As the virus was better understood, as people got vaccinated, and as new restaurants opened and others reopened, owners — and the public — returned with a better understanding of the importance of IAQ in reducing the spread of airborne germs. Tapped by the White House, ASHRAE put together a committee of experts from many fields to develop IAQ standards that would reduce the spread of airborne illnesses.

Meghan McNulty worked on that project, which resulted in the publication of Standard 241, Control of Infectious Aerosols. A mechanical engineer who consults on energy efficiency and IAQ projects in existing non-residential buildings, McNulty is also an ASHRAE volunteer who chairs its technical committee on ventilation and who had contributed to its Standard 62.1 for IAQ in commercial buildings.

The ACHR NEWS recently sat down with McNulty to discuss ASHRAE IAQ standards, especially as they apply to restaurants. The conversation has been edited for clarity and length.

ACHR NEWS: The standard on the control of infectious aerosols was just developed this year, correct?

McNulty: That was really done just in the first half of this year.

ASHRAE had been in touch with the White House COVID Response Team, and ASHRAE was asked to quickly develop a national pathogen IAQ mitigation standard. There was a really interdisciplinary group, people with backgrounds in infection control, and epidemiology, and public health, health care, facility management, engineering, and indoor air quality — all those things — to write a brand-new standard. It took, like, four and a half months from start to publication, which is lightning speed. There was a lot of missed sleep during that period.

But it is so critically important to take everything that we’ve been learning over the past three and a half years about airborne transmission — about the engineering controls that are effective, the strategies, modeling — taking everything we’ve learned and distilling it down to what is the minimum that needs to be done in a building to substantially reduce risk.

The best thing about it is that it gives you a target. We’ve had all this guidance: Ventilation is good, filtration is good. But how much? Do I need to keep adding more?

Standard 241 answers three critical questions. The first is: How much clean air do I need? What are the mitigations that are appropriate for this space, based on the number of people that are there and the type of activity they’re doing?

The second thing the standard does is create a standardized way to account for clean air. There are a lot of strategies and technologies that were hard to quantify; there weren’t uniform effectiveness standards or safety standards for different technologies. So what this 241 does is pull together the existing standards that it can reference for different technologies. It also has a technology-agnostic test method for effectiveness and safety, which is huge, because we haven’t had that, and there had been a lot of uncertainty.

So we now have a target for clean air. We know how to account for how much clean air all of these strategies provide.

The third thing is: Now, how do I do this in the real world? And there is an assessment process. There’s an implementation process. There are tools for users to calculate numbers, do the heavy lifting of the math so that you can focus on making this work. And it’s all in one set of pages instead of being kind of all over the scientific literature.

ACHR NEWS: With restaurants, you have different kinds of activity. People are eating and drinking, they’re talking. There are cooking exhausts, cooking smells. That would be very different than a retail boutique that people just drop into every once in a while.

McNulty: The framework for all of these is the same, but the amount of clean air that is required in 62.1, the amount of outdoor air, ventilation air — that varies with two conditions. One is the activities of the space. Are there extra smells, like cooking? Are people more active? So as people are more active, as there are more odors, possible pollution sources associated with the activity, then those requirements are higher. So a restaurant does require more outdoor air at baseline than an office.

And then, in 241, we’re really only worried about infection control, controlling infectious aerosols. So that scales solely with how many people, how dense it is, how active those people are. It’s based on people’s activity. So a restaurant does require a lot more equivalent clean air than, again, an office. But the framework, the strategies, those are all the same.

ACHR NEWS: When you say “framework,” you’re talking about the way of getting that clean air into the facility?

McNulty: These standards, they set requirements for how these systems should be designed, how they should be maintained, if there are any special components that they need. But how the system looks is really up to the designer. There’s a whole world of things that you can design, and you can get really creative. As long as you hit these requirements, you can design it however you want. It’s very flexible in some ways.

ASHRAE is focused on education and awareness. By educating their members, making sure that members are aware of all the best practices and state-of-the-art research, that can kind of disseminate knowledge through the industry, and hopefully, all the good indoor air quality practices get everywhere.

ACHR NEWS: This restaurant that I own, hypothetically. I’m trying to improve the IAQ on a budget. What are the things that you would most recommend, the most important things I should get for that restaurant?

McNulty: Before I get to HVAC, I’m just going to throw out a non-engineering option: Can we get some outdoor seating? Can we move some things outside that maybe allow you to de-densify inside, or just provide more service to more people and to people who would prefer a lower-risk dining experience than being indoors?

It’s not going to universally work in every scenario. There are tons of constraints: weather and winter, summer, wildfire smoke. Maybe you don’t have rights to use the land around you. But if this is an option, people love a patio. I love a patio.

ACHR NEWS: But I’m in Detroit, and that window is closing fast right now.

McNulty: (Laughs.) So let’s talk about the building.

ASHRAE puts out position documents, and that would be the official statement of, “Here’s what ASHRAE believes.” This is what it says: “Engineering controls demonstrated to reduce the risk of exposure to infectious aerosols include dilution with outdoor air provided by mechanical or natural ventilation, filtration of indoor air, indoor air-flow patterns, and disinfection by germicidal ultraviolet light and other technologies proven to be effective and safe.” So we have a menu of options.

We now have Standard 241. We can point to a test method, say, “Pass this to prove that you’re safe. Do these things to quantify your effectiveness.” Those are all the things that we can we can work with.

And so my recommendation for this restaurant is, I would spend money on maintenance. I would get someone to come and check the unit. Is it working? Does it work when people are there? Does it get outdoor air — it should — and how much is it getting? Am I just meeting the minimum standard? Is there a filter? Is the filter in good condition? There are quarterly and semiannual maintenance requirements.

You can have the greatest system in the world, but if it’s off, then you get no clean air. So I would say, spend some money on maintenance. Every five years, you’re supposed to have the outdoor air measured and all those components calibrated to make sure that you’re getting the right amount.

Filtration can be budget friendly; you might be able to upgrade the filter in your central system. You can put in room filtration to get a dedicated filtration system. There’s from DIY up to installed systems, central systems, that get better filtration.

MERV 11 and above, those filters are rated to capture the small particles that are particularly bad for health, particles of all kinds. And that also overlaps with the size of respiratory aerosols that could contain a pathogen. Good all around, not just for infectious disease, but wildfires and pollution from cars and pollution from all sorts of sources.

Nothing anywhere is 100%. But a small percent of a big thing is really effective.

ACHR NEWS: I have an unlimited budget now, for some reason. What should I invest in?

McNulty: All the same things. Maintenance. You could invest in better maintenance. You can invest in better filters. But I think what matters is having a target, because there are going to be diminishing returns.

We don’t necessarily need to do all the things or want to do all the things. You may have infinite financial resources, but we have limits to physical space in the restaurant. You might be unlimited upfront in your costs, but what are the costs over time? The numbers, the targets in Standard 241, those are based on a risk assessment that is balancing kind of all of these things.

If I had unlimited money, I would ask an engineer to figure out, How do I make my restaurant compliant with Standard 241? Figure out my target and look at all of the engineering controls and figure out what makes the most sense in my restaurant. As long as you have at least the minimum outdoor air, the rest of that target is whatever works best for your space, from that menu of things mentioned earlier.

ACHR NEWS: Thank you very much. Is there anything you would like to add?

McNulty: On the maintenance thing, don’t be surprised if things aren’t working, because things break all the time. We very frequently find that things are not working as we had assumed they were. And if you do nothing else, figure out, Is it on? Is it providing some amount of outdoor air? Is it on while we’re there? Just get those basic requirements, because we find that so many buildings do not meet those without a focus on maintaining those minimums.