Seeing is believing: Effectiveness of facemasks

Researchers use flow visualization to qualitatively test facemasks and social distancing

June 30, 2020

Science Daily/Florida Atlantic University

Using flow visualization, researchers assessed the efficacy of facemasks in obstructing respiratory droplets. Loosely folded facemasks and bandana-style coverings provide minimal stopping-capability for the smallest aerosolized respiratory droplets. Well-fitted homemade masks with multiple layers of quilting fabric, and off-the-shelf cone style masks, proved to be the most effective in reducing droplet dispersal. Importantly, uncovered coughs were able to travel noticeably farther than the currently recommended 6-foot distancing guideline. Without a mask, droplets traveled more than 8 feet.

Currently, there are no specific guidelines on the most effective materials and designs for facemasks to minimize the spread of droplets from coughs or sneezes to mitigate the transmission of COVID-19. While there have been prior studies on how medical-grade masks perform, data on cloth-based coverings used by the vast majority of the general public are sparse.

Research from Florida Atlantic University's College of Engineering and Computer Science, just published in the journal Physics of Fluids, demonstrates through visualization of emulated coughs and sneezes, a method to assess the effectiveness of facemasks in obstructing droplets. The rationale behind the recommendation for using masks or other face coverings is to reduce the risk of cross-infection via the transmission of respiratory droplets from infected to healthy individuals.

Researchers employed flow visualization in a laboratory setting using a laser light sheet and a mixture of distilled water and glycerin to generate the synthetic fog that made up the content of a cough-jet. They visualized droplets expelled from a mannequin's mouth while simulating coughing and sneezing. They tested masks that are readily available to the general public, which do not draw away from the supply of medical-grade masks and respirators for healthcare workers. They tested a single-layer bandana-style covering, a homemade mask that was stitched using two-layers of cotton quilting fabric consisting of 70 threads per inch, and a non-sterile cone-style mask that is available in most pharmacies. By placing these various masks on the mannequin, they were able to map out the paths of droplets and demonstrate how differently they perform.

Results showed that loosely folded facemasks and bandana-style coverings provide minimal stopping-capability for the smallest aerosolized respiratory droplets. Well-fitted homemade masks with multiple layers of quilting fabric, and off-the-shelf cone style masks, proved to be the most effective in reducing droplet dispersal. These masks were able to curtail the speed and range of the respiratory jets significantly, albeit with some leakage through the mask material and from small gaps along the edges.

Importantly, uncovered emulated coughs were able to travel noticeably farther than the currently recommended 6-foot distancing guideline. Without a mask, droplets traveled more than 8 feet; with a bandana, they traveled 3 feet, 7 inches; with a folded cotton handkerchief, they traveled 1 foot, 3 inches; with the stitched quilted cotton mask, they traveled 2.5 inches; and with the cone-style mask, droplets traveled about 8 inches.

"In addition to providing an initial indication of the effectiveness of protective equipment, the visuals used in our study can help convey to the general public the rationale behind social-distancing guidelines and recommendations for using facemasks," said Siddhartha Verma, Ph.D., lead author and an assistant professor who co-authored the paper with Manhar Dhanak, Ph.D., department chair, professor, and director of SeaTech; and John Frakenfeld, technical paraprofessional, all within FAU's Department of Ocean and Mechanical Engineering. "Promoting widespread awareness of effective preventive measures is crucial at this time as we are observing significant spikes in cases of COVID-19 infections in many states, especially Florida."

When the mannequin was not fitted with a mask, they projected droplets much farther than the 6-foot distancing guidelines currently recommended by the United States Centers for Disease Control and Prevention. The researchers observed droplets traveling up to 12 feet within approximately 50 seconds. Moreover, the tracer droplets remained suspended midair for up to three minutes in the quiescent environment. These observations, in combination with other recent studies, suggest that current social-distancing guidelines may need to be updated to account for aerosol-based transmission of pathogens.

"We found that although the unobstructed turbulent jets were observed to travel up to 12 feet, a large majority of the ejected droplets fell to the ground by this point," said Dhanak. "Importantly, both the number and concentration of the droplets will decrease with increasing distance, which is the fundamental rationale behind social-distancing."

The pathogen responsible for COVID-19 is found primarily in respiratory droplets that are expelled by infected individuals during coughing, sneezing, or even talking and breathing. Apart from COVID-19, respiratory droplets also are the primary means of transmission for various other viral and bacterial illnesses, such as the common cold, influenza, tuberculosis, SARS (Severe Acute Respiratory Syndrome), and MERS (Middle East Respiratory Syndrome), to name a few. These pathogens are enveloped within respiratory droplets, which may land on healthy individuals and result in direct transmission, or on inanimate objects, which can lead to infection when a healthy individual comes in contact with them.

"Our researchers have demonstrated how masks are able to significantly curtail the speed and range of the respiratory droplets and jets. Moreover, they have uncovered how emulated coughs can travel noticeably farther than the currently recommended six-foot distancing guideline," said Stella Batalama, Ph.D., dean of FAU's College of Engineering and Computer Science. "Their research outlines the procedure for setting up simple visualization experiments using easily available materials, which may help healthcare professionals, medical researchers, and manufacturers in assessing the effectiveness of face masks and other personal protective equipment qualitatively."

https://www.sciencedaily.com/releases/2020/06/200630111449.htm

Wearing surgical masks in public could help slow COVID-19 pandemic's advance

Masks may limit the spread diseases including influenza, rhinoviruses and coronaviruses

April 3, 2020

Science Daily/University of Maryland

Surgical masks may help prevent infected people from making others sick with seasonal viruses, including coronaviruses, according to new research that could help settle a fierce debate spanning clinical and cultural norms.

In laboratory experiments, the masks significantly reduced the amounts of various airborne viruses coming from infected patients, measured using the breath-capturing "Gesundheit II machine" developed by Dr. Don Milton, a professor of applied environmental health and a senior author of the study published April 3 in the journal Nature Medicine.

Milton has already conferred with federal and White House health officials on the findings, which closely follow statements this week from the head of the Centers for Disease Control and Prevention saying the agency was reconsidering oft-stated advice that surgical masks aren't a useful precaution outside of medical settings. (The debate takes place at a time when clinicians themselves face dangerously inadequate supplies of masks -- a shortfall other UMD researchers are scrambling to help solve.)

The question of masks has roiled society as well, with some retailers refusing to let employees wear them for fear of sending negative signals to customers, and cases of slurs and even physical attacks in the United States and elsewhere against Asians or Asian Americans who were wearing masks, a measure some consider a necessity during a disease outbreak.

The study, conducted prior to the current pandemic with a student of Milton's colleagues on the Faculty of Medicine at the University of Hong Kong, does not address the question of whether surgical masks protect wearers from infection. It does suggest that masks may limit how much the infected -- who in the case of the novel coronavirus often don't have symptoms -- spread diseases including influenza, rhinoviruses and coronaviruses.

Milton, who runs the Public Health Aerobiology, Virology, and Exhaled Biomarker Laboratory in the School of Public Health, demonstrated in a 2013 study that surgical masks could help limit flu transmission. However, he cautions that the effect may not be as great outside of controlled settings.

Nevertheless, he said, the chance they could help justifies taking a new look at whether all people should be encouraged to wear them when they venture out of their houses to stores or other populated locations during the current COVID-19 lockdown.

"In normal times we'd say that if it wasn't shown statistically significant or the effective in real-world studies, we don't recommend it," he said. "But in the middle of a pandemic, we're desperate. The thinking is that even if it cuts down transmission a little bit, it's worth trying."

Previous studies have shown that coronavirus and other respiratory infections are mostly spread during close contact, which has been interpreted by some infectious disease specialists to mean that the disease could spread only through contact and large droplets, such as from a cough or sneeze -- a message that has often been shared with the public.

"What they don't understand is that is merely a hypothesis," Milton said. The current study (along with earlier ones) shows, by contrast, that tiny, aerosolized droplets can indeed diffuse through the air. That means it may be possible to contract COVID-19 not only by being coughed on, but by simply inhaling the breath of someone nearby who has it, whether they have symptoms or not. Surgical masks, however, catch a lot of the aerosolized virus as it's exhaled, he said.

The study was conducted at the University of Hong Kong as part of the dissertation research of the lead author, Dr. Nancy Leung, who, under the supervision of the co-senior authors Drs. Cowling and Milton, recruited 246 people with suspected respiratory viral infections. Milton's Gesundheit machine compared how much virus they exhaled with and without a surgical mask.

"In 111 people infected by either coronavirus, influenza virus or rhinovirus, masks reduced detectable virus in respiratory droplets and aerosols for seasonal coronaviruses, and in respiratory droplets for influenza virus," Leung said. "In contrast, masks did not reduce the emission of rhinoviruses."

Although the experiment took place before the current pandemic, COVID-19 and seasonal coronaviruses are closely related and may be of similar particle size. The report's other senior author, Professor Benjamin Cowling, division head of epidemiology and biostatistics, School of Public Health, HKUMed, and co-director of the World Health Organization Collaborating Centre for Infectious Disease Epidemiology and Control, said, "The ability of surgical masks to reduce seasonal coronavirus in respiratory droplets and aerosols implies that such masks can contribute to slowing the spread of (COVID-19) when worn by infected people."

Milton pointed to other measures his research has found is even more effective than masks, such as improving ventilation in public places like grocery stores, or installing UV-C lights near the ceiling that works in conjunction with ceiling fans to pull air upwards and destroy viruses and bacteria.

"Personal protective equipment like N95 masks are not our first line of defense," Milton said. "They are our last desperate thing that we do."

Hong Kong University contributed to this report.

https://www.sciencedaily.com/releases/2020/04/200403132345.htm