Health & Wellbeing

New videos illustrate why valved masks will not slow COVID-19 spread

New videos illustrate why valv...
New modeling effectively depicts how a valved face mask disperses exhaled air into the surrounding environment
New modeling effectively depicts how a valved face mask disperses exhaled air into the surrounding environment
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New modeling effectively depicts how a valved face mask disperses exhaled air into the surrounding environment
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New modeling effectively depicts how a valved face mask disperses exhaled air into the surrounding environment

A new flow visualization study from the National Institute of Standards and Technology (NIST) starkly demonstrates why face masks with exhalation valves are not effective for slowing the spread of COVID-19.

As we close in on the end of 2020 it is clear widespread face mask use is recommended in most parts of the world as a vital tool to prevent COVID-19 infection and slow viral spread across a community. While researchers are investigating what materials in a face mask are most protective, other experts are suggesting we need to avoid some specific kinds of masks.

Face masks with exhaust valves have been flagged for months as potentially ineffective in stifling exhalations and NIST engineer Matthew Staymates set out to visualize exactly how these kinds of masks can project droplets into the air.

“I don’t wear a mask to protect myself," says Staymates. "I wear it to protect my neighbor, because I might be asymptomatic and spread the virus without even knowing it. But if I’m wearing a mask with a valve on it, I’m not helping.”

Why masks with valves do not slow the spread of COVID 19

Staymates’ latest experiments, published in the journal Physics of Fluids, use two flow visualization techniques to illustrate exactly how these kinds of masks allow exhaled air to disperse into the surrounding environment. Across two videos Staymates demonstrates why these masks are fundamentally useless at controlling respiratory droplet transmission during a pandemic.

"When you compare the videos side by side, the difference is striking," he notes. "These videos show how the valves allow air to leave the mask without filtering it, which defeats the purpose of the mask."

Why masks with valves do not slow the spread of COVID 19

These kinds of N95 masks have grown in popularity as they are much easier to breathe through compared to a regular face covering. However, they were primarily designed for uses such as protecting construction workers from dust or hospital staff from infected patients.

It is important to note these videos do not demonstrate the movement of viral particles. Instead these kinds of airflow visualizations offer easy-to-understand depictions of how exhalations can escape a seemingly secure mask. Staymates hopes his work will help the general public understand the importance of wearing the right kind of face masks.

“My hope is that this work will help inform a large audience that valves on a mask are not helpful as we fight this global pandemic together,” he concludes.

The new study was published in the journal Physics of Fluids.

Sources: NIST, American Institute of Physics

10 comments
Daishi
Valved masks aren't as effective at protecting other people from you as makes without valves but they are still more effective than not wearing a mask at all. I can understand why they don't meet official guidelines but if someone near me with COVID was going to cough into the air or into a valved mask I'd still chose the mask. Even if the air is just redirect without filtration it would reduce the particle velocity and distance large particles would travel (allowing social distancing to work better). Another thing is that the severity of symptoms if you get COVID is based partly on the dosage of the virus you get with measures in place (distance, masks etc.) if you still manage to get infected anyway you are less likely to get seriously ill or die than if you got sick with no measures in place. This could be one of the reasons that with cases still rising that fatality rates for infected people are falling.
Bob Stuart
Well, duh! What those valved masks actually need is a nozzle, so that you can blow dust from your work.
DavidSkipper
First, not getting sick protects others, so a N95or as I wear, N100 valve mask is step 1. Wearing a homade mask that is the supposed 12-17% effective is a good way to get sick. Wear an N95 or N100 and add the same ineffective filter the homade mask has over the valve, now max protection for you and same for them.
DavidSkipper
I don't disagree with the photos but I do believe not getting myself sick is a better way to not spread it. I also think it should be reported that valved masks are not for asymptomatic contagious persons nor symptomatic contagious persons. Symptoms or not a test positive person should be isolated not out and about wearing a mask. A homemade mask is not going to protect us from a contagious person.
Porsche911
Not all valved masks are constructed in the same way. I have a couple of valved masks, and while using them I exhale through SIX layers of filtration ! These include activated charcoal, non-woven polypropylene, plus tightly woven cotton, etc. I inhale through nine layers in total. Not extremely easy to breathe with these, but they do filter well, both ways. Masks must be evaluated individually for function, plus the fit of the mask to your face is quite important, as is wearing it correctly.
Titus
There is a mask (just in production) that has UV sterilisation included. the picture looks a bit like dark Vader mask. I would recommend that for anyone in a country where Covid-19 is not under control. There is a small chance that once infected a vaccine will not work.
Nobody
I haven't seen anyone wearing a valved mask in public although they are quite common in the work place. These photos are quite deceiving since they only show very large droplets and not the tiny virus which is small enough to pass freely through the mask. Try spray painting black paint with almost any of these masks and you will be spitting black boogers for several days. It's also funny how OSHA standards for masks are almost never mentioned. Most of the news about masks is just hype since even the best fall short of a hazmat suit with positive air ventilation and most are pretty much worthless. N95 or better masks are likely somewhat effective but WE ALL WILL BE EXPOSED SOONER OR LATER.
Baker Steve
A few points. A valved mask does not necessarily allow air out through the valve all the time. In those that I have tested (N95 and N99), if you exhale gently the valve does not open, the exhaled air passing out through the filter material itself. Also, at least one supplier of valved masks that I have seen offers an adhesive tab to disable the valve. And as I think someone else has commented, an N95 or N99 mask is FAR more effective that a simple cloth mask. However, if you wear one under your nose, as I saw one member of a supermarket's staff doing recently, you might as well not bother at all.
martinwinlow
MOG! Do we *really* need 'research' to point out this *cosmically* obvious fact?
drBill
IMO, a mask is to protect the wearer and if everyone is wearing, even the valved release will not get through the others' masks. Yet I agree with the decision to downplay the use of valved masks for viral protection, as the recirculation even enhancement of viral-laden droplets (if the wearer is already infected) adds to the burden on everyone else's masks.

Indeed, I modified my N95 3M dust mask (no valve) by painting on nano-silver, which nano-scale Ag kills
viruses, and restores its killing merely by exposure to sunlight. The papers revealing this have been forwarded to 3M, and it's up to them to make such nano-silver coated N95 masks available. Presumably, they will confirm the reports before deciding how or whether to do that.

The valved masks are meant for dust protection, not for viral protection.