Researchers have developed a low-cost and accessible way to assess the effectiveness of face masks.

A person makes a face mask in this image to accompany an article about the proposal of a cheap and accessible test for mask effectiveness.Share on Pinterest
Non-medical face masks can be an effective barrier against COVID-19, while new tests could evaluate the effectiveness of different face masks.

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A new study has outlined an affordable and accessible test to determine the efficacy of face masks in blocking droplets projected from a person’s mouth.

The research, published in the journal Science Advances, may help organizations determine the most effective face masks to purchase during the current COVID-19 pandemic.

A major way of managing the current COVID-19 pandemic has been the use of face masks. As time has gone on, a growing consensus has developed around their value in blocking the transmission of Sars-CoV-2.

For example, although initially reluctant to advise mask-wearing due to a lack of evidence, the World Health Organization (WHO) now recommend in high transmission situations where social distancing is difficult, the general public should wear non-medical face coverings. This is in addition to specific groups of people who may be more vulnerable.

According to the Director of the Centers for Disease Control and Prevention (CDC) in the United States, Dr. Robert R. Redfield, “[c]loth face coverings are one of the most powerful weapons we have to slow and stop the spread of the virus – particularly when used universally within a community setting. All Americans have a responsibility to protect themselves, their families, and their communities.”

According to the CDC, the rationale for face masks is that COVID-19 primarily spreads through respiratory droplets that project when someone coughs, sneezes, or even talks.

These droplets carry Sars-CoV-2, the virus that causes COVID-19. If they come in contact with another person, the infected droplets could enter their respiratory tract, where the virus can take root and replicate itself.

Masks are also necessary because someone with COVID-19 could still spread it without having any symptoms. That means if someone does not wear a mask in a situation where they can’t socially distance, they could unknowingly expose other people to the virus.

When people wear masks in these scenarios — which are increasing as countries relax lockdown measures to sustain severely affected economies — the chances of exposing others to the virus are reduced.

However, not all masks are equally effective at stopping the spread of the virus. Standard tests to determine how they perform are yet to be agreed on, in part because the precise way the virus transmits is yet to be fully understood.

The first step in examining mask effectiveness is to develop these tests. Further, it is important to design cheap and accessible assessments. Global supplies of medical masks are currently limited, so alternatives, including homemade masks, are being encouraged as a fallback.

A team of researchers has now developed a system to determine the effectiveness of face masks for restricting the number of respiratory droplets a person projects.

The test involves a person who stands in a darkened enclosure wearing a mask. They then speak in the direction of a laser. Any droplets that cross the beam scatter light, which is picked up by a phone’s video camera. These droplets can then be measured using computer software.

In designing the test, the researchers focused on keeping it relatively inexpensive and replicable by non-experts, to ensure it can be widely distributed.

They estimate the test equipment costs around $200.

To demonstrate the test’s feasibility, the team ran the experiment 10 times, with a range of participants. They also added steps, such as measuring people without a mask, to act as a control.

After testing 14 common mask types — ranging from professional N95 masks, surgical masks, cotton masks, and bandanas — they found most were effective at reducing the droplets projected while a person spoke. These included N95 masks without filters, surgical masks, and cotton masks.

However, they found bandanas and fleece masks had minimal positive benefits. In the case of the latter, the results were worse, as the fleece broke up larger droplets into smaller particles.

However, the focus of the study was not to determine the performance of different masks, but to demonstrate the effectiveness of the test itself.

According to Martin Fischer, the corresponding author of the study and an associate professor at Duke University, Durham, U.S, “[o]ur work was a demonstration of a simple measurement method, not a systematic mask study. More work is required to investigate variations in masks, speakers, and how people wear them.

“We also want to extend our method to other droplet-generating actions, like coughing and sneezing. Further, we want to explore the effects of incorrect placement and moisture saturation.”

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