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 taking a closer look at the issue of air circulation within buildings with Dr. Richard Corsi, Dean of the Maseeh College of Engineering & Computer Science at Portland State University.
Let's start, if you wouldn't mind, giving me a little bit of your background and how you've been tackling this topic. You're not approaching this from the medical point of view, but importantly these days, science and engineering, as we learn how to live with this virus.
Yeah, correct. So I've worked in the indoor air quality field for about three decades, on a whole range of projects related to indoor air quality. And much of my work has been focused on reducing the exposure of building occupants to all sorts of different contaminants inside buildings. So this pandemic certainly has piqued the interest of myself and a large number of people who work in my field. So we're focused really on best strategies for reducing the inhalation of airborne viruses - you know, SARS-CoV-2 - in air, in all sorts of different buildings. And that's what I've been focusing my attention on.
Has this question of reducing viral exposure, been much of a studied thing in the past? I know we've talked about indoor dust or mold or all kinds of contaminants, formaldehyde. But have we focused much on viruses in the past?
No, not that much, especially the airborne route. So much of the focus on viruses in the past has been to reduce exposure by close contact where you're right up against somebody, a couple of feet away and also contaminated surfaces. But the airborne route certainly hasn't received as much attention as it deserves, especially since measles, 60-70 years ago, was a big issue.
And from what we understand, that was one that did have an incredible capability to linger in an indoor space and infect people.
Exactly. Both measles as a virus and tuberculosis as a bacteria and we now know from some great research done over the last 10 years, most influenza viruses are effectively transferred by the airborne route as well.
Okay, well let's get to questions here cause we've got quite a few of them. And these have been sent in by our listeners to email@example.com. Okay first question: I work in a small two-story office building with about a dozen suites. Since I work alone, I've generally felt it is safe for me to be in my office and not necessarily to wear a mask. The AC or heat is controlled by another suite. My concern is about when everyone's back to work and the HVAC system is working full time too. For now, I've kept a window open to let fresh air in, but that won't be possible if it gets too hot or cold outside. How much do I have to worry? What might I suggest to our building management?
That's a great question. It depends on how many other people are in adjacent suites or outside of the office. I would caution with windows, that opening a window can be a plus or a minus. So what you really need to know when you open a window is whether the air is flowing in or out. So what you really want to ventilate is for the air, be flowing in the window. But if the building is positively pressurized, the air will flow from outside of your office, into your office, to leave the window. And so if there are airborne viruses outside of your office, they can come into your office by opening a window. So it's a little bit trickier than most people think.
I think what you can do in most offices is use a portable air cleaner that has a HEPA-based filter with a clean air delivery rate - a CADR - of greater than 250. And most websites that sell respectable portable air cleaners will give you that rating. We're purchasing a large number of those for the building that I'm in at Portland State University for our staff and for our faculty. And certainly when people come back, I do think it's worth thinking about - I do think it's good to wear a mask when you have everybody back at work, even when you're in your office.
These HEPA filters - I have one humming away right behind me here, and I'm very grateful for it - they come in different sizes as you indicated in terms of their volume, but they also sometimes have add-ons, like this one says, plasma wave technology, some have ultraviolet light. Your thoughts on those things?
Those things are not needed if it's a good HEPA filter. If it's a HEPA filter and if it's an effective HEPA filter, it's gonna remove particles for all the sizes do you want to remove, that are the actual carriers or the conveyors of SARS-CoV-2 virus. So those extra add-ons, you know, I don't really want to comment on those other than to say that they're not needed, the HEPA filter does the job.
And in terms of cleaning or replacing filter elements, do they run for quite a long time?
Yeah. So it's a great question. If you're running it while you're at work and you're turning it off when you're not at work, you probably - depending upon how dusty your environment is - need to change the filter out every six months in some cases a year, if you're turning it off and on when you're at work. So it doesn't have to be replaced that often. Sometimes the replacement filters are quite expensive even relative to the device itself. I would caution when you do replace the filter, that it's important to take procedures that don't expose you to viruses that might've recently deposited on the filter. So best thing to do is to wear gloves, wear a mask and get a big garbage bag and carefully take the filter out, put it in a big garbage bag and tie the garbage bag.
I'm part of a study group with my school district. We're trying to determine the appropriate number of air filtration devices for classroom. Are HEPA filters good enough? How many and how should they be positioned?
Another great question. So I'll tell you what we're doing at my university, cause we've been addressing this issue with portable air cleaners in the classroom. So if the classroom is less than about a thousand square feet in size, portable air cleaners can actually work remarkably well at helping to remove aerosols - these tiny droplets or particles in the air that might convey the virus. If it's a big lecture hall it doesn't work so well. So if you have a HEPA-based portable air cleaner that has a CADR greater than about 250 - which stands for 250 cubic feet per minute - if it's that size or higher, especially rated for environmental tobacco smoke, which is probably the thing we should be comparing this against, it can drop the particle levels in the air by about 50% or more in a thousand square foot or less classroom.
How safe is the air in airport terminals? A passenger can spend considerable time in a terminal while passing through security and waiting to board a flight. The windows and terminals do not open, so I wonder how good the ventilation is.
So most airport terminals are pretty well ventilated. They're designed to be because, primarily, we don't want the build-up of odors and those kinds of things in airports. So the main concerns in airports are going to be close contact because you're so close to so many people when you're waiting in an airport terminal and if somebody is infected and they're speaking or they're coughing, they're gonna release these tiny droplets from their respiratory system and if you're close to them, you're going to inhale some of those droplets. So I think it's really good to be wearing a mask when you're at an airport. Avoid close contact, to the extent that you can. There may be some background aerosols in the air - there will be in airports - but I suspect because of the volume and because of how well they're ventilated, that'll be relatively insignificant compared to the close contact exposure route.
If you're in a room where the windows don't open, does it help to use a fan? Does it help to diffuse the virus or just circulate it more or do nothing?
Another good question. I don't think it helps to use a fan. It may actually be counterproductive, it's possible. We don't know this yet, there haven't been enough studies done on SARS-CoV-2 and droplets that deposit on surfaces, but fans can cause what are called shear forces on surfaces that may re-suspend the virus, if it's deposited on the surface. So you have to be a little bit careful about adding too much kinetic energy or mixing in a room with a fan, in that respect. And fans would simply, they're really just going to mix it and cause circulation in the same room. It's better to use a portable air cleaner if you're going to do something like that.
I have a dance studio with 16 foot ceilings. Do the high ceilings provide better air quality indoors?
They can. If there is decent mixing in the room, then you're mixing over a larger volume, which reduces the overall level per unit of volume of air of viruses that are associated with these tiny droplets. So it's really a matter of mixing. Sometimes you can have tall ceilings and not have good mixing and so you still have things that are sort of concentrated closer to the floor.
Is there any way for lay people to determine that? Is there some specialized equipment? How is this generally figured out?
It's not easy for the lay person to do it. The way we do it in research oftentimes is we'll put relatively inexpensive carbon dioxide analyzers at a lot of different points in the room, and then we release carbon dioxide and we'll see how well it mixes into the room. So what we'd like to see for a well mixed - if we wanted a well-mixed room, we don't always want that - but if we wanted that, we'd want to see the carbon dioxide levels at the various points around the room to be roughly the same as one another. In which case we would say it's pretty well mixed from top to bottom and across the room.
I've heard that the spread of COVID-19 could be fast and wide due to air conditioning systems in enclosed spaces. What can be done about that in public transportation systems like Muni and BART trains where you can't get fresh air? I'm an essential worker and I use these trains to get to my work. How can I better protect myself while using public transportation?
Another great question. It's something that we grapple with in Portland as well. So definitely wear a mask when you're on mass transit, absolutely wear a mask. It should be hopefully enforced that everybody should wear a mask, that'll help a lot. The other thing to remember is the time that you spend and when you spend it on public transportation. And I've advocated for this in Portland - to the extent that we can sequence work schedules and not have everybody coming to work at 8:00 AM so we can spread things out so we can have more physical distancing on mass transit. Everybody should wear a mask, that will help a lot. So pick the times when you don't have as many people that you're bumping into, then you're not breathing as much air that's going to potentially have infectious viruses in it. That's the best thing you can do, is really timing and wear a mask on mass transit.
I have an air purifier. Do I have to turn them on 24/7, or only when we're home? And does it help with coronavirus?
I think we've already established the answer to part B is yes. So best practices would be leave it on all the time or leave it on only when you're in the place?
So if there's somebody in the home that's quarantining or who might have been exposed or showing symptoms, that person should probably be in isolation, which means that they should be in a separate location in the home that's under negative pressure. And you can do that by opening a window and sticking a box fan in the window blowing out, outside the home, that'll help to negatively pressurize the space they're in. And in that case, then using a portable air cleaner in the other parts of the home 24/7, if you think somebody has been infected, is a good thing. If you don't think anybody's been infected or come in contact with anybody, then, I don't see an imperative to have it 24/7 in the house. Just turn it on when you're home.
I'm part of a group trying to safely open a large housing facility on a university campus for 30 girls to sleep on bunk beds in a cold air dorm. We have distanced all beds, placed occupants head to foot and got an approval of the local health department. However, we're still concerned about the air circulation. We've mandated all the windows be open, but the occupants object to turning off the window air conditioners during the hot weather.
Oh boy. Okay, this is a tough one and I'm probably going to upset some universities. I don't think the dormitories are going to be very healthy places in the fall. I'm concerned about that. I personally wouldn't want to spend much time in a dormitory and I certainly don't think having multiple people in the room is a good idea. But you know, ventilation is really important, bringing outdoor air in, having effective filtration. There are ratings for filters called MERV ratings and with this coronavirus, we want to replace whatever filters we have with filters that are at least what we call MERV 13 or above. MERV stands for minimum efficiency reporting value. And so improved outdoor air flow, improved ventilation, improved filtration. And I would not have more than one person in a room. Sorry to say that.
I'm supposed to be staying in a home where people who haven't practiced social distancing or mask wearing have recently moved out. Apart from opening all the windows is there anything I should do to feel safe? How long does the virus live in such close spaces without a human host?
Great question. So the aerosols, those viruses that are associated with tiny droplets in the air, those tiny droplets, they're going to stay in the air in a home for anywhere from a few hours to 10 hours, something like that. And so they'll be gone if you just wait 24 hours, certainly they'll be out of the house. The bigger concern is contaminated surfaces, where viruses, depending upon the nature of the surface, whether it's plastic or stainless steel or carpet or whatever, the viruses can linger and persist and not completely deactivate for some time. I think something on the order of 48 to 72 hours, probably 72 hours would be safe to return to the house so that any viruses that are in the house would probably be at least deactivated, and if they were in the air they'll be gone by that point. So if you just wait three or four days, you'll probably be safe, yeah.
What are the best practices for staying safe as a passenger inside a car for an hour long ride, if you don't know for sure whether the driver has been exposed?
So this is a question that comes up a lot, actually. So certainly wear a mask, hopefully have a driver that's wearing a mask, you and the driver wearing a mask will help a lot. And then crack the window open three or four inches or halfway. So opening a window in a traveling car, even a little bit provides a tremendous amount of ventilation and it will dramatically reduce aerosols, these tiny droplets that carry the viruses in the air, in the car.
How is the air regulated on cruise ships? What can be improved? What can you do to improve the air circulation?
This is a tough question for me. I've never been on a cruise ship and I probably never will go on a cruise ship. It's just not my thing. And so I haven't studied cruise ships. I know that cruise ships, oftentimes they're not registered in the United States and they're registered in other countries. I don't know what the regulations are in those other countries. I don't know what the regulations are in the United States. I'm going to have to actually pass on this one, but to say that we know it can happen on a cruise ship now. I appreciate the industry is going to have to deal with that.
Let me turn this one around a little bit though, and ask you with all your years of experience. If I'm going to go and stay at a hotel, I'm going to ask them, what's your protocol and presumably they're going to tell me the truth. How would you determine if there was a safe rate of air exchange or enough mixing of outside air? Are there numerical values you could ask about?
Yeah, you could ask them what type of filters they're using, right? If they know the ratings of their filters. As I said, right now, I think I'd suggest MERV 13 or better. My university actually is moving to replace many of its filters on campus from a lower MERV rating to a MERV 13 rating, which I think is fantastic to help protect our students and our staff and faculty. The other thing is to ask them if they're ventilating according to what's called ASHRAE design. I suspect the people that are working at the hotel that you ask that to may not know, or they won't know, but they would have to talk to their facilities people. So ASHRAE is an organization which provides guidelines for ventilation and filtration, et cetera, in all sorts of buildings and is essentially the gold standard that mechanical engineers design to. And they have new protocols out for the age of the coronavirus. So they have developed new protocols for that. It'd be good if hotels were actually following ASHRAE guidelines at a minimum.
How effective is ionized hydrogen peroxide at purifying air? Is it safe to be used when people or pets are present?
Oh boy. So I've only seen one paper on ionized hydrogen peroxide in the published literature. I suspect that if it's done right - and it sounds like from your question, it's talking about injecting it into the air - if that's the case, then I would be very concerned if people or pets were present, if it's injected into the air. If it was to decontaminate specific surfaces or duct work or that kind of thing it may be effective. I mean, hydrogen peroxide itself can be very effective as a disinfectant. And we know that for all viruses. The ionized part is a little bit of concern because I think that basically means that you're going to be forming what are called hydroxyl radicals and hydroxyl radicals are incredibly chemically reactive, and they will chemically react with all sorts of other things in the building and form chemical byproducts. And some of those chemical byproducts can be anywhere from irritating to potentially toxic. So I have to say, my answer to the question is I don't know, because I don't know the specific situation and there's not much literature on this technology, but there's a little bit of a red flag with respect to the generation of hydroxyl radicals and what might come from those. And no, I would not have anybody present inside the building if large amounts of hydrogen peroxide are injected in the building.
How safe is it for a hairstylist to use a blow dryer in a beauty salon?
Wow, that's a great question I hadn't heard before. So if the person whose hair you're working on has been in an environment where in the last eight hours, something like that, where they might've had close contact with somebody who was infected, who might've coughed and the SARS-CoV-2 virus is in their hair, then blow drying could certainly release that virus back into the air. Now, one thing we don't know yet is what's called a dose response relationship for this virus, right? We don't know if you inhale this amount, this is your probability of getting ill. And so if there's, you know, one or two viruses in somebody's hair and you're blow drying it, the chances are that you're not going to have a very high dose if any dose at all. But if there's a lot of viruses in somebody's hair - you know, let's say that they were at a choir practice earlier that morning and everybody was singing and they were standing in front of somebody who was singing, which releases huge amounts of respiratory droplets. And the person behind you is infected, your hair may be drenched in the coronavirus.
This is the definition of a bad hair day right here.
Yeah that's a definitely a bad hair day. Now, that's a very specific situation and the likelihood of that happening is pretty small, but in theory, it could happen.
I've seen AC filters on the internet that have either copper or silver fiber infused filters. So these work to kill viruses?
Yeah. So certainly we know that viruses tend to deactivate quicker on copper surfaces and there has been some work with this specific virus, SARS-CoV-2 that shows that on copper surfaces, it tends to deactivate quicker than it does on say stainless steel or plastic surfaces. It doesn't mean it's instantaneously deactivated, it still takes some time to deactivate. Without having seen any tests for this specific filter it's hard for me to say whether it's effective or not, but in general viruses, including this virus, do deactivate quicker when they're in contact with copper.
It's been said that COVID-19 is distinctly different from the flu and other respiratory infections. Of all the things that could be known about this virus, but aren't yet, what's the one thing you're most worried about?
Well, I'll give you two things. One is the viral load, you know, when somebody coughs or speaks or sings, we still don't know what the concentration is or the levels of viruses that are coming out of their respiratory system that are attached to and conveyed by these tiny droplets. And I think the one thing we really need to know, what we really need to know is this dose response relationship. So if you inhale this many viruses into your respiratory system, what is the probability that you're going to get COVID-19? If we actually had that, then as an engineer, it would make it much easier for us to design indoor environments to make sure that we didn't get to a dose that gives us a high probability of illness. We don't know that yet and we really need to know that.