#7.2 - Henry Burridge: The Impacts of Indoor Air Quality on Health, Performance, and Mental Wellbeing

Part 2
Henry Burridge - Is a Senior Lecturer in the Fluid Mechanics section in the Department of Civil and Environmental Engineering at Imperial College London.

Henry has a background in Mechanical Engineering and a PhD in Civil and Environmental Engineering from Imperial College London.

Following his PhD, Henry has worked as a Post Doctoral Researcher at the University of Cambridge, initially in the Engineering Department and then in the Department of Applied Mathematics and Theoretical Physics.

Henry's research focuses on fluid mechanics for the built environment. And includes the practical application of this understanding to the human- and climate change-focused ventilation of buildings, amongst much more.

He  is a Co-Investigator for the Tackling Air Pollution At Schools (TAPAS) network and the Future Urban Ventilation Network (FUVN): The Breathing City

Henry primarily applies his expertise to indoor air quality and ventilation, presenting evidence to the Common Select Committee for Health and Social Care and contributing to the Technical Advisory Panel on Ventilation for the Government's Cabinet Office, and being an author for the 'Indoor Air Quality and Health' chapter within the Chief Medical Officer’s annual report 2022: air pollution.

A focus area for him is schools, and Henry currently leads the initiative towards School Air Quality Monitoring for Health and Education via the SAMHE project, seeking to establish large-scale monitoring in UK schools and engage pupils with their school environment.

He is a Co-Investigator on  CO-TRACE, investigating COVID-19 transmission in schools. And joint Principal-Investigator of the Department for Education's pilot project investigating the 'Changes In the Ventilation Of Schools when monitoring CO2.

Needless to say much of our discussion in the podcast was about schools, the challenges that particular sector faces, the impact of air quality on children and teachers and how projects like SAMHE are engaging kids in the science of air quality. We discussed much more of course including the value of observatories for indoor air quality.

Henry Burridge - https://www.imperial.ac.uk/people/h.burridge
SAMHE - https://samhe.org.uk/
FUVN - https://breathingc

Chapters

• 0:01 Indoor Air Quality and Particulate Matter
• 10:20 Air Quality's Impact on Health and Learning
• 22:47 Understanding Fluid Dynamics and Air Quality
• 32:46 Importance of Air Quality Observatories

Transcript

Simon: 0:01

Welcome back to Air Quality Matters and part two of my conversation with Henry Burridge. Out of interest, what are the monitors that you're using in SAMI recording what are the indoor air quality parameters that are being recorded?

Henry: 0:30

So, indoor air quality, we record carbon dioxide levels, pm levels, particulate matter levels and then T-VOC total volatile organic compounds, and then, in terms of sort of environmental factors, we also record temperature and humidity.

Simon: 0:49

We haven't really talked about particulate matter. That increasingly is going up the scale of interest in all sorts of environments. Are you seeing some interesting data from a particulate matter perspective in classrooms?

Henry: 1:06

I think the answer is yes. Scientifically we're at the early stages of data gathering really, but we're already able to see interesting things. For example, we've just written a short sort of technical report to provide some information to schools based on what we're able to see, because they obviously see the data from their one monitor. They don't get to see the data from all the other monitors, but because we've got this big network of monitors out there. There was a Saharan dust event which originated from the Sahara, happened in early September more or less, as UK schools English schools were going back of course the Scots go back a lot earlier and what we were able to do is get outdoor air quality data and look for the spikes in PM levels outside and then look at those indoors and there was an amazing correlation. We could actually analyze the data in a way that we could see that the indoor and outdoor air were best correlated when you put in an offset of about three hours. So what was happening outdoors seems like the levels took a few hours to see those peaks indoors.

Henry: 2:41

But these are the sorts of things you can do with particulate matter. What's the reason that people are so interested in particulate matter, so ambient PM, outdoor PM that is, has probably the best established links to health effects of any air quality metric. The trouble is, you know, I always say this to my student why are we measuring? You know, let's say, why is Sammy measuring those three things? It's one because they're interesting metrics. It's two because we can. We have sensors that are relatively affordable that can measure particulates with a suitable accuracy. And so we know that not all PM is the same. You know, trees and other vegetations give off a lot of particulate matter.

Henry: 3:42

Is that the same as, as you know, the brake dust that's that's being generated as people drive their cars around cities. Is it the same as the emissions from you know, combustion, either in cars or or you know our cookers, even the health effects? It's nonsensical to suggest that they're all identical. So far, the best data that we have cannot distinguish between the effects of different types of PM and identify that difference. So where we are at the moment is is we're sort of enslaved in some sense to to having to think, as all PM is being the same, and and that may be in part because we focused on outdoors I'd love to see studies that investigated the, the, the health effects of indoor PMs, separate to outdoors. Somehow. I don't know how we're going to do this scientifically, but you know, is a PM concentration of, you know, 10 micrograms per cubic meter indoors, does it have the same?

Henry: 5:10

level of implication is 10 micrograms per cubic meter outdoors. We don't know the answer to that.

Simon: 5:21

That's a really good point. Arguably, we could say that about so many pollutants. You know TVOCs, for example, are measuring the total amount of chemicals we see in the space. If that same TVOC sensor was outside, it could have exactly the same number but be measuring totally different organic chemicals. So compounds it's one of these things, isn't it? Is that there's so much more to learn. We know these things are impactful on our health. I think that at this stage, is fairly unquestionable. The key is understanding why and breaking that apart. I think you said something to me the last time we spoke which I took away with me, which was describing PMs is a bit like describing animals as a PM being a canine, where in fact a PM is really all mammals. So we've kind of got to start breaking apart this description of some of these pollutants into more meaningful ways, particularly if the control mechanisms for it, beyond the engineering controls that we can apply, are based on source control. We need to start understanding where the sources of these PMs are coming from, don't we?

Henry: 6:49

We absolutely do. Yeah, and that's a lovely quote that I'm going to forget the reference of now, that about PMs being like all mammals rather than a single species. It's just obviously true and it's almost where it's really. If you start looking at TVOCs, the sensors work in a subtly different way, so they are more or less sensitive to different species of a VOC, so even the total number is almost certainly always wrong.

Henry: 7:24

So, yeah, there's a lot of work to be done, but I think your point about the importance of it being highlighted by the right solution, which is source control, is a really good one and it's a really strong motivation, I think, to do these sorts of investigations to evidence what within the PM and what, if anything, within the TVOCs we're measuring is really harming our health. You know, for example, lots of people have these diffusers that give off scented mists. They give off a lot of VOCs. If there's negative health consequences associated with exposures to those chemicals, to what extent are they offset by the mental, the positive impact, if that's having any positive impact on someone's mental well-being, if it's making someone feel less stressed, we know that has positive health effects. So it is a very complicated subject.

Simon: 8:48

I guess, talking about those types of products, I guess there's a crossover between when something's a VOC and when something's a particulate. I mean, these products aerosolize something and at some point they're a particulate but they're also a VOC at the same time. Often you've got chemicals bound with, particles bound with. You know it's a heady mix when you get down to the nitty-gritty, yes, and the chemistry, the physics is complicated and then it's utterly heterogeneous.

Henry: 9:30

What you choose to do in your home, your office, your school if you had one is going to be completely different to what I do in mine. This is where it's, this wonderful melting pot of human behavior having sometimes unintended consequences. I think it gets most serious when One person is making a choice that's actually affecting others, like we would not accept someone smoking in the same room as us. You know, when I was a kid, everyone was smoking in the pub. That's just. We're never going back there, but you know we do. You know vaping is increasingly common. Lots of other things we choose to do affects the air that other people are breathing, and I think we have to sort of accept that and and see good air quality behaviors as being part of being a good citizen, really, because we're when we look after the air around us, we're we're helping other people.

Simon: 10:43

And I think it's Joseph Allen, says the guy from Harvard, your building manager probably has more of an impact on your health than your GP does over your lifetime, which is Kind of strange thing to say, but when you actually break it apart, it's probably not Untrue. The people that manage the spaces that you occupy through your lifetime We'll probably have more of an impact on your health than the fella in the local GP surgery. I think it's quite a bizarre thing to think about. Something else I wanted to mention was we didn't really get on, but when it comes to classrooms, on why this is important for kids, that there there is at this stage some pretty good evidence that the quality of the air that our kids are exposed to impacts their learning and health outcomes isn't there.

Henry: 11:37

Yeah, so for health outcomes, there's definitely evidence that the impacts of poor air quality are more significant on on children than they are on on on adults, for example, and that's because you know they are in a developmental stage and that makes them inherently more vulnerable. And I think, I Think that's, within some forms, that's the right message to motivate things you know, motivate positive changes, through this health message. I think, as you say, education is in some forms, you know, a more appropriate mechanism because Health effects, they're often Only realized after long periods and it's hard for any one individual, it's impossible for any one individual to tie a specific health event to their air quality exposure. It's actually not impossible, is it? There's some very well documented, very famous Tragic cases where that is true, but they're, you know, a handful around the world.

Simon: 13:03

Maybe explain to people why that's the case, henry, because it is your exposure to a particular environment, the. The first questions that are raised are what underlying medical conditions you've got? What age are you? What was your journey to work or school like? What's your home life like? What's your social economic status? What's your you know? What genes are you carrying from previous generate? I mean the? Your health outcomes to a specific Exposure is very difficult to draw a straight line from, isn't it?

Henry: 13:39

Oh, absolutely yeah, and I think you know so many things that you do in your life, maybe a contributing factor to, to the outcomes that you realize, and they can be both positive and negative. So you might not Observe a negative outcome because you're you're offsetting it in some other, you know, often relatively unconnected, way. We've had two cases in the UK, one relating to outdoor air pollution and one relating to indoor air pollution, where the death of children has formerly been associated with with poor air quality, exposure to poor quality air. And I think you know, outside of those you know rare case, rare and tragic cases, this, the health effects had to be observed at a very large statistical scale to to be able to say that what are the likely effects of Of air quality on, you know, populations or at least regions of the population.

Simon: 14:59

But that's not the case necessarily. With something like learning outcomes. We can be quite a bit more precise, can't we that the, the environment that you're in, is having a specific impact on performance?

Henry: 15:11

same, Exactly, and what I like about it is, you know, telling people that something is bad for them can be scary with education and it actually translates directly to productivity in the workplace. Same thing with education. We're telling people it will be better if, if you improve your air quality, you will see your pupils being more alert. You will see pupils fulfilling their potential to a greater extent. You know through their learning and what they go on to do, and so I think you know schools is a great example, because every teacher went into teaching to help children learn, and if you're telling them, if you improve the air quality, you're going to help your children learn that little bit better that that's just playing to their own. You know existing motivation and I think that's a really positive angle to come at things.

Simon: 16:21

Yeah, and much like the workplace hell, the amount of time and effort and resources that go in to squeeze fractions of a percent of improved performance out of spaces. And if you can improve outcomes by, even conservatively, two, five, six percent in a in a place, and all the people have to do in order to do that is just breathe, could there be an easier win? You know you can. It's. It's a slam dunk from a business case perspective. We often talk in workplace environments of this three, thirty, three hundred rule or that 90 percent of your costs as a business are tied to your people. So any impact on the performance of your people in the business far outweighs the kind of bottom line impact that you can have by reducing energy by, say, 20 percent. And in an education setting, how much money is being poured into tweaking and squeezing performances out of classrooms? And you could have an impact by just getting the kids to breathe if you get it right.

Henry: 17:33

Yeah, and I think it highlights that there are different Roots to motivating the same end goal. You know, not just in a single. You know space, like schools, but between you know different work spaces, there are different motivations and productivity for for workplaces is is obviously key, I think. You know. I think we, as a sort of community of engineers and scientists, we've spoken for so long about, oh, we must improve, you know, energy efficiency and get you know good ventilation with with you know low energy means and that's absolutely true like vital to make an impact on, on climate change.

Henry: 18:31

You know the the amount of energy we use in buildings is huge.

Henry: 18:35

It needs has to come down, but in terms of the motivation, it's no good because companies are just like well, you know, my energy bill is a fraction of my costs, so you save me, you know, a big chunk of a very small piece of my bills. If you tell them that you're going to get, you know, absenteeism down or increased productivity, staff are a massive part of their costs, and suddenly they listen and they do, you know you end the set. You reach the same end goal but motivated in a completely different way, and I think we need to kind of find, for each building typology, what these motivations are and at what level. You know. So I think schools, for example, it has to be at a sort of ultimately a school, even classroom, level. But if we're thinking about the NHS, what, what, what level should we be thinking? And I don't know the answer to that and I think you know. Should it come right from the government or should it come from NHS trusts? But changes need to happen definitely.

Simon: 19:42

And I think we can learn an awful lot from other things that have happened in the past about how you engage at a national level to try and enact change. I mean the reality. Even if you take something as singular as schools, even within that vertical there are so many stakeholders that that can have an impact On an outcome. You've, as you say, you've got the kids who can get engaged. You've got a teacher who can get engaged at a classroom level. You may have a year ahead who can manage teachers more effectively if they have the data to understand that Mrs B in classroom two, for some reason, is just constantly having poor air quality outcomes in her classroom. So there's a management piece there. You then have a head of school level management stakeholder to get buying from everybody and boards of management and governors and so on. They then have to fund and invest it and all the way up to state and government level investment in the sector.

Simon: 20:44

So even something as vertical as education has an enormous number of stakeholders that actually need to be engaged to get a good outcome and each of them will need slightly different presentation of that data and risk to understand how it fits within their world view. So it's enormously complicated. What I wanted to do, henry, if possible, was just bring it back to you for a bit. I'm fascinated to know how you ended up in the Faculty of Engineering and lecturing in fluid dynamics, because I think you have an unusual journey, perhaps to where you've ended up and, as an aside for people, maybe an explanation of the link between fluid dynamics and ventilation, because it doesn't in plain English doesn't seem to make much sense, but I think, once explained, it's quite an interesting perspective.

Henry: 21:42

Yes, fluid dynamics is just about how liquids and gases move, and the key thing about liquids and gases, which is different to solids, is that they have an ability to more easily deform when you try and move them around, and so fluid dynamics cuts across all sorts of industrial and environmental processes. And, of course, when we're thinking about cities and air quality, we're thinking about air quality moving around our city. That's just the physics that moves it. We call that fluid dynamics, and that's exactly true when we come inside our buildings too. So you get some fascinating air flows in buildings that we're always learning more about and they actually play in.

Henry: 22:47

Understanding these kind of physics is important for air quality. You can get very easily have a lot of air passing through a space, but if the corner that you're sitting in doesn't feel the effects of that air passing through the space effectively, the space you're in is very poorly ventilated, even though the room as a whole might be well ventilated. So you get these kind of dead zones, recirculating zones, forming in spaces. So we do need, at a very detailed level, to keep understanding these better.

Simon: 23:25

So it's a very broad area of learning. Then fluid dynamics To the layperson, I don't know what you imagine or what I imagine when I think of fluid dynamics, but I think of people doing CFD modelling and looking at air movements in space and stuff. But I guess it's an incredibly broad subject when you actually start breaking it apart.

Henry: 23:47

Simon, my advice to you is get two pint glasses, fill one with you know, salty water. You know five to ten percent of the glass that's salty water, salt, and then add water, mix it up, put it in a bottle, shake it. Two pint glasses, one full of salt water, one full of fresh water, and put you know five or six ice cubes in each and watch what happens, which melts first and think about it, and I think most people will be hooked on fluid dynamics after that.

Simon: 24:23

Well, there's something for the listeners to go away and have a think about. So where do they write to in Imperial College when they don't know the answer and want to go and learn?

Henry: 24:33

Oh, just Google me.

Simon: 24:37

So explain to us, then, your journey to Imperial College, because you did a bit of time at Cambridge. In fact, you were even in finance at some point, weren't you, henry?

Henry: 24:47

Yes, you asked about my journey and I thought the one word that sprung to mind was convoluted. So I originally did engineering as a first degree in Bristol and then I did spend about six or seven years in finance and I enjoyed it. But I kind of accidentally fell into finance. I didn't really expect to get a job and all these sorts of things and I knew it was never going to be a lifelong career and I wanted to get back into engineering. So I tried to apply to all the grad schemes at all the big engineering firms but I didn't have. I hadn't got an engineering degree in recent years it was six years ago, seven years ago by then so I wasn't able to apply. So I thought a long time what to do and ended up going back to do a PhD in fluid dynamics, not unconnected, actually, to indoor air flows. And I went into the PhD thinking it was a sort of win-win in that if I didn't like research, I thought then I'll have a recent engineering degree and I can go back out into industry, or if I like research, I'll try and stay in it. And I loved research and I've never looked back and I think I moved from London to Cambridge and back to London again, I've increasingly become.

Henry: 26:34

I started as a very sort of applied physics person, I suppose. I did very controlled laboratory experiments and they have implications for indoor air flows. But I didn't just want to be an esoteric person doing experiments in a lab, and so I've increasingly tried to sort of work with operational spaces. Think about, put the humans. Cath notes, very early in my career, said what you do is great, but you should really be putting humans at the center of your engineering of buildings, and I think she's right. We don't have buildings for the sake of buildings. We have buildings for the occupants, and so you have to think about things that way around, even if you are an engineer and, frankly, occupants are extremely inconvenient. They do lots of things that you don't predict they're going to do and they changed the way the building responds from what you had expected. So they're occupants are the real challenge.

Simon: 27:48

Yeah, if all we had to do was build empty boxes, engineering jobs will be really easy and much less risk involved. What kind of stuff are you working on now? I mean, obviously you've got Sammy, which is in the midst of it all. What kind of areas are you researching at the moment? That's pushing your buttons.

Henry: 28:09

So one one that I think is really important that I've it's a particularly challenging one is we think a lot about the interaction of air quality and the movement of heat and around our buildings, but we don't think very much about the heat transfer mechanism mechanism, radiation. It's really complicated to put into models, but it's really, really important in terms of actually understanding how the air will move around our spaces. So that's, I think, a big research challenge that we're just starting to try and tackle. Yeah, I do some work on cloud physics which is quite interesting, and it's actually weirdly linked back to my original PhD work. It was all about sort of cold air coming up and falling back down, which we would call a fountain, and I think I think the real, the real challenge, I think, is it starts.

Henry: 29:26

We need it's going to take a decade or so at least we need to start building up more and more data and usable data on our indoor environments.

Henry: 29:41

We've done quite a good job actually, particularly in the UK on outdoor air, for establishing big networks of sensors which measure data, and that's why we've been able to make these really important findings about the health effects of particulate matter, for example.

Henry: 30:01

We need to do a similar scale thing in buildings, but it's an order of magnitude more challenging. You think about just look out your window and you can think about the air you're seeing over quite a large space being relatively well connected to each other. And then look in the building that you're in. The walls mean that the air concentration on one side of a wall can be very different concentrations on the other, and so we have this and buildings are owned very differently to outdoor space. So there's all sorts of challenges that need to be overcome to really get the understanding that's needed about the importance of indoor air quality and also to evidence the benefits. It's this thing that if people are doing a good thing and they don't know they're doing a good thing, then they might stop. But if they're doing a good thing and you show them the evidence of the changes, the benefits that they're yielding because of their behaviours, they're going to continue, and that's really important.

Simon: 31:13

And do you think some of that challenge in both the scale and size of the built environment but also the scale and size of the research that's going on at the moment as well that is, that where you're interested in things like an indoor air quality observatory comes from that this needs to try and start pulling some of this stuff together at a grander scale? I know I've been involved with you a couple of times now looking at what they've done in France with the observatory of indoor air quality over there. Is that the kind of thing that's sparking your interest in air quality observatories?

Henry: 31:56

Yeah, I mean, I think I definitely share the motivation to gather this data and I think the best way to do it is through some formal observatory. I think the French observatory was set up over 20 years ago and I think the methods that are available to us now in terms of low cost sensing and cloud storage of data they are revolutionary compared to 20 years ago. So the methods are probably going to should be probably quite different, but I think there's a real way, the scale of research, henry, is much bigger as well than it was 20 years ago.

Simon: 32:38

I mean, the sheer scale of research into indoor air quality is orders of magnitude bigger than it was 20 years ago.

Henry: 32:46

Well, absolutely right, simon, and that's actually a risk because, you know, at the moment, as a country and actually globally, there's a lot of investment in research around air quality measurements, where these measurements get made and they're used for a particular study and then they're not, even if they are technically, you know, openly available. There's no centralized mechanism to do shared analysis and the like, and I think that needs to change. So you know, now sitting at the core of the air quality observatory idea has to be that researchers you know initially perhaps from all over the UK and, let's hope, globally at one stage, can put research data and ongoing data collection results into a repository. So we don't get siloed research where you know one group is looking at, you know, one group is looking from this perspective and has this data which is useful for their hypothesis and another group has a different set of data to look at a different hypothesis. You know we need to be bringing this data together so that all groups can look at the big data set and we'll reach more valid scientific conclusions at a much lower cost if we have this centralized system of sharing data.

Henry: 34:30

But it's really challenging because context is key, right, I mean we can all chuck time series, data of concentrations in cloud storage and access it, but it's meaningless unless we know you know where the monitor was something about, you know the space it was in, you know how that space is being used ideally. These are real, real big challenges, but they're the sorts of challenges that I think we're at the right stage to really start tackling them, and I think we. It's difficult because it doesn't. These sorts of ideas do not fit into a typical funding mechanism for research in the UK. So I think the challenge is really getting things started and finding that money to support such an endeavor for a period that we can realize benefit from, and once we're realizing benefit, then I think it will be much more self-sustaining.

Simon: 35:38

And I don't know if it's already too late, but the importance to get something like this done early is that it's not just academia that is recording environmental data at scale. Now Industry is doing the same thing. I was talking to Tyler Smith, who's the vice president of Johnson Controls Healthy Buildings, there a couple of weeks ago on the podcast, and the scale of data that a company like even Johnson Controls is capturing is such a missed opportunity if it's not coordinated in a way with other sets of data and bringing all of this understanding together. Because we don't really even understand the boundary conditions of usefulness of this data, because we're not seeing the true scale of it. It's hard to know how much context we need when we're not seeing the full scale of the big data that's available. Just as a simple example, even Johnson Controls internally as an organization is managing 100,000 staff across 2,000 buildings across six continents, so the scale of data collection even within their own buildings would blow most academic studies out the water.

Simon: 37:04

So there's enormous opportunity here, with something like an observatory, to pull as much of this stuff together as early as we can. Otherwise there is potentially, as we lose control of it altogether, that it moves completely outside of academic rigor and we end up with all sorts of different ways of collecting data. That makes it much more difficult to pull in at a later stage. So I think it's a fascinating idea. The observatory have you any sense of how that might progress? What a next step might look like for an observatory in the UK?

Henry: 37:45

I mean I have ideas and I'm trying to have conversations with the right sorts of people. I think it's got to come at some level from government. I would have thought at least some of the money needs to come from research councils, but then there's lots of Well. Basically every government agency is affected by these things. So you know, I think it needs. It either needs to come very centrally or from sort of all government channels, you know but, I, think, yeah, it's a conversation that it's the right time to have it now.

Henry: 38:33

You know, the Chief Medical Officer devoted his 2022 annual report to air pollution and he explicitly stated that indoor air pollution is an increasingly important part of the challenge. And that's true, and an observatory would be a sort of recognition of this fact. And what would be nice is if we act now. The UK can take a lead in this. We don't, you know. We can show other countries. You know how a modern air indoor air quality observatory should be and I expect that you know, over the coming years, we wouldn't be the only one. I think there's so much interest around the world.

Simon: 39:20

Yeah, really interesting. I mean, what's your, what's your hopes more broadly over the next five to 10 years for perhaps the indoor air quality community, academic community, but more broadly out in the built environment? If you were looking at this in 2028, where would you hope would be?

Henry: 39:47

I think it's obvious we're going to have a lot more data. I really hope that we've done a good job of managing and structuring and doing appropriate quality assurance on that data, because if we do, then I think we could. We should be in a place where we're much better informed and we can link to. You know other well established communities. You know healthcare professionals. You know people who who work on changing people's behaviors, people who look at you know educational and productivity outcomes.

Henry: 40:29

You know the one thing we haven't talked about today that's that is really important is the impacts on on. You know psychological well being, people's mental health. We know that people's environments are really important for their mental health. Mental health has been such a strong part of the COVID story, had a really detrimental impact on so many people's mental well being, and we need to recover from that. We, as you know, a society, and I think that understanding, better understandings of the links between indoor environments and mental health is a really important one that I don't there's not much being done on it, and I think it's one of those ones that would be well addressed by you know large scale data sets.

Simon: 41:29

Yeah, very interesting and what a fabulous you know what a fabulously well resourced sector to do resourcing, mental health he says somewhat ironically yeah, but but in incredibly important to do. You're absolutely right, and it also speaks more broadly to the general framing of this stuff that we need to get better at communicating and talking about air quality. It's one of the things I've been very cognizant to try and do in these podcasts is to keep things very plain English. We can make air quality sound quite complex and frightening sometimes because it is complex and nuanced. There's no getting away from that. But actually often the routes to improving it are founded on very well known and well trodden paths of hierarchies of control and managing spaces. Often the solutions aren't that complex, are they, henry? Although understanding this chemistry and this physics and this fluid dynamics is complex, often the things we need to do to get a better outcome on Absolutely.

Henry: 42:44

Yeah, I guess you can look at it in a number of ways. One is to say, which actually start from quite a low, low bar. I mean, you know, a lot of our indoor spaces are not well conditioned at the moment, and you're right. In those cases there's often really simple things that can be done that would have dramatic impacts on those environments. So absolutely.

Simon: 43:10

Henry, thanks so much for your time today. It's been a pleasure to talk to you, as always. It would be great to have you on again sometime, particularly to get an update on Sammy and how it's gone. I think lots of people will be interested to see how that project finally finishes up. So thanks very much for your time. We'll speak again soon.

Henry: 43:32

I look forward to it. Thanks a lot.

Simon: 43:34

Thanks a million.