266 - Compartment fire framework with Vinny Gupta

Why Compartment Fires Matter

Wojciech Wegrzynski 0:00

Hello, everybody. Welcome to the Fire Science Show. I'm really excited for this one because today we're talking compartment fires, and compartment fires is, uh, for me, that's the thing in the fire science that I enjoy the most. And, uh, compartment fires, th- this is an important concept in fire science that kind of structures, in a way, a lot of fire safety considerations, and it, it has been with us for many, many decades and kind of shaped both research, engineering, and also fire testing and whole industry behind basically making sure that our buildings are safe, especially with regards to the structural safety. And therefore, this is something so, so fundamental for our discipline that I think it's our obligation to understand it very well as fire engineers. And like many things, it also comes with caveats and limitations and, you know, golden numbers and, and some things that are perhaps a little bit hidden within the assumptions or data that helped formulate those concepts. And all these things we will be discussing with Professor Vinny Gupta from the University of Waterloo Vinny has ,done his PhD on that and recently published another paper at the recent IFSS at La Rochelle, where, where he again revisited a part of the concept of the compartment fire, introducing new fuels. And I took this opportunity to invite him to the podcast and go through it. Go through it from the history, from the works of Kawagoe and Thomas, to the modern developments, to traveling fires, to growing fires, and also the stuff that, uh, shows how sensitive compartment fire may be to the fuels which, which he has presented recently. So in this podcast episode, we'll go through a lot of stuff from the basic concepts that shaped our discipline until the, the new research frontiers that find-- that I find very, very exciting. So I hope you will enjoy this journey alongside with us. I've enjoyed it thoroughly. Oh, and also one more thing that I really, really have to mention before we jump into the episode. after we've recorded this conversation, Vinnie went to Kyoto for Combustion Institute Symposium, which I've mentioned here. And in that Kyoto, something interesting happened. Vinnie and his team have received the silver medal from the Combustion Institute for the best paper on the previous symposium. I've teased you a lot of times about Vinnie's work with, uh, with water mist and lasers and optical diagnostics, and that's the work that has been recognized by the Combustion Institute as, as the best, uh, w- work in the previous symposium. That's actually quite huge. So huge, huge congratulations to Vinnie. I wish I knew, I knew that before we did this interview. Perhaps we would twist it a little bit more towards the, the water mist as well. But I think it opens opportunity for future appearances of, of Vinnie in, in the podcast. So, uh, once again, congratulations. And for compartment fires, uh, let's, uh, spin the intro and jump into the episode.

Sponsor Message From OFR Consultants

Wojciech Wegrzynski 3:31

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Defining A Compartment Fire

Wojciech Wegrzynski 4:32

Hello, everybody. I am joined by Dr. Vinny Gupta from University of Waterloo. Hey, Vinny

Vinny Gupta 4:37

Hi, Wojciech. Uh, it's good to, good to see you

Wojciech Wegrzynski 4:39

Man, it took me 260 something episodes, but, uh, but you're, you're finally here. Uh, so I'm, I'm, I'm really, really happy. Uh, in ancient times, I remember Dr. Gupta was doing, uh, his PhD and was doing a lot of interesting compartment stuff, and then he found out some laser stuff and disappeared from the normal science, started doing some very weird things with optical imaging. And then, uh, a few weeks ago, he reappears, uh, with a compartment fire paper at the IFSS. Welcome back, Vinnie.

Vinny Gupta 5:10

Oh, no, no, no. Tha- thanks a lot, Wojciech. it's been good. Uh, and, uh, you know, I mean, it, it's o- one of those interesting things where I, I've always been around, right? E- even I guess during my period in the wilderness. So, so no, it was really good to go back, uh, a- and see the community, see yourself and, and what everyone's been up to at La Rochelle in France

Wojciech Wegrzynski 5:30

well, I'm of course kidding. Of but, uh, I mean, uh, for me, you know, compartment fires and compartment fa- fire behavior at large is, one of the purest, you know, and I don't know, most fundamental forms of fire science, and, uh, I appreciate research being done at this scale, a lot. And I, I really want to talk uh, about the, the compartment fires with you, and I wanted for, for a long, long time. Um, Vinnie, let's treat this episode like something introductory to compartment fires, uh, and how fire physics, uh, fire science understands compartment fires. So maybe let's, start, uh, with defining why would we like to define a fire as something living within a compartment? Like what, what, what do we need this distinction for?

Vinny Gupta 6:17

Yeah, yeah, sure. A-a-and I think that's a, that's a really important distinction, right? Which is that, you know, you've got two words there, right? Which is the word compartment and the word fire. a-and even if you take, say, the word fire, it's always really interesting when you talk about fires with combustion people, right? Which is

Wojciech Wegrzynski 6:35

Hmm

Vinny Gupta 6:35

they have a, guess, a conceived notion of what they believe a, a fire to be. But, you know, in, in our space of-- and we operate in, I, I guess, the fire safety science or, or, or fire safety engineering space. I mean, when we talk about fire, right, it's, it's not just the, the chemistry that defines the, the onset of, of, I guess a combustion process or, or an exothermic process. It's the fact that you can have this interaction between a fuel, you know, producing some kind of heat under some exposure that generates a flame, then you get this kind of feedback process, and that generates things, like a fire, like a plume that, you know, can, can turn into smoke. And you have all this kind of interaction that, that you have to, to start dealing with. And, and often this is what we, we think of as a fire, right? I think where a compartment comes into play is that, you know, from a safety science point of view, I mean, most of our applications really deal with the fact that fire is often enclosed, uh, and it's positioned or, or, or put or occurs in some kind of enclosure. And what, what becomes quite important for us to understand is what are the implications of enclosing that fire,

Wojciech Wegrzynski 7:49

Hmm

Vinny Gupta 7:49

because that does actually change a lot of things and, and introduces a lot of complexity that we as fire scientists or engineers need to try and resolve

Wojciech Wegrzynski 8:00

think it's, uh, really important fundamentally for the whole of fire science, not just, you know, building fire science. Interestingly, I, I've, I was doing inter- a lot of interviews recently. I chatted with Ar- Arnaud Touvet. I've, uh, chatted with Stephen Welch, and, both of them, when we were discussing fire problems at the very large scales, wildland-urban interface, city conflagrations, we still came back to, you know, compartment fire as your primary unit at which the fire is happening. So even at those largest-- But perhaps if you're in the wilderness and you're researching your forest type of fires or maybe outdoor pool fires, okay, you probably don't need a compartment, uh, physics, uh, out there. But as soon as, as your fire lands in the city, anything enclosed, it's, it's really fundamental. And for me, the, the interesting thing is that you can actually, m- characterize many phenomena based on in the environment they happen, because we also know the link between how the compartment looks like and what, what kind of fire can live in, in, in it. It, it-- In a way, the fire is also defined by the compartment, right?

Vinny Gupta 9:11

Oh, absolutely, right? I mean, just, just, uh, a-and, you know, I mean, this is something that when we teach fire safety engineering, uh, at my university and I'm sure most, most other programs, I mean, by enclosing your, your fire in some kind of or, or enclosing your fuel in some kind of compartment fire, you introduce some really, you know, interesting and, and complex physics. I mean, for, for instance, right, you can now generate and form a smoke layer, and that smoke layer evolves in both time and space, And, from a safety science point of view, I mean, that's a, a really important problem for us to try and deal with, right? You know, it, it defines when we need to try and evacuate people from a room. It defines when, you know, as you start trapping more and more smoke in, your, your compartment starts heating up, right? That smoke itself can, can hold, you know, some, some degree of heat, too. So your compartment starts heating up, and that defines the, the, I guess the, the onset of the, the thermal hazard getting more and more onerous. And of course, you've got interaction. I mean, you can release some of that smoke, say, through doors or windows, so that goes elsewhere. Say, for instance, if you're in an apartment building, which is something that you may need to consider, or if it's leaving through a window, you, you may, you know, it's hot gas, right? So it's subject to buoyancy, so it may rise up to, to the floor above it. and then you're dealing with the fact that the actual walls themselves are, are kind of holding everything in, right? And those walls are gonna heat up, so we need to understand what the, the thermal and the mechanical response is, of the walls itself and of course the, the fuel itself. I mean, you know, typically i-in a compartment, I mean, if, if you look at the furnishings in a, in a room or, you know, i-in some kind of structure, you have all kinds of different things and as things start heating up, uh, or as your smoke layer starts heating up or the walls start heating up, I mean, you're going to subject a lot of that heat back into whatever is, uh, is unignited, right? So you can actually accelerate, the onset of the hazard by heating up the remaining fuel that you may have in, uh, in, in, in your room and that contributes to-t-towards releasing more and more energy, right? And, and you can often find that this turns into, to almost like a, a positive feedback loop

Wojciech Wegrzynski 11:23

fa-- yeah, and also like, uh, we will go into complexities of open plan compartments later on. you also eventually the, the insane richness of the physics inside as well. Uh, at your IFSS talk, you were talking about, flows inside and how they can shape the fire and change the fire. In my studies, I've observed, you know, optically thin layers of smoke, optically thick layers of smoke, and completely different outcomes. You put a beam inside of your experiment, it's a different experiment because suddenly you no-not only have a, a ceiling jet, but you also have a kind of a localized smoke layer with the different properties than you find elsewhere in your room. So, insane richness and complexity that arises.

Preflashover Versus Postflashover Priorities

Wojciech Wegrzynski 12:01

But let, let, let's start with the, the simplest and or, or maybe the p-perhaps the first useful understanding of compartment fires, as I have been taught in my fire engineering, university times. Uh, the fire regimes, which I believe come from Thomas and Hassell, then Regime One, Regime Two, and they're, qualified by, by the opening o-of the room. So, so if you would like to, teach us about we distinguish them and what's the... w-what's the role of the opening i-in them?

Vinny Gupta 12:31

Yeah, yeah. No, no, for sure. And I, I guess the, the first thing to kind of realize is that there are different stages to a compartment fire, right? And, and I think what you're, you're kind of referring to is post flashover, right? When, you know, you've got a fully involved fire, all the fuel

Wojciech Wegrzynski 12:47

Yeah, perhaps. Yeah, you're, you're right. Perhaps let's start with pre-flashover and post-flashover first, and then move to fire regimes for post-flashover fires. Yeah. Good, good

Vinny Gupta 12:56

So, so, and, and, and I think that's a, a really important distinction, right? because, you know, within the context of, what you're dealing with as a fire safety engineer, right? you, you, you may find that your, performance objectives that you're trying to achieve for your building change, right? I mean, we often associate pre-flashover with the, the init- the incipient fire growth and, things start, start evolving and, and so on with your, your primary, uh, article that's burning. and that often defines when or, or the criterion by which we need to get people out of, either our, our room or our building, right? And that's where often, you know, we'll, we'll talk about egress and we'll try and understand how can we detect our fire in a timely manner. can we employ different types of, uh, response measures, whether that be suppression other, other factors. a- and then, you know, in that case, we're, we're often trying to understand what is the growth or the spread of that fire, right?

Wojciech Wegrzynski 13:50

Yeah, yeah, yeah

Vinny Gupta 13:51

and, and that's, th- that's certainly one, one area that's, that's really important to, to try and capture.

Wojciech Wegrzynski 13:57

I, I mean, perhaps I've-- the, the, the reason I immediately jump to a post-flashover fire in my head when talking about compartment fires is because that's when I use models that would treat the whole compartment. Because if I'm

Vinny Gupta 14:12

And,

Wojciech Wegrzynski 14:12

in...

Vinny Gupta 14:12

the most striking interaction, right? It's, it's when you imagine a compartment fire, right? Or, or when someone imagines a, a room fire or an enclosure fire, there's all, there's all kinds of things you can call it. You think of a room, there's, uh, huge flames coming out of a window

Wojciech Wegrzynski 14:28

I, I mean, yeah, and, and also, you know, if I'm doing my job as a fire safety engineer and I'm designing fire safety systems, flashover also kind of means a failure of my work because I'm supposed to design a fire smoke control strategy that doesn't really lead to, to a flashover. Or, or, or, you know, if I'm designing a, a shopping mall, I would not like to have a flashover in my shopping mall. so that's a different class of, models. But, you're right that, there's also a richness of, of the fire spread characteristics which also, was covered i- in, in your PhD. Le- let's do it chronologically, Vinnie. Whether we like it or not, Thomas Haselden were first post-flashover fires were deemed

Vinny Gupta 15:08

can e-- I think you can even start before

War Roots Of Modern Fire Research

Vinny Gupta 15:10

then, right? I mean, when, when you think of how, a lot of, I guess, what we call contemporary compartment fire research started, it did start with your individuals like Thomas. a-and I mean, a lot of it actually started from World War II, right? I mean, you

Wojciech Wegrzynski 15:23

Yep.

Vinny Gupta 15:24

the, the Allies and the Axis powers

Wojciech Wegrzynski 15:26

trying to burn each other's, uh, houses more efficiently

Vinny Gupta 15:31

yeah, correct, right? I mean, there, there was a huge race towards trying to-- I, I mean, it was a scenario of total war, right? So you're, you're trying to come up with, situations or, or scenarios in which you can impose the, maximum amount of damage. So a lot of, um, early fire research work, was very much based on, on how trying to promote, room fires, right? And trying to use, you know, single or multiple room fires towards engulfing a building with the hope that you could try and almost translate that room or that building to what we call an urban conflagration, right? And, and we saw examples of this, with the, the, the firebombing of Dresden in, in Germany or the, um, the firestorms in the, in the wooden cities in Japan which, uh, you know, that, that end up, ended up killing more people than the, uh, the atomic bombs, there, right? So, so, know, there, there was a huge amount of push i- in the fire research space, during World War II, and it was very much in the post-World War II era during the, the reconstruction, of both, Europe and, and Asia where, uh, a lot of key characters realized that, that much of this science and, and know-how, and I guess more importantly experimental data, could, could be used towards trying to improve resilience, against fire. and, and that's very much where this started. So, so you have characters like, Kunio Kawagoe in, in Japan at the, uh, the Building Research Institute and, Philip Thomas at the, the, uh, at the Fire Research Station, uh, in the United Kingdom, where, they, you know, during the '50s, they established teams towards trying to understand, well, if we can what most severe fire looks like in, say, a room, then we can come up with protocols towards designing for that case, right? that limit state. And, and we can use that as almost an anchoring point for the development of codes and standards, i- in, in both respective regions.

Kawagoe And The Ventilation Factor

Vinny Gupta 17:29

so, so that's very much where a lot of this started and, and it wasn't really formalized, um, until Kunio in the late '50s published a, a very famous report. I, I think it's, uh, Fire Behavior in Rooms, or

Wojciech Wegrzynski 17:43

Hmm.

Vinny Gupta 17:43

I can't remember the exact, uh, title You know, incredibly famous report, right? Where, where essentially what they did was they had these, uh, large structures, uh, a- and essentially they were throwing wood in the structures, right? And, and, and what Kawagoe was trying to look at was what happens if I start, altering the openings, in my structure, right? and you know, they, they had incredibly simple diagnostics, uh, back then, you know, like a very, very basic measure of temperature. They, they essentially were weighing, what the fuel looked like. And what Kawagoe was, you know, what he essentially formalized when he came up to the realization with this was that, you know, if you put enough fuel, particularly wood, i- into a room, then in essence, you would-- you could actually control how much of that wood just by playing or modifying, your airflow into the compartment, right? And the, I guess the key intuitive link that he made, and I mean, it's a, it's a link that still persists with us today and almost every single fire engineer has to use it, is the fact that you can control the amount of air that enters a compartment solely by playing with, uh, the openings, there. And, and that's just by virtue of the fact that you've got draft or, or entrainment of air from, know, your exterior into the interior of your, of your compartment, and then the compartment essentially will expel the, the hot gases, through the, the same opening. and I think that finding was, was, incredibly transformative.

Wojciech Wegrzynski 19:16

Mm-hmm.

Vinny Gupta 19:16

Um, a- and then essentially in parallel, uh, in the United Kingdom, uh, Philip Thomas a- and his team at the, the Fire Research Sta- uh, Station essentially came up with the, the same findings, right? Uh, they, they started formalizing things a little later, and at some point both of them got into, into contact, you know, across the, uh, from the U- UK to, to Japan a- and started exchanging notes.

Wojciech Wegrzynski 19:40

Yeah. And, also the link made, uh, was that, i-i-if you put infinitely more timber into the compartment and keep your, your opening, at the same rate, if it was only the opening that's driven it, it, it would just reach the peak potential by the opening, and it shouldn't change anymore. But that was not the case

Vinny Gupta 20:06

right? Which is that, you know, if I keep throwing more and more wood into my, room, this was all formalized, you know, it was just believed that, okay, it'll burn hotter, It'll burn hotter, which means that you'll, you'll release more energy. And essentially what Kawagoe figured out was that there was a limit,

Wojciech Wegrzynski 20:23

Yeah, but it's not a limit that you reach it and you maintain it. It actually putting more beyond the limit actually makes you go down and release less energy at some point

Vinny Gupta 20:33

yeah. Precisely. You, you start actually releasing less, right? And which for the time was quite counterintuitive. You know, a-and, and what, what essentially he formalized was that, well, at some point you're putting in so much fuel... And, and I mean, the, the basics in terms of the chemistry of this was, was really well established at the time. it's incr- it-- like in the '50s, it was really well known that, you know, it takes from just a simple chemical balance that, you know, per unit mass or per unit volume of, uh, of fuel that I put in, it requires some air, right?

Wojciech Wegrzynski 21:03

Hmm

Vinny Gupta 21:03

you know, if you know how much fuel you put in, you know how much free volume of air you've got in your room, you can kind of approximate and, and come up with a limit at which, well, there's no more, at least within my compartment, there's no more, uh, oxygen available, right? And what Kavagoe figured out was that if I restrict just through the opening the amount of oxygen that can get in, then essentially I can't bring in oxygen fast enough in order to, to react with all of my, my wood. this is the whole concept o- of what we call oxygen depletion or, or completely oxygen depleted, uh, compartments or underventilated.

Wojciech Wegrzynski 21:42

Yeah. So if you're

Vinny Gupta 21:43

that you could reach this state of underventilation by not having a large enough opening to bring enough, air into, i- to keep fueling your fire

Wojciech Wegrzynski 21:52

which again is, is a fundamental thing for our discipline now up till today, because if I design a fire experiment, full-scale fire experiment in the modern times today, what I calculate is exactly the opening factor, and it's gonna, you l- you know, kind of tell me what kind of a fire I can expect in that compartment. So it's, it's a part of my decision-making process today, you know, this exact physical observation from the '70s

Thomas, Heat Loss, And Temperature

Vinny Gupta 22:20

Yeah, yeah, yeah. Precisely. And I, I, I think where the, the genius actually came into it was that, both Kawagoe and, uh... So Kawagoe formalized what we call the ventilation factor, and he realized that you could actually, you know, correlate all of this, and it had a incredibly solid theoretical basis from just fundamental fluid mechanics, that you could essentially describe that rate at which you consume your fuel provided that you are in this state of, of underventilation, purely in terms of what we call a ventilation factor, which is essentially, you know, a measure of the opening size, right?

Wojciech Wegrzynski 22:58

Hmm.

Vinny Gupta 22:58

where Thomas extended this, so, so Thomas then, you know, took a lot of this knowledge, and I mean, he, he commanded a, a pretty, large team in the UK where, I mean, they, they were, they were essentially doing these kind of multi- multiscale experiments, small scale, large scale,

Wojciech Wegrzynski 23:14

Mm-hmm.

Vinny Gupta 23:15

and they were modifying everything. You know, they, they were trying wood cribs of, of different sizes, you know, playing with the porosity of the cribs, the aspect ratio of the cribs, the aspect ratio of the compartments, the, everything you can imagine, you know, putting a burner in place of a crib and, and whatnot. So they tried every single permutation to, to essentially try and build up a uh, a database. And, where he extended that concept was to define what we call, I guess, an opening factor, which was that he really-- he came to the realization that you kind of have two competing forces, at least in, in these smaller compartments. You know, competing force one was the energy generation, right? And which if you're in this state where it's underventilated, the energy is solely dictated by the rate at which you can bring air through the opening But then that has to be counterbalanced by the energy losses. And, and what Thomas realized was that at least for the compartments, know, contemporary at the time, so, so re- you know, very much related to, to the type of construction from the '60s

Wojciech Wegrzynski 24:17

In UK

Vinny Gupta 24:17

yeah, right, in the UK, that most of the, the heat was actually lost through the boundaries of the walls, right? so in essence, you needed two things. You needed to know you know, what area my compartment, was available to essentially take heat away from my room and how much energy or what was the area of the opening by which I could bring air in to keep f- uh, generating energy, right? And this is the inception for what we call an energy balance, right? And, and from the first law of thermodynamics, your representation of an energy balance or, or one of the outputs from it is a temperature. so where Thomas kind of took it was, you know, he used th- this concept from Kawagoe which defined essentially a rate at which you have burning, and if you defined a rate at which you have burning, you could determine how long the compartment burns for. Thomas was essentially able to fig- figure out, well, not only can I tell you how long it burns for for a given type of fuel load, but I can tell you what temperature it gets to. And then he was able to essentially take all these configurations and come up with these very el- incredibly elegant plots that showed you what the maximum temperature was, you know, depending, you know, as a function of the geometry

Wojciech Wegrzynski 25:28

Hmm.

Vinny Gupta 25:28

a function of the fuel

Wojciech Wegrzynski 25:29

for the practical u-use, we, we define it today as the area of walls, uh, divided or, or total area divided by, uh, the area of...

Vinny Gupta 25:39

factor.

Wojciech Wegrzynski 25:39

Yeah, yeah.

Vinny Gupta 25:40

Yeah, which is the, the area of the openings multiplied by the square root of its, uh, height

Wojciech Wegrzynski 25:45

Yeah, which is a clever way to dictate how much air is coming in, how much air is coming out. Of course, that's, that's the, uh, 1970s, fundamentally not that much has changed since then. I mean, Jose had a, a brilliant paper, at, uh, IFSS. w- was it in Canterbury? I think it was Canterbury 2014. I, I don't-- I, I didn't participate back then, but I've read the paper multiple times revisiting the compartment fire where, where, where he goes even further with the energy balances of, of, of that model, uh, explaining it, it further. I think it's fundamentally important, but, one thing that is kind of, you know, well, not missing, but it, it's interesting is the complexity in the whole problem is that you're talking about British compartments of 1980s. And boy, a lot has changed, like, uh, both in terms of size and materials, and those together create, uh, regimes or regions in which, this stops being really applicable. and, and that, that's kind, that's kind of funny

Vinny Gupta 26:46

So, so this was, I, I, I think this was the, the brilliance of, uh, of individuals like Philip Thomas. Um, and, and you know, you have others too that, that really participated i- in kind of the, the development of the theory. I mean, here in Canada there was, uh, Thibault Hamathy, who was the, the head fire person at the NRC in Ottawa. a- and then of course, you had individuals like Howard Emmons at Harvard who was trying to model a lot of this phenomena. You know, Jim Quintieri the US who was kind of leading the next generation of experiments and, and theoretical developments and,

Wojciech Wegrzynski 27:19

Yeah.

Vinny Gupta 27:20

to, to tie everything, right? But

Wojciech Wegrzynski 27:22

had Margaret Lowe who tried to use all the,

Vinny Gupta 27:24

yeah.

Wojciech Wegrzynski 27:24

of that in, but in real, world-class engineering projects

Vinny Gupta 27:28

like, you know, she, she, she-- so she worked with Philip Thomas, right? at the, uh, fire research station and then took a lot of that knowledge and, and actually, you know, synthesized it in a way where it could be applied in an incredibly practical setting, right? But I think where the brilliance really comes was that, all these key quantities that you need for design, things like temperature, things like how long something burns for, the rate at which it burns for, the translation that to, say, a heat flux, uh, which, which is incredibly important. A- and all of these kind of aspects, I mean, how much radiation is leaving the opening so I can try and use that to dictate separation or the external flame. There are all these outputs that, that essentially from this framework. But where the brilliance really comes in was and this group of people were essentially able to establish all of this with very clear assumptions and incredibly clear limitations,

Wojciech Wegrzynski 28:23

Mm.

Vinny Gupta 28:24

So, you know, they were able to define by virtue of having all these experiments by, by doing the hard work and, and the theoretical developments to explicitly state where this would work, under what conditions, and where it would not work, And, and in essence, the argument that, that Phil Thomas made then was that if I can define exactly where this framework works, you know, I can use that as the basis for quantification. So, so what ended up happening was that this theory works real-- or, or this whole, you know, concept of opening factors and so on works when you can deplete all of the available oxygen in your room, So we need

Wojciech Wegrzynski 29:03

All right. Yeah.

Vinny Gupta 29:04

we need to try and come up with compartments in which we can deplete all of the oxygen in the room. So what, what did that essentially mean? Well, they knew from their experiments that essentially that required relatively small compartments with not so massive openings, right? So you essentially could fill up the entire room with smoke, consume all of the available oxygen, so that when the windows break, essen- or, or, or, or if, you know, the, the, the door fails or, or whatnot, the sizes of the openings were what would be controlling the overall fire behavior and the fire dynamics. And then in essence, if that's controlling that, I can quantify all the outputs that I need for building design So that was incredibly useful at the time because you know... I mean, that was essentially what was pushed into code in the UK, right? And, and that's why if you go to the UK now, they're incredibly small compartments that have relatively small openings that dominate the landscape left, right, and center.

Wojciech Wegrzynski 30:01

Hmm.

Vinny Gupta 30:02

which, which shows the massive amount of influence that, you know, someone can have on, you know, overall architecture, which, which is quite fascinating. uh, and, and I think the key finding was that, well, we're gonna call this kind of regime where we satisfy this, the, the fact that we consume all the oxygen, we're gonna call it, you know, the underventilated regime. could call it, say, regime one. Uh, there, there are all kinds of different names for it. but i- in essence, they, they more or less mean the same thing, right? And then at the time, there was this definition of another regime which, uh, you know, they, they referred to it as fuel controlled or regime two, whi- which kind of was everything else that was not regime one

Wojciech Wegrzynski 30:45

And, well, since the times of Adam and Eve, people were not, uh, really good at, uh, following constraints or limiting themselves. We obviously now have a lot of buildings and compartments than they had in the times back then, uh, where-- which would es-escape those sets of rules and limitations for regime one. Regime one was an interesting case because later on, uh, parametric fires were built on that concept, where, people realized Pe-Pettersson is in-- Pettersson Magnuson from, uh, Sweden are important names in here. They realized that the standard fire curve perhaps doesn't tell the whole story. Yes, there are fires that, uh, Vinnie, I once had a fire experiment where we, like, nailed the standard curve, like almost as perfectly as in a furnace. And I'm like, "My God, people are now gonna use it against me. You see? It's a real fire." I'm like, "Ah, yes." Like by virtue of luck, we just got that one...

Vinny Gupta 31:42

that's kind of where the first curve came from, right? Like the

Wojciech Wegrzynski 31:46

I know. But, but anyway, regime one, fine. We, we-- Th-there's a story to it. It, it went further, but not that much further, and it's still useful. We still have parametric fires in the Euro codes. It's still being used, but yet, uh, the limitations have never changed because those are physical constraints to the physics of the fire.

Vinny Gupta 32:05

Yeah, yeah, yeah. Precisely.

Wojciech Wegrzynski 32:07

so what, what's interesting is, all the interesting stuff from the physics point of view, like the richness of the fire physics, is really in what, back then they would call the regime two. But today we also know there's so much more to, to this regime and so much more into, the spread physics, which you went very deep into your PhD.

Vinny Gupta 32:26

Yeah, yeah, no, absolutely. A- and I think, I think it's first important to recognize, you know, that these regimes, right? I mean, you know, th- these were defined at a time where, instrumentation, uh, you know, the sophistication of experiments could... I mean, yes, they were, exemplary at the time, but, their age shows, right? A- and I think one of the important things to first

Wojciech Wegrzynski 32:47

No CFD

Vinny Gupta 32:48

exactly. I mean, you know, the, the, the, the key equations for, for most LES codes was not even written, wh- when, when a lot of this came out, right? So, but I think the important thing to, to realize is that these regimes, really what they're intended to represent are limit states, right? You know, they're just limiting regimes, right, of behavior. and they were essentially used to kind of bound, one type of behavior, which is where I have complete oxygen depletion, so I can actually take advantage of that and employ a huge range of simplifications, but they're all justified and grounded, right? And then the other regime, which was kind of everything else, where I'm not really 100% sure how to quantify this, and I'm not sure what's relevant, and it, it, it may be context dependent. So, you know, if you look at the experiments of the '70s, they were even able to come up with approaches towards trying to correlate it. And they, you know, for the experiments in the '70s, they essentially came to the implication that in, uh, 90 or 95% of the, the cases, the overall thermal lo- solicitation to my structure, which was what they were interested in at the time, which essentially defi- defined your capacity to maintain compartmentation of a room, was that, in most cases, it's not as severe. I get a lower temperature. and that's kind of where, where the story ended,

Wojciech Wegrzynski 34:12

and the practicality is in the worst-case scenario, which is not this one.

Vinny Gupta 34:15

the practicality was in the worst case scenario, right? So that if I was looking, you know, in this other regime, in regime two, well, by virtue of it not being in regime one, I could use a lot of the tools outside of its bound of applicability. But I have confidence that it's not as severe, maybe, you know, I, I, I can at least justify it, right? And, and to try and add on, you know, redundancy to that, you have individuals like, uh, like Tipu Hamathy in Canada who proposed, "Well, what I'll do is to reduce that uncertainty, I'll incorporate sprinklers." Which is why in North America you have sprinklers everywhere. and, and that enabled the creation of, of much larger spaces than you may have in Europe, for instance. so that's kind of where, where, where things ended. But I think at some point there was a bit of a disconnect, which was that, the, the recognition that regime two exists was not just because, you know, I, I actually have oxygen or, or whatnot. It, it, it's more so that, the, the fire behavior that you get is incredibly context dependent.

When Old Assumptions Get Forgotten

Vinny Gupta 35:19

So as you said, right, if you look at, you know, we're in 2020 right now, in the 2020s, the, the nature of our buildings, the type of materials that we use, the, you know, the geometry, the sophistication. I mean, we have things like incredibly complex HVAC systems. We have all of these things that really make contemporary architecture quite distinct from the 1970s. So

Wojciech Wegrzynski 35:42

And the space effic- the space efficiency, the utilization

Vinny Gupta 35:45

Yeah, the utilization, the level of air tightness

Wojciech Wegrzynski 35:49

of the spaces that promotes a certain open kind of, setups where you can adjust and, uh, I, I think that's also a huge factor in the modern engineering

Vinny Gupta 35:58

Yeah. Yeah, absolutely. A-a-and I think what we're, we're, we're finding right now is that been some kind of disconnect that's happened between the c- the formation of a lot of our classic compartment theory and today. And, were all these assumptions and limitations and whatnot defined, but at some point, those assumptions and limitations were forgotten, and all we remembered was the solution.

Wojciech Wegrzynski 36:22

Yeah

Vinny Gupta 36:23

So we're finding ourselves in a position where we're now trying to extrapolate that solution all of this complexity that we have today without actually realizing that, is that solution contextually relevant? those, uh... I, I, and I think that's the, the danger that we're finding ourselves in

Wojciech Wegrzynski 36:41

which also is like the point of, of this podcast and talking to people like you because, like, uh, we, have unimaginable riches of golden numbers and, you know, hidden assumptions that, that, that stay there somewhere. I mean, they're useful.

Vinny Gupta 36:57

And they come for a reason,

Wojciech Wegrzynski 36:58

They come for a reason. Exactly, you know

Vinny Gupta 37:00

to know why. It, it's not just important to know why they became that number, but also, what was the context for that number and, and where does that... you know, being able to recognize what is the limitation or the bound of applicability for that number

Wojciech Wegrzynski 37:16

Okay. So let, let, let's go again let's assume we have this regime two. We understand that it's incredibly complex. We've already agreed that it's a regime in which the assumption that depletion of oxygen is not complete within the whole compartment. What does break once you start to increase the compartment size towards the modern, the modern compartment?

Open-Plan Floors And Traveling Fires

Vinny Gupta 37:38

So, so where things start getting complex, right? you know, and this is where, you know, several years ago I, I got involved into this my PhD supervisors, uh, you know, Juan, Juan Hidalgo and, and Jose Terrero, And, and this is just an example of a regime too, which is an open floor plan type of compartment, right? Which is, when you think of an open floor plan, it's, it's almost the exact opposite of a traditional UK-style room from 1965, You've got incredibly large geometries. I mean, the aspect ratios are, are, are quite significant. You've got, you know, massive openings, I mean, windows or, or glazing around the entire, you know, border

Wojciech Wegrzynski 38:18

uh, Vidi, I always smile because like open plan compartment, you know. When we were looking for an open plan compartment that really the best reassembles, uh, the modern office,

Vinny Gupta 38:30

Yeah

Wojciech Wegrzynski 38:30

the building we found was a cow house. That was, that was the closest thing we could find to a modern office, an industrial cow house from the '50s. So

Vinny Gupta 38:43

really, it's really funny 'cause, uh, you know, one of these tests, uh, this was before I started my PhD, but my supervisors, uh, ran this, uh, it's quite a well-known test, the Malvera Fire test, which was done in Portugal. I mean, that was essentially done, uh, that compartment, which is also a representation of a,

Wojciech Wegrzynski 39:00

Modern office

Vinny Gupta 39:00

a section of a, of a modern office or an open floor plan is a slaughterhouse or was a slaughterhouse,

Wojciech Wegrzynski 39:06

so much similarities between the meat and, uh, and office industry

Vinny Gupta 39:10

Uh, yeah, I'd like to think though that it's more so that it's more so the, the fact that trying to find spaces in which you can undertake large scale fire testing that meets the, let's just say, meets some of the, the standards that the fire service would have or, or other stakeholders is, is non-trivial, right? 'Cause I mean, then you have other impressive feats like the Cardington test, right? Where it's all

Wojciech Wegrzynski 39:35

Hmm.

Vinny Gupta 39:35

know, it looks incredibly uh, the setting of it is incredibly professional. It's not done in a slaughterhouse or, or a meat house. so, so no, it's, it's quite interesting. but, but when you look at open floor plans, right, I mean, so, so what are the big challenges that you may have when you start, you know, going to these large sizes, right? I, I think the first that the, the original conception of a compartment fire was that all the fuel in my room gets involved in the fire, and it's by consuming all the fuel that I deplete all the oxygen.

Wojciech Wegrzynski 40:07

Yep. At the same time

Vinny Gupta 40:08

f- you know, yeah, and it happens at incredibly rapid per- uh, you know, time, right? Essentially at the instant of, of flashover. The issue that you may have in an open floor plan is that what happens if I don't, right? You, you have to get to, to pretty significant thermal levels in your room to start involving everything over a large floor space, right? And, and they've been, this, this was, had been known for a while, but really was exemplified on a, on a public level during the World Trade Center tower fires,

Wojciech Wegrzynski 40:41

Mm-hmm.

Vinny Gupta 40:41

right? where essentially you had your plane impact a section of the building. it, it ignited one component of a, of a very large open floor plan across several floors, and you have this prolonged fire that kind of moves around, and you can actually see it from the, the videos if you, you step forwards in, in large time steps. The fire's kind of moving around and at no point does the entire floor plate, you know, si- you know, engulf in an incredibly rapid period fire. so just by virtue of not reaching that state, there's some implications there, and I think the first implication is that you have oxygen in your room, right?

Wojciech Wegrzynski 41:20

Mm-hmm.

Vinny Gupta 41:20

always going to be some degree of oxygen around. And then the second is that, well, the fact that I haven't been able to engulf everything on fire means that I may not have enough smoke, there, which means that essentially may have significant flows occurring, right? Uh, you know, I don't have this nice static smoke layer. I actually have flow that's kind of moving around, pushing my flame or delivering air into certain pockets and whatnot. So what that suddenly means is that the openings may not be as important as you originally would've hoped Uh, whi- which starts invalidating a lot of the underpinning assumptions for many of the tools, uh, that we would've otherwise used.

Wojciech Wegrzynski 42:01

Hmm

Vinny Gupta 42:02

and then, okay, so if I'm playing around with where the smoke is, it may not be uniform, the flame dynamics may not be uniform. I may run into a problem where now the heat that I'm imposing on my structure is not uniform.

Wojciech Wegrzynski 42:17

Mm-hmm.

Vinny Gupta 42:18

I don't have a small little hot box. It may be really high in one location and low in another location, it may evolve in both space and time. A- and this was one of the key problems that, that we found with open floor plans, which is that essentially, you, you almost have this kind of fire spread, type of issue where, you know, you can have, I guess, what we call a traveling fire where... And, and we, we tried to, to group these depending on, on, I guess, the, the dominant physics.

Wojciech Wegrzynski 42:47

Mm-hmm.

Vinny Gupta 42:48

But you may have a, what we call a traveling fire, where it's an incredibly localized fire, it's kind of moving around in time. So the implication there is that it imposes some degree of heat locally, but it can burn for an incredibly long period of time, right? Which is incredibly different to just having everything on fire simultaneously.

Wojciech Wegrzynski 43:08

Hmm

Vinny Gupta 43:08

can impose, in the context of my building and my structure, a different type of, uh, of thermal load that may warrant consideration. then for instance, what happens if it starts accelerating? I mean, maybe I start building enough smoke layer, I involve enough of the fuel depending on what I put in there, that it starts growing. So I may need to consider that. Or what happens at some point, maybe not at one particular time, but later on I So, so one of the things with open floor plans is that very quickly start realizing that you have all these complex, different type of phenomena that are, that are occurring that you need to think about. And, you know, what makes, what can make things even more complicated is that I have materials all over the place. Um, it may not be uniformly distributed materials. Um, I could have, you know, almost like islands or packages, that are discreet. I could have, windows, uh, in certain locations, um, being influential. What, what ends up happening is that the characteristics of the space incredibly important towards defining the local fire behavior. and that's a problem, or that's a situation that's incredibly difficult to generalize and, and something that, warrants us actually analyzing and trying to, to understand what, what is actually happening

Wojciech Wegrzynski 44:26

Brilliant. I always liked the distinction with the velocity of burning front and the burnout, part to, to characterize the, the behavior of the fire. I found this observation that comes from one of your papers. Uh, was it this, was that the proceedings? I think it was the proceedings paper.

Tracking Flame Front And Burnout

Wojciech Wegrzynski 44:44

Yeah.

Vinny Gupta 44:44

the, the, the basic idea, right, a- and this was a similar kind of approach to, to how a lot of compartment fire research was done, right? Which is, know, by doing a lot of experiments, by taking a lot of observations from other experiments, y- once actually start understanding the problem, you, you can start up with ways of simplifying it, right? So one of our approaches was, could we simplify... So we know that what I just described to you is extraordinarily complex, and I don't even think we could do a, a CFD model of it, right? look, I'm not a CFD person, but, uh, I, I guess you are, Wojciech, so, you know, you tell me. But

Wojciech Wegrzynski 45:27

in the planet who more or less succeeded with that, but I don't believe they have a general solution.

Vinny Gupta 45:35

so, so,

Wojciech Wegrzynski 45:36

Yeah.

Vinny Gupta 45:36

other words, though, we don't really have the capacity using CFD as a, as a almost like, like a design tool for this case, right? This is incredibly specialized R&D, uh, type of work, right? You know, we're really pushing the forefront of where the models exist to try and capture the, these kind of behaviors. So what we've tried to do was, well, can we at least simplify the problem a, a little bit, uh, more just by virtue of understanding some of the details of, of what's going on? So, you know, and we, we tried to essentially rely on the fact that, well, a compartment fire really is just all these individual elements of fire science that are kind of packaged together in an enclosure, right?

Wojciech Wegrzynski 46:18

Mm.

Vinny Gupta 46:19

So it's just a matter of kinda defining what is important and what is not so important. So that was at least the, the thought process there. So, well, if I'm looking at an open floor plan, what I really need to try and determine, I, I think what's, you know, really the defining characteristic is how big is the fire and how much energy is it releasing?

Wojciech Wegrzynski 46:39

Hmm.

Vinny Gupta 46:40

how does that change with time and space? so what we tried to do was, well, we need to first determine, you know, is the fire going to accelerate or deaccelerate, or is it just going to kinda move together? So came up with experiments and, and numerous other people came up with similar experiments where, you know, we tried to s- track at least the overall fire s- fire size along a, a floor plate by looking at, say, its flame front position and its burnout front position, right? And essentially the delta between those two is how big the fire is, at least geometrically, right? And, and there are all kinds of approximations and simplifications, uh, embedded in there, but it a- allows you to do is, well, all I then need to do really is just track that a- and try and understand, you know, what cases in my compartment enable me to keep that kind of uniform fire size, but it burns for a long period of time, or under what circumstances does it really start accelerating and I get to this kind of flashover type of, case or, or what we call like a, a fully developed, uh, fire, right? and, what we essentially came up with was that your fire dynamics essentially can be grouped almost into three kind of modes, right? You've got this traveling fire behavior where it's kind of like a constant fire that's just moving along and it imposes some kind of heat. you've got this more transient stage where it's accelerating, but it may be accelerating slowly or it may be accelerating rapidly, and that may depend on the characteristics of your compartment. And heavily depends on how the fuel-- So if you look at like flame spread theory, and I, I think you've, you've, you've got several podcast episodes from, from very, uh, notable flame spread, uh, individuals, what really defines it is the preheating. So if I have a smoke layer established, whether it's thin, thick, in terms of size and also the le- amount of smoke, so if it's a, like a optically thin or an optically thick, so if it's really sooty or, or not so sooty, of that essentially defines how much of the fuel ahead of the fire is getting preheated, right? The more the preheat, the faster it's gonna spread. The less it's preheated, slower it's going to, to spread. So that becomes really important in defining that. And then, and then the final one that we looked at was, well, what are the cases where the entire compartment is engulfed in flames? and that's where essentially your spread rate relative to your burnout rate is, you know, kind of tends towards infinity. And that's we-- I mean, that's essentially the classic idea of regime two from, from Philip Thomas

Wojciech Wegrzynski 49:21

Mm-hmm.

Vinny Gupta 49:21

or Homothy and so on. And in that case, you, you actually get heat exposures that are significant. Um, they're extremely high. They vary in both space and time, and you can get exposures that actually are even higher than regime one, right? So under the context of modern compartments, it-- you may not necessarily, have the tools to define a worst case. So, so we just tried to really understand the science of this. Under what circumstances do you get different types of behaviors, and can you come up with simplifications or ways of approximating, the kind of exposures that you get? But the issue that y- there's only so many experiments that exist, right? So you can only... You can capture a subset of what exists and the, the obvious question is, what happens if we start changing fuels or what happens... I mean, most of these experiments were done with gas burners, pool fires, and wood cribs. What happens if we have plastics? Uh, what happens if we start changing the geometry rapidly? So if we start playing with the aspect ratio or if we reduce the size of the windows

Wojciech Wegrzynski 50:29

Or just have a real windows that break

Vinny Gupta 50:32

if you have real windows that break, I think that's an incredibly important... I mean, you know, modern, modern glazing technologies are, are pretty impressive right now. It's, it's

Wojciech Wegrzynski 50:40

It is.

Vinny Gupta 50:41

difficult to break a window.

Wojciech Wegrzynski 50:42

It is. Yeah

Vinny Gupta 50:44

and, uh, and, and of course, I mean, a big one that's concerning our team at, like, Waterloo and, and several other people, uh, several other, uh, uh, you know, I think it's a, it's a, I mean, it's a massive problem, is what happens if you have combustible linings like mass timber, which is, you know, one of, one of these, these, uh, you know, where you're potentially, you know, increasing your fuel load substantially and you have an incredible need to maintain compartmentation of your, your room, right? Where, where your, your fire, you

Wojciech Wegrzynski 51:17

Absolutely.

Vinny Gupta 51:17

within its room of origin.

Wojciech Wegrzynski 51:19

Absolutely. As soon as you started including timber, the, the whole compartment science suddenly needs a, a revisit. Uh, I've had Carmen in the podcast. She talked about, uh, her journey with the Thomas and Hasleton plot and, and figuring out how to put, uh, CLT into, into that. It's a very interesting, uh, uh, story and, and a good episode I recommend to everyone. But also recently at La Rochelle, you came with, with, with a paper, uh, also related to timber-encapsulated, uh, compartments with different, uh, fire experiments. And, and you suddenly start messing with my regime one fires that I was very happy and comfortable with them for so many... For 50 years, we, we had no issue with them, and you found one. Thank you, Vinnie. Like, uh, explain yourself.

Timber Compartments And Fuel Sensitivity

Vinny Gupta 52:03

Yeah, look, I mean, so, so essentially what, what we, uh, what we presented-- So this was with, uh, collaborators from the University of Queensland, um, from University of Waterloo, UCL, and, uh, ZAG in Slovenia and, uh, DBI and several other places. the idea is not that new. I mean, once again, incredible luminaries like Margaret Law, Phil Thomas, Jim Quintiere, Homothy had all actually asked the, the same exact question. Uh, we, we just added timber to it and we kind of wanted to, to revisit

Wojciech Wegrzynski 52:36

Uh-huh.

Vinny Gupta 52:36

this phenomenon, you know, once again, you have to think, where does this knowledge come from, right? Like, comes back to we have a body of knowledge that exists, we often take it for granted. You know, what were the underpinning assumptions and limitations? So if you go back to, you know, this theory for underventilated fires or, uh, regime one, uh, one of the, the-- or, or what we call, uh, that's the word, ventilation controlled or ventilation limited, is that many of the experiments, that define this theory and have explored this phenomenon essentially utilize wood cribs. So these are essentially sticks of wood that are layered orthogonally each other, to create, a very nice clean fuel load, right? And this is a fuel that even today, most experiments, a-and we even do this, uh, in, in my laboratory, uh, everyone uses wood cribs as a, as a fuel source. It's so well known, it's so well used that it's codified in I-ISO standards and, pretty much every single standard involves a wood crib, to some extent, a-and in some context. So we essentially tried to look at was, well, if you have a, a cross-laminated timber compartment and we try and fit it to, you know, the geometry of it and the opening of it to guarantee that it should, in theory, be very well suited to this conception of regime one, right? This conception that all the oxygen gets depleted, it essentially becomes a hot, smoky box and, and doesn't become clean. So what we tried to do was, well, what if we take two different fuels, so a wood crib, which has always been classically used, and another type of fuel, and in this case, what we did was we picked almost the, the virtual opposite of a wood crib, which in our opinion, is, is a pool fire. And the, the reason why you kind of pick a pool fire is that it requires... Wood cribs essentially don't require too much oxygen to, to burn with wood when, when wood d- decomposes into its molecular, its gaseous molecular compo- uh, composition, the hydrocarbons from a pool fire are typically quite heavy and require a lot of air to burn with, right? So, so these are kind of the two limiting fuels we took these two, and what we tried to, to understand was, well, what happens you take, say, a s-- the same compartment fire and you use both of them? and essentially what we found was that in theory, it should be ventilation controlled. In other words, the fuel should be irrelevant

Wojciech Wegrzynski 55:07

Mm-hmm.

Vinny Gupta 55:08

in theory there should be no oxygen, in both cases. So if there's no oxygen in both cases, then all that really should control is just the amount of air that you br- can bring into the compartment. And then in essence, if you can control that, should more or less get the same level of burning. So in our case, what we, we essentially had was cross-laminated timber walls. That the burning of the cross-laminated timber wall should be identical. and essentially what we found was that you could be further from the truth. In fact, they were completely different. one of the interesting things, I mean, the, the kind of two, two interesting phenomena that you have, and I think the first is probably something that you talked about with Carmen, is that the fact that you've included timber into your compartment kind of changes everything. You, you can-- You, you're generating flow, you're accelerating things. In fact, the, the kind of underpinning assumptions start really breaking down when you have a timber compartment. So that's problem one. And then problem two is that, well, if it's broken down and I have a fuel that's essentially a stacked up, you know, layer of wood and a pool fire where, you know, it's a completely different geometry and, and makeup here, the flow now becomes important, so the interactions that you have with the actual fuel articles themselves become incredibly important. And essentially what we found that the overall compartment fire behavior that you have is incredibly sensitive to the fuel. Now, the really interesting thing with all of this is that it's not actually that much of a new finding So if you, if you look at all these, all the work back from the '70s, they all did that just without timber.

Wojciech Wegrzynski 56:49

Mm-hmm.

Vinny Gupta 56:50

all found the same thing, which is that, a lot of the exist- a lot of the knowledge really starts breaking down when you start using plastics or pool fires. Uh, and you know, part of the reason that it breaks down is that you, you kind of get two The first is that when you deal with plastics, they're incredibly sensitive to e- radiation that you have in a compartment. Which means that if you have excess radiation in the compartment, that radiation essentially gets sent down to the fuel and plastics liberate a lot of, uh, you know, they, they don't have a super high, what we call a lat- you know, a latent heat of gasification, right? So, so they don't require too much energy in order to release fuel. So they start releasing extra fuel because you're supplying extra radiation to the fuel in addition to just the, the, the general flame that sits above it. Whereas in, in the case of a wood crib, which has con- traditionally been used, the fact that you've stacked all the sticks on top of it, it's kind of like a campfire where if you're trying to accelerate or if you're trying to get your campfire to, to really start burning vigorously, often have to really blow into the campfire. just by virtue of having so many sticks, it almost acts like a shield, where all the burning of the crib is not really due to the flame above the crib, it's actually due to the fact that you've got all these sticks on the inside that are essentially oxidizing, uh, and smoldering and trapping the heat inside of the crib. by shielding where everything is burning in a crib from everything outside, it's quite insensitive, to what's happening. so in essence, you can get incredibly different phenomenon, uh, in that case. So you have one case, say, uh, this is what all these folks found in the '70s, where is really sensitive to changes in the compartment, and it's incredibly sensitive to the smoke layer, the radiation, and in the other case, it's insensitive. In the case where it's insensitive, all that really matters is am I bringing enough oxygen in or not? So this is, now you start trying to, uh, you know, you s- you start actually coming to the realization that, oh, a lot of the original theory works because I'm using a crib, because I kind of mask sensitivity of the fuel such that all it really depends on is just the amount of air I can bring in

Wojciech Wegrzynski 59:11

Hmm

Vinny Gupta 59:12

And is not that much different when you come with-- when you, when you have timber compartments. the only key difference is that its sensitivity is amplified even more so,

Wojciech Wegrzynski 59:22

Yeah.

Vinny Gupta 59:23

um, whi- which can be a bit of a problem

Wojciech Wegrzynski 59:25

No, I, I love that. So when you were giving the talk, there was just time for one question I've lost, but now I can interrogate you how much I like. No, I

Vinny Gupta 59:32

Of course.

Wojciech Wegrzynski 59:33

I just have one, one,

Wind, Flow, And Research Opportunities

Wojciech Wegrzynski 59:34

one question. Actually, the question back then, you shown a picture of a fancy compartment and you called this a normal compartment, and I wanted to challenge you on, on the idea of what the normal compartment is. But on a serious note, if we start liberating ourselves from the rigid limitation o-o-o-of the theory, I think an incredibly important variable is the assumption of the initial flow conditions at your opening. Because we, we kind of assume... And, and that's the way how most of the experiments are done. We kind of assume that the ventilation is the product of the fire physics, where it, the reality is not that. Like the, the wind, the flows in the building. Like it, it-- Like unless it's a compartment ventilated to an indoor space without any outdoor connection, yes, that's perhaps, uh, that. But un- as soon as you have any interaction with the exterior, the-- I, I feel this kind of, you know, external wind effects. I'm not even talking about wind-driven fires, which of course are a different class of things, and we,

Vinny Gupta 1:00:39

Sure

Wojciech Wegrzynski 1:00:39

we know that. But, even-- I o- I once had a, a big research grant, and one of the goals of the, of the research grant that I've put into the writing was I'm gonna try to find like a wind velocity at which we can say it's irrelevant, so when I do my experiments, I can say, "Oh, this wind is irrelevant." But I even seen changes with like one meter per second, and I'm like, "Wow, there, there's no irrelevant wind." So that, that's a really challenging factor in this, right?

Vinny Gupta 1:01:11

Oh, no, I completely agree. I mean, a- and I think, with the kind of, I guess once again, right, like if you, if you look at these compartments that are so-called ventilation controlled or, you know, what underpins, say, our use of zone models and so on, they all rely on essentially the fact that we've got stratification in our

Wojciech Wegrzynski 1:01:31

Square root of height, right? Of the opening

Vinny Gupta 1:01:33

yeah, yeah. Precisely. So, so it relies on the fact that you've got a very, you know, either a, a singular hot layer or a hot layer and a cold layer, right? A-

Wojciech Wegrzynski 1:01:41

Yeah

Vinny Gupta 1:01:42

and that hot layer and cold layer is essentially more or less static inside of the room, and if it's static inside of the room, all the flow exchange is done at the opening, right? The issue is that at some point, if you get to conditions where you've got gradients or you don't have a clean hot layer or a clean cold layer, you know, by definition you're not stratified, which means that flow effects become incredibly important, uh, inside of your room, right? So when you start blowing even small amounts of wind, I mean, one-- what you say one meter a second,

Wojciech Wegrzynski 1:02:20

That's nothing

Vinny Gupta 1:02:21

surprise me because one meter a second is kinda how much a compartment in trains,

Wojciech Wegrzynski 1:02:26

Yeah

Vinny Gupta 1:02:27

a pretty s- you know, significant, you know, onerous compartment in trains in through the opening, right? So even a small gust of wind, I, I think a lot of us who have done outdoor compartment experiments for one reason or another can attest to the fact that even small gusts of wind or, you know, if you've got draft, through a building, these can make significant, effects. So I, I, I mean, and I think I don't really see this as a problem in terms of being incredibly limiting. If anything, I think it means that there's so much opportunity for, for us as researchers and for engineers and, and particularly for young scientists to really contribute a lot because, they're, they're all these... I mean, we've now opened essentially this box of all these different parameters that, uh, you know, we're operating in a space now where our compartment incredibly sensitive to all these things, which means that we need to understand that degree of sensitivity. We need to come up with, with theory, we need to come up with design tools, we need to come up with, with methodologies by which we can incorporate them into a design setting and a design context. So, I think there's, yes, there's a lot of work, but I think that's also means of, uh, considerable opportunity

Wojciech Wegrzynski 1:03:41

Yeah. I mean, l- look at it. Windows that can break or may not break, fire safety systems interaction, doors being left open or being left closed or automatically closed or maybe not completely closed, uh, wind around you. Uh, it's

Vinny Gupta 1:03:56

We're dealing now with like airtight buildings,

Wojciech Wegrzynski 1:03:59

Oh, exactly. E- exactly, exactly. Ex- so, so much, so, so much to play for generations and generations of fire scientists.

Vinny Gupta 1:04:06

Yeah,

Wojciech Wegrzynski 1:04:07

I-

Vinny Gupta 1:04:07

are all incredibly important lessons. I think we have some tools to try and an- answer this, but, I think there's a huge amount of room for, for knowledge and, i- i- you know, and I think one thing that we don't need to try and jump straight to is just immediately jumping to a large-scale demonstration test. I, I think we actually need to focus on understanding, you know, the problem. I mean, one of the, the, the reasons why these experiments that we keep talking about, right, from the '50s, '60s, '70s, and we keep talking about them, and even today, you know, if you go to any classroom, they're all taught, right? and all the theory that came out of it is taught. I, I think part of the reason is that it was so systematic, in its execution that you were able to actually, propose hypotheses, theories, and answer them. And then by virtue of having enough data, by having clear direction, you could actually develop solutions that were incredibly applicable. unfortunately, I don't think we're doing that to the level that we need to. We're, we're, for the most part, I mean, we're, we're relying a little bit too much on really large burns, which are very good for identifying key phenomena and problems, but it is incredibly restrictive in, in, in terms of being able to truly find out what is important and how we can simplify things to a manner in which we can have, you know, a, an elegant theory or a solution a- and a practical approach.

Wojciech Wegrzynski 1:05:35

Yeah. I mean, if any- anyone in here is listening, uh, just entering the profession, I mean, you're entering a beautiful world where, uh, there's way more questions than answers yet

Vinny Gupta 1:05:46

Oh, yeah, yeah. I mean, there, there's no shortage of, of problems and, you know, e- even in sp- uh, it's, it, it's quite fascinating, right? Because, of course, you can think of all these technologies that are introducing new problems, you know, things like PV panels, batteries, WUI, or wildfires in, in, in the urban interface, and there, there are all these sub-problems that you can create. But even going back to something as classic as compartment fires, there's a huge amount of room for improvement a- and room for transformative development that, um, young scientists and engineers can, can really make. Uh, and, and there's no shortage of, of work in that space.

Wojciech Wegrzynski 1:06:29

Yep, absolutely. And, um, wherever you go, Wii batteries, uh, name it, you, you will always return to the compartment fire concept eventually

Vinny Gupta 1:06:40

that's a really interesting thing, right? I mean, where, you know, I'm, I'm fielding conversations now where people are trying to understand, well, what happens if I have a scooter, like an electric scooter in my, in my compartment? How does that change my fire behavior and my fire dynamics? Or if you look at the, if you look at the, the, the case of a WUI, I mean, WUI, like the wildland-urban interface is fascinating, where usually your compartment fire starts from the inside of the room and grows. Whereas in the case of, you know, the wildland-urban interface, the initiation is actually the inverse, right? You're, you're trying to understand how fire ignites from the outside or, or imposes some kind of source from the outside, and how that then a-and, you know, leads to an ignition on the inside, which then grows. that once again, that requires you a, a incredibly incredible deep understanding of compartment fire behavior and all the, the subareas of, uh, of fire science that, that really underpin it

Final Takeaways And Sign-Off

Wojciech Wegrzynski 1:07:37

Brilliant, Vinnie. Uh, thank you so much for, for, for this, uh, short venture through the history, uh, past, present, and the future of compartment fires. I guess we can, we can say we've covered a bit of each of those, uh, spaces. Was, was a pleasure, uh, talking, uh, to you about this, and I'm looking forward to, to more interesting compartment fire research coming from your group at, uh, the Waterloo

Vinny Gupta 1:08:00

Yeah. Thank you. Thank you so much for the opportunity to talk, Wojciech. And, uh, yeah, I look, I look forward to catching up with, uh, with, with yourself, uh, in the near future

Wojciech Wegrzynski 1:08:08

And that's it. Thank you for listening. I guess it's just me, but, you know, this compartment fire thing for me i- is the essence of what fire science really is. Uh, I guess I've been scientifically raised, uh, by Professor Konecki, late Professor Konecki here in Poland, who was a brilliant person who understood all of this very well. And, uh, since I have worked with him on my master thesis and PhD later on, I was just mesmerized by, you know, the conceptualization of, of a fire within a compartment focusing on, on the physics of this heat and mass and, uh, transfer combustion phenomena inside. It, it's, it just, you know, feels the fire, fire science for me, and I'm, I'm really thankful to Vinnie for taking invitation to this podcast episode and doing an episode like that. It, it, it was a pure joy to dis- discuss this. And I hope, uh, while for me it was a great way to revisit, you know, the, the whole concept, perhaps structurize it a little bit in, in the historical, uh, chronological order, uh, like, like Vinnie knows very well from, from his PhD, um, I, I hope it still opened some areas for you and allowed you to learn a little bit about what are the limitations of the fundamental concepts that we apply every day, where they break, and why we, we need to find new concepts and, and, and new ways of representing the fires that fit better to the modern world. And, and this is something that I think Vinnie captured very well with his, uh, with his group and i- is, is currently developing, and I, I found it very, very interesting. Uh, so for me, that's enough fire science for this Wednesday, but you can be sure that, uh, next Wednesday, a new dose of fire science will be coming your way. So I hope you will join us there again, and perhaps we'll be talking about compartment fires once again. Thanks for being here with me. Cheers. Bye.