154 - Fire Fundamentals pt. 8

Transcript

MattHost00:09

Hey friend, what are you doing this Wednesday? Isn't it the perfect day to learn some fire safety? Cause I know a show that'll blow your mind. Come give it a listen, who knows what you'll find? Cause there's a whole damn world on fire out there and the show's gonna cover it all. So come and spend an hour with my friend Wojciech. I know you're gonna have a ball. How fast can you leave if you have a disability? Or maybe you have problems with some smoke and visibility, or maybe timber buildings are of some concern? If you have an object, I'll tell you how it burns, cos we're gonna talk to every fire expert, or at least the ones we know. So plug in your headphones this Wednesday and listen to the Fire Science Show. Plug in your headphones this Wednesday and listen to the Fire Science Show.

WojciechHost01:24

Ladies and gentlemen, dr Matt Bonner, my good friend and the star of episode four of the fire science show. When you hear this song playing before the fire science show episode, it means we are about to celebrate something, and indeed today's a great opportunity to celebrate, as the fire science show is having its third birthday. Happy birthday, fire Science Show. Thank you all for being here with me for three consecutive years, 150-something episodes later, more than 130 interviews carried with some of my good friends and people who I've met for the first time, with students and the legends of fire safety, with the brilliant women of fire engineering and the rising stars of our industry. What a pleasure it is to be in the middle of all of that and deliver this podcast to you. Together, we've created more than 150 hours of content. If listening to Fire Science Show was your day job, it would take you a month of work to go through our library, reaching almost 5,000 fire safety engineers globally, having almost 140,000 individual podcast episode downloads. Altogether, the transcripts of the Fire Science Show are approaching 10 million characters, which is a lot. That's like half of the Fire Science Show are approaching 10 million characters, which is a lot. That's like half of the SFP handbook. When I started this project three years ago, I had no clue that that would be the impact that this project will create, and I'm glad that you're here with me three years later. I'm glad that the podcast is still reaching new people. I'm glad that I can do my mission, which is to deliver fire science to all of you in the most approachable way, in a way that makes you enjoy it, in a way that perhaps is fun, in a way that doesn't cost you too much effort to participate in, and also in a way that you actually learn a lot. I learn a lot and I hope that you learn a lot with me as well. Super thankful to the audience, super thankful to all my fantastic guests and, yeah, let's keep going. Let's keep doing this project for more and more years.

03:39

I will not set a target. I simply want to deliver high-quality fire science to all of you for as long as I can and as we speak about delivering high quality fire science. That's the point of today's episode. Whenever we try to celebrate, I try to battle myself with some of the most interesting subjects within the fire safety or the fire science that I can find, the topics that really excite me and that I simply love, and unfortunately, these topics are difficult and hard. So I really hope I won't fail you this week. I've picked perhaps the most difficult of them all up till today, and that is the compartment fire. So in this episode, which actually is a part of the fire fundamentals series, we will be discussing the compartment fire, but I'm not going to drop tons of equations on top of you. I'll rather do fundamentals, in a way that I want to tell you how fundamentally important the compartment fire model, or understanding the compartment fire, is for modern fire science. I'll tell you where we don't really understand it and where we do understand it but we don't really benefit from the knowledge that we have. I'm going to highlight three aspects of the compartment fire that are, in my opinion, critical to modern fire safety engineering that I believe we need to implement more and more in the design of the fire safety features of the buildings. So, yeah, there's still the podcast intro to be played and I will be back to the compartment fire.

05:24

Welcome to the fire science show. My name is Wojciech Wigrzynski and I will be your host. Okay, you know very well that after the intro, there's one more mandatory part, and this time, instead of reading the ad, I'll say something from the bottom of my heart. Thank you, ofr consultants, for supporting the Fire Science Show. Almost half of the existence of the podcast you've been here with me, helped me deliver the content that my audience deserves and every fire safety engineer, including you, enjoy. I hope you've been a dream come true partner for the podcast, giving me complete freedom in the way how I want to shape it, who I want to interview and how I want to deliver the fire science to everyone around, yet supporting me in every crazy idea I had and taking the financial burden of what kind of became my second full-time job nowadays. So, thank you. I would not be here if not your support.

06:34

When in the first episode and I still say that I said that I find you as the UK's leading fire and risk consultancy, I truly meant that and I truly believe that Orphar is a fantastic place to work in. I truly meant that and I truly believe that OFR is a fantastic place to work in. I work with them. It's great. I think the engineers in there are quite happy. So if you're someone on the job market, if I was there in your place, that would be the first place I would call Thank you, ofr consultants for being here with me and cheers for the next years of collaborations and creating fire science content for our beautiful community.

07:08

And now back to the compartment fires Boy, I really like to pick difficult subjects for myself but, yeah, compartment fires feels kind of special. It's something that really brought me into the world of fire science. I did my master's thesis on corridor fires, which is in a way part of compartment fire science. I was under strong influence of my mentor, then my master's supervisor, later my PhD supervisor, professor Marek Konecki. Marek unfortunately passed away during the COVID times. That was a horrible loss for the Polish fire safety community. I was given the honor, the privilege, to finish his lectures because he passed away in the middle of an academic year and he was giving actually compartment fire course in the main school fire service in Poland and I was asked to continue the lectures from the point where he left them. And wow, what a crazy challenge it was to just step inside the course in the middle of it and just continue. I mean that was a lot of hard work to prep myself to actually give those students a really good impression of how a lecture on compartment fire looks like For me a chance to refresh the entire framework, the entire knowledge I had on compartment fire, and rediscover why that was a topic that I truly felt in love with many, many years before.

08:41

So if you think, what's a compartment fire like, is it a model, is it a framework? For me it's actually a space. If you consider fire science as a continuous space, the compartment fire theory would be the place where the king built his castle, you know. It would be the place where the knights would battle in the tournaments. For me, compartment fire is an elite part of fire science, when the biggest and brightest minds of our discipline have built the most beautiful theories, where they truly master the understanding of fire science, where they were looking for the limits of this understanding, and not just within the fire science but also in all other disciplines around it in thermodynamics, in chemistry, in fluid mechanics. Because eventually the compartment fire theories reached a point where you couldn't solve them anymore without moving the entire science forward. And I would say it's still not solved. Like we don't have a sound, robust theory for any compartment and I'm not sure if we will ever have. That's the level of the complication within the compartment fire framework and the consequences of all the variables which influence the development of a fire when you confine it.

10:04

So what's a compartment fire? Basically, it's a fire that has been confined. It's a fire that has been placed within some architectural boundaries. It's a fire that's not in an open space. If you have a pile of fuel and it's set in a place outside, if there's no wind, it's just going to burn down. You set up another fire that looks the same, united in the same way. It's set at a place outside, if there's no wind, it's just going to burn down. You set up another fire that looks the same, united in the same way, it's going to burn the same way. If there's wind, it may behave in a different manner, but still quite controlled. However, when you put this pile into 10 different buildings, you'll receive 10 different fires. That's the beauty of the compartment fire.

10:44

The compartment is a part of fire, even though it does not burn Well, unless you build it from timber. That's another story. But even though the compartment is not technically part of the fuel, it's not technically part of the combustion processes, it's not part of the chemistry. The compartment does shape the outcomes of the fire, does influence the fire, the feedback loops that occur within the compartment, the re-radiation is a critical factor that dictates how big the fire will be. How quickly will it spread? How fast will it grow? The ventilation, the openings in your compartment or just the size of the compartment itself dictate how big the fire could be. The height of the compartment and the fuel inside, of course. But architectural constraints of compartment will often dictate what is the maximum temperature we can get in the fire.

11:39

There are many, many characteristics of the fire itself that are determined by how the space in which the fire is confined looks like, and I think within fire science we don't really appreciate this enough. I think it still is a part, you know, of this nice curriculum that you learn as a fire safety engineer. It's a part of those lovely zone models that you can use. It's a part of the sacred knowledge that some fire engineers have but very few use in practice. In fact, the modern fire safety engineering at large appreciates the compartment fire theories but does not use them that much, and that's a pity, because the compartment fire frameworks are not there to just be admired for their brilliant understanding of the fire phenomena, but they can provide really useful knowledge in designing our buildings. In fact, they show us that the way how we shape buildings is as impactful on the size and the consequences of the fire as what do we put in those buildings and what do we build those buildings from.

12:56

So if you would like to learn a lot about compartment fires, there's a lot of reading in front of you, my friend. You should read Quinteri, you should read Drysdale, you should read Carlson and Quintiri and Quintiri again. You should read the original papers from 72 by Haramathy. You should touch the brilliant papers by Kawagoi from 1960s. You perhaps should also touch the revisit of the compartment fire framework by José Torero in 2010s and recent papers by, perhaps, vinnie Gupta about the compartment fires. There's a lot, a lot of resources on compartment fires.

13:33

In here of course I'll bring some of the basics, because that's the point of Fire Fundamentals episode, but I would like to put the focus on the practical aspects, why you should learn that, why you should understand the compartment fire. What can a fire engineer really learn from that and how can they benefit? And I think there are three aspects that I would say that are a critical benefit of knowing fire compartment, fire framework, three consequences of the physics of compartment fires. The first is the impact of the openings. The second is the impact of the materials and the third is how the fire behaves in the large spaces. That's completely different from a tiny confined boxes that most of the research was performed at. So let's try and start with the openings. So, first of all, if you go and take a look on the definitions of compartment fires, I like the one by Drysdale when he says that it's a fire that's confined to a compartment. The fact it's confined, it basically means that the fire itself is perhaps limited by the compartment that it is confined to, and I think that's a very simple yet powerful definition. And here, to take it forward, let's consider the growth of the fire within the compartment. Imagine there's a pile of material inside of your compartment that has been set on fire, it basically can behave just as if it was in an open space, if the fire is small enough. When the fire is large, then what will happen? You will have smoke accumulating in your compartment, which means there will be heat underneath your ceiling re-radiating to your fuel. So you no longer have your pile burning on its own, but you have a pile in conditions in which the fuel in the pile is preheated before it burns. It definitely affects the rate at which your solid fuel can burn and, by the way, I'm not going to go deep into the solid fuels in here. I'm working on the next episode of the Fire Fundamentals on that topic. So if you're listening to this in the future you're certainly going to enjoy those two one by one. Back to compartment. You have the fuel that is easier to ignite now. That is easier to spread the fire because it has been preheated.

16:08

At some point the radiation in your compartment may be high enough to simply set ablaze everything around. The flash-over phenomenon could be understood like that that the radiation caused by the accumulation of the hot gases in your room simply leads to self-ignition of everything around and your combustion suddenly becomes volumetric in your space, it's now the entire room that is burning. But if the fire is confined to a room, the room is completely sealed. There's a finite amount of oxygen in that room, oxygen necessary for the combustion. If the fire burns long enough, it could eat out all the oxygen and self-extinguish. If there are openings, that's a different story. Suddenly you have a mass exchange between the compartment and exterior, your smoke flowing outside being replaced by fresh air containing oxygen flowing in. This oxygen now, at this point, can support the combustion happening in your compartment and allow fire to grow further. So that's pretty much the story of the development of a fire from something that has been a localized event, a single item, your first item, single pile of combustible material burning into a fully developed fire, something that suddenly can endanger the structure, that generates a ton of carbon monoxide, something that's difficult to put out and something that we all would like to avoid fully grown fire.

17:39

At this point, if you considered what's happening inside your room and at your openings, there's obviously air flowing in, smoke flowing out. The question is is there more fuel in your compartment or is there more oxygen flowing to your compartment? Is there more fuel than oxygen necessary to burn it down. So the limit on the size of your fire is dictated by the oxygen. Or perhaps you have immense amount of air flowing into your compartment and it's a matter of how much fuel and how quickly the fire can spread in your compartment that dictates the maximum size. This is, you know, something that's obvious for modern fire safety engineers. This is something that every student learns. It's what we called the fuel and ventilation control, or fuel and ventilation limited. Fires are regime one, the ventilation controlled, and regime two, the fuel controlled fire. No matter how you call them, these are fires that have a limit, that have a limit depending on how much fuel there is in your compartment and how much air you have to support the combustion of that fuel.

18:53

And one could argue that the compartment fire framework that's been developed over the last six or seven decades was meant to understand well, to understand that we first had to realize that these regimes exist. You can attribute that to, perhaps Haramathy, to Thomas, to Margaret Lowe, a lot of brilliant minds that were studying the behavior of the fires in large compartments, trying to figure out those different behaviors from large data sets coming from fire experiments, and then trying to understand how different are the combustion phenomena in those two regimes? However, I think that the modern fire science, we need to recognize the limitations of our understanding, the limitations of the theories, the limitations of the experiments that led to establishment of those theories. Because when you start reading Dreisel, one of the first things that you will find is a word of caution, that everything here is limited to compartments of approximately hundreds cubic meters and perhaps four and a half meter tall, and that's it. That's the limit.

20:03

Most of the experiments that we had, the experiments that led to establishing of this fire science, were done in fairly small compartments, usually few by few, by few meters, three by three, by three, two and a half by two and a half by three, these types of tiny cubicles in which you could pretty well observe the differences of the fire behavior and try to parameterize either the amount of fuel or the size of the openings. These were fundamental to our understanding of the fire physics in confined spaces. However, the caveat is, once you start moving to larger compartments, the physics also a little bit different. I think my guess would be that the time phenomena are important. You know how quickly you can ignite, how quickly stuff burns, how quickly the fire transitions as well as the oxygen transport at large within the compartment. Where does the air reach in the compartment? Where actually in air reach in the compartment? Where actually in the compartment you have oxygen support burning, these things will start to dictate the location and the size of the fire, perhaps even more than just the presence of the opening or the quantities of the fuel you have. Well, that's my assumption. For bigger spaces. I said that's part three of the episode. Let's go back to part one opening. Why opening is critical In 2024, it's easy to say you know ventilation control, fire, fuel control, fire.

21:30

It's easy to say that because we know how fires behave. We have experiments in large-scale compartments. I've been part of those, I've seen those fires. We have CFD modeling. We can look inside the fires using computational fluid dynamics to understand what's happening inside.

21:47

But if you travel back in time, it was not so obvious In the times when the iso-time-temperature relation was defined, for example. We did not have an understanding of fire like that. We have not realized the relevancy of openings in fires. In fact it can be traced to the post-war studies first done in Japan at the Building Research Institute there. I'm also an employee of Building Research Institute in ITB. No, it's not the same company but it's the same spirit, it's the same type of institution. So I'm really proud of my Japanese BRI colleagues, kunio Kawagoye and other titans from that time who were among the first to realize that if you change the opening, the fire changes. And by changing the opening you've not just changed the architectural outlook of your compartment, you've changed the ventilation setting of your compartment. You allowed more or less air to come inside. And from those experiments, albeit limited in the use or in extrapolation for larger compartments, those experiments they've realized there's a relation between the size of your opening the square root of the height of the opening, which in some way you can correlate to the smoke layer height in your compartment, and the size of the fire that you get, the severity of the fire that you get inside. These relations were then studied a lot by different people.

23:23

I actually highly recommend reading the Kargois paper from 1958. It's available in the internet. It's very interesting to see what was the understanding of the fire science at the birthplace of the modern fire science. It's just really, really interesting to read. Anyway, this knowledge was then built upon, but by other giants of the discipline.

23:43

This knowledge was then built upon, but by other giants of the discipline, as I said, thomas L, margaret Lowe, mccaffrey, a gentleman called Haramathy.

23:50

He did a lot of interesting work on the impact of ventilation on the size of the fires, correlating hundreds of experiments together on one very beautiful plot which clearly shown that up to a specific size of the opening, there was the relation that followed the size of the opening, and from some size this relation stopped. There's a flat line, the fires do not change and the fire severity do not change anymore. This was the introduction of the fire regimes and our understanding that you can have either fuel or ventilation controlled fire Something I've said just a few minutes ago. That sounds absolutely obvious in the modern times, but yet it took a few decades of discovery to establish this very basic understanding. Well, not basic in physics, it's actually quite beautiful derivation but our understanding of what's happening in those fires? Now, why do I think understanding openings and the impact of openings on fires in your compartments is critical? If you talk to any fire scientists who've run compartment fire experiments, ask them the question did they open the windows during their compartment fire experiments?

25:10

because many of us have learned the painful lesson that you prep your fire experiment. It costs a lot, it takes so much time to prepare. It's the day that you are waiting for you know Excitement that you are running your fire experiment. Finally, after months of preparation, you put the fire to your crib. It's growing, you see the temperature plots and everything, and then it stops and then it slows down and then it painfully dies and it did not grow to your full-size fire that you wanted to study. And then you realize I should have opened that window. I'm not sure how many fellow fire scientists had this kind of experience. I certainly did, and it's an interesting one.

25:58

The reason why those experiments fail or well, they do not fail from the scientific perspective, they just develop and die because of the oxygen starvation. The reason why they starve is because there was no mass transfer established between the compartment and exterior. If your compartment is completely sealed it, the fire will burn through the oxygen inside your room and will die off. If there is an opening, that's completely different, because suddenly you have oxygen to support the growth of the fire. Perhaps the fire reaches a point where it can break your windows, and when the windows are broken, you have established a very solid mass exchange platform for your compartment fire to fit it Now, most of the models, theories that we use for evaluating the final size of the fire.

26:52

Because if you ask yourself what I want to learn from a compartment fire model, usually that outcome is the effects that the fire has on your structure or characterization of the severity of the fire to your structure. That's usually a thing that we need compartment fire models practically for, and to get that you use the models. In those models you define your openings because that's an input to the model. The openings are always a part of all of the equations that are used to define the temperatures within a compartment fire. And what do you put in there? You usually put the size of your windows, the frames of your windows, kind of assuming that the windows will fall off during the fire. In fire experiments you do the same.

27:45

If we run a massive fire experiment, full-scale fire, we usually don't put real windows into them. We assume that windows would have fallen off at some point and that is not necessarily the truth. In reality, there is a very particular size of the opening factor, the size of the openings in your compartment opening factor. Perhaps I should define that. That's the ratio of the total area of your surfaces in your compartment, which in a way represents the heat losses to the area of your windows multiplied by the square root of the height of those windows. So that's a parameter we call the opening factor. But you can also build a relation of all those physical parameters to the size of the openings themselves, and there's the assumption that perhaps when you have the most openings that will lead to the most severe fire.

28:40

The second aspect is the duration of the fire. Different ventilations will lead to different lengths of the fire. So it's hard to say that this one particle fire, with all windows falling off, is the most severe of them all. You actually do not know that Yet because the experiments are so costly yet because the models are so uncertain. Because the experiments are so costly, yet because the models are so uncertain, it's very hard to run a parametric study showcasing outcomes of different wires in your compartment. Even harder, there is no good model that you could simply use in your engineering to model the glass breakage and the window falloff, a model that could actually account for those new ventilation pathways to be established and allow you to actually include those in the definition of the growth of the fire. If we had that, it would be so much better than today's fire science. It would allow us a completely new set of pathways to define the fire criteria for our structures. If we had the ability to actually model the transient evolution of the ventilation conditions within our compartments. I highly recommend it.

29:53

There's a bunch of fire science show episodes out there that you could listen to. That kind of touch on this. There's an episode on the glass breakage with Yi Wang. There's the World Trade Center investigation with Kevin McCratton. There's an episode on the glass breakage with Yi Wang. There's the World Trade Center investigation with Kevin McCratton. There's an episode on mass timber fires with Carmen Gurska. A lot of episodes that actually touch on this in one way or another, and I really think that one day we will have a good model of glass breakage. We will have a model that will allow us to include this dynamic opening factor as a part of compartment fire framework, something we do not have today and something that, in my opinion, would bring us so much closer to reality when we design. Because, no, the biggest fire or the fire with the most openings is not always your most severe condition for the building. I feel kind of funny saying that because I say nothing different. That Haramati would say in the 70s, or you would learn from McCaffrey or Margaret Lowe, or even that you can read Kawagoye's papers from the 60s. It's something that we know, yet it's still not the part of fire safety engineering that is used every day day.

31:14

Another aspect of the compartment fire framework that I think is extremely interesting and kind of like not mentioned that much in the fire safety engineering is the impact of the properties of the materials that you build your walls from. If you go into Drysdale's book, there's like a bigger part of chapter nine. I think the pre-flashover fire chapter is devoted to that and it looks like it's kind of well-known and well-established. A ton of experiments in 1980s, bjorn Sundström experiments in 1990s really a ton of experimental and theoretical proof, yet something we don't discuss that much. So what do I mean by the properties of the walls? The way how fire grows can be connected to all those feedback loops that occur in your compartment. Here we're talking about the pre-flashover fire, a fire that has not grown to the full potential it can have in a compartment, but it's something that can actually turn into this massive configuration.

32:13

I've said that before at the beginning of the episode and I'll reiterate the amount of heat accumulated in your smoke layer and the temperature of the surfaces within the compartment, those things will dictate the amount of radiation from the smoke layer or from the walls. This radiation eventually targets the fuel in your compartment and affects the way how that fuel burns. Now, if you have the walls, it's kind of simple Stefan Boltzmann's law. You have a temperature, you have emissivity. You can evaluate how much radiation is going there in different wavelengths. If you have gases, that's a little different. Many people don't realize that, but the thickness of your smoke defines the emissivity of your smoke layer. So if your smoke layer is thin enough, even if it's very hot, it's not going to radiate that much because it's not optically thick. That's the subject for perhaps another episode of the Fire Science Show.

33:12

Anyway, the amount of heat will define how much feedback you have. The more feedback you have, the faster the fire will grow, actually at large scale. It makes a huge difference. It can make a difference between a flashover in 3 minutes to a flashover in 20 minutes. That's the difference you can get when your surfaces are highly insulative or behave as heat sinks. Actually, if you think about how heat transfer works on solid boundaries, if you have a highly insulative material, the heat has huge difficulty to penetrate the depth of the material, but at the same time, the surface of the material heats up to very high temperatures. These high temperatures power of four radiation heat feedbacks. I think you can see the pattern the more insulative walls you have, the easier it is to radiate towards the fuel in the compartment and, in the consequence, to ignite the fuel in your compartment or spread the fire. In contrary, if you have wall materials that can act as heat sinks, materials that can take a lot of heat and transport that heat into the midst of that wall if you have a very heavy concrete wall, for example this heat will dissipate into the wall. The surface temperature will be lower, the re-radiation factor will be lower, the radiation factor will be lower and you'll end up with a fire that grows more slowly, that's less vicious, that's less prone to turn itself into flashover.

34:42

I really struggle. Why are we not discussing that? Why the industry is so obsessed with the fire resistance. Why industry is so obsessed with fire protection materials, where you can significantly impact your fires by introducing more heat sinks into your buildings. I have no clue. Why are we not recognizing this aspect of fire science, like if I had a choice, you know, of fire protected two hour wall with a very highly insulative material and a pure concrete wall that can take like 60 minutes fire, half the fire resistant, half the fire resistance, but acts as a goddamn heat sink. That thing will slow down the fire. We don't recognize this. And yeah, of course the market is built so that the companies you know make products, they sell the products, they want to market the products, of course. But we fire engineers, we should know that, we should understand that.

35:44

A similar aspect to the properties of materials the size of the compartments. If you build a taller compartment, you will have a lower temperature of your smoke layer. That's the outcome of smoke entrainment in the plumes. That's how physics works. You cannot cheat physics. If you have a taller space, you're going to have a lower smoke temperatures. Perhaps not after an hour, perhaps not after heat accumulated there, perhaps not after the fire eventually grown to a flashover. Yes, in those cases it's not going to be such a massive difference. But in the early phases of the fire it can make a difference between the fire growing into the stage of flashover and fire not reaching that point. Same for smoke control. I know a ton of fires which led to a complete collapse of the structure despite the fact the smoke control was there. I'm not saying that in every single scenario the smoke control will prevent fire reaching its final phase, but if you design a smoke control in a smart way, you can delay it. You can reduce the probability of such a scenario occurring and perhaps save the building.

36:52

These are the aspects of the compartment fire physics that I think to some extent are neglected. We are obsessed with fire resistance, we are obsessed with our description of the properties of fire safety partitions and elements that we use inside our buildings and we are blind to the physics that defines how big the fire will be and how quickly will it grow. It goes both ways. If you have a well-insulated compartment with combustible structure hello, that's timber, that's a really good insulator you're going to have a double the effect. You're not only having a combustible structure that can now participate in the fire and change completely this compartment fire framework. You also have highly insulative surfaces in your compartment that enhance those feedbacks that we've just discussed.

37:44

There's a ton of physics that needs to be accounted for and I feel really stupid that we don't. We really should be doing better, guys. We really should be including this understanding of compartment fire dynamics that, for seven decades, has been built by brilliant minds of our discipline devoted to building the communal understanding of a fire. We should be using this, and I have a feeling we're not. This is my second take on compartment fire framework. This is why I think it's critical for fire safety engineers to understand it so they can actually find elements within the compartment fire framework that they could put into use when they design buildings.

38:28

Now we can move to the third and final important aspect of the compartment fires that I think needs more recognition in the world, and that's the impact of the size of the compartment. You've heard this already in the fire science show we had traveling fires episode. That's exactly the thing I'm talking about. If you have a very large open plan compartment, it's not acting like as a single. You know, small compartment it does not have uniform fire conditions within the compartment. At this point, the time in which the phenomena take place is important. The speed at which your fuel ignites, the distance to which the oxygen is transported from your openings. All of that will impact where, physically, the fire is at a given time in your compartment.

39:16

Now, if you consider traveling fire framework, it has been developed for open plant compartments. I had a really good episode with Guillermo Reyn on the development of that methodology. I had Pano Gattis-Casavinos on Code Red experiments, so there's a lot of resources on the Fire Science Show development of that methodology. I had Pano Gattis-Casavinos on Code Red experiments, so there's a lot of resources in the fire science show that you can listen to to learn more about the methodology itself. I would like to emphasize that traveling fire methodology is not meant to be the physical model of the fire itself. It's a useful generator of boundary conditions for structural analysis, for parametric structural analysis. So you can include a lot of different scenarios for your building to figure out if there are any to which the building would be very vulnerable for. So that's an important distinction.

40:09

However, traveling fires do describe a sort of physics of the fires that occurs in large buildings, in very large buildings the way how fire spreads. At some point the spread of the fire may be as quick as you know, the burnout of the fuel, which leads to a situation in which the fire is igniting the fuel in front of it, but at the back of the fire it's dying out already and you end up with, you know, this front of the fire that eventually moves throughout your building. It can take many hours for this fire to travel across your building, depending on how large it is. In our full-scale experiments we've seen anything from like 20-ish minutes to and I'm talking about almost 400 square meters compartment 20-ish minutes to a few hours. We have seen rapidly growing fire that has not stopped. We've seen a fire front that was perhaps one or two meters long and just slowly ate its way through the fuel crib that we have created for it in the compartment.

41:15

So, definitely a different range of outcomes. And yet, yes, those outcomes give completely different exposures to the structure and it's very difficult to say which of them is the most critical one. Why I say it's important? Because I've already said before, we don't really know which fire is the most severe for our structure. We do those things. We use the compartment fire framework, we study the temperature within fires to understand how our structures are exposed to the fire, hopefully with the assumption that we prepare structures that are resilient to the fire, structures that can survive the fire, hopefully with the assumption that we prepare structures that are resilient to the fire, structures that can survive the fire, structures that will not collapse on our firefighters.

41:58

If we do that, we usually employ the fire resistance paradigm. So we assign fire resistance classes based on the standard ISO curve tests. I've also had a podcast episode with Piotr Turkowski fire resistances, whatever you like it to be. Super highly recommend that one. If you haven't heard that one, it's going to blow your mind about your understanding of the standard fire testing. Anyway, the thing is, the standard fire test is just a test. It doesn't cater to all possible fire scenarios in your building and there could be there truly could be fire scenarios that are more severe, that you could have a structure that fulfills the fire resistance requirement yet would fail in a traveling fire of a certain size.

42:51

This is because the part of the structure is preheated by the fire that is far away. So you have a few hundred square meter compartment. The fire burns far away from your column. This column is not in the ambient air. It's exposed to smoke and hot gases coming from that fire, perhaps not at a thousand degree level, but a few hundred. That's enough to dry off the water in the fire, few hundred. That's enough to dry off the water in the fire protection systems. That's enough to preheat the structure. And then, when the fire front comes and your column, your beam, is exposed to very high temperatures, it may be subject to collapse, even though if it had a two-hour or three-hour fire resistance, that's something that we've seen in modeling. These are conditions that we've seen in the experiment that could happen inside the building, and this is not just traveling fires.

43:40

Previously I've talked about the impact of openings. Again, not always the fully open compartment will lead to most severe, the longest, the most vicious fire that will cause the destruction. Well, actually, you don't even have to have a fully grown fire to be a very destructive one. We know localized fires that have not transitioned to flashover that cause significant structural damage to your building. It's possible that the localized fire will create a severe damage. Of course, we protect against that, designing multiple load-bearing pathways in our buildings. So there are ways to mitigate, something we've learned after Ronan Point accident. But still, these are scenarios that need to be considered and these are scenarios in which understanding, knowing the compartment fire framework becomes critical for fire safety engineers.

44:34

Yes, there are toolsets like the parametric fire curves that come from Eurocode. They date back to the research of Peterson in 1970s, who has taken time, temperature distributions for different fuel loads and different opening factors and just calculated a ton of different fire curves and different opening factors and just calculated a ton of different fire curves. It was further parametrized by Schleiss and others and introduced into the Eurocode. It's widely used in Europe, a very interesting methodology. Yes, you can use that and perhaps it's in use, but it's a method that gives an outcome, not really a method that builds an understanding of fires in buildings. I think structural engineers and fire safety engineers should have a really good understanding of the fire physics, not just understanding of what temperatures they could expect in the structures. So to wrap it up, the compartment fire episode.

45:26

I have not went that deep into the compartment fire framework itself. As I've said, there's a ton of models, a ton of research. You need to do your reading to get up on those. The important thing is to recognize that the fires in compartment behave different than fires in an open, unconfined space. That the fires can grow differently depending on how our compartments look like. That the same fire in different compartments will lead to completely different outcomes of the fire. That's perhaps the most beautiful outcome of the compartment fire theories that fires in very large compartment will act completely different than the ones from the small compartments upon which the entire framework was built on. These are the beautiful aspects of the compartment fire framework that I think need more recognition in the world of fire safety engineering, that are impactful over our design and especially important when we start introducing combustible structural materials into our buildings, such asimber. I hope there are brave people out there to take the torch, take it forward and build up our understanding of the compartment fire physics further. For me, it's a magical world of the most beautiful fire physics. I love to get deep into that and I can only promise you I'll try to bring more episodes on the compartment fire into the fire science show. One could argue they're maybe not the most practically useful, but I think this physics is simply beautiful. That would be it for today's episode.

47:06

Thank you for being here with me today and thank you for being with the fire science show for the three years of its existence truly a remarkable journey for myself. I've changed a lot while doing this podcast. I've met so many people. I have learned so much. You would not believe how much I've learned. I listened to every single episode of the fire science Show at least three times, so I'm perhaps one of the most religious listeners of the podcast as well, and I truly enjoyed. I truly value the knowledge given to me by my guests. Perhaps I did not emphasize this enough in the intro, but I'm so thankful to the guests. I'm really blessed with the fantastic community that wants to participate in my project, that responds to my emails, that wants to spend some time with me talking, which opens up and shares their knowledge. They don't care if they look bad, they don't care if someone misunderstands it. They simply want to deliver fire science to others, and that's the passion that is common among us and that makes this project really worthwhile.

48:22

Nowadays there's a lot of fire podcasts. I sympathize with all of them. I think it's a brilliant thing that there are more fire podcasts out there. I think the market is growing, which means each of us is growing. Yet I still hope you know, kind of selfishly, that a fire science show is on the top of this list. That is a mark of excellence.

48:45

I've never tried to sell you anything. I've never tried to unethically change your mind into thinking of something that I would not believe in. Perhaps you have not agreed with me. That's a part of scientific discourse. However, you can always be sure that whatever I say in here is what I mean, what I truly believe in. And, yeah, one thing that is really important for me is to deliver a high quality content that you deserve. I think it's my one and best shot to give it to the community, and for three years I'm taking that shot and I will keep doing that for another years to come. Thank you for being here with me and it will be my biggest pleasure to have you listen to the fire science show again next wednesday and the next wednesday and the next wednesday. I'm not sure about you, but I will be here, so see you around there. Thank you for being here with me. Cheers, thank you.

154 - Fire Fundamentals pt. 8 - Compartment Fire