assess the effectiveness of face masks. and other personal protective equipment “, She added.

Source : Physics of Fluids

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