Answering Your Questions On Making Indoor Spaces Safer

KCBS Radio is answering your questions about all things coronavirus every weekday at 9:20 am

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 at indoor air quality, air conditioning and your safety related to the current pandemic with Max Sherman, retired Senior Scientist at the Lawrence Berkeley National Laboratory and member of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Epidemic Task Force. 

Before we get going, in doing my background research I came across a paper that you were involved in over 20 years ago. You were the man who found out the duct tape didn't do it's job on heating and ventilation ducts.

Yes, that's right, I'm Dr. Duct Tape.

You know, it's great to know that there are people who have been spending entire careers worrying about the stuff most of us take for granted. You come in the office, and about your only gripe is it's either too hot or too cold in here. But this is an area of serious research because indoor air affects all of us.

Yes it is, it's one of the most significant hazards that we face as a population.

So let's talk a bit about where we stand right now before I start getting to the questions. When everybody got sent home from the office the problem kind of went away, but now people are starting to come back. So you're working with others on this, what's the nature of that work?

Well ASHRAE deals with heating and cooling in air conditioning sorts of things and was very concerned that as people were in their buildings, they could be getting the disease. So the task force was created to try to come up very quickly with a set of recommendations for different kinds of buildings, different aspects, what you could do to lower your risk.

One of the things that I noted right away was an early call to simply say, open the dampers and let the outside area in. Outside air is better?

Outside air is better with regard to COVID because the virus itself doesn't like sunlight. It dies very quickly. So outside air skews virus free and you can dilute indoor air that may contain virus.

I assume not all HVAC systems are created equal - and this could get geeky pretty fast - but what are the standards and what are most of us breathing when we're at work these days? Any way we can know?

Well just being inside, there are a host of things that get into the air, obviously, from ourselves, what we breathe or the euphemistically called "bioeffluents". Then there are the things that different machines might emit, different surfaces might emit. So we need a continual amount of outside air to ventilate all of these various compounds and keep them at a safe level. And there are standards, both in California and by ASHRAE as to how much air you need at a minimum.

And in terms of filtration, most of us don't know much about anything except the temperature in the room. Is this air I'm breathing here in Studio A being filtered or not?

Well, I don't know. Most likely there is a filter in the system, but there are many kinds of filters. What we know is that the small particles, the teeny, teeny ones that you can't see, are actually the thing that makes air the most hazardous from a population standpoint. It's what leads to chronic respiratory diseases and other sorts of things. And HVAC systems will almost always have filters, but filters only filter down to a certain size particle. So it may be a very crude kind of filter that keeps bowling balls, small children and pets from being sucked into the system but doesn't keep the very small particles out. Or it could be a very good filter, which keeps the air very, very clean. An easy test for that was back when we had the wildfires, did it smell inside like wildfire or didn't it? That kind of told you how good your filtration system was.

Okay, that's a good litmus test. And we've heard the phrase "ultraviolet irradiation" rattled around, is that used in building air quality systems?

It is used, but not commonly in all systems. It works by killing bacteria, viruses, fungus. It's sometimes used to help keep the coils clean. It's sometimes used in health care situations to kill viruses. But it's a technology which has been out there for a long time.

Expensive to retrofit systems to bring them up to modern standards, or doable?

It can be reasonably cost effective. It kind of depends on what the whole system looks like, how hard it is to put it in. But it's doable, and a lot of the portable air filters that you can buy off Amazon for your own home have it built into them.

Well let me get to questions that have come in from listeners to our email inbox at First one right here and a lot of people talking about this: how safe is the air in an airplane?

So actually, the air in an airplane is very safe. The systems that are used in aircraft usually have high efficiency filters that take out a lot of stuff from the air. The risk that you face in an airplane isn't from the air system itself. If you're sitting next to somebody who's infected, then the air system can't do very much about that, you know if they sneeze on you or breathe on you such that you get a direct transfer. That's probably the highest risk, which is why the airlines are keeping people spaced out inside the airplane. But the air itself, the air filtration system is pretty good.

What is the recommendation for a self contained classroom? All day with the class of 15 students, what kind of air filters are the best? I think the implication is it would be something portable or that's not already built into the system.

Right, well there's lots of portable air filters that are sold. And they're sold usually with an estimate of the square footage that they cover, so you can kind of judge what you need by the size of the classroom. You still want outside air - outside air doesn't have any virus - and you still need outside air to dilute all the normal stuff. But in terms of COVID, you can buy air filters that do a good job even without the UV stuff in them. A HEPA air filter, which is normally what they are, will take out almost all the particles in the air, which is where most of the virus lives.

Let me ask you parenthetically here, outside air sounds like a great idea. What if the outside air is crummy? And you mentioned wildfires, but some people live in a part of town with a lot of exhaust or dust.

Well, you still want a minimum amount of outside air to dilute the stuff that's generated inside, the emissions. But if the outside air is really bad, you want to keep that at a minimum and use portable filters or built in filters to clean the rest of the air.

For those of us who use filters in our central home ventilation systems, what MERV (Minimum Efficiency Reporting Value) rating is suggested for clearing virus? The higher number the better, but it's also louder, so is there a sweet spot? We use MERV 8 normally and MERV 13 during wildfires.

That's right, MERV 13 would be the recommendation. MERV 8 doesn't take out any of the particles that affect health, it takes out the particles that you can see and that might build up on your system and make your ducts dirty, but doesn't take out the health-bearing ones. MERV 13 is the lowest one which will take out the very tiniest particles, which is what you want. So MERV 13 is a good place to start; higher is better, but older systems may not be able to take the higher MERV filters because of the pressure drop, and if you're getting a lot of sound that's probably due to the high pressure drop.

Are these filters something that needs to be replaced regularly on most of these systems? Can they be cleaned and reused?

Generally speaking, the typical filter you buy has to be thrown away after a certain length of time. The length of time depends on how dirty the air is and how thick the filter is. If you're putting in a new place to put a filter, you want it as thick as possible - like four inches thick. Sometimes they're only one or two inches thick, which means you're going to have to change the filters more often.

Can an office still open if they tell employees to wear masks but they don't make changes to an old ventilation system? The air recirculates in my job, but there are no windows available.  Are there requirements all offices need to meet before they open? I only see recommendations on OSHA and CDC guidelines.

Well it's a bit early to develop hard and fast requirements. We're all shooting from the hip here and trying to do the best we can. If you look on the ASHRAE website, which would be, there's a whole set of recommendations for what you can do in all sorts of building types, from your home to your office to hospitals and a lot of questions are answered there. The answer often depends on the specifics so it's hard to give a general one, but there's a lot of recommendations there for what you can do.

How safe is the air in a supermarket or grocery store where it's not always possible to maintain a distance of six feet from other shoppers as they pass in narrow aisles?

Well, it's the same sort of thing. All buildings have heating and cooling ventilation systems, so it depends on what level of filtration they've put in. When you're in a supermarket, you should be wearing your mask and you should maintain a distance as much as possible. And we all hope that the supermarkets have done their due diligence at having filters that take some of stuff out of the air.

My office is in a building with several individual office suites, each one walled off but with a common HVAC system. Should I be worried about virus particles being carried from one office to another by the ducts?

Well there can be some of that, but hopefully they put in filters in place so that before the air leaves one space and gets to you, it's passed through one set of filters. If you're worried about it, you could buy one of these portable air filters to keep in your office. I know I have a lot of friends who have done that themselves.

I'm a hair stylist/barber and work in a building on Market Street downtown. Most of the building is offices, however our floor is a group of hair salon studios. 26 mostly single spaces with one chair and one shampoo bowl, each about 100 square feet. Some have windows, some do not. The landlord is having the HVAC deep cleaned and serviced as well as increasing the mix of fresh outside air circulating in the studios and upgrading to MERV type filters.

I already have an Austin HealthMate Plus air purifier in my own suite and I'm considering an air purifier with bipolar ionization as well. Let's get to these questions one after another. Do you think bipolar ionization is effective in killing the virus?

Well, the bipolar ionization is one of those things that we really don't know enough. ASHRAE recommends making sure that the systems don't emit ozone, and some types of ionizing systems can emit ozone. But there are standards that show low or no ozone production for various equipment and so we recommend that you only buy equipment that has met those standards. The issue with ionizers where the ions leave the equipment itself and go into the space is one that hasn't been thoroughly investigated as to whether they will actually reduce COVID exposure or not. Things like UV, which kill the virus when it's inside the equipment are much better understood. So the ionizers are a bit on the "we don't know" side right now.

The next question: is the air flow from the air purifiers dangerous in terms of spreading the virus? This is from the same questioner.

Well generally not, because it's gone through a filter - and especially if it's gone through some UV - the air that's coming out of the filter has no virus in it. It's like outdoor air. So that's the safe air, it's not spreading.

Okay, and the final question from the same person was, do you have any suggestions for maximizing ventilation and healthy air in my situation? This sounds like kind of a warren of these little 10x10 rooms, some of which have windows and some of which don't.

Well it's tough to know without knowing the details. And just maximizing outdoor air isn't always the best anyway, because there are energy and humidity consequences of doing that. So once you have the minimum amount of outdoor air, you want to minimize your exposure to the virus and either more outdoor air or a filter can do that.

Is there something like a Good Housekeeping seal (I'm probably giving away my age with that) for those HEPA air cleaners? How do I know they're really working? And also, how do you decide how big a unit you need?

Well, many of them are rated for what's called CADR, which is a "clearing air delivery rate". And so that tells you how much air they produce, and along with that rating is a recommendation for how many square feet they're intended to cover. More is always better, but that gives you an idea of size.

In terms of the UV or ozone emission for the ones that have ultraviolet or ions in them, the state of California and the California Air Resources Board has a list of recommended and not recommended units on its website. And you can find out if your unit is on the recommended or on the not recommended lists. And then there are a bunch of newer ones which take a while to be rated, which won't be listed at all.

How much better are ionizing air filters than a paper type filter?

Well ionizers - the ones that emit ions into the air - they precipitate particles onto the surfaces all around you, so they don't collect it, except it all lands on the walls, ceiling, floor and furniture. If you have an ionizer where the ions are kept inside, then it winds up on a surface in there. Generally speaking, paper filters are good because the bad stuff is collecting on them and then you throw them out after a while and get new ones.

I'm a teacher (high school math) and I'm wondering if there are some solid, reliable guidelines that could be used to decide how many students could be allowed in a classroom, how far apart, et cetera?

Well that's an ever increasing part of research and that has not to do with the direct air itself as much as person to person contact from coughing, sneezing, touching. And those guidelines are continuing to come out, the CDC is working on those all the time. I don't know what the most current ones are for schools.

Can you ask your guest if he knows whether the coronavirus can survive in air conditioning ducts? Haven't we had problems in the past with diseases living in air ducts?

We have, and those were mostly diseases where the stuff actually grew in the air conditioning equipment itself like Legionella. This virus is actually a bit on the fragile side. We think, probably, not only doesn't it grow in HCAV systems but it will probably die after a while. What we don't know is whether "a while" is a few hours or a few days. We know outdoors it only lasts a few minutes in sunlight. So it's unlikely that the HVAC system is going to become a source like it is for some molds or Legionella, and the filters themselves are actually going to help us a lot by taking the stuff out of the air.

Okay and just a final take away then, the best practice would be: outside air, longer run times on HVAC systems, good filtration, all of that?

All of that, and which balance of that you can do is up to the individual circumstances.