As we continue to navigate these unprecedented times, KCBS Radio is getting the answers to your questions about the coronavirus pandemic. Every morning at 9:20 a.m. Monday-Friday we're doing an "Ask An Expert" segment with a focus on a different aspect of this situation each day.
Today we're looking face masks and the science around it with Dr. Kim Prather, director of the NSF Center for Aerosol Impacts on Chemistry of the Environment and a distinguished professor at the U.C. San Diego Scripps Institution of Oceanography. She can be found on twitter @kprather88.
Your name popped up as one of a number of people involved in a paper that is calling for a stronger push for mask wearing. Your particular specialty is around aerosols; can you tell us a little about where all of this interfaces? Aerosols, masks and COVID-19?
Yes, my background is in aerosols and I think aerosol scientists for a long time, for decades have been looking at the airborne transmission of disease, respiratory disease. There's sort of been a disconnect and the traditional sort of more medical view. We focus much more on droplets. Basically, if the someone coughs or sneezes how do we avoid catching it from touching surfaces or being too close to that person.
But what's become really clear - every virus behaves different but this virus that produces COVID, it actually appears to be one of the main pathways that it is being spread around is through what we call aerosols. And what aerosols are is they're just really tiny particles. So with droplets you can see spray, but they're tinier than that. For every drop, they estimate there's probably about 1000 aerosols, and those aerosols are invisible to the naked eye. But when aerosols released in the air, they don't know six feet distances, right? They can just fill a room, for example, and then a lot of people are exposed. A lot of people can breathe that air and then become sick. We've been seeing that happen over and over again.
So this may be a gross oversimplification, but I can see when somebody sneezes or coughs. Something flies in the air; that's a droplet, but I can't see the little aerosols. Do the aerosols break off from these droplets or are they coming out separately?
They come out separately. What happens there is it basically gets in the air and the big droplets will just fall. There are videos of this, you can see the big droplets falling to the ground. And that was the early research. And then aerosols scientists came along, and we have made ways of detecting the little ones that you can't see and there's a lot more of those.
And the extra sort of push, I think, for the spread that we talk about in this article is that this particular disease is being being propagated by people who don't have any symptoms. They don't know they're sick and so basically they can walk around and just by talking - not coughing and sneezing but by talking - you will emit thousands of aerosols. And so if you happen to be in a room with the person that doesn't know they're sick, then they can just basically be constantly putting that out `while you're in the room with them. And so indoors is particularly bad. And so that's why suddenly you saw the CDC shift and start saying people should have face coverings. The mask is actually to cut off the aerosols that are being produced by someone who is sick and doesn't know it. They can spread for five days before they know they're sick.
So one last question from me before we get to our listener questions. Is this a fair way of visualizing the way aerosols behave: those little dust motes you might see flying around in a room, do aerosols kind of float around like that?
Yeah, or just think of a smoke cloud. If you think of somebody smoking and you see them release their smoke, you can just watch it float up in the air. In there, there are aerosols and that's exactly how they behave, yes.
OK great, let's get to listener questions that have been sent in to askus@kcbsradio.com. This first one says, I have a friend who sent me a link to a World Health Organization page that says if you're healthy you only need to wear a mask if you're taking care of a person with COVID-19. Is that an outdated web page or is that still the WHO's recommendation?
That is still the WHO's recommendation. They're behind. I would follow the US, CDC has actually been shifting over time and now the CDC recommends that everyone wear some sort of face covering when they're in a public place.
Social distancing seems to have gone out the window during the protests around the country the last week or so. How worrisome is that for you?
Well you know, it's all relative I'm worried for a lot of reasons about these protests, but yes, certainly we're seeing a lot of people getting very close to each other. A lot of people have had masks so that's good. But having this lead to more spread is an area of concern. So yeah, it's something that I have noticed for sure.
Is there a difference between speaking quietly? Shouting? Breathing? What do we know?
Yeah definitely, you generate more when you yell. Definitely. And some people - this is the other weird thing about this particular virus - some people generate 1000 times more. We don't even know why. And so if you're near one of those people then the chances of you know inhaling it gets even higher.
What do we know about the viral load per aerosol particle? Is that variable across different people? How do we assess that?
We do not know for this virus. It's been investigated for influenza and basically they've shown that that respiratory virus appears in the smallest particles, there could be really high loads. But for this virus, that is something that people are just looking into now.
I know a lot of information is evolving, but I'm wondering if there's a place where I can get some solid information that would let me assess risk when using various masks. For example, if I knew a certain mask was 10 times more effective than some other one, that might influence my decision. Do you know of any such risk or effectiveness based data?
Yeah, there's been studies done. They're just coming out now, like every day. There was a really good one last week that's been written up a lot. But what I will tell you is a surgical mask cuts out about 90% of the this size virus, so that's that's really good. People wear N95 mask and everyone thinks that's a lot better, but in fact, the problem with masks is you have to not just wear a mask, you have to make sure that it fits your face. And so the N95 masks are notorious because unless you had it fit to your face, they don't fit. And that means that the aerosols just leak out. They don't work very well.
So the ones that are proven and the easiest to wear if you wear it properly is the surgical masks. Homemade masks actually work surprisingly well, 70%, 80% some of them 90% if you start to double up the fabric. There's various studies, there's quite a bit on the web. I've been tweeting about this. A lot of people are putting out a lot of information about this right now. But I always tell people who are worried about, is my mask efficient? I always say something is better than nothing. So that's sort of the standard. But yeah, there's lots of ways to get masks now.
Can you ask your guest if health professionals think we really need to wear a mask when we're riding a bike or running by ourselves? Or is this just for appearance's sake.
It's not for appearance's sake. If a person, again a runner, is sick and doesn't know it, they will under exertion be producing a lot of infectious aerosols. And so the concern there is that you would not want to be in the airstream behind that runner, right? And so the runners are wearing masks, cyclists are wearing masks to protect those that are behind them. Because these aerosols, as we've talked about, can just get caught in the draft. And if they flow right to you and you're behind them for some length of time, that entire time you're potentially inhaling infectious viruses.
I know a few weeks back, this headline-grabbing theory came out from a wind tunnel expert in Europe around this, and it got everybody's attention, and then it was sort of debunked because it didn't seem to have any actual viral science around it. What's your take on that? I think everybody knows what we're talking about.
You're absolutely right, there is a disconnect. I think people get worried when they see something like that and they did get worked up because they felt like that was creating fear unnecessarily. I push that further to say it's better to exercise caution. And until we acknowledge and accept that aerosols are a big part of the transmission of this particular virus, how are we gonna protect ourselves properly? And we're not. Basically if we're just treating it as all on surfaces and we wash our hands - which are all things we should be doing - but we're ignoring the aerosol route, we're being exposed. This is a very flexible problem. It's just you have to acknowledge it. Places like the CDC need to acknowledge it, and then we can actually fix it. So I always think past the fear part, right? I was saying, those videos are really accurate for the flow. Yes, we do not know yet the viral load in those, but you can be sure that some of them most likely contain the virus.
First I heard we were supposed to wear masks because a lot of people have the coronavirus but aren't showing any symptoms and might be spreading germs. Now I keep hearing that is to keep from getting the virus. Is that true?
It's both. But it's more true that you're trying to cut back on the asymptomatic spread, you know people who don't have symptoms. That is the number one reason. But masks filter in both directions, so you benefit too. You're protected and you're potentially protecting others.
They've been doing this in Asian countries for some time, if someone is sick they immediately put on a mask out of respect for those around them. And that's where we need to be if we want to go back to a functioning society. And we have to recognize that places like Taiwan put on masks in February and they have never shut down. And so we complain that we're locked up: well we don't have to be if we will take the precautions that are necessary. And they only ended up with 400 cases.
Are scarves and bandanas safe enough to cover your mouth during shopping or running errands in stores?
They aren't as effective because they don't fit to your face. Aerosols can - if the covering is hanging - they'll just go right around the corner and come out. They will block the droplets though if somebody coughs or sneezes.
I've seen Salinas police use a mask with a flexible fit around the face. Two elastic bands around the head and a small valve in the middle. I'm not sure exactly what this is, but the question says, is this the best type of mask for someone over 65 to use while shopping?
It's not a good mask to use, because that mask will only protect the wearer it doesn't protect against this asymptomatic spread. That valve lets everything from your breath go back out. So all the viruses will be released if you're sick.
A friend sent me a graphic showing the contagion probability of contracting the virus, while wearing a mask, from someone who's positive and also wearing a mask is 1.5%. Is that probability realistic?
I mean, again, it depends. There's just so many unanswered questions with the viral load. So I think that that's a stretch right now until we know a little bit more.
I'm asthmatic and I find it rather uncomfortable to wear a mask for a duration of a few hours and not be able to breathe well. I find condensation builds in the mask, which causes my nose to drip. What's the best type of mask to wear? Also in humid weather, what recommended type of mask could be somewhat bearable and breathable?
I mean, the standard ones that work and work for me and I wear them outside - yeah they'll get a little moist - but it is the medical, the surgical masks. And those are the ones that are most readily available. And I personally find those the most comfortable.
I have N95 masks leftover from the fires and I've been wearing one when I go to Safeway - I think you already know the answer - it has a valve on the front that makes it easier to breathe. Someone told me my mask was not protecting other people from me, is that true?
That is correct.
I read that 60% of Tel Aviv residents own a gas mask to guard against threat of biological attack. Would gas masks not provide 100% safety and also make the six foot rule obsolete?
Gas masks are definitely a better filter. So yeah definitely if you can filter everything out then distance isn't as important. But those are harder to access, I would say. It's gonna be much harder for people and if you've worn one for any period of time, they're not very comfortable,
So many people walking, running and biking on my street in Berkeley. They're not keeping six feet distance. In fact, they seem oblivious. Most don't wear a mask. Same in the hills above Berkeley and Oakland near the Cal campus. What can I say to educate people about mask use?
(laughs)
"Call Dr. Prather, she'll talk to them."
(laughs) Tell them to read our Science article, that seems to have been downloaded, like, 800,000 times now. So it's getting out there. I think I see more people with masks, maybe I'm just hopeful. You know I wonder the same thing when I'm out. I see people and I really do believe they are at this point just oblivious that the reason you should be wearing it is to protect other people. But if you try to tell someone that it can get contentious. I have seen some of those standoffs. So I'm still trying to figure this one out myself.
I see many folks on TV wearing masks covering their mouth, but not their nose. I think both should be covered. Comment, please. Why are we not telling folks how to wear the mask?
That's correct. So the CDC actually has a design for a mask, they actually tell you how to wear the mask. It's really good. But I agree with you. Most of the ones on TV that I've seen talking or people at the store, with their noses hanging out: no, that's not gonna work.
I understand that plans for self-contained classrooms in schools will require teachers to wear a mask at all times but children under the age of 12 are not required to wear them. Will this be a safe protocol for schools?
I mean, I think this gets back to who is the most likely generator of aerosols that could be infectious, and the teacher will be talking more so potentially generating more. And then the teacher will be protected if the kids have it. But yeah, I've been asked that question a lot and I'm still trying to figure out again, like, what's the distance? I had a teacher asking another day would it be better if we taught outside? The answer is yes. Always, going outside is a better answer because it dilutes things down a lot.
And so inside is still going to be an issue unless people start doing things also fix their air handling and things like that. So there's a lot of factors to put into consideration and I'm just starting to see those implemented. And I sure hope schools do it because, yeah, kids can carry this too.
What's the best way to evaluate the quality of face masks being sold online?
That's a good question. I was looking at some of them and a lot of them, I noticed, have the valves. That's why I just go for the standard surgical mask. You can buy a box of 50, they're very inexpensive and we know the filtering efficiency of those and how to wear them. That's what I go with.
The other ones that are homemade, there's been very few studies done on them. So it is a risk.
I'm going to the eye doctor soon. Should I do something to make sure the mask I wear is not only protecting others from me (I've been home since March 9th) but protects me from them since I'll be very close? Also, the equipment used for the check touches or almost touches my eyeball. Are there any special precautions I should take?
Yeah, we haven't talked about that. The other way this virus can get in is through your eyes so people have been asking me about goggles. Eye coverings are important, too.
But back to this question; presumably the eye doctor is making sure that everything is sanitized before it touches your eye. But yes, of course, when you go out anywhere, you should be wearing a mask. In this case it sounds like more to protect yourself.
Are the plastic face shields just as effective as a cloth face covering?
If the cloth face covering is not tight, not fitting your face, they are similar. Just think about those airflow lines. If you have a face shield the problem with those is that they're made to block big drops whereas aerosols just bend right around and go out the gaps. Same thing with loose fitting cloth face coverings.
I use two bandanas folded over, giving me four layers of cotton over my nose and mouth and they don't move at all when I blow on them. Is that enough protection?
That's troubling because the four layer part is promising, but what you want to see - and this is how my mask works - you actually want to see it blowout, expand when you blow and then come back against your face. Because that means the air is definitely passing through the material, which is where your filter is. And so if it's not moving, then it means it's going through some other gap.
How long is too long to be in a crowded room, even if I have a mask on? Could I safely stay twice as long or maybe longer with a higher grade mask. Any way of assessing this?
This is all being looked at right now. It really depends on that room and how well ventilated that room is. The risk definitely gets a lot higher when you go inside and as I say, it just takes one infected person. We've seen this with nursing homes, meatpacking, choirs. We've seen all these cluster episodes. That's because they've been inside and one person probably was infected, right? And so it's always risky being inside.
But if the air is filtered, if the windows are open, just get fresh air flowing through that will reduce the risk quite a lot and allow you to stay longer. This question is very astute in that it's not just what you're exposed to but for how long you're exposed to it. And being inside for one hour, the risk is actually pretty high if that room is not well ventilated.
Can I ask a side question: HEPA air filters, what do you think of those?
I think the stand alone ones for the aerosols, I think that is the way to go. That's what they did with the original SARS virus. So the virus, it was very much like this in 2003, it was airborne. So that's why it's shocking to me that we're not saying this one is, right? And in that case, they used these stand alone air filters - I have one - and those will take out this virus, no problem, in your house.
I'm looking at the one behind me and I'm smiling. Thank you, boss. OK, last question for you. How good are disposable KN95 masks in protecting against COVID-19? How long can you use them and can they be reused?
Yeah you can reuse them and there's all kinds of things on the web more anecdotally I would say, than anybody has really studied this. I've been re-wearing, N95 masks last quite a while, they're pretty robust. But eventually you can just see they start to break down. It depends on how often you wear it and everything else. That's a tough one to give one answer to, but they definitely are reusable. And FYI I take my mask when I'm done, I stick it in the windshield of my car with the outside up and it bakes. That's what I do. Bake those viruses, they don't like heat at all. Some people do microwaving, there's all kinds of things. Spray it with ethanol and let it dry out, there's all kinds of information about this on the web. Again, kind of anecdotal, no solid science on this yet unfortunately.
