Health & Wellbeing

Mask safety: Study finds some materials may cause more harm than good

Mask safety: Study finds some ...
A new study has shown all masks are definitely not equal when it comes to preventing the spread of disease
A new study has shown all masks are definitely not equal when it comes to preventing the spread of disease
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The various mask designs and materials tested in the study
The various mask designs and materials tested in the study
The results show neck fleece as the worst performing type of mask/material
The results show neck fleece as the worst performing type of mask/material
A new study has shown all masks are definitely not equal when it comes to preventing the spread of disease
A new study has shown all masks are definitely not equal when it comes to preventing the spread of disease
View gallery - 3 images

Scientists from Duke University have demonstrated a simple technique designed to test the efficacy of different face mask fabrics and designs in reducing the spread of respiratory droplets during normal speech. The research strikingly suggests some alternative face mask options not only offer little protection, but could be more harmful than wearing no facial covering at all.

Face masks have become a mandatory public health necessity in many parts of the world as the COVID-19 pandemic continues to spread. With dwindling supplies of surgical masks and N95 respirators, which are rightfully being diverted to health care environments, the general public is often urged to use whatever they can to cover their faces when out in shared spaces.

Ideally, homemade face masks should have two to three layers, but in the absence of anything better many health authorities around the world have suggested alternatives such as scarfs, bandanas or neck fleece. “Any face mask or covering is better than none,” espouse some experts.

The genesis of the new study came when Eric Westman, from the Duke University School of Medicine, was trying to figure which face masks to buy for a non-profit organization helping at-risk local communities. He quickly realized the market was full of products making extraordinary claims but there was no testing process to verify the efficacy of these masks.

“We were trying to make a decision on what type of face covering to purchase in volume, and little information was available on these new materials that were being used,” says Westman.

So Westman turned to his colleague Martin Fischer, director of Duke’s Advanced Light Imaging and Spectroscopy facility, for help. Using a number of common lab materials, all commercially available, the researchers developed a cheap and simple system to test how effectively different face mask materials blocked droplets during normal speech.

“We wanted to develop a simple, low-cost method that we could share with others in the community to encourage the testing of materials, masks prototypes and fittings,” explains Fischer. “The parts for the test apparatus are accessible and easy to assemble, and we’ve shown that they can provide helpful information about the effectiveness of masking.”

As a proof-of-concept testing the new technique, the researchers trialled a number of common masks and mask alternatives. The test involved a speaker wearing a mask repeating the phrase “Stay healthy, people” for ten seconds while a laser illuminated any droplets coming through the mask.

The various mask designs and materials tested in the study
The various mask designs and materials tested in the study

“We confirmed that when people speak, small droplets get expelled, so disease can be spread by talking, without coughing or sneezing,” says Fischer. “We could also see that some face coverings performed much better than others in blocking expelled particles.”

Unsurprisingly, a fitted N95 mask resulted in the most effective reduction in droplet emissions, with a surgical mask relatively close behind. However, most homemade cotton masks tested delivered strong results, blocking droplet emissions at rates not far off what was seen in the surgical mask tests.

The notion that ‘anything is better than nothing’ didn’t hold true

But not every type of facial covering was effective in reducing droplet emissions, unfortunately. Knitted fabrics and bandanas were notably weak in reducing droplet volumes from a speaker. But it was the results from testing neck fleeces, also known as gaiter masks, that really surprised the researchers.

“The notion that ‘anything is better than nothing’ didn’t hold true,” says Westman, discussing the results of the neck fleece test. Westman says the number of particles emitted through the neck fleece resembled the volume seen in baseline tests with no mask at all.

“We attribute this to the fleece, the textile, breaking up those big particles into many little particles. They tend to hang around longer in the air and get carried away easier in the air,” he explains.

The research concludes that wearing this kind of mask may be ultimately counter-productive, causing greater risk of transmission than wearing no mask. But this conclusion is still resolutely hypothetical and the research does not explicitly prove wearing a neck fleece heightens viral transmission. Instead the research suggests the frequent adage “something is better than nothing” may not be true.

It is important to note these kind of droplet transmission studies only investigate the physical properties of droplets exiting our mouths while speaking. There is no evidence so far to suggest these studies can be used to generate conclusions regarding viral transmission.

The results show neck fleece as the worst performing type of mask/material
The results show neck fleece as the worst performing type of mask/material

Another limitation of this particular study is the inability for this test set-up to detect the smallest of aerosol particles. The commonality of the materials used in the test, including a smartphone camera as a recording device, means small aerosol droplets cannot be measured. While the science is still unclear on whether aerosol emissions are a significant form of SARS-CoV-2 transmission, this novel technique only offers data on what kind of face mask material effectively reduces larger droplet emissions.

When it comes to exhalation valves, the study found little difference in droplet emissions between a N95 mask with an exhalation valve and a non-medical cloth mask, making it less effective than an N95 mask without the valve. This suggests that valved N95 masks, while protecting the wearer, are not especially safe for persons surrounding the wearer because the exhalation valve generates strong outwards airflow – a finding recently echoed in updated CDC mask guidelines urging against the wearing of masks with exhalation valves.

Inexpensive way to test face mask effectiveness in reducing COVID-19 transmission

Fischer suggests a lot more work is needed to understand what kinds of masks are optimal in our new COVID-19 reality. In the short term he hopes this simple method developed by the Duke University team can be easily appropriated by mask manufacturers to test the products they are developing.

“This was just a demonstration – more work is required to investigate variations in masks, speakers, and how people wear them – but it demonstrates that this sort of test could easily be conducted by businesses and others that are providing masks to their employees or patrons,” says Fischer.

The new study was published in the journal Science Advances.

Source: Duke Health

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Daniel Bircher
Thanks for the interesting article. It would be helpful to link the mask samples (w numbers) to the graph with droplet count for easier reference. Thanks
20,014,574 infected, 734,755 dead, and only NOW we see the first basic study into whether or not masks work, with the researchers themselves saying "lot more work is needed to understand what kinds of masks are optimal" ???

No wonder it's so bad - the entirety of humanity, and especially everyone in charge, are all total morons. Not that we didn't know that from the beginning I guess...
1, ‘Surgical’ * Surgical mask, 3-layer
2, ‘Valved N95’ N95 mask with exhalation valve
3, ‘Knitted’ Knitted mask
4, ‘PolyProp’ 2-layer polypropylene apron mask
5, ‘Poly/Cotton’ Cotton-polypropylene-cotton mask
6, ‘MaxAT’ 1-layer Maxima AT mask
7, ‘Cotton2’ 2-layer cotton, pleated style mask
8, ‘Cotton4’ 2-layer cotton, Olson style mask
9, ‘Cotton3′ 2-layer cotton, pleated style mask
10, ‘Cotton1’ 1-layer cotton, pleated style mask
11, ‘Fleece’ Gaiter type neck fleece
12, ‘Bandana’ * Double-layer bandana
13, ‘Cotton5′ * 2-layer cotton, pleated style mask
14, ‘Fitted N95’ N95 mask, no exhalation valve, fitted
‘Swath’ Swath of mask material, polypropylene
‘None’ * Control experiment, no mask
Brian M
No surprises here, just begs more questions to be answered about the use of non-tested/standard face masks.
Is there a risk of building up an infectious dose (either direction)? Does it reduce social distancing due to over confidence in their use. Do re-used mask/discarded mask pose a risk.

With all this 'great hygiene' practice are we at risk of losing the ability to build up immunity to other virus/pathogens as a herd?
I recall reading that a mask made from an old cotton t-shirt was effective due to the tightness of the weave.
Laurent Coquilleau
The data shows that MOST mask covering have a significant impact in the number of emitted droplets. ONLY 1 out of 14 is worse than no covering. And this is the one you decided to highlight in your bold comment: "The notion that 'anything is better than nothing' didn't hold true".

Even if this is not false, Cherry picking is not science.

So let me summarize the true results of the study:
* Out of 14 different mask coverings, 12 SHOW A REDUCTION OF DROPLETS BY AT LEAST A FACTOR OF 3 !
* A simple bandana reduces the number of droplets by a factor of 2 !

Just do not wear a neck fleece. Because this material has a tendency to breakdown large droplets in smaller ones and let them go through, this is the ONLY tested face covering that is worse than wearing nothing.

Your interpretation of the data is intellectually wrong and socially irresponsible.
The only reason I wear a mask is to avoid making others uncomfortable. Washing your hands and using sanitizers is the way to go. And if possible, avoid touching door handles and other common things in public places.
You know, I've read studies of the efficacy of masks here in the USA since mid-March, but no one has really looked at the total viral load of a mask worn for several hours along with all these studies comparing mask materials one to another. Having had to purchase filtration systems in the past, I've always wondered about depth filters and their accumulated filtrate on the continued product stream. An example - I have a carbon filtration system at home for drinking water. It is supposed to be good for more than 1000 gallons (around 4000 liters), and I don't have a flow meter on my tap. So if I am drinking water at the 4250 liter point, how filtered is my water? Well if I am teaching a class for 8 hours wearing a mask, I may be collecting a good amount of my own aerosolized particulate matter, but how much of it stays with my mask, how long should I wear the mask before my constant breathing through it starts pushing the collected aerosolized material out the other side? Rather esoteric question given that we know masks reduce aerosolized spread in hospitals, and with highly infectious pulmonary diseases the properly fitted N95 is the standard of care. When in surgery, I generally change my mask each time I leave the operating room and put a fresh one on before the next procedure. When in the ICU I usually keep a mask around my neck and wear it properly when approaching a vulnerable or contagious patient. And I NEVER wear an N95 with an exhalational vent - those are for healthy workers in an environment like coal mining or sand blasting. Heck, they should use the complete "space suit" battery powered ventilation systems in those settings but they do cost money to obtain and maintain.
Your headline will encourage the crazed anti-maskers out there. Way to go! /s
Sow the seeds of doubt!
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