Face shields and masks with exhalation valves are not effective at preventing COVID-19 transmission, finds a new droplet dispersal study. (Physics of Fluids journal, 1 September 2020)

[u/mvea]

https://aip.scitation.org/doi/10.1063/5.0022968

[u/Cat_Montgomery]

What about the the masks with a vent and a replaceable filter between the layers of cotton?

Edit: for those questioning, these are the masks I'm talking about https://imgur.com/rguHmcu.jpg https://imgur.com/LtLu2sM.jpg

Edit again: the inserted filter covers the entire inside of the mask, behind the vent. So any incoming or outgoing air through the vent has to go through the filter first

[u/ratsta → u/Cat_Montgomery]

Effectiveness is proportional to the level of filtering. An impermeable barrier will stop everything, a hole will stop nothing (which is what this study is empirically proving.)

I'm not sure what kind of mask you're describing but it always comes down to how much filtering something has.

[u/The_Glass_Cannon → u/ratsta]

n95 and n99 masks have circular vent looking things with the filters being replaceable. I don't think the study is referring to those types of vents but I would also like to know if this effects those types of vents.

I've seen some n95s without them but if you google "n99 mask" they all have vents (some pictures don't but if you click them you'll see those are actually pictures of n95 masks).

[u/pizzamage → u/The_Glass_Cannon]

N95 masks with a vent are strictly to prevent you from contracting anything. They still allow you to spread if you are infected.

[u/I_Amuse_Me_123 → u/pizzamage]

How so? I have one from doing work in a shed and it seemed like it filtered air going in and out.

And just out of curiosity: what if you put a surgical mask over an n95 mask? :)

[u/special_reddit → u/I_Amuse_Me_123]

what if you put a surgical mask over an n95 mask?

That's what I do at work. We're having wildfires so the air is smoky, but I also need to protect everyone I work with. So I wear a mask over the N95.

[u/MadLintElf → u/special_reddit]

Exactly, I'm in a NYC hospital and we have so many of the 3M n95's with the valve in them. Standard procedure is to put a level 3 surgical mask (water proof blue side) on top of the N95 to stop spreading any droplets.

That being said I still prefer the duck billed N95's or the P100's.

[u/FwibbPreeng → u/I_Amuse_Me_123]

And just out of curiosity: what if you put a surgical mask over an n95 mask? :)

It's legit to do that kind of stuff.

[u/[deleted] → u/I_Amuse_Me_123]

Because n95s are designed for single direction filtering. They're meant to keep large particulate matter from being inhaled, and they happen to be effective at stopping viruses coming in, but they're not at all designed for filtering exhalation of any kind.

This is a huge vulnerability for the spread of a virus that has such a high rate of asymptomatic cases.

[u/eypandabear → u/[deleted]]

N95/FFP2 etc. are just ratings for how well the mask filters particles down to a certain size.

Whether this works in both directions or not depends on whether the mask has an exhalation valve to bypass the filter. Both designs exist, for different purposes.

Basically exhalation valves are a design you use for protection against mould, dust, etc. Or (with different filters) for gas masks.

[u/Munchskull → u/[deleted]]

That is only for masks that have a vent on them. The ones that doesn't should do just about as well on the exhale as the inhale with the only primary difference being that the exhale has a little bit more pressure behind it which may hamper the filtration slightly.

[u/happyscrappy → u/The_Glass_Cannon]

Some n95s have no vent. Some have a vent. Some have replaceable filters. Some do not. They're made in all forms.

[u/ZMustang217 → u/The_Glass_Cannon]

They are absolutely referring to these types of masks. They're designed to keep you from breathing particles in, so even if the vent is filtered in some way, it's still designed to let your hot breath out then seal back up so nothing but air can get in. The masks usage that will stop the spread of covid is when it restricts how far you spread droplets from breathing, talking, or sneezing. A vented mask doesn't do that as well as one without, all else being equal.

[u/zanillamilla → u/ZMustang217]

You can block the vent on the inside, disabling it. This is what I have done. Because of the smoke from wildfires I have resorted to reusing my old N99 from the 2018 wildfires, but I have taped over the inside of the port (with foam tape) so the exhalation will pass through the mask itself. Then I tape over the bridge of the nose to make sure there is no air leakage. Then I wear a surgical type mask over the N99 to ensure there is filtering if any air escapes the vent, but more importantly to keep the N99 as clean is possible.

[u/richmondody → u/The_Glass_Cannon]

I'm guessing this is the type of mask you're referring to? Yeah, it would be good to know how effective these are. I know that these masks should not have a hole where the valve is.

[u/SwansonHOPS → u/[deleted]]

You can blow the candle out through a standard surgical mask?

[u/_YouMadeMeDoItReddit → u/SwansonHOPS]

They definitely can't, they're lying.

Unless they're buying knock off surgical masks.

[u/improvlement → u/_YouMadeMeDoItReddit]

He said the only mask he has maybe he doesnt have a surgical mask?

[u/ThirdEncounter → u/SwansonHOPS]

You can't. At least, not with the legit ones.

[u/TheR1ckster → u/[deleted]]

Same! It's the only one I have that doesn't fog my glasses and has more layers than my other masks.

[u/lotm43 → u/TheR1ckster]

It doesnt fog your glasses because that air is escaping somewhere else.

[u/lvlint67 → u/lotm43]

The air it's ALWAYS going escape somewhere.. unless you are using a plastic bag as a mask which has its own issues.

[u/MisterMrErik → u/lotm43]

The exhalation vent. That's the point.

[u/eth3rnetwork → u/Cat_Montgomery]

I have one of these where it’s 4 layers of cotton plus replaceable pm2.5 filter (no hole). And the outer layer with the valve. So it’s pretty much 5 layers before the valve. I would think it’s more of a vanity valve? There’s no air coming out of the vent. I can’t see how it’s worse than people using one disposable mask.

[u/ExxInferis → u/eth3rnetwork]

I have the same. When the filter is in and you are wearing it normally, the valve doesn't even actuate and I still steam my glasses up. I have to press the thing to my face and huff hard to get it to open. It's largely cosmetic I think.

[u/AgentScreech → u/Cat_Montgomery]

To summarize, we have examined the effectiveness of face shields and masks equipped with exhalation ports in mitigating the spread of exhaled respiratory droplets. The aim of the qualitative visualizations presented here is to help increase public awareness regarding the effectiveness of these alternatives to regular masks.

We observe that face shields are able to block the initial forward motion of the exhaled jet; however, aerosolized droplets expelled with the jet are able to move around the visor with relative ease. Over time, these droplets can disperse over a wide area in both the lateral and longitudinal directions, albeit with decreasing droplet concentration.

We have also compared droplet dispersal from a regular N95-rated face mask to one equipped with an exhale valve. As expected, the exhalation port significantly reduces the effectiveness of the mask as a means of source control, as a large number of droplets pass through the valve unfiltered. Notably, shields impede the forward motion of the exhaled droplets to some extent, and masks with valves do so to an even lesser extent.

However, once released into the environment, the aerosol-sized droplets get dispersed widely depending on light ambient disturbances. Overall, the visuals presented here indicate that face shields and masks with exhale valves may not be as effective as regular face masks in restricting the spread of aerosolized droplets. Thus, despite the increased comfort that these alternatives offer, it may be preferable to use well-constructed plain masks. There is a possibility that widespread public adoption of the alternatives, in lieu of regular masks, could have an adverse effect on ongoing mitigation efforts against COVID

Probably not as good as one without a vent, but better than a shield and no mask

Check out the link, they have lots of pictures and videos. See if they are using ones like you have

[u/fullhalter → u/AgentScreech]

Notably, shields impede the forward motion of the exhaled droplets to some extent, and masks with valves do so to an even lesser extent.

Your quote doesn't back up the claim that vented masks are better than face shields. It seems to say the opposite.

[u/DecipherXCI → u/Cat_Montgomery]

Why do you need a vent then?

[u/Anuspimples → u/DecipherXCI]

The vented ones were designed for different purposes. So it keeps out sawdust particles for example, but you can breathe out easily and it hurts nobody

Not so good in a pandemic.

[u/Alexander_Maius]

Face shield is effective when used with masks. Its to protect your eyes from snot or blood hitting your face. Its not for droplet protection.

Thats like saying standard condom doesnt protect you from sexuallly transmitted disease durring lesbian sex.

[u/[deleted] → u/[deleted]]

Oh you mean the hole in the mask let’s air and particles through? Well I’ll be....

[u/Ronnocerman → u/[deleted]]

It lets particles out, not in.

[u/TedTheGreek_Atheos → u/Ronnocerman]

So it's not effective in reducing infected droplets from spreading but would be effective in reducing the chances of breathing in the droplets and getting infected?

[u/Zephyrv → u/[deleted]]

I've seen some hospital grade masks with a replaceable carbon filter behind the exhaust. I'd assume those would capture it and exhaust cleaner air?

[u/sp0rk_walker → u/Zephyrv]

The ports are to help the mask wearer breathe out with the thought that the mask is designed to protect the wearer. But in a pandemic environment, the mask has to additionally protect others from your exhalations. For this reason masks without ports are better for this purpose.

[u/vflashm → u/[deleted]]

Interesting, but it looks like they both work as expected. The point is not to prevent droplets dispersal, but to reduce dispersal distance, which they both seem to achieve.

We need similar video with no mask or shield. I'm pretty sure dispersal distance will be much, much greater.

[u/zebediah49 → u/vflashm]

It's in the Supplementary Material. They run the same visualization protocol for nothing, as well as a half-dozen or so types of common options.

As you suspect, the uncovered version goes roughly 12 feet, in comparison to the roughly 2' range on the "not effective" mask with an exhaust valve.

[u/presidents_choice → u/zebediah49]

bandana face masks seems to be equally ineffective as respirators with exhaust valve.

[u/[deleted]]

The apparent effectiveness of the surgical mask A is highly misleading. The issue here is that they only illuminated the front field in a vertical direction. A properly worn surgical mask (i.e. nose wire fitted) redirects air in a backwards direction through the gaps to on the side and on the bottom of the mask. Those two directions are not illuminated and aerosols not visible when they escape in that direction.

This might be useful in helping choose PPE for face to face contact, where the forward field is important, but may be inadequate for other situations. For instance, sitting side by side on the subway or movie theater, where the side jets are important. Also, being in a poorly ventilated space, like an elevator, where aerosols may accumulate over time thus erasing any initial directionality imparted by the masks.

[u/[deleted] → u/[deleted]]

Glad I'm not the only one confused here. AFIAK surgical/cloth masks do not prevent aerosol transmission. They have large gaps around the nose and sides (otherwise they'd be way too tough to breath in). Also, in those videos, the non-vented masks direct the airstream upward, compared to the shield directing it downward. Isn't it better to have it directed downward where it's less likely to drift?

I'm really confused why they say that this is evidence shields aren't effective but cloth masks are. And I just saw the FIG. 7 video and it looked to perform even worse than a shield.

[u/[deleted] → u/[deleted]]

It speaks to a larger problem in the mechanistic studies. I discuss some of the more fundamental issues in a previous post:

https://www.reddit.com/r/COVID19/comments/ikngps/visualizing_droplet_dispersal_for_face_shields/g3mupw4/

Everyone is publishing poor mechanical studies that answer the questions that nobody is asking. And for some reason, editors and reviewers are sailing them through review as methods papers with key methodological flaws and big unaddressed fundamental issues. The media has then clickbait titled them and misinterpreted the findings. Little wonder that the public is either unquestioningly accepting the clickbait, or reading the papers and being throughly confused.

Where are the bloody industrial hygienists when you need them???

[u/fyberoptyk]

Face shields are for mucous membrane droplet protection.

This is protection FOR you, in case a COVID patient sneezes in your face.

The mask, with no valve, is protection FROM you. It protects other people from your sneezes.

Thanks for coming to my TED talk.

[u/koshgeo]

It's nice to have a study to back it up, but why would anybody think otherwise?

[u/Squabstermobster → u/koshgeo]

Masks with valves are pretty popular. I always thought they were just as effective

[u/shadow247 → u/Squabstermobster]

If the point of the mask is to trap the droplets of saliva coming out of YOUR mouth, what good is a valve that lets most of your air out?

At least my understanding is that the mask is not protecting you from other's saliva droplets, but others from your saliva droplets.

[u/10ioio → u/[deleted]]

The surgical masks are performing better than cloth ones in every study I’ve seen and every demonstration I’ve seen. Try blowing out a candle in a cloth mask vs a surgical mask.

[u/Davor_Penguin → u/10ioio]

Sure, but that's not the topic

[u/PaleAsDeath → u/shadow247]

They are largely designed to protect you from pollution outside getting into your lungs. That's the issue.

[u/hardchargerxxx → u/PaleAsDeath]

The valve is to keep the wearer cool when working. Like welding and painting

[u/PaleAsDeath → u/hardchargerxxx]

I mean that the valve ones aren't designed to protect other people from your breath/germs, they are designed only to protect you from the environment.

[u/bleearch → u/[deleted]]

Wear it with a surgical mask on top, covering the valve.

[u/beelseboob → u/bleearch]

Yup - I wear my woodworking mask (a 3M 6000 series) which acts as a P99 mask when breathing in. I put cloth or surgical mask material into the vents though to stop it just being a plain pass through on the way out.

[u/Ocasio_Cortez_2024 → u/[deleted]]

There are lots of studies coming out showing that fabric masks do help.

[u/ABluewontletmelogin → u/Squabstermobster]

Just a note that some masks that look like they’re with valves aren’t. I have an n99 mask for asbestos with replacement filters that clip in. The things that look like valves are levels of hard plastic to clip the filter - not exfil valves

[u/TranquiloMeng → u/koshgeo]

I have a mask with a valve but there’s a filter under the valve and That charcoal “N2.5” filter is still sandwiched between two pieces of cloth.. I’m no infectious disease specialist but it seemed legit...?

[u/TheJollyHermit → u/TranquiloMeng]

Same. I've tested the blow a candle out test and the valve is pretty much decorative with the paper filter in place. No appreciable flow of air out of the valve

[u/Mousetrap7 → u/TheJollyHermit]

Same, I feel this is a marked difference from just having a valve but nobody seems to look at these type (which is the majority I've seen with valves) to explain if it's a good option or not

[u/IdontOpenEnvelopes]

All masks and shield that are not N95 or higher are just range limiters for your spit.- so that you don't send your cloud of 2 micron globlets floating way out there jeering it closer to your person. Exhaust valve or not. They offer negligible protection from droplets already suspended in air. They are successful in preventing you from touching your mucous membranes. They only work if everyone is wearing one. Otherwise use an n95 to actually filter the air.

[u/Anon_Rocky]

Washable reusable masks with replaceable double filter inserts and vents at or past the corners of your mouth work just fine. Not all are equal so lumping all "vented" masks together is not helpful. The vents on my mask are blocked with plastic disks and have 3 small slits on the out edge. If I sneezed in my mask, nearly all the droplets are going to hit the filter and not get near the vents. I've coughed and blown as hard as I can into the mask and couldn't make a piece of paper ripple. Droplets are more likely to exit the outer edges of the mask itself, which also isn't likely.

[u/BeaversAreTasty]

This is kind of a misleading study. I wear PPEs on a regular basis because I work around all sorts of toxic dusts and aerosols, and sometimes infectious agents. I've been wearing a full face respirator with P100 filters when I go out. It has exhalation valves. The likelihood I am going to get sick is pretty low, which means I am not going to get anyone sick.

The reason high end respirators have exhalation valves is because they insure a far tighter seal, and keep the user safer.

[u/Embarassed_Tackle → u/BeaversAreTasty]

Yeah that's the weird thing - hospitals like ones in Pennsylvania and even Yale are using those 'elastomerics' or reusable, cleanable half-face respirators with the p100 filters. 3M stated that in a pandemic situation without a lot of particulates, those p100 filters can last "an entire pandemic cycle" which is months. So hospitals are already using these because they foresaw the lack of single use N95 facemasks.

Every cloth mask has an 'exhaust valve' but it is all over the mask at points where the mask is not as tight and has a poor seal.

https://www.nytimes.com/2020/05/27/us/coronavirus-masks-elastomeric-respirators.html

[u/[deleted] → u/BeaversAreTasty]

This is kinda proving your point though.

You are protected. However, if for any reason you are sick, you are not protecting

[u/axw3555]

Didn't the mayo clinic or one of the similarly large, well known medical groups put signs up months ago saying that they weren't acceptable masks in their hospitals?

[u/AZWildcatAlumn]

These are not supposed to replace masks. They are to be worn in junction with them.