ASHRAE Journal:
ASHRAE Journal presents.
ASHRAE Journal:
ASHRAE's vision is a healthy and sustainable built environment for all. The healthy part of that vision primarily has to do with providing appropriate indoor air quality. For the first century of ASHRAE's existence that meant determining and providing minimum ventilation rates. Over the last few decades however, research both within ASHRAE and in the health community has shown us that the ventilation-only approach cannot always achieve the vision because of the diversity of sources and the potential contributions of other removal mechanisms. On the other hand, consideration of sources and their impacts can lead to improvements in both health and sustainability.
Max Sherman's 2024 technical feature from the ASHRAE Journal, IAQ Paradigms—The Next Generation, covers the evolution from the first paradigm, ventilation rate, to the emerging harm paradigm, which has recently been enabled by important research.
Drew Champlin:
Welcome to this ASHRAE Journal Podcast episode. My name is Drew Champlin. I am the ASHRAE Journal editor. And on today's episode, we will speak with Max Sherman, a Fellow ASHRAE, life member ASHRAE, about his July 2024 ASHRAE Journal article titled IAQ Paradigms—The Next Generation. This paper was awarded ASHRAE Journal Paper of the Year at the 2025 Annual ASHRAE Conference in Phoenix, Arizona. This award is voted on by the Publications Committee at each winter conference and awarded at the annual conference.
So Max, before we get into discussion of the article, why don't you share some biographical information about yourself, anything you want listeners to know?
Max Sherman:
Sure. Drew, happy to be here. I got my Ph.D. in physics in 1980 in Berkeley, and it was on air infiltration in buildings. So I've been studying air a long time. Originally it was about looking at the energy impacts, but after a decade of doing that, I realized that soon we were getting to the point where we weren't going to get enough air from air infiltration to provide indoor air quality, and that was going to be a problem. So the big question becomes, well, what is enough air? And that's when I started doing my research on ventilation and indoor air quality.
Drew Champlin:
Max, what inspired you to write this article?
Max Sherman:
Well, doing all that work, I had watched the changes in ASHRAE, the changes in society, the changes in what we were doing with ventilation and indoor air quality, and I realized that right now we're sort of at a cusp of a new paradigm change of why we ventilate, what we think about indoor air quality. And I thought it was time to give it some context, to go back in time and look at how we got here and what was soon going to be the way that things were going to work. That's why I have a lot of history in the article.
Drew Champlin:
You write, "How we address IAQ, however, has changed over time as both technology and our understanding of the science of IAQ has evolved." When we say IAQ, everybody knows hopefully that's indoor air quality, but accordingly, the paradigms that we use have evolved. We are likely in the midst of another paradigm shift.
Before we get to the paradigm shift we may likely be in, do you want to give a history lesson, some background on IAQ?
Max Sherman:
Sure. Happy to. Let's start way back. When the first humans were around two and a half million years ago, they did the quintessential human thing of learning how to use fire. Well, when we moved from the savanna to be inside caves and things, the fire was a pollutant. It was an indoor air quality problem. People learned it the hard way, coughing and choking and all of that. So they had to learn how to ventilate for a fire, which was always with humanity.
Interestingly enough, that had actually been solved five million years before the first human walked this Earth by another resident of the savanna, the mound-building termites. If you've ever seen these termite mounds, they are impressive, going from six feet to 30 feet in height. And you might think that that's where the termites live, but they don't. The termites live in nests underground. All the termite mound is is a giant natural ventilation system. It's there to keep the nest at the right temperature, at the right humidity, and with the right air quality.
We didn't have time for evolution to make us do those things like the termites so we had to figure things out by ourselves. And ancient peoples figured out how to use natural forces to ventilate their homes. The Minoan palaces of three and 4,000 years ago were just like termite mounds, except they were constructed by humans rather than spit and dirt by termites. So that was really an important thing.
And early health concerns of the same time with ancient peoples were really quite an interesting thing. The archeologists have found lots of papyruses from the Egyptian period. Most of them are pretty boring, about bills of lading and delivering grain to this person or that person. But one of them I found very interesting was that one of the overseers had noted that his key slaves, that was the stonemasons that were building the pyramids, tended to die young when they worked indoors. And so he had all of his people move outdoors or under lean-tos so that they got ventilation. Presumably this was the dust from the stonework that was causing the problems. They didn't know that, but they did know that in fact people were dying early and ventilation was helping.
That's one of the first health concerns that we can find in the record. Not surprisingly, that same health concern was what happened during the Industrial Revolution. At the turn of the 20th century, when factories were putting people to work, some of the industrialists figured out that when they ventilated those factories, they had fewer sick time with their workers, they got more productivity out of it. And that in fact was the start of the ventilation industry as we know it now. AHSRAE and CIBSE, it's our UK counterpart, all started at the end of the 19th century.
But the science of ventilation actually began earlier in the 19th century. There was a famous Scottish physician named David Boswell Reid, who was known as Reid the Ventilator because he wrote this tome in the 1830s all about ventilation, all about the hazards of ventilation and how to do it. In fact, a guy named Thomas Tredgold was the first to use that science to figure out how to ventilate something. And the very first ventilation rate was for Parliament, the English Parliament, and he determined that four CFM per person was the right amount of ventilation to control odors in Parliament. Probably the reason why Parliament stinks is not just the odors from people, but what they do but that's a separate issue altogether.
So that was the very first paradigm, an odor paradigm. But soon thereafter, people were beginning to understand that ventilation affected health. So during the Crimean War, Florence Nightingale, in fact, determined that people were less infected if the ventilation rate were higher. So all through the end of the 19th century, people like Florence Nightingale, Max Von Pettenkofer and a bunch of others were causing the rates to go up. By the time the ASHRAE was formed, the conventional rate was 30 CFM, and that was there for health reasons, to protect your health against other things.
But by the middle of the 20th century, the general feeling was that sanitation and hospitalization and medical care was good enough that you didn't need that. And the paradigm shifted back to odors. So in the middle of the 20th century, the general guidance was 10 CFM per person, a bit higher than the Tredgold number, but still based on what was felt to be acceptable ventilation from odors and other comfort issues. And that really was the way things went. ASHRAE, in 1973, had its first standard, Standard 62, that used that 10 CFM per person number as its basis. And that's the way it went until we got closer to the end of the 20th century.
Drew Champlin:
Max, can you discuss ASHRAE and ventilation standards around the start of the 21st century?
Max Sherman:
Sure. Well, so what happened was that ASHRAE lost its way in the last two decades of the 20th century, began not knowing why it was ventilating. There were a lot of pressures in the '80s and '90s. One pressure was the fact that we wanted to lower ventilation rates for energy purposes. There was an energy crisis going on and ventilation was costing a lot of energy. But at the same time, there was an understanding that there were contaminants of concern in the indoor air that you wanted to ventilate.
And Standard 62 has had since the '80s an indoor air quality procedure that was trying to address that issue, but never did so very successfully. There were other pressures, however, from the industries, like tobacco and formaldehyde, that were likely to be regulated if you looked at contaminants that kept ASHRAE from doing very much, as well as an old guard of people who thought that we should only be ventilating for comfort and not look at health issues.
So this was a period that Andy Persily called “ventilation for no particular reason.” It was very confusing what we should do. And it stayed that way until the board of directors decided to weigh in. And they did a report led by Lynn Bellinger, who was a member of the board then and would become eventually a president of the Society, who basically said that ASHRAE has always been involved with health and will always be in health, and that health was a really fundamental part of why we ventilate and why we have ASHRAE standards.
And that led to a change in definitions in the 62 standards and a change of view, which made health a key part. The purpose of 62—62 standards—is to provide acceptable indoor air quality. And our definition of acceptable indoor air quality has two parts. One of those is comfort, that is odor, and the other is health. And those twin poles have been with us since that time, and that's what both 62.1 and 62.2 base what they do on. But up until recently, the IAQ procedure has still not really been a big part of what we do, but now I think it may be going forward, a big part of what we do.
So Standard 62.1 is based on what we call a hazards philosophy. It's what we're all used to seeing, that there are a list of contaminant limits generated by cognizant authorities, governments or other people, who say, "Thou shalt not have more than a level of a certain contaminant," whether that be formaldehyde, particulates, ozone. These are issued by various groups. And what the IAQ procedure in 62.1 attempts to do is say, "okay, if you meet all of these things and have some minimum amount of ventilation, then you're okay.
That's sort of a hazards approach, but it really doesn't make a lot of sense when you stop and think about it because each of those limits were generated in a political environment based on a trade-off between how strong the health people were, how strong the industry was, what was the cost of providing those and all in an absence of considering the other things. Now that works fine in, let's say, an industrial environment where you're only being exposed to a thing for one hour a day or eight hours a day and you're not exposed to anything else, but any typical indoor environment, we're exposed to a lot of things. And so what we want to know is what is the harm that we get by doing that? That's the difference in philosophy, and that's the paradigm shift of moving from a hazards-based area to a harm-based area.
Drew Champlin:
Yeah. I wonder, Max, if you want to talk a little bit more about that, especially as you get into what kind of research has been done since 2000 in IAQ and ventilation.
Max Sherman:
Right. There's been a lot of research since the turn of the century looking at harm. We didn't have the information at the turn of the century. We couldn't do some of the things we could do now. There was a metric for harm called DALYs, Disability Adjusted Life Years. This is not something that was invented in ASHRAE, this was invented by two groups of people. One were lawyers who were trying to quantify the harm for, let's say, when you get in a car accident or when you have your leg shot off or something else, so that various lawsuits could proceed in determining what harm had been done to people and what the fair thing to do was.
The second group of people who used DALYs is the public health people. The regulators, the policymakers, who want to be able to do cost-benefit analyses of saying, well, a particular thing, like an emissions requirement on your car, will change what you're exposed to. How much is that worth to you and your health versus how much it costs? Also, it's used by people who care about the global burden of disease. That is, if you look at how much a particular disease, could be yellow fever or anything else, is affecting people in the world. You use DALYs to quantify it. This is something that's been around for over 30 years, but it's only recently that we've applied it to the indoor environment.
Drew Champlin:
Well, Max, how can the DALY approach be used as you get into Standard 62.2?
Max Sherman:
62.2 never had an indoor air quality approach like 62.1, but it does now. It was just approved by Standards Committee, by the board of directors, and will be in the 2025 version of 62.2. And it's based not on the hazards approach, like 62.1, but on the harm approach.
In order to do the harm approach, we needed to know several things. First of all, we needed to know what the harm intensity of a whole bunch of contaminants were. That is how much does a given amount of a contaminant, like PM2.5, hurt you? And the second is, what are the typical concentrations that we see in buildings, in homes, of those contaminants?
And that research was started when I was working at Lawrence Berkeley Laboratory, and the modern version was finished by the University of Nottingham quite recently, where we looked through the data, we looked at all the research papers to determine these numbers. And the interesting thing comes out that there are only a half a dozen compounds out of the 45 that we studied that matter at all. There are a lot of compounds that are there, you can measure, that have standards, but they have almost no harm involved in them at all.
And 62.2 is based on the three most important ones, which are particles, formaldehyde and nitrogen dioxide. And the standard itself has two basic pieces of it. One is a minimum ventilation rate to control odors, which is about 7.5 CFM per person. And if you have controlled the harm to the level in the standard, you don't have to go above that. But if you haven't, then you have to increase the ventilation rate until you can control the harm. The harm is done with a harm budget, where you basically take a weighted average of those three contaminants, or a weighted sum actually, and see if you've meet it or not.
And the interesting fact is that the most important one by far is particles. Most of the harm we see in the indoor environment is due to particles. Particles come from both indoors and outdoors, but fortunately for us, it's the easiest contaminant to clean. Filters are known, they're easy to use, they're easy to buy. There's a big industry. So that's really a good thing. That will allow us to improve indoor air quality and save energy at the same time.
The story of the English is rather amusing. For over 2,000 years there have been recorded fires of burning down the City of London. That seems to be a popular English pastime, to burn down the City of London. And several of them have had very interesting consequences. In 1631, King Charles II was the first one to pass a ventilation standard or a standard you would recognize as ventilation. And basically he said that all buildings had to have windows, the windows had to be a certain size, and they had to be taller than they were wide. And this was to allow for ventilation.
Well, in 1666, London conveniently burned down in what's known as the Great Fire, and then it all had to be built back up, and it was built back up under the auspices of the great architect, Sir Christopher Wren, and he made sure there were lots of windows. And the indoor air quality improved a lot. People really appreciated it. In fact, they appreciated it so much that the English government decided 100 years later that they should tax windows because everybody was liking them. And of course, a government finds something that you like and they tax it, but that's a different story.
Then in 1834, there was another great fire, perhaps not as great as that one, but it burned down Parliament. And that's, as I mentioned before, when they decided to develop standards, do some science to figure out what the ventilation rate of Parliament should be. And that's what kicked off the whole English history of learning about the science of ventilation. Most recently, as I mentioned, the English have contributed because the University of Nottingham did this fundamental research that gave us all these harm intensities that allowed us to put all this harm stuff together.
Drew Champlin:
All right, Max, to wrap up this podcast, what paradigm shift may we likely be in now? And also, what do you think is next?
Max Sherman:
The current paradigm shift is underway. It certainly hasn't happened completely yet, but it seems to me that we're moving from just talking about comfort and odors and we're moving away from hazards, to talk about harm. And 62.2 has started that. I think other parts of ASHRAE will catch on, and it'll take quite a while to come to fruition with that. And so it's difficult to imagine what the next paradigm shift will be from that, but it's usually only in the rear-view mirror that you can tell when you've had a paradigm shift.
But I do see that there's something important that could be happening within the context of the current paradigm shift, and that is getting back to control of infectious aerosols, like we did under Florence Nightingale. We have Standard 241 now, and that helps us during pandemics or epidemics to control things, but we should also be able to use the harm paradigm for infection control. That is, the medical community actually knows how many DALYs a COVID infection is worth or how much even the regular flu is worth. We are still missing some data in order to apply the same rules that we do to infections, but I see that as something that could happen within the next decade. So that may be the future of this paradigm.
Drew Champlin:
Max, that will wrap up this podcast. If you want to go read Max Sherman's article, please go pick up your July 2024 ASHRAE Journal. It is in that. It's called IAQ Paradigms—The Next Generation Max has been a frequent ASHRAE Journal contributor. He even co-authored a column in the July 2025 ASHRAE Journal, which you should go pick up and read after you listen to this podcast and maybe go back to episode 26 of this. Max and Bill Bahnfleth did a podcast with ASHRAE's Emily Toto on understanding Standard 241. So Max, thanks so much for joining the podcast.
Max Sherman:
You're welcome. Glad to be here. Glad to contribute to the 50th podcast, and maybe I'll come back in another 25 podcasts.
Drew Champlin:
We hope that's the case. If not, before. And that will wrap up this issue. Please search and subscribe for ASHRAE Journal Podcast on any podcast platform. Until next time, thank you so much for listening.
ASHRAE Journal:
On behalf of the ASHRAE Journal team, thank you for listening to the 50th episode of the ASHRAE Journal Podcast.
The ASHRAE Journal Podcast team is editor, Drew Champlin; managing editor, Linda Rathke; producer and assistant editor, Allison Hambrick, assistant editor, Mary Sims; associate editor, Tani Palefski; and technical editor, Rebecca Matyasovski.
Copyright ASHRAE. The views expressed in this podcast are those of individuals only, and not of ASHRAE, its sponsors or advertisers. Please refer to ASHRAE.org/podcast for the full disclaimer.