Welcome to our new website!
Aug. 2, 2022

061 - Glazing in fire with Yu Wang

061 - Glazing in fire with Yu Wang

The relation between ventilation conditions and fire severity is quite a fundamental one. You don't even have to be a fire safety engineer to realize that more air means a bigger fire. But how does air get into the compartment fire in the first place?

Through broken windows of course!

And here we come to the subject of today's episode. Because with all the considerable improvements in glazing technologies for building facades, is it really okay to assume that the glazing has failed and all we are left is a giant hole that allows the air flow inside? How does the glass fail, and when and what exactly are the consequences of this failure? These are the questions asked to professor Wang Yu of the State Key Laboratory of Fire Science (SKLFS) at USTC, China. Yu takes me through his research from his PhD at Edinburgh, and through more recent experiments carried out by his group in China. We discuss FEM modelling of glass and some specific behaviour of modern glazing technologies exposed to different kinds of fires.

If you would like to learn more about this fundamental topic, here are some great further reading resources (Yu has so far 29 papers on this subject and these are just the tip of the iceberg!):


Transcript
Wojciech Wegrzynski:

Hello, everybody. Welcome to the fire science show. Finally, it gets you the episode that was talking a lot about in the previous episode. And that is the glass in fire experiment. Extremely important subject in fire and fire dynamics studies, and very, very relevant for the. Whole fire engineering concepts of buildings. And yet not that many people researched it and it's not very easy to, to find experts on modern glazing virus. So I'm really, really happy that I found one in that is. Really, really good. And that is, uh, professor Wang. Yu from USTC in China. Yu is a prolly better known for his involvement in the Iris project on informal settlements where this project. won like all the awards that were available to get in the last years. And that was an amazing development and something that eventually must come into the podcast because I would love to share that with you. Anyway , Yu is also has on his PhD on glass and fire and he did extensive research and lazing in fire. And during his time in Edinburgh now he's continuing that in, in China. So , he has really great experience experimental and modeling experience in the glass behavior. a lot to learn from him. Uh, this episode is probably more engineering and technical than, than the usual podcast episodes. So there's a lot of terms flying around without warning. So maybe I'll, try to give you a little background on that. So we're talking about the glazing and different glazing technologies. If you think about a simple glass panel, like the simplest form of glass, that would be something we call the float glass. And, that's just glass, nothing else. Now if you subject this glass to temperature during the process of tempering. And then cooled it down. You pre-stressed the glass and you receive something that we called tempered glass, and that's something that behaves completely different as Yu will explain. And this is something that is. Very focal to his studies because this type of glasses very. force, strain resistance. So it's used for. Facades. Especially facades in large buildings, you can build a really big glass panel out of different types of glass than, than that. So it definitely is an important type of class to be considered. There's also more there's there's laminated glass. So you take. Piece of glass and you put the foil on it that changes some of the properties of the whole glass system. You receive a, basically a float glass that sticks to a layer of foil. And then the foil changes the behavior because suddenly if you crack the glass, The pieces will not fall off because they are stick to defaults. So again, different behavior. And met many times in the episode, you'll hear a name, PVB foil. That's a Or something foil that. It's a key component in this. In this laminated bill, hasn't connecting the glass layers together and it has certain characteristics, certain properties that we need to study to understand. How the glass behaves as a system. And finally, well, you'll learn that in the episode, but glass is really critical for compartment fire dynamics. The development of fires. We make many assumptions related to the ventilation conditions in which the fires take place. But do we really consider if this conditions can occur in our buildings? Like, It's really modeling. A huge compartment fire. Taking into account that. 200 square meters of windows are already open when the fire starts. Is this really a realistic fire scenario? I don't know. I hope you make up your own opinion after this episode and you learn a lot about. The glass behavior of fire. And I was, I was thrilled to finally have someone to chat about this topic because I find it one of the fundamental for the modern fire safety. So yeah, it's a little longer introduction than usual. I hope the episode meets your. high hopes. so yeah, let's not prolong this anymore. Let's spin the intro and jump into the episode Everybody. Welcome to fire science show I'm today with Professor Wang Yu from State Key Fire Laboratory of the USTC from China. Hello, you great to have you on the podcast.

Yu Wang:

Hello? Yeah.

Wojciech Wegrzynski:

thank you for taking my invitation. I was looking for an expert on glass or, or glazing in fire, for a while. And eventually you get recommended and I'm, super excited to, uh, do this interview because this subject for me, with every. Fire experiment I make is more and, and more important. so maybe let's start with, a nice, way so maybe, can you tell me about your previous studies on, when did you build your interest on glazing in fire and how did it develop for you?

Yu Wang:

actually I'll start, these areas from the, my PhD study. I mean from nearly 10 years ago. Uh, yeah, so during that stage, uh, we conducted the some experiments and also developed numerical software using the finite animal method to predict the summer stress wearing and the strand during the fire on the, or the similar load. And we successfully, predict the crack path and, crack propagation uh, of the glazing and after that, so that we can, make some, full scale experiments and regulate our, simulation. so we started this area from, uh, there, And, for now, we are conducting some experiments to understand, you know, the interaction between the glass and component of fire.

Wojciech Wegrzynski:

This is, uh, yeah, this is exactly why I brought you here because this interaction is, very fundamental to understanding, fire and fire design in, in buildings. first maybe let's start with, with the glass because, you know, if you look back. 30 40 50 years ago in, into the golden era of, of fire science and experiments being conducted. The glass used in buildings 30, 40, 50 years ago was a completely different thing than what we use today. In terms of its thermal properties for the buildings, but also in terms of properties to fire. Now we, have this, uh, modern glass technologies , with tempered glass, laminated, glass, different infill panels, different, layers, two layered windows, three, layered windows. can you try and comment on, on how this modern technology differs from this old, type like single glass panel windows from the, from the far pass?

Yu Wang:

Yes. Uh, sure. it's a very good question. So actually, 30 - 40 years ago, you know, like , they started very research to study the, to the non tempered glass breakage mainly in fire. So they developed a, a good software, which is called a brick web, and, they can, use this software to predict the temperature component and then predict the temperature difference of non temperature glass. but that kind of glass is primarily used for the windows. not for the glass facade. So actually in the very recent 10 years, from my PhD started, we started to focus on the glass facade on high-rise buildings. So like what you said, it's very different. They, for example, in China, it required a lot. You have to use the tempered glazing, in the facade. so I think the most different is that the tempered glass, when you manufacture temper, actually it's, is manufactured from the non temperature from the float glass. And during the manufacturing, if you reduce the, the glass temperature very quickly, then you will get some pre stress in the glazing. So namely it has three layers of prestressed the, the, and the compress. So you choose this pre stressed that the glass can withstand much more, uh, much higher temperature than the float glazing so I think this a red difference. So that's why I think when we started the glass, we have to, go into the stress under the fire and, uh, the combines, the some stress and the pre stress together. to then to get the critical point of crack initiation. Now, after it is crack different from the float one for the tempered it will totally fall out for the single glazing. Because they have to release the energy in the pre stress yeah, but for photographs, they have a lot of crack path, so that's, that's totally different. So actually, you know why we are now starting the tempered glazing because first the float to work, if we want a fair out in, in the fire. So it have to be a crack ignition crack pass, then press cross each other to forming the island. That some pressure may happen, may, may press on the grading or some fire. So make it fall out,

Wojciech Wegrzynski:

like a part of the glass where the island of cracks has made, and then this part will fall off, not the whole window, right in the

Yu Wang:

Yeah, not the whole window. Yeah. Only the islands. Yeah. so it may fall out gradually? Uh, So for example, maybe 20 % and 50%. Like that. Uh, so it's very difficult to practice that, to be honest, a lot of, probabilistic problems. You know, the fire is often complicated and actually the glass, you know, also, you know, why the glass crack, because it has a lot of very tiny flaws, which you cannot see it on eye. Yeah. So, the tiny of flaw disrupt very, in a very random. so both the glass crack initiation, both the, and the, the. Are very, probabilistic, so very difficult to crack that, but for, uh, so it's very difficult, topic, to be honest. uh, and now when we are focusing on the tempered glazing, so you have to deal with the pre stress problem, but the coolest thing is that once it crack initiation, then you can assume all the wall cracks. Right. You can assume a new it formed. So it's kind of easier than actually, but, but the prestressed is much more complicated, so it's very difficult to, to develop a model of this, but now we are focused on in this areas and the way eventually develop a numerical model, but it's still on the validation of bio.

Wojciech Wegrzynski:

And do you have any experience with laminated glass? Because it is commonly used in Poland. Like they, they would use, I think it's float glass, but with the layer , of plastic foil on one side, can you maybe tell us more about that?

Yu Wang:

yes. we indeed, uh, conduct agreements about the laminated glass but for laminated glass is much, is much more expensive than the single one. So, so before research, you have to, consider the advance. But if you can, uh, with standard like advance, so of course laminated glass is a better one to, to give the better fire resistance. Cause from our experiments, even the float glass cracks, uh, even for the float glass I mean, not, they still can stay together. With a PVB layer or some materials. Yeah. So, it's very difficult to fall out for this kind of, and you have to make the PVB Charing and, even melting but difficult actually, so that the glass can fall out.

Wojciech Wegrzynski:

my experience is also that, for laminated place, I, I I've seen like the cracks propagate through the glazing, like a spiders web, but it would still stay, in place. It would become soft. You could like punch it with your hand and, move the glass, not break, but move it, like make, a crater inside, but not, not break through, but it would not, fall out. So in the end you have, the world in which there. Literally three different mechanisms like float glass, where you would have cracks, propagate, and open islands in the glass and parts of the glass will fall out and you will have the glass, uh, exposed to fire from both sides. So this will, , quickly lead to more of the glass cracking and failing and more and more and more eventually the glass will, will completely fall off. You have tempered glass, which. Is much more resistant to heat, but once you pass the critical, , temperature, I dunno, uh, some.

Yu Wang:

A difference.

Wojciech Wegrzynski:

Yeah. Temperature difference, temperature gradient inside the glass. Once you pass that point, you have the cracks. You can assume the whole thing breaks out because of the release of the stress within the glass. And then you have laminated glass, which acts like float so you have the islands of cracks, but they don't follow off. They , they stay sticks to the, to the foil membrane. Until the file membrane is destroyed Did I get that correctly?

Yu Wang:

Yes. Yes. I think very, very correct.

Wojciech Wegrzynski:

Yeah, that that's really cool. And I, in Poland, I see this, especially laminated and tempered glass. I see them used together in projects. Like we often have, in the recent projects for tall building that I had, we had three layered glazing. First there was laminated, glass, then there was some argon layer, like part of the window filled with argon gas. Then there was a middle, , section which had some special foils to, um, reflect infrared and ultraviolet light to, to. Improve the thermal, uh, properties of the inside. And then the outermost layer was tempered plus because probably of its, resistance to, to stress and forces. So in essence, we, we had three glaze panels between the interior and exterior and they were also not made from like a single, it was not less single layer of glass. the laminated. Like three or four glutes together. The same in the middle, it was two of them glued. So in the end you literally have multiple layers of glazing on your way out. How do you deal with that problem in your modeling? Are you modeling just one layer or you're modeling all the layers and stresses in all of them separat, partly.

Yu Wang:

Yeah. And, actually you have to evaluate, uh, some other factors. For example, you have to know heat transfer analysis for . You have to validate the temperature inside is. And also the ambition side of the glazing. We have done that. So I think FEM method can, will do this work and that after you get the temperature and temperature gradient, I think then you can know when the ging can break. And, after that, we have to understand more about the, perhaps understandable about a PVB properties. And actually for this calculating, I do not. It may fall out very easily in a normal component. Fire, not easily, but, but, why it can fill out. we have, we also have done some, you know, double layer Australia grid. I mean, not, not, not PVB , but by some airspace, they felt out actually the primary cost by the frame. Deformation. Yeah, you have to, you have to focus on your attention to these areas. For example, we have down full scale. I mean, we, we build, we born two real compartments in, in China, my group. So actually the glass fall out, which is caused by the, the PVC cast frame you know, PVC, can even burn

Wojciech Wegrzynski:

Mm.

Yu Wang:

yeah. In the. So when the, the structure loss is stability. so then the frame with the glass, we totally fall out. I think this often happened in the real fire. Yeah. but in the previous research, we did not consider the frame constrained a lot. but you know, in Edinburg, David and I were supervising a masters student together, , that students have done very good master thesis. Uh, that is about. Yeah, his name is Paris from Poland. Have very clever guy. So, he has done the, you know, the combination of the fire and also the deformation from a frame and the impact both impact together on the, on the glass pan. So that will be write different breakage. So I, I think for, for the case you mentioned, uh, I think we can focus on more about the frame and also more about the, the, PVB properties. Yeah.

Wojciech Wegrzynski:

I remember one experiment. We were doing like a full scale experiment and I am known for notorious sticking of my iPhone into fire experiments, trying to record. I I've got my hand burnt like five times already. And my, my hand is much, much more frail than the, the iPhone is. And, there was this window, We, we had a full compartment fire, like fully flashed over compartment fire, and there was a window frame in this room and they really, really, really wanted to capture on a video how the glass breaks and hand falls off. And I was standing there like an idiot. So, you know, for like good three or four minutes next to fully flashed over compartment, waiting for this di glass to break. And what happened was exactly what you've said. It was not the glass that would like, I mean, I, I could see like the layers inside crack. I, I could hear it cracking, but on my end, on my side, on the outside, I could not see cracks. You could hear them, but you could not see them. It was like dark inside and, and so on. So, in the end

Yu Wang:

so is three layer grading.

Wojciech Wegrzynski:

it was multiple layer glazing. I don't remember how.

Yu Wang:

Okay. Okay.

Wojciech Wegrzynski:

So, at at least three, maybe even more because it was for some sort of, very energy efficient housing. So for, for this project to use multiple, multiple layers of basing it, it was not a skyscraper. It was just a normal window. But eventually the gaskets, the rubber gaskets have failed the, the frame melted a bit. And then the whole thing, slide off, not,

Yu Wang:

Uh, yeah,

Wojciech Wegrzynski:

no not. And the glass was like, ah, it was horrible. I, I really wanted to capture the glass breaking and, and what I saw was glass falling. But that, that is an interesting behavior as well, because suddenly you opened the, the whole window, not a part of the window, like in the float class scenario that was mentioned previously. So maybe we'll, we'll move. to the fire side. so you you've mentioned you now researched, glazing failure in connection with compartment, fire dynamics. Maybe you can bring up the audience in line on why would we care about glazing, failures in, in fires? Why is it so important, for the fire dynamics?

Yu Wang:

Yes. actually, that's also good question, actually, in, in a lot of previous research, when we do compound fire, we often assume there are no glass paths on, in the compartment, right. We just assume a flashover already happened glass totally down, but actually in the real fire, especially, you know, in the power building fire with, you know, modern temper, gardening, or landing gardening, they are there even after fresh over. So you cannot simply assume they are gone. And, so we have to understand how and why it'll fall out because once it'll fall out, the new air will enter the compartment to get more oxygen to the fuel, especially in the, In the ventilation control stage of the component fire. And, uh, also, you know, when the glass break fall out is it gives a new path f it can suddenly change the flame spread direction, maybe to the facade, the building, the, the compassion of facade. And also maybe it can give the smoke. Lot of possibility to go to the other floors or the other rooms yet, which will cause much more depth. So I think so that's why this is important because before you understand this, it gives to give the practitioner for real fire spread in, in a higher buildings in our normal modern building. So I think, we have to learn these areas and because I think because primarily because the mountain gas is so tough to break, so it may not break out the flash. So we have to know even out the flash, when it may break. And how it can happen. , so that's why we started these area in recent years. Uh, primarily, you know, especially for some, high-rise buildings, the glass for other areas is a lot of glass facade areas. So once the glass fall out, the, the common farm may suddenly change it, from ventilation control to fuel control fire. So in our previous, maybe 30 years, maybe no problem. The window are always small, but now people like big window room. so it can change it, the opening factor, much more significantly. So I think we have to, to lend this areas.

Wojciech Wegrzynski:

in the very, very far past the go, you would rely on something like a standard time temperature relation For, uh, designing your, your structure in, in, well, you still do, but, uh, that was the only understanding of the fully developed fire back then. E eventually we got the compartment fire models, which, connect the size of the fire with the amount of air available through opening factors. Like you mentioned the ratio of. The part of the building that is open to the surface of the structuring side, more or less, that's not accurate description, but that's the physical meaning of it. And, and now if you want to understand the temperature in your compartment, you need to know this opening. In fact, you need to understand how much air is available through eintrainment into the compartment and how much can go outside of the compartment, from the fire. And we. when you would design, a building, You would know the area of your windows or area of glazed or, and you, you could mistakenly, assume that all of it is empty, that you have the maximum possible open factor because everything fell out, which may be the case after a few hours of your fire, like, or. An hour or two hours when you have exposed this, glazing for the maximum temperature for a long time. It, it could fall out actually. And, and it could be a, a description of the maximum biggest fire you can have in that room. But, if you have a fire that is growing. A fire that is building up and, and transitions to flashover. It has the, the, the whole glazing closed. Now a good question is, are the conditions in that early stage of the fire sufficient to break the glass easily and, in what amount. Do you have any experience in like pre-flash over fires, destroying glazing or opening this new flow paths or it has to be like, it, it must be conditions like in a fully flash over fire to destroy this modern glazing.

Yu Wang:

yes, uh, we have done some small scale and also done some, full scale, full small scale S when the temper got totally fall, fall out can see that the ejective flame, is very big. I mean, suddenly, um, maybe three times bigger than a normal flare. So I think, suddenly in maybe during only one or three seconds, but this is already very big threat, for the first spread. I think this is very interesting, uh, things and you know, it also can, when glass break for it can also change the, the distribution of heat flux so that means in the room, that means your structure will. Be subject to very different heating condition before and after the glass felt. So I think that's a very interesting thing, but for the full scale, uh, like, like you said, last year we, we have conducted them two full scales. One is, there's no window and no door we just burn a furniture. And the fire, you know, just developer as a normal stage, early stage and the flash over and something, but it's only, but it actually, it only as the bottom line to, to make a flash over happen. But you know, when after we furnish the glass panel,

Wojciech Wegrzynski:

Hmm.

Yu Wang:

And the door. Yeah. And during fact we close the window and close the door, then we ignite the room and something interesting happens. and the fire develops first and the then, due to lack of the oxygen, the fire, kind of self is, and also it may cause. Best if you open the door on the window, but so the room is in the, with the temperature of more than 400 degrees, for more than 10 minutes. So maybe there are some smoldering on the bed, on the sofa and, that what is interested in that even the smoldering fire at the last, make the glass cracks and make the fail out to. So then after the, after a while then the fire become much bigger than the Tesla web, you know, the flash work. Yeah. So I think, so that's also very interesting phenomena that, even make the fire bigger. If you install the glass pan and the glass, if the glass fail up at some, some point.

Wojciech Wegrzynski:

for me, an interesting topic is the natural ventilation of offices. And we were also doing, we're doing a lot of research in that field. I, I'm not sure what the, how it is used in China, but in Poland, in particular. We see a lot of, natural ventilation even in, very tall buildings. because it gives, many points in the green certificates, you know, LEED, BREEAM, you get many points for, for having access to, to natural ventilation. And it's not that you have a whole panels of, of glass opened in the facade. It's it's more like you have this, um, narrow. panels, maybe 20 centimeters wide, which you can open. And they're like close with the porous uh, steel mesh outside. So you cannot even put your hand, but you can let some air inside. So I, I think even in, in such conditions, when you have some sort of ventilation for the compartment, like natural ventilation, It would be very difficult to oxygen starve the fire, like in you case, but it would still be not enough to develop into fully fleshed over fire in a compartment. So it would be even closer to the conditions you've mentioned with the, with the smolder. It would be some flaming combustion adding to the energy. , so, so you could have this, Let's say pre-flash over temperatures for a very prolonged, time in your compartment. And the second thing that comes to my mind, if you think about the traveling fire methodology that is commonly used now to design offices in, in, in large buildings, it. Pre assumes that parts of your compartment are preheated by the fire that is far away. So you have a fire that is far away and, but the smoke is covering the whole compartment. So you still, even though the fire may be far away, you still have your glazing exposed, to some high temperature from the smoke anyway, before the fire comes. So, so these are 2 scenarios that come to my mind, thinking about. pre-flashovered fire can, create damage to the glaze. And did you try to, burn any objects directly against the window? Like, uh, I dunno, an arm chair, uh, a sofa next to a glazing does a can, can like, uh, a direct exposure to a fire, to an item that is next to a window destroyed that window.

Yu Wang:

you mean directly put the window,

Wojciech Wegrzynski:

Like, if you have a window in your building and you put a sofa next to the window and you burn the sofa. So you consider the, fire of that, item, not the fire of the compartment. Will that be sufficient to destroy a placed window or

Yu Wang:

okay. We, not this, but we do a pool fire you know, just beside the glass. Yeah. Similar condition, you know, like the ambition condition. Yeah. It can, it'll make it kind of make the, the, the float glass crack. Yeah. Non temper. But, but it's kind of difficult to. To make the tempered glazing crack and not, not, not. Yeah. Yeah. It had layers. Yeah. I think it's very difficult for the, in the open condition.

Wojciech Wegrzynski:

understand. Understood. I also wonder if you reverse the problem, when you discuss the separation between buildings or the, how fragile a building is to a wildland fire, for example, we often consider how easy it is for the fire to get into the compartment from. So I wonder also like from, if you reverses the perspective, I guess, because the, the windows are harder to break, they have better tele terminal properties. They have, infrared, uh, reflective foils inside of them. They must be also much better in protecting the building from the fire that is outside or, or on a separate building. Do you have, have you had any experience with that?

Yu Wang:

So, yes, when you put the fire inside the compartment, then it's har building fire, urban fire. But when you put the fire, you know, why we, we did the fire, just put me the pool fire just inside the window, because we want to S the, the WUI,

Wojciech Wegrzynski:

Mm-hmm

Yu Wang:

uh, situation. Yeah. So I think the radiation is a primary way to make it a. And, as I mentioned in the interview that, uh, I think also the, the frame material is also important cause you are subject to the fire brand issues. Uh, so if the window is closed, I do not think the fire brand may make the glass break, but it may ignite the, the PVC window frame or wooden window frame. Yeah. Especially I think, I know at time I know, but in China we don't use the wooden frame a lot, but in Europe and in. Especially in the WUI areas. People like to use wooden flat. So I think this is very important to, to make sure that make the glass safety to make the window safety.

Wojciech Wegrzynski:

And in terms of, the radiation being able to penetrate the glasses, it's still like the outermost layer that would, be the most exposed or maybe some, because you often use the, the shading foils inside of the compartment. We are not fully transparent to shade a bit, or to reflect infrared radiation. This would not be used or, or is it used on the external? I, I'm not completely sure on the technology. Maybe it's used on the external, um, layer of glass, but do you see it different, for example, temperature gradients inside the glazing in this scenario or, or, or it's the same?

Yu Wang:

I think they're similar because the, the maximum temporary difference often occur just as a border line between the cover areas. I mean, Fran cover and the Fran post areas. So no matter if the inside or outside, I think the maximum temporary difference is at that point. So the crack often initiates and in the middle of the

Wojciech Wegrzynski:

Mm.

Yu Wang:

is often as age. So, so I. There are no big difference, you know, between the inside

Wojciech Wegrzynski:

Yeah. And, and a stupid question. If you have half of the window shaded, like if the radiation hits only half of the window and the half is in the shade, because you had a corner or something, will that create a temperature gradient that can also be, uh, more difficult for the glass to handle?

Yu Wang:

Yeah, I a did a very clever question. so, Yeah. If you change the share, uh, forms, it may, changes the, the correct, location, I guess, because we, we also talk some numerical simulation about this, you know, we, we, we change different shade angle, So that will be D. but the best way that, you know, very changes the installation or changes the, the, the shade forms of the grading, we find that, you know, if there's a hidden frame, no, no gas frame there. We do not make it a break,

Wojciech Wegrzynski:

mm-hmm

Yu Wang:

but there are no such big temporary difference, uh, by subject to a

Wojciech Wegrzynski:

mm.

Yu Wang:

You're no friend, for example, you, you are just a hit the glass, the glass, we are not great. Yeah. So I think maybe this is some, some way to prevent the, the crack, just imagine, you know?

Wojciech Wegrzynski:

yeah.

Yu Wang:

Yeah. Because yes, because in har building, they are hidden from, uh, hidden

Wojciech Wegrzynski:

We see them a lot. Yes. Yes.

Yu Wang:

Yeah. But the problem is the glue, you know, the structured glue, the grass and the area. So.

Wojciech Wegrzynski:

And, uh, in the description of your previous experiment, you've mentioned the glass was exposed to approximately 400 degrees for like 10 minutes. that is a lot of temperature, like. In my school of engineering, how I was told, you could assume that the glass will fail at 300 degrees, maybe 250. You could see some cracks. I wonder do you have numbers of, what temperature to assume for this, glazing to fail? or it's too complicated than you need to go. Uh, FEM modeling

Yu Wang:

yeah, actually for the engineering, I think you assume it's critical condition for crack and, actually, factor for gas break, is the temperature difference. I mean tempera gradient rather than the temperatures. So even though , the room temperature, is for me, maybe 500 degrees or, 900 degrees, but you cannot see what temperature it is on the glazing and what temperature difference. So you have to measure the temperature difference on the glass stuff is So that you can determine okay. crack or not crack or not. So I can have assume that. Yeah, I think a room tempera. I think crack cloud crack in a very wide range of room temperatures because room temperature is not the, the critical factor for its break.

Wojciech Wegrzynski:

Mm-hmm . And, in your modeling, do you now have a, a way to couple this into the simulation because if I model my compartments in FDS, One way to do the glass breaking, you would set a device with a temperature trigger on it. And once this temperature is met, the glass would disappear and the, the wall would open that. That is a common way. We, do this, in CFD modeling, You you think at this point it's a correct way or more sophisticated models are needed. And if so, do you see these models be created and implemented in FDS in future?

Yu Wang:

Yes. I, think, because now, uh, while my students are doing, you know, something you mentioned with the FDS, you know, once the temperature reached some point or hit flex reach from, you know, it just remove the,

Wojciech Wegrzynski:

it disappears. Yes.

Yu Wang:

it disappear. So yeah, it, can simulate to some event in that, uh, Difficult for you to, to match the, the experiment last, I mean, break time and the break time in the new macro simulation. Very difficult. So I think, FDS, cannot practic very well for the glass breakage. but we need some more specific and some more complex modeling, I guess. So actually you can also is actually that is, is similar to the, the structure fire.

Wojciech Wegrzynski:

Hm.

Yu Wang:

You get the temperature distribution of the glazing, and then you do the FEM analysis in another

Wojciech Wegrzynski:

Mm-hmm

Yu Wang:

software that you get the correct, you know, the clear condition then it'll change. So, so I think that you, it is very similar to structure, search your fire.

Wojciech Wegrzynski:

It's interesting. like if you have just the float glass or, or, or just a single layer of tempered glass, I mean, this approach you've mentioned, or, or I've mentioned would be okay-ish to model that, you know, if you have just one layer, but if you have multi-layer glass, especially with the zones inside the, the, the glazing. So it, it makes a very comp and the PBV fall. Uh, it makes a very complicated, thermal boundary condition inside. I mean, FDS has this, uh, one D and 3d, uh, hit transfer models inside. So you could technically, solve for that, but it could be interesting to have a, you know, uh, a glass boundary condition that you could put and the software would know it's, uh, layers of glass that will break. At this temperature gradient, and it could know that. Okay. Uh, now 1, 2, 3 layers have failed. The fourth layer is exposed. Okay. Now it broke completely, uh, disappeared element. that, that would be an interesting development. Maybe you guys would, developing your models will be able to, to build something like that. Are you

Yu Wang:

Yeah, this is what we are doing, actually, you know, I got a project from the start of this year, so we are doing focus on these areas. So that's very interesting. Actually we hope, you know, we not want to make things very complicated. You know, we, we want understand the complicated issue and make these things very simple to be used. So we hope, you know, even in the current FDS, if we do some as assumption or some cation that we still can, uh, kind of, accurately, I

Wojciech Wegrzynski:

mm.

Yu Wang:

accept way the, the project, the glass breakage. So I think that's also very cool, because you know, the, computation, time also another factor we have to consider if we. You know, single cleaning, you know, so a lot of, things to, I think that's not very, efficient in the engineering. Yeah. So we want to make the, things as sync as possible, but in our accurate way.

Wojciech Wegrzynski:

Mm-hmm . I also think the coupling outside and insight, like back and forth would be difficult because so far, I, I know it is fairly easy or very easy to, extract from FDS to FDM models. I just had Thomas Gernay on the podcast and he was, talking, aboutI how it does this, um, extraction of the data that there's already a model building FDS to helps that extraction. But if you extract to another software, And then would like to come back to FDS with the information. Okay. Now it broke and destroy the window. I think it is quite, quite difficult at this point. Are you working with other numerical models as well besides FDS or this would be development for, or, or is just unrelated to software is just a, a third party model outside of any CFD.

Yu Wang:

Yeah, we, because we have inhouse software, uh, for, yeah. For, for, for crack initial. So maybe we, we get this temperature, then we can get the crack, in our in-house software. Yeah. So, but this is still ongoing. so the servants are fine and, to compare the results with experiments. Yeah. So to, to, to modify. Some numerical simulation often need a lot of, you know, assumption or a lot of time to be validated. Yeah. So we are doing this. Yeah.

Wojciech Wegrzynski:

Very very good. Maybe just as a final question, how do you see the, the near, uh, future of glazing? Is there any new technologies emerging that, will change everything in the next 10 years? Like the temper and, and laminated last changed the, the last years, or we are now in a stable region and just. And just slowly improving the technology, what the future holds.

Yu Wang:

Actually, I, I treated this area as a boundary condition of the fire dynamic problem. So, uh, we do not, uh, you know, focus too much on the glass technology. So we cannot predict what kind of new. Glass can appear or maybe yeah. but what we can practice as the glass will be used as more often and more widely, much more widely in the future because, I think it's similar to the, you know, people are like using the timber. Building because Tim will make you feel very nature and very, very nice the glass where I can say in China, you know, many buildings are using much, much more crazy, even the channel of the flaws. And, uh, you know, in, in maybe five years ago, they like to use the concrete and still better people. You, you like to use fast. Everywhere. So I think a glass may be much more, widely used in the future. I think this, this is more important than, than previous years. Yeah. So this is what, this is what we can see that

Wojciech Wegrzynski:

and, uh, so sorry, I, I told you it will be two questions, but it's like now, now the question number seven, but it is so interesting. right. We also have this, double skin facades. Where you would have, a facade of the building, then let's say one, two meter cavity, very large cavity, and like an external covering, facade, I guess, in this we scenario it also be very good because you would have this frontal panel that can take the heat. And did you have an experience with this type of facades

Yu Wang:

yes. I think the problem for this kind of top skin is, is a smoke movement rather than the glass breakage. It's more about the flow

Wojciech Wegrzynski:

Mm.

Yu Wang:

Yeah. So the smoke entering the, the, the cavity between the facade and the second skin. Yeah. So, only it depend on where the fire happened. If the fire happen in the room. So after the break, the, the window, so the smoke can let go out. But I, do not think it's very easy, you know, to, to break the, the glass, you know, in the floor. I think the problem is the smoke will, may go, go up and maybe enter the

Wojciech Wegrzynski:

as I, as I said, you can have natural openings in Poland in these buildings. So you have a natural openings to which the smoke could reenter the building, creating a very dangerous dynamics. This is actually something to consider with the, that should be a podcast episode. I'll note that down. I need to find a double skin facade expert now that's so cool.

Yu Wang:

yeah.

Wojciech Wegrzynski:

Okay. And, and for the end we have talked something about, the future technologies and, one, future technology that I see am developing is different. Approaches to create energy generation within, uh, glass panels like embed, some sort of, Silicon, uh, foils or, or perovskite foils inside to generate electricity within the glazing. And I don't expect an answer, but I think this could be also a thing that changes the way how facades are built used and how they behave in fire. Do you have an opinion on these new technologies?

Yu Wang:

You mean the PV panel

Wojciech Wegrzynski:

Yeah, but even, like PV panels, when you put them on a facade, that's one topic. And I, I see that happening. I, I know there was like one building in China, which had like the whole, uh, facade of the building covered with, with PV. And that was amazing. It was insane generation of energy, but I read, in like, Pop science, magazines that, they would like to embed the, the, the PV inside the glass, like a foil inside the, so it would be a part of the glazing. You would probably not even see the, the foil being in there. So you could cover the whole building with this, uh, type of files and, and panels.

Yu Wang:

Yeah. Yeah. Actually this is the new research research direction in my group. so, so I think the substantial issue is like, is a glass breakage issue. Actually, what you mention is similar to them,

Wojciech Wegrzynski:

It's similar. Okay. So, so similar challenges. I, I also wonder how we will handle the, the, all the cables inside the, the, the facade structure, especially if it's PVC . I see a risk in with the cables and, and energy transport and, and firefighting operations on, on, uh, FACS that are under electricity. So that is a whole array of challenges emerging.

Yu Wang:

Yeah. Yeah. Much more complex. Yeah.

Wojciech Wegrzynski:

much more complex. Uh, okay. Uh, Yu uh, this was very insightful. I, I look forward for the, uh, work of USTC in, in the field of facades and every, and every other field that you are researching. I know your group at your laboratory is like, One of the biggest, if not the biggest in the fire science. So I'm really happy that the Fire Science Show finally came to China and had the guest from the biggest group out there. Uh, yeah. Congratulations on what you are doing and all the best for the future. Xiexie

Yu Wang:

Oh, . Thank you. Thank you V. Thank you for partition and thank you for the audience for listening. Yeah. I will show this, this very good shoe. I will assure it to the, the co and the, the students in our state.

Wojciech Wegrzynski:

And that's it. Thank you for listening. And, , Thank Yu for, coming through the first issue and telling us all about the, the glazing and fires. It was certainly a very. Interesting and, and packed with information episodes. I could not extract a single number from Yu on what temperature. The fire will break the glass, I guess. We have to stick to the literature reviews and, Yu has written some great papers. I'll cite them in the. Episode. show notes. So you can then Ravel. Uh, you really enjoyed talking to them. I really enjoyed the research they're doing in development surging at USTC especially the ones related to creating new models. If we get gather last breakage model. That we could implement somehow into FDS or other Those are being used. And just have a glass boundary condition and just have the software figure out. At the bold point, the glass will break crack. Fall off and to what extend that follow-up will be. We would enter a whole new level of modeling. Today, we were doing that in a very simple manner by creating devices, opening. Parts of the model. As soon as certain temperatures are reached. I mean. W it works. It's better than nothing, but I think. Thanks to models like the ones created by Yu's steam. Uh, we can really up this game and really improve our modeling skills and make this simulations more realistic. And if we couple that with, uh, Models that use real fuels. They use ignition solid, solid phase, um, pyrolysis, this combustion, uh, They smelled the fire actually. If you couple that with a really good model for ventilation conditions. We are closer and closer to modeling real compartments fires in, in our CFD. And that's a beautiful direction. And, as soon as I see something emerging in the field that. brings us closer to the solution. And the, helps us understand real fires better. You may be sure I'll bring it into the podcast. And that would be it for today's episode. I also hope it will let me reach some new listeners in China. I really hope for that. Yu as promised me. To share this episode with their internal mainland channels and help spread the word about the podcast. I really hope to find new listenership in, in China where I did not have that many and, uh, that would be great news for the podcast, reaching more engineers and more scientists around the world. And as usual, if you know an engineer, if you know a fire scientist, you know, a. A firefighter. Or anyone else who could Benefit from listening to the fire science show placed at the note that the show exists. yeah. And thank you for listening. See you here next week. Next Wednesday. Cheers