038 - Fire resistance is not always enough for timber with Daniel Brandon

Hello and welcome to the fire science show. Episode 38. First, if you came here because someone referred this podcast episode to you as a good source of knowledge about wood in fire. And the issues with fire resistance. You're in a great place. Please listen till the end, because. This episode is jam packed with, insights that it's very hard to find. Elsewhere. In such a convenient form. So. Dear listener if you're here, because you're curious about. The wood in the fire. You're going to like it. I guess, well, maybe not. What we have to say, but you're going to enjoy the new knowledge that is being shared here. By people who actually research timber in burning fire. And to All of my trustee listeners. Welcome again to the Fire Science Show. It's going to be a fun episode again. I know timber in fire is one of the favorite topics on the podcast, and I'm going to bring more of that. And today I'm bringing you Dr. Daniel Brandon from RISE in Sweden, who is a researcher on timber in fire, on mass timber in tall buildings. Who has done multiple large scale fire experiments with exposed timber. And knows quite a bit about the difficulties related to this subject. And for this talk I chose the theme to be fire resistance because, I am very curious was Daniel opinion on fire resistance, but as you will hear. Well, we ventured quiet away from that in the episode. Into some of the very important things that matter when designing timber building in fire. So yeah, maybe, maybe the topic is not correctly picked. But I like it. So I left it like this. And, yeah, I hope you stay to the end. It's a great episode. Full of great insight. I hope you enjoy it. So, yeah, lets go. lets spin the intro and jump into the episode. Hello everybody. I'm here today with Dr. Daniel, Brandon from RISE in Sweden. Hi, Daniel. Great to have you here.

Hi, good morning. good to be here.

we've met like in 2019, I think it wasn't. You were, at this point receiving some NFPA awards and I think it was also related to timber fire, right?

Yes. That was a project we did, in collaboration with NFPA and NIST and NRC, Canada. And we got an award for the project.

That's so cool, because today I've invited you to talk about another aspect of timber in fire, which is a very popular theme in the podcast. And, so far I I've talked with Danny Hopkin about, the overall fire engineering of, mass timber buildings and implications of that, both the positive and the negative ones. I had Felix Weisner who did, talk in depth about the role of adhesives the physics of, moisture transport in wood and some really, really interesting things about how it behaves and that's. in all of these talks, we often come to the concept of fire resistance and I need to talk with someone about this concept in relation to fire. And so I figured out you were going to be a great guest in, in that topic. So to set the theme of our talk today, we're, going to be talking about, the concept of fire resistance in timber buildings. Maybe you would like to introduce the listeners to, to like, what is the fight resistance? Because I have this feeling, you know, that, fire engineers who work in laboratories or are researchers have a completely different comprehension of what fire resistance would be then an architect or a non-fire stakeholder, which is the root of the problem. In my opinion,

Yeah, sir, there are many misconceptions about fire resistance testing and I will get to the misconceptions later. but fire resistance testing, is usually done on, structural members. It could be walls ceilings or floor slabs, columns and beams. then we have structural fire resistance testing and we have, a compartment dividing, fire resistance testing and a combination thereof. So you can have fire resistance sets where you look at, the ability of a wall to, define. Compartments, to bear the loads, in a building during a firearm. And, the problem is that we don't actually look at real fires in a fire resistance test. weave in a fire assistance test. We follow prescribed, time temperature curve, and that is actually defined by the, ISO 8 3, 4 standard.

So the thing is that it's not a fire. It's more like temperature, boundary condition in posts on the sample. And, we know it, let's say worked for hundred years more or less, even if we hate the concept and that we know it's unphysical, but, but it's somehow worked for the industry so what, why coming back to it now? W what is the difference when you put the timber frame or combustible wall inside?

well, if, if you're a specimen is combustible, and it becomes involved during the fire test, it actually adds to the heat. the furnace. So you're, combusting wood adds to the heat energy and the temperature. however the temperature is controlled and that means that you somehow have to lower the energy input. And the only way you can actually do that is by lowering, your fuel input in the furnace. And that means that your burners will you have to reduce the burner efficiency in your furnace, um, It is actually possible that your, specimen contributes enough to completely shut down the burners. And in those cases you can still control the temperature by increasing the ventilation through your furnace and reduce the temperature by reducing the ventilation, through your furnace.

I'll ask you a brutal question that I'm often being asked by, people who disagree with with me, questioning this feature of furnaces. And I also feel uncomfortable turning off my furnace when I'm doing fire resistance test. In that case, maybe we should call it, the cooling, fire test or something. When we use the furnace to reduce the temperature rather than increase it. But, I'm often being asked. So what I mean, the sample burns, but the temperature is inside. So what, it doesn't change the temperature condition, but I feel that it's still wrong. What's your opinion.

it depends. It's actually, this is a very difficult question, but it does depend, when people talk about these kinds of questions, they somehow refer to real building fires as well. So we actually have to look at both and real building fires. The energy contribution of wood go somewhere. I guess there are three options. The energy combusts inside the compartment, the energy commerce outside of the confinement, or it doesn't combust at all. and I guess, it is possible that it doesn't combust at all, but because it's just combustible gases that eventually don't combust, but it's not actually very likely. So it's either combusting inside or outside. when it combusts inside, it actually increases the temperature. however, in a ventilation controlled fire, the gases cannot combust the inside. There is not enough oxygen in that case. It combusts outside and it might influenced a fire exposure to your facade. but it doesn't increase, the temperature inside the room. What it can do is actually extend, the fire duration. so in, most cases, the fire is influenced by the contribution of the wood. and that is not the case in fire resistance testing. However, if the ventilation controlled condition, in real buildings, the contribution of the wood has the least impact on, the internal compartment, fire conditions.

Thank you. I'm just writing a rebuttal for a paper about fire testing of food that this will be helpful. And, but, for seriousness, I think you touch a very important thing that, when, We question and the fire resistance, the discussion is magically move towards fires in buildings. Whereas, as long as we don't discuss timber in buildings, fire resistance is, discussed, you know, as a testing protocol, not, a real fire phenomenon. So I feel that there's some acrobatics happening, you know, when did you justify an opinion? We, we suddenly start, saying that that fire resistance is a good representation of a building fire when or it's not, especially not, a fire on its ventilation control, not a fire in a fairly small compartment that is ventilation controlled, which we know that may have much higher temperatures than the standard fire in, the first 30, 60 minutes. For sure. And. There's also this, you know, parametric fires and there's this magical gamma parameter, which describes the ratios of openings, the walls and everything. And there's the value of that, which is one where the fire is exact as the standard time temperature relation. And I must admit in some fire experiments I've seen the configurations like that in any truly did look like a standard fire. So I'm not saying that fires like that do not exist in reality, but I've seen so many where the peak would emerge so early in the fire and would be like in the, in the range of one thousand one hundred thousand one hundred degrees, much more higher than, and then the standard curve or the peak would arrive very late when, when we did traveling fire experiments and that the peak arrived after 30 minutes of, very, low temperatures. So. You cannot put the parallel between the furnace and the real fires, and you cannot use real fires to defend, the furnace when something is not right. I wanted to ask you, because I know you have been involved in, a large mass timber project Fire Safe Implementation of Mass Timber in Tall Buildings carried in RISE and, you've observed firsthand the behavior of, of large compartments with, multiple surfaces exposed, of exposed timber. how did that fire dynamics look? Did you observe differences in the compartment fire dynamics when changing the amount of exposed wood? Because you had the same compartment over and over, right.

Yes. So we, did do a number of tests actually in total I've being involved in 18 compartment, fire tests. So not only that project, but, , the exposed wood does contribute, , to fires in several ways. And, the project you talked about, most fires for ventilation controlled in those fires, you don't actually increase the temperature inside compartment. if the baseline test with everything without exposed wood is already ventilation controlled, you can actually expose wood and the temperature doesn't increase. However, the duration of the fully developed phase did increase. And also, the external combustion did increase, in compartments for the larger opening we actually saw that you can actually increase the temperature, in those cases, the fire is ventilation controlled, and it might, extend the fire duration. but we haven't seen a significant extension of that failure duration for those compartments. I guess the conclusion is the energy goes somewhere, but if it's a ventilation controlled fire, it doesn't really go inside until the end of the fire. When, when your, fuel on the floor starts to burn out. Then it's still possible that your, timber structures keeps your, fire fully developed for a while.

Yeah. So, that would be the consequence in fire dynamics now in terms of exposure, right. I you say plots and you say that the ventilation control doesn't increase when you expose wood but you are already touching like 1200 degrees Celsius. So, I mean, there's not much more space to increase from that because you're almost at the flame temperature with your upper smoke layer. So, so there already has been, yeah, there they are. I mean, in standard fire, this temperature would be reached I don't know, at sixth hour of sun or something. So after 30 minutes, you, you have, 800 something degrees. After one hour we have 930. So that's a quite a vast difference. And, in real fire you can expect temperatures well above a thousand. And in a test, you subject your specimen to temperatures around 800, 900 ish Celsius. And, we need to remember that, radiation is in the fourth power of, of temperature. So the differences between these two values in terms of the heat flux are insanely high. degrees between and a thousand is a I mean, a hundred degrees between 900 and a thousand is a really, really big difference. so now in your compartment, fire experiment, you have completely different exposure of the surface of the woods than you would have in the furnace. And. In the, in the furnace, we know that, we sometimes do, well, maybe not us. Maybe it's the costumer, so the clients, but. you know, you design a sample to pass the test. You don't design a sample to be the best sample in the world of samples. You design the sample to pass the test. And in terms of passive fire protection, you choose how many protection boards or what's the depth of the intumescent paint, or how much wood you need to put on it to just pass the test in terms of wood, this engineering is often done in terms of chairing. Like you would have this depth of char in your, test specimen, which will make it okay at this exposure. But then you go into real compartment. It changes completely that you observe, quicker child formation or stronger char fall off in this experiments compared to what would you see in, in, in a resistance tests?

yes. Yeah, definitely. the charging rates are much, uh, they can be much higher in a, in a real compartment test, than we speak of without delamination. You can have one millimeter per minute, quite easily, with delamination, , temporarily, it goes really much beyond that. It goes two millimeters per minute, for a while, and then it quickly lowers. yeah, I think, one thing that, is important to mention is that affects of de lamination in a compartment. Fire are much more significant than effects of delamination in a furnace. So in a furnace test, we might have some additional charring. and, eventually to meet the criteria and to, to meet the requirements, you might need an additional amount of material. So you can say you need a certain percentage of extra material to together fire assistance of two hours. but in reality, if you allow, delamination in a real compartment fire, it actually can have very significant consequences actually can mean, the difference between a building with standing of full natural fire, or are actually a building collapsing eventually, during the fire. and then we don't talk about a certain percentage of additional material. You just talk about, a very significant

You've

of the fire.

In ITB and we did let's say a funny experiment. we've built a walls with OSB sheets on a timbers substructure. , very simple wall that was calculated to withstand something like 30 minutes of standard fire exposure and we've went into, okay. So if we want the furnace, we have this standard temperature relation in it. Let's find. How much heat the furnace does need to actually hit itself up to this standard temperature. So we've closed the furnace, with, a wall that's built from the same material as the furnace. So there was no sample, it was just a furnace. and we've run a 30 minute fire resistance test on the furnace itself. And we've captured, this, we called it the baseline heat release rate. Like we we've captured how much heat does the furnace need to heat itself. Then we've placed the OSB wall. We've done a standard fire resistance test. It didn't go well because we couldn't control the temperatures. we maybe have used two small furnace for that, but, the temperatures were already like a hundred degrees above both the standard curve and we couldn't have not do anything more about it. It was very hard to control and then we've did the same test repeated it, but we've imposed the condition on the furnace that, okay, you can lower the heat release rate, but you can never go below this baseline curve that we determined that you need to hit itself. And the idea was that. wood is a very good insulator So, we will impose at least this amount of heat that you would need to heat up an insulator to the standard 10 time temperature relation and whatever would contributes from itself it's contributed. And it will just raise the temperature. And here we got like 200, 300 degrees above a standard curve. The test duration has decreased from 28 minutes to 23 minutes if I recall correctly. so the, difference was quite striking. It was so much quicker to destroy the, sample. And then we did a third test in which we have, done the same. I in the second one, but we've over ventilated the furnace. So we said, okay, now you have the baseline heat. You can combust and you have all the oxygen in the world you want for combustion. So burn as much as you want. And we actually lost some turmeric couples. It was insane. The fire in the furnace and the sample got destroyed in like 16 or 17 minutes half of the time, then it took to destroy the same sample in the standard test. And of course it was just, an OSB wall, nothing fancy, nothing really designed. It was not structural timber or not nothing really like, it was a sample that that's it. We didn't have any, agenda behind it to show that OSB walls can be great. We just wanted to test the conception, that idea that if you impose like a baseline heat released and the test goes quite different and. The funny aspect is if we have put the same condition, like there is the minimum heat release rate into any other tests, like any other non-combustible test, it would not do anything because the tests were already above the threshold because of the furnace action and the, he transferred the sample and sample not contributing to the furnace. So it only affected, the sample in the furnace. So I found it really astounding that when you change this little in the test, And we did add literally 200, 300 kilowatts to the furnace was not a huge amount of heat that we add. And you suddenly cut the fire resistance period by 30%, by 50%, that's astounding. And now in your ventilation control room, we know that there is damaging going in the, in the compartment. You may lose doors, you may lose windows. You may, have cracks in the wall that suddenly give some oxygen near the sample, and then it will contribute. So it will be somewhere between our experiment two and three. So I wondered if you ever tried, something like that

yeah. And that, that is, very difficult question that I don't have the answer to, but I think, it's good to discuss the problems that we face. So in a furnace is designed to maintain the heat. and we have very insulated walls small ventilation, very little ventilation usually. and if he add the contribution of wood, yes, it will be very significant, and it will be more significant than in most building fires. So in a building compartment, we have, lost his through walls, but it will be, likely more than the heat loss through, uh, furnace wall. we have usually much more ventilation, especially in case of a flash over. if he add the energy of wood in a compartment fire condition, it will have a different effect than the energy of wood and a furnace condition it's is however, very interesting. it's a good attempt to include the contribution of wood. However, there doesn't seem to be a very easy way to do that, in a way that is relevant. So another method that, includes to contribution of wood in addition to the fuel is, a radiant panel testing. we, at the university of Edinburgh developed, , the H Tris test where a radiant panel moves towards a specimen. Actually, those were the first fire tests I've ever conducted at the university of Edinburgh and what it does is it oppose imposes, radiation to a specimen and the specimen combis and, it leads to, flames as well. And those flames radiate to the specimen as well. So there, you can see you actually, separated the heat source, and the fuel contribution, and both are included in the test and this test can be relevant in some scenarios. However this test is actually done, in room conditions and you have a lot of oxygen available, and that is sometimes the case, in a building, but actually only right. When most of the times, when you have a flashover fire, you do have a low oxygen concentration close to your, timber surface. And, what we found is that this age stress test, I guess it's useful for some scenarios, but not to represent a fully developed fire or a flesh over fire where oxygen concentrations are low. one issue that timber has an high oxygen concentrations is that the char that comes to exist, starts to oxidize and that results in additional energy and in low oxygen concentration environments this char doesn't oxidize. At least it can, reach very high temperatures of around 1200 degrees without oxidizing. and therefore it doesn't, lead to this additional energy, but it also, it also maintains the char layer, which is also an insulated

it's really, nice that you've already made the paralell between the fence and the environment that in fact, in a furnace edition of the timber combustion will be more severe because of the, of how the furnace is constructed versus how the compartment is constructed. And we need to keep that in mind. Thank you. Thank you very much for that. That's a very important thought. and obviously there is no simple answer. We did it as in literally exploratory experiments because we just wanted to see what happens. You know, we are and I, I guess you say you share the same passion for fire. You know, there is only one way to find out what happens it is by setting it on fire. And, I think, and H-Tris is also an interesting approach, but I think we somehow need to fit the, the timber in the furnace because of the paradigm of the industry. You know, fire resistance is so prevalent in the industry that. If you want to have an effect on how buildings are built, you need to go back to fire resistance. The architect will not care about whether wood oxidizes or not. They will care if it's 60 minutes or two hours, because that's what the code tells them to put in this, barrier. And I think the battle may be already lost. Like we will not be able to change the paradigm, at least not easily. Like we will not be able to tell from today, we're not working with fire resistance periods because It would be too difficult for the other stakeholders to comprehend. So we need somehow to find a way to, give a number on the timber structure that is maybe a little more realistic, but, would be comparable with everything else. And I have no idea how to do that. That's a hell of a problem.

yeah. I do have an answer, I guess. I've got, I've got an opinion. So the problem is that, we work in and prescriptive regulations. We work in, classifications and this system has been used for classification for a long time, for more than a hundred years. and in artists you use that in a useful way, that led us actually to challenge and, whether we can use it is actually, dependent on what you want to achieve. if you ignore timber or the combustibility of timber, if we look at concrete structures in the past, fire resistance testing has been to some extent, useful to, to prevent collapses in buildings who can say, okay, the, the exposure is not very realistic, but you can say if you, if your fire resistance requirements is high enough, let's see we take a fire assistance of, six hours In a concrete building, it's very, very unlikely that your structure will collapse. and no matter what the fire curve is, you need such a high fuel load and such a severe condition that is actually in reality, very unlikely. So for timber, and that actually changes a bit because there is a scenario where your timber just continuous to contribute to the fire. You can say if the, a contribution to the fire of your timber structure, doesn't stop, until it's fully consumed, then you have a problem because then you don't have a timber structure anymore. You will have a collapse and that's, one difference. Uh, so if the assignment is, the goal is. prevent collapse in any natural fire, without relying on something or someone extinguishing the fire, then you need more than fire resistance. You would need a whole set of prescriptive regulations. You need a limitation of how much timber you can expose you need, , requirements regarding material behavior. For example, if your CLT is allowed to de-laminate, it becomes really difficult to actually guarantee that the fire will extinguish at some point. so you need to prevent those things you need to prevent, gypsum fall off, which has pretty much the same effect of your gypsum boards protection falls off from your, , timber wall. Then it actually, will suddenly start to contribute to the fire. If the fire is hot enough, you also should probably prevent a significant contribution of protected wood, even if it's still protected, but it's charring. It still contributes to the fire. And unfortunately this, this heat produced can be trapped, partially trapped between the gypsum and the, wood. And it might actually make extinguishment, completely impossible. but those sets of regulations, plus, potentially more, you need to prevent a collapse in real buildings. So you would need a whole set of, prescriptive regulations to do it. Or you go to a performance-based approach and where you need to Marin, you need to show that your fire, actually decays at some point, which is also

that's this is good one Uh, already a good

do that.

That's this is a really good one there was already a good one. Then if your tests, your let's say concrete wall, and it gives you two hours fire rating. When you put the two hour wall into the building, I will now make horrible mistake, but it's loud. You could say that. Okay. It can take two hours of a fire. And, and. or if the fire is shorter, it will just survive. And be there in reality is more complex than that because of the, of the, how he transferred works and how natural fires developed. But in essence, you would have just let this wall can stand for two hours and that's it. Then you turn off the fire, the walls, still stands. In terms of, of combustible structural component, your two hour span, you say, okay, the fire is gone and now we have to put out the construction because it's still burning and still contributing. So, so that's the paradigm shifting difference, you know, that, in the previous world where we didn't really have that much exposed combustible, structural elements, you passed your. test duration and you're done with the test it's it has passed a high five and let's sell it in here. You pass the two hour test and you are left with the problem of, the structure contributing now, not just the fire that has gone off or has burnt out completely, but you have a, still a contributing source of a fuel that you would not have before if it was in combustible. And now I'm now in a two story building, build of wood and I'm very comfortable in it. And I love it. And I can imagine why people would like to, have in the city center the same, feel of the warmth and beauty, as I have in here But when you have a 30 floor skyscraper, It is a challenge to, you know, put that structure of, on the 30th floor, compared to what you can do from the ground level to apply water, to, to do an external action, to actually stop this, contribution. So I guess that's the most challenging aspect of tall timber in fire, not the fact that it has insufficient fire resistance, not the fact that it, will it generate char layer quick enough or not, will it laminate or not that, I mean, these are technical issues, but the true issue is like, if the structure is a part of the fire after the fire has ended, what do we do with it? And that that's the biggest challenge, right?

yes. I agree with that. I think that that part of the research, challenges, hasn't been focused. The focus wasn't on that for a long time. and I guess it, it is. for a reason, like 20 years ago, it was very unlikely to build a higher than four stories actually in timber. now the world is changing and people are really pushing to build higher with timber structures. It becomes a much more important question. Something that you may reasonably assume in a three or four story building is. At some point, someone will either extinguish the fire or it is somehow acceptable that the building could collapse. and that becomes increasingly less reasonable. if you build taller and taller and I don't think there are many people would, who would say, yeah, but, it's a 30 story building everyone left, so it can collapse it's then that's actually quite unreasonable. It will damage many things that it will cost a lot. It will be a risk to neighboring buildings, but it will damage the whole industry. so they shouldn't allow such a building to collapse. It's also very, unreasonable to rely on the fire brigade, extinguishing a fire on the 30th floor or 20th floor it's and it's actually also not, good to rely on sprinklers only because also sprinklers have a limited reliability

though they are even have Uh, I to even though they have fairly high, reliability, I guess from 85 to maybe 95%, actually I'm supposed to do a podcast episode on that and that's, that's going to be a good one. but it it's, you know, sort of Russian roulette with fire. If, if your sprinklers, if your sprinklers work, you're fine. If they don't, you lose your building and it's, even if it's like 5% chance that you lose your building, is it, acceptable that you have 5% chance of a one in the 50 year events that you lose?

No, it's I think it needs to be in, imbalance. So if you say we rely on sprinklers to extinguish the fire. well, if it's in one in 10 of the cases that the sprinkler doesn't work, the damage, shouldn't be much more than 10 times as high, right. Then you basically reduce, on a big societal level. You reduce safety by, reasoning like this.

It's also, you know, the fact that in many types of structures you would receive completely different outcomes depending on your location, which means, for example, you have open plan compartment. If you have the fire at the facade, you could maybe expect the larger damage to the facade in the first 60 minutes. If you have it closer to the core of the building, you might have the damage to the core of the building. If you have it in the bathroom, you're okay. If you have it in the, your, sleeping room that that's probably was, if you have it in the kitchen is a different like every of this fire leads to completely different set of outcomes. And each of them has their own probabilities. While if you imagine the building with all surfaces of exposed, combustible material, wherever the fire happened, It will eventually lead to the structure being involved. And that can lead to pretty much the same set of outcomes. You either put it out or it will destroy the building, right? I could imagine the location or the size or the, you know, the triggering event stops having this huge impact on the outcomes of the fires, where in normal building you, that would be a factor like you might have small fire, you may have large fire, you may have a flashover fire. You may have a local fire of a trash bin. They all have different set of outcomes, but here, each of them can lead to ignition of the, of the structural elements. And once they burn, they will not just magically go out themselves. They will contribute until it's being stopped. And it all leads to the same level of damage. That's really frightening to me because we lose this, you know, margin of safety from the uncertainty of the firesides. We usually have.

Yes. Yeah. so I think in many countries, the fire development, part is regulated choosing, reaction to fire classifications, at least in Europe. That is the case. yes, and it, it can be, in some cases, ignored. I know in, in a country like Sweden, you can install sprinklers in a building where it doesn't, it isn't required. And then you can exchange it for, another requirement such as the reaction to fire class. And that, that is actually, the something that, that not be very reasonable to do.

that's, the I think this considerations are the things that are being missed by the society a lot. Like when we only focus on this one parameter, which is fire resistance, which we already discussed is partially flawed in terms of timber structures. Like you cannot just focus on that. There's so much more into that. And maybe these things that we omit are actually more important than the fire resistance, because technically if I saw an engineering of a tall building that took into account the growth of the fire, the compartment, fire dynamics, and how the wood will impose the management of this additional energy, which will go somewhere. If I saw that, then someone said, okay, and then my walls will be 60 minutes. I have nothing about the walls. I mean, they, okay. Let them be 60 minutes. If you manage all the other threads, that's, that's beautiful. That's the case is solved. You did your fire engineering because the problem was not in the fire resistance. It was. The other things it's just, it's so hard to convince the society. Think about the other things that I feel we need to do something with the fire resistance to already include some of these ethics in it. That's that's my personal opinion. okay. So, to go on with the effects of the fires, you've mentioned the extinguishing and we sometimes talk about self extinguishment of wood and, uh, that's a challenging thing. I would love to hear your personal opinion as a, as a fire engineer, who, who researches wood. When would you say it has self extinguished? Is it when the flaming action stopped? Is it when the smoldering stopped? Is it when it burns out completely and disappeared?

well, I actually try not to use the word self extinguishment, but, um, I usually refer to continuous decay. well, so some people refer to, extinction of flames. I think that is just not enough. Because that can occur at a very high, heat fluxes. And it, could correspond to around 600 degrees plate thermomete r temperature, which is still very high and you still get structural damage and still get charring and smoldering, extinction of smouldering is better, but it's actually an impossible task to design a building for extinction of smouldering, I guess. It may work, but you might just have, the users of the buildings, installing some piece of equipment and choosing a screws and a hole in the timber. And it might just, keep smoldering there. Or you might have a piece of furniture, that is close to a wall like I've got in my house, a tree trunk table. It's very thick. It will burn for a very long time if it is placed next to a wall, which is the case and the wall would be exposed, I guess there will be an interaction between this table and the wall for a very long time. and the smouldering. Wouldn't stop XD. It wouldn't I so you table, is gone. with I guess it would likely not stop

I don't know if you saw the recent paper by CERIB and ARUP with Imperial I think CodeRed, it's, it's called, I think. And, in that paper, they have this example of, a smoldering above a beam where. after like 40 something hours after the flame extinguished, there is no more flaming, but the smoldering is ongoing above a beam. And eventually after two days have burned a hole through the above the beam, like all the way through the ceiling. And we also saw something similar in our experiments where we had a beam and a CLT slab above it and above the beam, you know, there was this funny configuration of surfaces, which retaliated on each other and just to stay in this smouldering action on and on and on at that. And it went really, really deep. So I would assume that if we have not extinguished it with water, it would just go on and continue. So eventually you're allowed with the problem. You need intervention. Like you assume that there must be intervention. Otherwise, this will continue out until all the fuel is consumed in the region where this phenomenon happens.

Yeah, so I think that's right. you need at least someone to check, uh, whether they're a smaller smouldering and extinguish that smoldering. So that's sort of what we try to incorporate in our last, project. so after the test we use thermal cameras, we had the fire brigade checking where they actually need to check for awhile. You kind of just check off sort of fire and leave. You need to

Monitor yeah.

there. Yeah. And we don't know how long, but we saw after half an hour, you can, actually in solve the

Ensign

there. They extinguish smoldering.

was he then some specific points, like, I dunno, join, solve the structure, or you mentioned stats. Ensign

yes. Connections that, most connections didn't need it, but if the sealant wasn't correctly applied, then, then yes, then it continues. And, we also saw, where we had lamella stat didn't follow up, but they stuck to the wall or the ceiling that behind lamellas between the CLT and the lamella. It, continues. However, I think that is a location where eventually it might die out by itself, but the connections, led probably continues. Until it burns through, at some point. And I know, I know they experienced it in a set of German tests that also the next day there was a hole but I believe that in that test, uh, it did lead to a hole in the wall, in the floor. I believe that, it didn't need extinguishment We build there's not a part of a structure or a building it's hard to tell what the here if

that's interesting because now we're experiments. We usually build a insulated compartment. You know, that there's not a part of a building structure or a building frame. And here if the damage is to the joints or into some, let's say fragile connections, it, it will be very hard to fix that afterwards. The fire, like in, in general, I assume fixing a timber framed building after a fire could be like quite challenging to replace a slab in the building. That's standing. Was this a part of any considerations of your group? fixing after the fire.

Yeah, so that is a very new area. So we, uh, repaired a part of the ceiling after our very last compartment fire tests, and there was a CLT ceiling and that was relatively successful. I guess we, got, the, bending capacity back and the fluctual stiffness. it is, more difficult if you have, cavities and walls. So timber frame will be, more difficult. However, I know one example in Sweden, I don't think they published a report yet, but where there was a real building fire, this building was built of modules, so no parts of the compartments were made in the factory and then assembled on site. but they disassembled the modules, brought them back to the factory and then repaired the module separately and brought it back. and in that case, they, at least what I've heard, not officially through the report is that the costs were, reduced very significantly to 10% of the original building cost is in previous cases, it, it actually did occur, that the whole building had to be demolished and

all of this is, is, is really interesting. and I love how we, opened with, you know fire resistance and finished with all these important aspects of what you can consider beyond the fire resistance. Maybe I've put the wrong question into the title of this episode about fire resistance. Maybe it should be all about the consequences, but I think it's still was needed. I still think. It's necessary for people to hear how the discussion can be separated between the fire resistance and the consequences of, of the fire. And if more people did separate these things from each other, the least problems we would have, and least stupid articles on LinkedIn would be published every, every week. and that I would truly love that world. For the end, I will link the resources, that we've discussed in this talk. And I will link the project on, mass timber in tall buildings. There's a YouTube channel with all the experiments. You can see what Daniel meant by additional fire energy going somewhere. if you open them side by side two experiments, I would recommend experiment three. I liked that one. It seemed interesting. I think it's the one that you had the coroners exposed, from your perspective as a scientist, did it make such a difference to expose the corner of, the experiment?

something that we don't know much about and I'm trying to, um, perform more research on is the interaction between exposed walls. and if you want the fire to decay, at some point, this interaction should, be, insignificant To allow a fire to cool down. If you have two timber slabs that are very closely spaced with that high fuel factor to each other, they might burn forever until one of them is completely burned out. , and the same happens a bit in corners. So you have interaction between the walls, and we think it is, any creation of many things, but, one of them is the oxygen content. and that's why we think we saw it, the effect mostly in the bottom of the compartment. and another part of the equation is the material behavior itself. So. Behaves like a rock solid, timber member or whether it's, let's I Sweden of dating structures this famous opens up a little bit at least we the Swedish the timber like

I think in Sweden you are masters of rear dating structures There is this famous camping technique called at least we referred to it as the Swedish fire log where you cut a log of the of the timber like with a chain. So in like a four, you make four cuts or six cuts in the, in the log. You you put some something inside to ignited and then all the walls burn each other and you can cook on it. you can, you can, you can, you cook it. That's a, that's the Swedish fire log. and so it's the but to use the for the benefit of having delicious meal in your camp, not a burning, a building and any where are you going right. that's really good to like Swedish used it for ages now. They used it in buildings. That's frightening. one last question. where are you going now with the timber research or you're dropping the field and you're going to do batteries like everyone else?

Uh, no, I think there actually many questions that still need answering. So, I guess the smouldering aspect in the end is interesting. It's I know it's challenging, but well, we can improve. Definitely. there is, rehabilitation after a fire. Well, I think it's very interesting after the test at, , CERIB in collaboration with Arup is how to, , Actually been in the in the experiment uh, use noncombustible structure

I've been in the in the experiment one, , the one we did with use noncombustible structure with the same fire load. And I remember how huge and frightening that fire was. And then Guillermo told me that the, the CERIB fire was like twice a peaker and I, I really cannot comprehend how big the fire must have been ended. it's really scary. And, especially the aspect of the, in that paper that they show that the spreads through the ceiling, which for me, it was surprising, how quick the fire accelerated through the, through the compartment then that I, I'm also doing a lot of experiments with OFR on CLT for Structural Timber Alliance, Special Interest Group CLT, and we did burn, compartments. That was seven meters long. We've seen this propagation. It was really fascinating. Now we are doing, small compartments with different parts of it exposed or, encapsulated with the differing amounts, like a parametric study on an encapsulation, which is really, really interesting. So, having this ARUP experiment on, on, on the bigger side, our experiments, with the, with the ceilings, your experiments with compartments, I think we're eventually reaching a point where we have really overwhelming amount of experimental contribution, to propose some general ideas on the timber. Compartment fires, you know, in three or four years when every of this is finished, all of this is published. We will have small compartments with small openings. We will have small compartment with huge openings. We have your compartments, which were medium-sized and had different, opening factors. We have our experiments with all of our, where the opening factor was irrelevant , like the opening was, was like on the, on the far, far side of, ventilated regime. We have, a CLT compartment, fires 300 square, 270 square meters from France where they also play with like, we are reaching this point. maybe you remember Cardington papers where they had this, , charts have different opening factors in sizes of compartments. And from that they would, they were able to, to produce some generalized, theory for steel frame buildings. Maybe, maybe we will be able to reach something like that in mass timber soon ish in like five years. And that would be amazing.

yes. I think, I think that's possible as long as the goal is clear, what is acceptable and what isn't. And that, that is probably the big, biggest challenge to agree on that. And then it becomes, different for different occupancies of a building, but also the height of a building. So I guess most people would agree a two-story house doesn't need a lot of requirements and, they do agree that, very tall buildings need much more requirements, but everything in between. Uh, it's just a matter of opinion. so we, I guess, if there is some kind of system in that, then you can see okay. To achieve that. Either, this set of requirements and it shouldn't be only fire resistance. It should be some specific location of how much wood can be exposed if at all at a certain height, what the material behavior should be and everything that is protected, how much protection there should be on those, members, also their reaction to fire, classification should be sped a specified. It actually, it needs a whole framework, but, at least in Europe and felt Please say something good agreement between what is needed at which, building height and what is needed for different occupancies.

You're leaving me here with very uncomfortable felt Please say something positive. Can we build safely with timber?

well, I, I didn't want to indicate that you cannot build safely with timber. I just stated that, uh, using fire resistance alone, doesn't always get, it gives you a sufficient level of safety, especially in buildings, where, a collapse would lead to very high consequences and also. Buildings where you cannot rely on, someone or something extinguishing your fire. if that is the case, if you actually, cannot rely on these things, you, can have a good set of prescriptive regulations, that would next to just requiring a fire resistance would also require or give limitations of how much you can have feasible and related to the potential consequences of, fire in such a building. But also, um, the configuration of what can be exposed and what can be feasible, how far can they be a part of what could be the view factor between them and, for the protected services, there needs to be a requirement of, um, much protection. Those surfaces need. If it's gypsum boards, how much gypsum boards would they need our in, Europe, you have the key classes and they should be used, but then based on research of, fires that actually aims for, decaying fires. but if you don't have that, there are only few countries that actually have, adjusted to recent research and that research has led to improvements. It's not only research at RISE for you. You also talked about the OFR tests and the whole, fire safety engineering community. Actually has worked a big part of the fire safety engineering community has worked, to improve the performance of such buildings. but if the national regulations didn't adjust to that yet, then it usually comes down to, just safe engineering. You need a very competent engineer, especially if you need performance based. you need a competent engineer, but even a competent engineer would need validated methods. And, those, we were still working on them. There are a few methods, but all, all methods have their own limitations. And I think there need to be more in the future.

Okay. That that's, that's much more positive. I like that. So there is a way out to build safely with timber, maybe not with a fire resistance as the ultimate proxy of fire safety on its own But considering all the circumstances, basing On peer reviewed science and, having competencies in place. That's the elements you need. The fire resistance is not enough, but we can make it work. Right.

Right. Yes, I think so.

That's good that I can leave you now that on this point we can finish up. I like a positive ending with the way out and especially one that, emphasizes on why we need fire safety engineers and why we need. Competent once in the field. Thank you so much, Daniel.

yes. Thank you.

it was a great pleasure to have you on the show and they asked you around.

Yes, it was an honor. Thank you. Thank you very much.

It starts to be slightly boring. Whenever I get an expert on fire. It usually ends up the same way we need to fire safety engineers. We need competencies. We need holistic view on compartment fires. We need to look beyond fire resistance. We need. To include all the effects this will have on the building fire. And as Daniel said, the energy will go somewhere. So we need someone who can consider that. And. Why does those experts cannot just say that wood is stronger than steel in fire or the char layer will prevent anything. And you can say for the build to a thousand meters with wood, Well, They seem to be unconvinced um, obviously I'm, I'm sarcastic as usual, but yeah. As you see from this episode from episode with Danny, from episode with Felix. It is a complex issue. It is an issue so complicated. There's just absolutely no way you can frame this problem into a fire resistance problem. It never was a fire resistance problem. To start with. It's just one measure, one out of many that we can, and we should use when designing. Timber buildings. And well, then you're sad about unit configurations, the arrangement of materials to view factors. How much encapsulate, how much do you expose? This, this is happening right now. We are researching that there's many groups researching that. already. Now you could probably use the knowledge we have and applied and design quite a robust timber structure that will be safe. And in few years, you will be armed with excellent research with excellent peer reviewed research on this subject. That will allow you to design safely. I'm just really worried that no matter how much research, we do no matter how much we publish, no matter how much insight we gain. It will be difficult to beat the fire resistance paradigm. And show to the world that it's just a measure. I hope you will help me on that mission. By sharing this episode and having informed discussions with your colleagues about this issue. And I hope all three episodes on would in fire have brought you. Some really good insight into how it can really work and where the issue is. that's my dream that the, I did army with this and I, I hope I've achieved that. So, thank you very much for being here with me. And, Some housekeeping items. First I'm very thankful to all the supporters to the podcast. Who donate to the show with. From my website, then I really appreciate that every dime you send goes to equipment and software and licenses and servers and so by participating in this, you helped me a lot. And, I would also like to ask you, to go through your podcast app. That you're using wherever you're listening. And maybe pop a five star review there. Which helps me with algorithms and stuff. So the podcast is more easily available or more easy to find for ones that don't know about its existence, but may, may need it at some point. So thank you for all of this and see you next Wednesday. Bye.