Fire Science Show
Fire Science Show
197 - Fire spread through external walls pt. 2 with FSRI
When wildfire threatens neighbourhoods with closely-spaced homes, what determines whether flames leap from one structure to the next? The FSRI research team - Rebekah Schrader, Joseph Willi, Daniel Gorham and Gavin Horn - joins us to unveil their experimental series that methodically dissects the pathways through which fire spreads between buildings.
The team walks us through their massive outdoor experimental setup, where they created controlled compartment fires and measured their impact on adjacent walls and windows at various separation distances. They discovered that even non-combustible exterior cladding like fiber cement board won't necessarily protect a home when the underlying sheathing is combustible—especially at close distances where heat fluxes reach a staggering 75-125 kW/m².
Windows emerge as perhaps the most vulnerable component, with their research revealing dramatic differences in performance between glass types. Double-pane tempered glass significantly outperforms plain glass configurations, but the surprising finding was how much window frame materials matter. In one experiment, vinyl frames completely failed while the glass was still intact, causing entire window assemblies to drop from the wall.
Another aspect of their research are the measurements of the heat transfer through intact windows. Using specialized measurements, they found that significant radiant heat penetrates even unbroken windows, potentially igniting curtains or furniture inside before the window itself fails. Low-emissivity coatings proved remarkably effective at reducing this heat transfer.
This research offers crucial insights for homeowners, fire safety engineers, and policymakers working to create more resilient communities. The findings extend beyond wildland fire applications, providing valuable data for urban fire safety engineering across multiple contexts.
Find the research papers at:
- https://onlinelibrary.wiley.com/doi/10.1002/fam.3278
- https://link.springer.com/article/10.1007/s10694-024-01685-8
- https://link.springer.com/article/10.1007/s10694-024-01656-z
And additional resources at:
- https://fsri.org/research-update/journal-article-reports-heat-transfer-through-different-window-constructions
- https://fsri.org/research-update/journal-article-investigates-role-residential-siding-materials-spread-exterior
Thank you to the SFPE for recognizing me with the 2025 SFPE Fire Safety Engineering Award! Huge thanks to YOU for being a part of this, and big thanks to the OFR for supporting me over the years.
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The Fire Science Show is produced by the Fire Science Media in collaboration with OFR Consultants. Thank you to the podcast sponsor for their continuous support towards our mission.
Hello everybody, welcome to the Fire Science Show. Last week we probably had the longest introduction to an experimental series ever in the Fire Science Show, as I had an entire episode devoted to the rational. Why are we talking today about external fire spread? We've set up the stage, we've connected the topic to the ever-growing threat of wildland fires entering our urban habitats and causing urban conflagrations, and today we will talk about the nitty-gritty of what has been researched by my colleagues at the FSRI. I'm joined today again by the same crowd Rebecca Schroeder, joseph Willey, dan Gorham and Gavin Horn and together with them we'll go through three large-scale experiments that were performed with focus on the fire spread through external walls at different distances, through the damage done to different types of windows by the same external flame, and also on how much radiation carries on through a pane of glass. So we're discussing three different mechanisms of flame spread. If your external wall ignites, you're going to have a bad time. If your window breaks, it creates a vulnerability in your structure and you're going to have a fire spread. And also, if you have a curtain behind your window and even though the window is intact and your external wall is also intact, if that curtain behind the window ignites from the fire radiation, well, the fire will start inside the house and it's lost again. So three different mechanisms of fire spread, three different targeted experiments to answer those questions, really good ideas on how to connect those experiments. And you know what? The data that they've gathered goes beyond wildfires and this fire spread problem. I can see immense use of that data in my everyday fire safety engineering, even though I'm not really doing wee stuff. So I'm sure this is very useful to all my fellow fire safety engineers out there. So let's spin the intro and jump into the episode.
Wojciech:Welcome to the Firesize Show. My name is Wojciech Wigrzyński and I will be your host. The FireSense Show is into its third year of continued support from its sponsor, ofar Consultants, who are an independent, multi-award-winning fire engineering consultancy with a reputation for delivering innovative, safety-driven solutions. As the UK-leading independent fire risk consultancy, ofar's globally established team have developed a reputation for preeminent fire engineering expertise, with colleagues working across the world to help protect people, property and the planet. Established in the UK in 2016 as a startup business by two highly experienced fire engineering consultants, the business continues to grow at a phenomenal rate, with offices across the country in eight locations, from Edinburgh to Bath and plans for future expansions. If you're keen to find out more or join OFR Consultants during this exciting period of growth, visit their website at ofrconsultantscom. And now back to the episode and once again, welcome to the External Firespread. I am here, joined again by my great crowd from FSRI, again with me, rebecca Schroeder. Hey, rebecca, good to have you back in the podcast. Hi, joseph Woolley. Hey, joseph, hi there.
Wojciech:Good to be back, dan Gorham.
Dan Gorham:Good to see you.
Wojciech:And once again, gavin Horn. Thank you, great beer. There are three independent research experiments that were published already, and I know there are some more in the making. One related to the external walls and facades, one related to window pane followed and one related to heat transfer to windows. Perhaps let's start with the external fire spread on the walls. Daniel, I think you were the one primarily involved in this one. So, given that we already had the high-level introduction in the previous episode, let's talk about specific. How did this research come into play and which particular aspects of stuff we've discussed in the previous episode this was responding to.
Dan Gorham:Yeah, so these were a series of experiments that use the source being a compartment fire with exterior facade, and so the thermal exposure from a close flashover compartment. So you have flames coming out of that single opening and a target facade adjacent to it, and so the thermal exposure from this flame is primarily radiative. But when they're close together at that you know six foot separation or 1.8 meters. Sometimes we're in contact and in the experiments for the target facade what we were looking at was that exterior wall assembly. So for residential structures, a lot of times we think of what we see on the outside, what is the siding, what is the cladding.
Dan Gorham:We looked at three different exterior materials for these experiments. One was T111 plywood, which is a wood material and fairly common in Western stage because wood is prevalent out there. Another option is a fiber cement board, again another pretty common material and siding material for residential structures across the country. Fiber cement board is actually a non-combustible material. And the third was actually a system ETHIS Exterior Insulating Boom System. So on the exterior, most surface we had a finished coat of stucco, but the assembly or that system actually had multiple components. And this actually gets to another important part. Think about fire safety is that it's not just the outermost material. That's what we first see, but for the fire spread structure to structure, it is actually really the whole assembly. So we looked at the target from the exterior surface all the way through the stud wall. So common wall assemblies from the exterior surface through the stud walls.
Wojciech:You're going to love it because I have like 10 follow-up questions. First, how big was it Like? Was it a compartment? Because it's interesting. You say it's a compartment fire, but I can imagine you're doing it in multiple ways. You can build a compartment, set it on a fire easy mode. You can build a small chamber, put a burner inside and calibrate it. Perhaps there are different intermediate ways. So how big was the compartment and how did you scale up the fire inside of it?
Dan Gorham:So the compartment, you know you could think of it as like a small living space. You might be able to fit a kid's bed in there and inside the compartments we actually had typical fuel. So it wasn't a gas fuel burner, it was a typical residential fuel load. We had two couches, a coffee table, carpet padding and the walls were lined with a combustible material. So the fuel load in this compartment fire was typical of modern structure. The fire was initiated by a small electric match and so we have that kind of that fire growth curve up through flashover, post-flashover and then a decay. And that's what generated this repeatable exposure between experiments at multiple different separation distances and, for the case of exterior walls, for the different exterior wall assemblies.
Wojciech:Perhaps I'm designing a very similar experiment right now. So I'm just going to, out of scientific curiosity, follow up on this one. And what were the ventilation conditions? Just going to, out of scientific curiosity, follow up on this one. And what were the ventilation conditions? Did you have another opening to the compartment, like imitating doors, or you kept the doors to your bedroom closed, like you should?
Dan Gorham:So this was just a single compartment and there was only one ventilation opening. It was about the size of a sliding glass door and it was open the entire time. So this wasn't a multi-compartment structure, just a single compartment with a single opening. So the kind of fire development in that compartment is simple insofar as fire dynamics is simple, but it was repeatable across all of the experiments. So you'd have a bidirectional flow through that opening. Correct, right, you had bidirectional flow through the opening.
Wojciech:Another question was about the targets. So how did the target work? You said you were placing some targets away. Were you interested about the effects of the fire at a distance? Or were you also considering what's happening above the window, like if there's two stories or three stories above?
Dan Gorham:So for these, experiments we were most focused on the effect of the fire on the target adjacent to or some distance away. The source compartment had a facade on it as well, but that facade was clad with non-combustible material and sealed up. So the fire jumping from coming out of that single opening did impact the source facade, but it didn't meaningfully or significantly contribute to the thermal exposure to the target. The focus of these experiments was this is a source for the purposes of a real-world scenario, it is a home that is fully involved and isn't able to be suppressed, but it's burning and causing exposure to a notation structure that is not yet ignited or is vulnerable to or susceptible to that. How did you measure that?
Dan Gorham:Heat flux gauges, sorry, yeah, water-cooled heat flux gauges, embedded from the backside and flushed with the front side of the target, and so what we're molding is total, so radiative and convective incident heat flux, again at those distances. And so for the wall assembly we had an array of heat flux gauges, five columns, three rows along the center line and then evenly spaced, and so what we measure is this heat flux incident, total heat flux to the target in like a field. So it's not a single point that we're actually measuring multiple points, so we get effectively a field that's very interesting, so you could like almost map the incident heat flux on the opposing structure right.
Dan Gorham:Yeah, yeah, and we did that consistently on some previous experiments inside a laboratory that motivated and informed these experiments up until the point that the target ignited, because now you have not just the flames from the source compartment but you might have, say, the burning of the wood siding or the burning of the insulation that's melted on the ground. So we can measure the source up until the point the target ignites, after which we still get measurements, but it's now the contribution of the source plus the target.
Wojciech:One thing I wanted to ask because I think either in our prep or even in the previous episode it was brought up that during your historical research study we're also trying to map the heat fluxes that those structures could be exposed to. Maybe Joe can answer that. So, in terms of your research and the damage observed in the real world, were you able to link the heat exposure maximum, or likely maximum, that structure was exposed to with the damage or severity of the damage of the structure? The context of this question is once again, in the previous episode we discussed that. Is it binary? If it ignited, it's perhaps lost. So I wonder if just answering yes it can ignite, no, it cannot ignite. Is this far enough? Or you're interested whether it was exposed to 15, 25, or 50 kilowatts and there's a difference in the damage.
Joe Willi:Joe, if you could comment on that, yeah, so that's one of the things that we were trying to evaluate and quantify to an extent with these experiments. So we had three different separation distances across both the residential clouding assembly experiments and the window pane experiments, and we were able to quantify a range of heat flux exposures for each one of those. So the closest separation distance was 1.8 meters and we were seeing heat fluxes within the range of 75 to 125 kilowatts per meter. Okay, that's a lot. That's a lot, yeah, but then at the three meter separation distance, which is, uh, where most of our window experiments at least uh were conducted, the range was, uh, more so, 40 to 65 kilowatts per meter squared. Okay, and then we also examined 4.3 meter separation distance and at that separation distance the exposure was 25 to 35 kilowatts per meter square.
Wojciech:That's still quite a lot. And to better create the image of experiment in my head, how big was the external assembly? Because you said that it was constructed with either T111 plywood or this foam system, or non-combustible, which perhaps is not that interesting in this case. How big was the external wall assembly compared to the window opening?
Joe Willi:So the total width and height of the wall was 4.9 meters wide by 4.3 tall.
Wojciech:Okay, so that's a quite large assembly.
Joe Willi:And then, as we mentioned, there was a matched facade that was attached to the source compartment, so like two large spiral walls. Yeah, exactly, and then the source compartment opening was 2.4 meters by 2.1 meters.
Wojciech:But did you not involve any like force flow in between those, or have you done a side experiment with some flows?
Joe Willi:No, and in fact in an effort to kind of help control the wind. I mean, we're conducting all these experiments outside, so they're subject to environmental conditions, but for one we measured wind speed. So if we had a particularly windy day we wouldn't test or we would move our tests to a later time where the wind had died down. But another thing we did to help kind of control the wind, if you will, was that these two structures were on casters, so we were able to orient the test structure, the setup, so then the wind was always coming from the same direction. So we oriented it so that the source compartment, the backside of the source compartment, was facing the direction from which the wind was coming.
Wojciech:Okay, that's a good possibility to not be the victim of a wind. I once tried to research what's the minimum wind velocity at which it stops affecting my experiments, but I did not really like the outcomes because I could not find one. So it's not very helpful, especially if you have multiple openings. If you have just one opening, then it's probably less vulnerable, but if you have multiple openings opening, then it's probably less vulnerable. But if you have multiple openings then it's pretty crazy. And that that's a another fsri episode with craig vasing like plug to that episode.
Wojciech:I'll put the link in the show notes where you can read about wind induced flows and and the flows in fire experiments in general. Dan, you've mentioned these different types of facades, so the fire inside the compartment is always the same. The doors leading to outside were open so you had ventilation to that facade. How did the experiments go with different exterior systems? I can assume that from the least flammable, the fiber cement board, which is non-combustible, it was just your baseline. But how did it look with the plywood and the foam system material?
Dan Gorham:Yeah, so you know, one of the things that we had talked about was, you know, is ignition the only thing that we care about? Does it or doesn't it light? And these experiments and post-fire analysis kind of suggest that, yes, ignition is very important and that was something that we studied. But we also looked at other reactions to fire events for the various different components. You know, looking at kind of paralysis components like off gassing and discoloration for some of the exterior wall and cladding materials. You look at components like cracking and spalling some of the exterior wall assemblies, the cladding actually detached Right. So now we're talking about not just what is on the exterior but what is inside, what are the different layers of the assembly. And then, you know, you think about relating this to real world and how does this matter?
Dan Gorham:We looked at both fire propagation, you know, not just ignition of a point, but fire spread across the surface of the exterior wall facade, and that's both horizontal and vertical, and fire penetration through to the backside, which I just want to mention. One other component these facade walls also had an eave component, so kind of like the gable end of a home, so the eave stuck out at the top. So when we're looking at building susceptibility and vulnerability. I think it's really important to recognize it's the mechanisms radiant heat, direct flame contact in embers, it's a combination of them. But also we need to think about not just individual components, not just the exterior wall, not just the windows, not just the roof, but where those components interface and these experiments actually shed some insight on not just having a non-combustible exterior, but where that exterior cladding meets the eave and fire spread up. So again, it kind of shows some of the things that you might suspect, and doing it in a repeatable and a controlled way can help us better understand and build back better.
Wojciech:Yeah, I also understand from the paper that it's not just about finding the maximum heat flux on the opposite facade, but it was also about finding that in kind of a time integrated fashion. So can you tell me about the time component in that research?
Dan Gorham:Yeah, so we use the time integrated heat flux or term, we use heat load, and so this is the amount of energy per unit area. So integrated heat flux, kilowatts gives us kilojoules and we oftentimes report in megajoules per meter squared, and so this is a way to kind of understand that amount of energy accumulation to that surface.
Wojciech:Like a dose on the wall, heat dose kind of.
Dan Gorham:Exactly, exactly. One of the things that limitation or a strength of that approach is again, it kind of integrates over time but what it gives us is that dose to the surface. Again, we talked about that. Exterior walls are oftentimes assemblies of any material. There's an interface between materials and so it doesn't necessarily give us that heat transfer through. Yet we see fire penetration through. So it's helpful for comparing across, but also recognize that there are additional heat transfer factors like conduction and convection through the wall assembly that play a role in how that wall assembly will respond.
Wojciech:You know what. I'll ask one more follow-up question and that foam system. You really did capture my attention about this exterior insulation finishing system. So if you could tell me more about technical aspects of that material and how it behaved in fire and I'm especially curious because in Poland I'm not really sure if we would have external insulation with foam. Probably it exists on the market but I wouldn't say it's very popular In here. We would just go ethics with polystyrene mostly on everything, like we love putting polystyrene on everything in Poland up to 25 meters above that. We like putting mineral wool.
Dan Gorham:For some reason, fire reasons, yeah yeah, yeah, can I talk about EFIS? And can I also mention an interesting point? I don't think I made the connection but I want to make an interesting T111, kind of the wood sodding is pretty simple. Wood ignites. I want to make a comment about the fiber cement clad and the OSB beneath it, so the T111 siding. There's been a fair amount of previous research looking at that and so the wood siding ignites at a point and then fire oftentimes propagated across the surface, so vertically and horizontally. A lot of times we would suppress and end the experiment before causing significant damage to the target. So the T111 results, while important to provide some context, were not all that interesting.
Dan Gorham:A couple of interesting observations. One for the fiber cement siding, we actually looked at two different form factors. One in the panels or the sheets, which is very common to create that board and batten look, and another form factor was the lat board which kind of gives you that horizontal. It looks almost like wood siding but it's made with fiber cement. So one these non-combustible exterior wall coverings, cladding sidings meet nearly all of the codes that are specific to WU. One of the compliance option is a non-combustible cover, so that covering, again without knowing every single one. Most of the big ones NFPA, california Building Code and ICC say that if you have non-combustible covering you meet the exterior wall. But the observation at the 1.8 meter separation distance so that's about six feet and it's not uncommon you can imagine fuels being separated by that or closer was while the cladding didn't ignite.
Dan Gorham:The assembly, which included OSB sheathing that the cladding was attached to, did, and so what we see is fire spreaded up this wall that's clad with a non combustible material and there's a little bit of a.
Dan Gorham:I didn't expect that. Or someone would say, oh, that's non-combustible siding that won't ignite. Yet we see examples of it. And so that the thinking about the wall assembly and not just what's on the exterior what's on the exterior matters, but what's beneath it matters as well and so you think about the different form factors, the panels and where they need, and you have the batten over top of it. When you have the lap board, you actually have a lot more interfaces, a lot more intersections, and one of the experiments we actually pulled the lap siding off and you could see in the OSB and the sheathing you know where it had burned, localized where the fiber cement board was. It didn't conduct through so there wasn't burning there, but where the interfaces were is where it had burned. So again, really important to think about, not just what we see from the outside, not just the siding, but the wall assembly that cladding is.
Wojciech:Now one another reason to really think about the systems, not just materials.
Wojciech:And in Poland also, in many cases you would only care about the systems, not just materials.
Wojciech:And in Poland also in many cases you would only care about the render, like external layer of the system, and it's two completely different fires if you have 10 centimeters of polystyrene or 30 centimeters polystyrene behind that render, so it creates completely different mechanisms.
Wojciech:Anyway, let's try to make a link to the Windows, because I really enjoyed that part of the research that using this heat load would allow you to compare again the time of exposure or the length of exposure of that or the size of exposure of that wall to an external fire and then try to compare it. Is it sufficient to create this new pathway to enter the building? So let's perhaps try the window fall-off research. So, joe, that's a paper with you as the first author on, so if you can tell me about how you've approached that, what was the scale of the experiment and some general design points, and then we'll move into the findings and perhaps we'll try to find a link with the research Dan just talked about and perhaps we'll try to find a link with the research Dan just talked about Dan Heldmanis Sure.
Joe Willi:So window pane failure experiment. We're looking at a similar setup as the exterior experiments, where we had the same source compartment and the same target facade wall in terms of overall dimensions. However, the wall itself had eight window openings and within those window openings was a custom fixed frame window assembly.
Wojciech:So, in your case, tell me how the windows were fit and what kind of assemblies did you choose.
Joe Willi:We were primarily looking at four different types of assemblies, different variations of plain glass and tempered glass. So one of the assemblies was both panes plain glass. Second one both panes plain glass. Second one both panes tempered. And then we looked at two with one pane plain glass, one pane tempered, in both orientations, so one with the plain glass on the exposed side, tempered on the backside, and vice versa, with tempered on the exposed side and plain glass on the backside.
Joe Willi:And then, as far as the windows, during the experiments within the target facade we had eight windows mounted, so two rows of four windows symmetrically spaced on the target facade, and this resulted in four different exposure conditions. So if you think about splitting the target facade in half to the left side and the right side, the uppermost, like the top row leftmost window, has the same exposure as the top row rightmost window. So we had these were double hung style windows, so we were able to get two pane assemblies per window opening and so that resulted with your two exposure conditions and then two pane assemblies per window. We had 16 pane assemblies that we were exposing per experiment.
Wojciech:Okay, that's a clever design. I have the paper in front of my eyes, so it makes interpretation much easier. The papers are open access and available to anyone who wants to take a look into them, and you can find the links in the show notes. It makes following up much, much easier if you can see that, but of course, if you're driving or jogging, let's stick to the audio description. So instead of having a wall with different facade system, like Downhead, you now have a wall with four windows. The windows are fit into some sort of non-combustible frame. Did you change that as well? Yep.
Joe Willi:So the wall itself was equipped with non-combustible siding. And then we had our windows themselves were custom built frames. So they were fixed wooden frames covered with a poly ash composite trim to kind of resist burning. And the reason that well, we did the custom frames for a couple of reasons. One was so we could vary the paint assemblies between the top and bottom sashes. But then also by having this solid, rigid frame we don't get out of plane stresses that you might see with other window frames, like vinyl. When they start to warp and melt that causes additional structures on the paint assembly. That would affect failure. And then we did one-off experiment with vinyl frames to see how that compared to our custom built frames.
Wojciech:And the frames. The custom frame structure was the timber. Was that combustible or?
Joe Willi:It was a wood base but it was covered by a composite.
Wojciech:Okay, so now let's talk about how a window can fail. What you were looking for a cracks, a complete fall off, a hole in the window.
Joe Willi:So the way we identified window failure was the first sign of a crack with plain glass that's just in some cases a small crack. In some cases it's a long crack that propagates. Sometimes it's multiple cracks, but then, with tempered, there's a feature of tempered glass that, more so, shatters when it fails, and those were two layered windows, so you were observing just the outermost layer or the innermost layer, both.
Joe Willi:Yeah, we identified both the failure of the outer pane and the inner pane, or the backside pane, and we labeled complete failure as when both panes of a window had failed and we were able to identify this through mounting high-definition cameras on the backside of each window. This through mounting high definition cameras on the backside of each window, so then we could go back and get a time resolved indication of when each of those failure events happened for each window pane assembly so you could also look into the progression of a failure, like time from first crack into complete time was something also you're looking at uh, not not for this
Wojciech:analysis specifically okay, cool, but again, because of your frames, you were not able to tell if the frame has failed and therefore the whole pane would fall off. Or is this something you looked into with the vinyl?
Joe Willi:frames Right. So that was not the case with the custom built frames, since they were solid material. That's one of the findings we discovered with the vinyl frame window experiments is that in the majority of cases, a three meter separation distance with the solid fixed frames, we did not have complete failure of two types of our window panes. Typically that both panes tempered and then plain glass, exposed side, tempered backside. So in the majority of those cases they survived. However, with the one vinyl frame experiment that we also ran at a three meter separation distance, we had all of them fail and that was due to the warping and melting of the frames and in some cases the whole sash would fall from the target facade onto the ground.
Wojciech:It's an experience that I also shared, like when we were doing one timber frame building experiment at ITB. We were having like a flashover fire in that room and it had, I believe, a vinyl frame window. It was like tilted away. I was really eager to capture a video of the glass cracking for my social media purposes and I was standing like very close to that window with my phone out like an idiot for like a really long time Refused to crack and then I gave up. I hid my phone out like an idiot for like really long time refused to crack and then I gave up. I I hid my phone and then, uh, the the whole window started like sliding off. You know the glass was not damaged but it kind of like started sliding out of the frame, like the frame was like losing its strength and it just fell out completely.
Wojciech:I'm not sure if that would make a good social media material. Definitely would drive my health and safety people crazy if I published that. Perhaps it's better I did not. But it was very interesting that the glass failure was not necessarily the failure of a window. Anyway, back to here. You were looking into time at which this happened, but also you're looking at this heat load, if I understood correctly, right.
Joe Willi:Yeah, so the way our experiments were designed was that we ran five replicates at the three meter separation distance at 16 paint assemblies per experiment. That resulted in us having 20 paired observations of each paint assembly type that we could compare, that run a statistical comparison on between the different types, and so we did that looking at the heat load measurement, which again is a integrated uh heat flux, integrated over time, similar to what dan did, okay.
Joe Willi:So we did this analysis for different failure conditions or just different means of failure. So we looked at the time and heat flux when the outer pain failed and when the backside pain failed and when we had complete failure, which again was both pains having failed, and what we found was that, unsurprisingly, the both panes tempered outperformed, both panes plain glass and, in the majority of cases, the double pane, both panes tempered did not fail at the three meter separation distance, whereas when we look at the ones that have one plain glass, one tempered glass pane, we found that the orientation of that pane assembly has a tremendous impact on when you have complete failure of that pane assembly Okay, we on. When you have complete failure of that paint assembly, okay. What we found was that if you have tempered glass on the exposed side and plain glass on the back side, that performs more like if you have double paint with plain glass, whereas if you have plain glass on the exposed side and tempered on the back side, that performed a lot more similarly to the bulk paint's tempered glass backside. That performed a lot more similarly to the bolt panes, tempered glass.
Joe Willi:And the reason that what we determined was the primary reason for this is because if you have tempered glass on the exposed side and plain glass on the backside, you have failure of that tempered glass, in some cases before, in other cases after failure of that backside plain glass. But if the backside plain glass hadn't failed yet, that tempered glass shatters. If the backside plain glass hadn't failed yet, that tempered glass shatters, the amount of protection that you had from that exposed side pane is now a lot less because the tempered pane has shattered and in some cases fallen out. But then there were other instances where we saw there was enough heat transferred through that exterior side pane to cause the backside plain glass pane to crack.
Wojciech:And to relate this to the heat flux. So you said three meters, so 45, 65 kilowatts per square meter, more or less.
Joe Willi:Yeah, and the exposure durations that we had were anywhere from four and a half to nine minutes post-flashover.
Wojciech:Four and a half to nine minutes. Okay, cool. And how about the results at the 1.8 meter separation and 4.3 meter separation distance? So first, like 1.8 meter, I saw in the pictures that the flame is like literally touching the adjacent walls. So how did that work out?
Joe Willi:As you mentioned, with the 1.8 meter you have a lot more heat transfer from direct flame contact and the exposures are just much more severe than the three meter separation distance. So at the 1.8, we were looking at 75 to 125 kilowatts per meter squared and we found that even the double pane tempered glass has a limit there. And we had failure in all panes except for one which was a double pane, both panes tempered, but it was at one of the lower exposure conditions on the outside and in this case all of them fail outside of this one, in the biggest separation, 4.3 meters.
Wojciech:So here you said 25, 35, if I'm not wrong, the heat flux, yep.
Joe Willi:So, with the 4.3 meter separation distance, we had heat fluxes in the range of 25 to 35 kilowatts per meter squared and we found that while we had failure of one pane, with the tempered-tempered pane assembly, as well as plain on the exposed side, tempered backside, none of those pane assemblies experienced complete failure, whereas the other two pane assemblies we had complete failure in all, four of each type.
Wojciech:So it's really, really interesting. I mean you've done this research to, of course, inform the fire spread between the structures, but because the way how you tested it, especially at this 1.8 meter configuration, it perhaps is also a good source of information of how windows can fall in a flesh-overed compartment. Have you tried to look at these results, thinking about compartment fires as well?
Joe Willi:Well, actually, in terms of window failure research, there's a lot of the larger closer-to-full-scale experiments that have looked at window failure have been a fire that's inside of a compartment and when the window fails from that.
Wojciech:But obviously with that you now have additional effects like compartment effects that could potentially impact the window failure I still think this would be an excellent reference point for for the especially growing fires in the compartments when you're yet not have a flashover, but you can still have quite significant heat fluxes or perhaps flames impinging your window to some extent. Anyway, I said there's a link between this and the Dan's part. So, dan, maybe you can explain the findings in relation of igniting the external wall and the window breakage. How did it rank what's more likely to happen your external wall igniting or window damage?
Dan Gorham:Like what's more likely to happen, your external wall igniting or window damage? Yeah, so you know, we found that at the 1.8 meter separation distance we only looked at that non-combustible fiber cement siding but it had a combustible components and in all four of those experiments the combustible component, the OSB, ignited. So at that really close separation distance the intensity is so severe, so intense that even with a non-combustible exterior siding it's possible in these cases, four out of four times that the wall ignited. And then relate that to Joe's experiment. These were walls with no openings. But if you had an opening in that wall, say a window opening, we tried to look at the differences between what would have failed first, what it had been the rear wall or what have been the windows. But that really close separation distance is kind of there's so much just kind of chaoticness of you know where it ignited. But as we start to increase the separation distance to three meters and 4.3 meters, we start to see some divergence in the heat load at the time of window failure or exterior wall failure. So kind of the short answer is that sometimes the window will fail, create an opening before the exterior wall does. Sometimes the exterior wall would have ignited, or some component of it would have ignited before the window opened.
Dan Gorham:But I think that this is an important time to highlight that, while the times vary and we may not have enough sample size to converge on what would have happened first or last, it's important to point out that when one failed, it created a vulnerability or an increased susceptibility of the other. So use the exterior wall igniting as an example. If the exterior wall ignited first, the window hadn't. Now you maybe have some localized flame from the burning siding or the burning wall component that is now in addition to that source exposure. You have some localized flame. So what would have caused that sooner? And then, at the same time, joe looked at the failure of the opening in the window. Now that we have a pathway for flames from that localized burning siding or embers, which wasn't a focus of these experiments. But in these urban configurations, the extra fires here also times can have firebrand embers that opening is a pathway for smoke, flames and embers into the structure.
Wojciech:And were there configurations in which you would see a failure of window but not the failure of the wall?
Dan Gorham:Yeah, so at three meter separation distance, which is where we had the most experiments in Joe's pain failure, we had the number for the other separation distance for the exterior siding, for the non-combustible siding, so that would be the fiber cement siding.
Dan Gorham:We did not have ignition of the wall assembly, right, so there was still the same OSD behind it, but at three meter separation distance we saw discoloration of the fiber cement board.
Dan Gorham:We might've seen some cracking, maybe some off gassing, perhaps from the OSD beneath it, but we didn't see that wall ignite at three meters. But at that same separation distance, with different experiment but similar replicate exposure source compartment for those experiments with the windows at three meters we did see that the windows could fail. And so this is an example where if you're replacing the siding on your home and you say, okay, I don't want this combustible wood siding, I want to put non-combustible on, that's great and maybe at that larger separation distance that component won't ignite. But you have to think about what also is in that exterior wall, like your windows, and if you have on that exposed side of the home windows that might be broken or fractured by that exposure, your siding doesn't ignite or your wall assembly doesn't ignite, but there is another building component, the window through it, that might fracture, as Jewish paint experiment should.
Wojciech:One more fire engineering consideration that I would add is like where the windows are against each other, because if your window is looking at the window of your neighbor, that's perhaps the perfect configuration for fire spread. But maybe one could design it in such a way that the windows are fairly far away from each other. You also create less of those vulnerabilities, right?
Gavin Horn:if I can, that might be a comment that could make you know a lot of these track built homes where you have very close separation distances here in the west. They're very common designs that are back to back to back and actually it's one thing that I see around here in oregon where you have a lot of those where windows are facing windows very near to each other because it's a very similar to the structure design, usually have maybe a handful of those layout and you can see a lot of those almost like a generic yeah, very.
Gavin Horn:Very much so. Very similar looking structures with some small differences, and oftentimes that ends up with one, if you do catch one on fire a vent coming out from one that could be very near to the window, or an opening on the nearby structure.
Wojciech:But it would be sensible to say that if you had a real non-combustible wall like a masonry structure and a tempered, tempered glass pane and a non-combustible window frame that doesn't deform at this 4.3 meter, if your window survives, it doesn't create a vulnerability, Assuming it's a completely non-combustible structure. You create no pathway for that. It seems fairly safe in that case from those two experiments, right?
Dan Gorham:I think so. I think that does. There's no opening in your scenario of a non-combustible wall and non-combustible window and component that don't ignite. But one of the things that it doesn't capture is heat transmission through those opening. So the window might not have cracked or might not have failed, but there is still some amount of heat transmission through it that might cause the combustibles inside of the structure, your curtains or your furniture, the things that we have in our homes to live in. Just because you don't have the ignition on the exterior, it doesn't mean you might not have ignition on the interior components.
Wojciech:And here comes in Rebecca with the third piece of research. So, rebecca, to your research on how the radiation through the window can create another pathway of fire spread. So again, if you could tell me, like, how did you design the experiment and what particular you were looking for in your experiments?
Rebekah Schrader:Yeah. So for these experiments we were really focusing on heat transferred through the window, looking at varying the glass types and the number of glass types, whether or not they were coated or uncoated, looking at differences in the fill gas between double pane window assemblies, and so to do this we measured the total heat flux about five centimeters behind the back of the window assembly, about five centimeters behind the back of the window assembly. And so some of the motivation from this is we've seen in previous post-Wooey Fire case studies mention combustibles on the inside of a home igniting or having thermal deformation prior to a window failing. We've also seen this in some of our own FSRI studies that weren't necessarily even focused on wildfire exposures. One study in particular for multi-story apartments, there was an exterior fire experiment where fire went up the back of a deck to an unit that was above the apartment where the fire was ignited, above the apartment where the fire was ignited and we saw some curtains behind a sliding glass door that actually ignited prior to that slider failing. So we knew that this is definitely a threat to structure survivability and wanted to study this at more of a repeatable high level of control scale.
Rebekah Schrader:So that's why we decided to expose windows to a radiant panel. We exposed them to heat fluxes between 10 kilowatts per meter squared and 50 kilowatts per meter squared for a consistent length of time. The windows themselves were 23 centimeters by 23 centimeters. This size was chosen so that way the entire window fit within the footprint of the radiant panel that we had. And then the six different types of windows specifically that we looked at were single pane plain glass windows, single pane tempered glass, double pane plain and tempered glass with a air gap fill in both of those two window types, and then double pane windows filled with air in both of those two window types, and then double-pane windows filled with air but had a low emissivity coating on them, and those were also tempered. And then double-pane tempered windows with a low emissivity coating but in argon fill gas. So those were the different variables that we had during these experiments.
Wojciech:What were you looking at? So you've measured the heat flux behind the window and were you also looking through the failure mode or time or heat load at which it failed?
Rebekah Schrader:Yeah, so we also recorded the time to glass cracking and then when the window itself failed and these experiments failure was for the tempered glass windows. Failure was defined as when the outer pane failed. Because of the mechanism of tempered glass failure the pane kind of shattered and so some glass kind of would sometimes get lodged in the radiant panel. So we shut down the experiment then, even though the backside pane was still intact.
Wojciech:So the heat flux you were exposing to that, was it something changing in time or it's just flat exposure?
Rebekah Schrader:It was a constant exposure.
Wojciech:Constant exposure, and was the heat flux behind the window changing, or was it also a constant? Because you know it's radiant heat transfer, so it's like immediate. How was it looking?
Rebekah Schrader:So initially, the heat flux measure behind the window would increase at the beginning of each experiment. Some of our experiments lasted up to 20 minutes if we didn't have any window failure. In that case we'd see the heat flux measured behind the window begin to steady out for the last little bit of the experiment. But in experiments that were ended earlier, we still saw an increase in heat flux exposure at the end of those experiments.
Wojciech:So my question is how much of this radiant heat flux does a window actually block out? So if you asked me this question before this interview, I would say it's like pretty transparent to me, at least to the daylight. So how does it look for radiation?
Rebekah Schrader:Yeah, so definitely it depended on whether or not there was a low emissivity coating on the window. These are some of the first experiments that we've seen where we're looking at the impact of a low E coating on how it impacts heat transfer through a window for fire exposure, not just looking at how low E coatings impact energy efficiency of a window. And so we saw a significant reduction in the heat transferred through the windows that had a low E coating compared to those that didn't have a coating on them.
Wojciech:What's a coating? Is it like a foil that you attach to the window? How does it? What's the technology? How does it work that you attach to the window? What's the technology? How does it work?
Rebekah Schrader:So there are different types of low-e coatings. This one was a film that was applied to the exterior side of the pane that was facing the radiant panel.
Wojciech:Is it reflect? What's the mechanism? Does it reflect heat? So?
Rebekah Schrader:it will reflect and then reduce the heat and light that's transmitted through the window pane.
Wojciech:And did it influence the time to the failure of the external pane? Is there a trade-off like less transmitted, but failure occurs quicker or not?
Rebekah Schrader:So we did see in the experiments with double-pane, low-e-coated, argon-filled windows for the fill gas filled windows for the fill gas.
Wojciech:we did see that those windows tended to survive longer compared to those that were filled with air. Okay, now, looking through the results that you've provided, I see the table. So indeed, the reduction of heat flux is very high. I assume that the final heat flux means the heat flux at the time when the window fails. That's what I assume.
Rebekah Schrader:At the end of each experiment. The end of each experiment did differ depending on the experiment itself. If the window did not fail over a length of 20 minutes, then we ended the experiment at 20 minutes. If the window failed beforehand, then we'd end the experiment there. So the times to each experiment end were different, but we focused our analysis on the heat flux measured behind windows 30 seconds after exposure began across all the experiments so we could have a consistent time mark to look at the difference in heat flux measured behind each window.
Wojciech:So I see that for 10 kilowatt exposure the windows have not failed, like all of them passed and the exposure is 10 kilowatts, and for plain window you, for example, have six kilowatts. On the other side, for double, you have 38, 4.3. So that's a significant reduction. That's like 40 to 60% reduction For higher heat fluxes, though, you start observing some failures. So what would you say is the target heat flux behind the window that could lead to ignition of, let's say, curtains or whatever material can be behind the window?
Rebekah Schrader:So we compared the heat fluxes measured behind the windows in the experiments to a couple minimum heat fluxes required for non-piloted ignition of combustible materials. So there has been some past research that has shown that we can have smoldering ignition of polyurethane foam at as little as 7 kilowatts per meter squared. Additionally, maple plywood can also have smoldering ignition around 7.5 kilowatts per meter squared. Additionally, maple plywood can also have smoldering ignition around seven and a half kilowatts per meter squared. And so those were some of the combustible materials that we looked at. There isn't a whole ton of research out there. Looking at non-piloted auto ignition of certain household materials you might see right behind a window, but those were some of the ones we could find. So we definitely saw that there is a potential for some ignition of different combustibles behind the windows that we studied over a duration of time at a constant heat flux exposure so the only values that bring that come to my attention, the ones above 10 kilowatts.
Wojciech:I would say that that sounds very dangerous to me. I only can relate that to to experiments done with a cone calorimeter, so you could perhaps observe some flaming ignition at that point. So 10.8 kilowatts for 20 kilowatt heat flux for single tempered. At 30 kilowatt exposure for single tempered you see failure at like 12 minutes into the test and 13.7 kilowatt behind the window. But in general the values don't don't seem that high behind the window. So can you comment like on some final findings of the study? How did you rank those windows and how likely is this scenario of having your window survive the external heat flux and the ignition behind the window being likely?
Rebekah Schrader:let's say yeah, so we definitely saw. Our overall conclusions are that double-pane windows obviously perform better than single-pane windows and the use of a low E-coating also significantly reduces the heat flux that's transferred behind the window. In terms of the heat flux measure behind the window, when we noted failure in these experiments, it is important to note that for the double pain windows that were tempered at that time, the back pain was still intact. So realistically, in a fire scenario you're still going to have an increased heat transfer through that second back pain prior to it failing. Just, with the limitations of this study, we weren't able to quantify that. So we definitely did see that there is a risk for heat transfer through a window impacting the inside of a home prior to it failing and then, obviously, once it fails. Now we have an opening for direct flames and embers to enter, which will further decrease the survivability chance of structure.
Wojciech:Yeah, but again I think you've reached a point in which you would not have a fire spread to the external facade. By Dan's research you would not have window destruction as in Joe's research, and again from your research you would find the conditions in which the heat flux is perhaps insufficient to ignite the stuff on the other hand of your window. So a combination of all three probably results in quite a resilient infrastructure for a given distance between the structures. Of course. If you put them 1.8 meters from each other with windows looking at each other, then perhaps it's not so optimistic anymore.
Rebekah Schrader:Yes, absolutely.
Wojciech:One more thing that's going through my head. Not so optimistic anymore, yes, absolutely. One more thing that's going through my head Is it possible to actually apply the low E coating to windows that already exist, or is it technology at the factory that you can only do when purchasing new windows? Is it something you can retrofit actually, because the difference is really big in your research.
Rebekah Schrader:They do make films that you can retrofit some of your windows with. Yeah and with that. There are many different types of low emissivity coatings that we are currently conducting some research on to see if changing the type of low E-coating impacts failure through EvoWindow.
Wojciech:Really cool. I think all of this combined creates some really nice and interesting actionable knowledge that people can actually use in creating fire resilient houses. So let's perhaps try to summarize. Where are you going further with that? I've been teased that there are still papers to be published. So what's more to expect from this?
Joe Willi:Yeah, sure, yeah sure. So with the window paint assembly experiments, as I mentioned, the one-off experiment that we did with vinyl frames showed that the impacts that frame materials could have on window failure. You could have the best paint assemblies in the world, but if they're mounted in vinyl frames that are going to deform and melt, then you're going to have window failure. You're going to have an opening into a structure. So based on that, we decided our next topic of research, or one of our next topics of research, would be examining different types of window frame assemblies and how they fail. So we're currently in the writing phase of those experiments. They've been conducted and we'll be submitting to a journal here shortly. So those results will hopefully be out within six months or so for people to view.
Joe Willi:But I mean, the long and short of it is that we looked at vinyl, fiberglass, wood and aluminum frame windows and overall the aluminum frame windows performed best. But we still found different mechanisms of failure with the aluminum frames. We saw cases where the aluminum frames would actually ignite and it wasn't the actual aluminum frame members that was burning, it was more so different components. Specifically the aluminum frame windows, had a rubber gasket around it that would ignite, and we also saw sometimes it wouldn't fail, but different components of the assembly would melt or deform to where the top sash would drop down, and again that's failure, causing a large opening to form.
Wojciech:And have you considered those, let's say, vulnerable solutions, but at larger separation distances? So let's say a vinyl frame, single pane, but at six meter or 10 meter separation, would that be also something sufficient?
Joe Willi:I think that'd definitely be an interesting topic to conduct experiments on in the future, but at the moment we haven't focused on it.
Wojciech:Yeah, but still, if you're a fire safety engineer, you know how to calculate heat flux at the distance from an opening. You can do some simulations. You can calculate the heat flux field, create the heat loads then relate it to the body of experimental research that's already there. Loads then related to the body of experimental research. That's already there. So it's still. Even though you have not tested such a scenario, given the knowledge you've published, it's already usable for such an exercise. Dan, you wanted to add something.
Dan Gorham:Well, I was going to add that I think you know the question that you're posing there, votek, is a really good one to relate what we're doing in these controlled experiments to real world.
Dan Gorham:I mean, these controlled experiments are fixed separation distances and maybe your separation between structures isn't those or is outside of that range, and it connects to kind of another aspect of FSRI's research work or work in the research space, particularly in this woolly field.
Dan Gorham:A couple of years ago now, we did the comprehensive review and analysis for the fires on Maui in August of 2023 and really in and heat load at the failure window panes, the controlled experiments and in these post-fire analysis looking at oh look, this is an example of an annealed glass and it's tempered and right next to it happens to be a tempered glass window and it's not a perfect surrogate for water-cooled heat plus gauge measurement we can start to see some relationships between the degree of or the magnitude of damage from the controlled experiments in these post-fires and similarly we can see damage and pathways in these post-fire analysis that can inform our research or can kind of vet into that.
Dan Gorham:So some of the additional work that we're hoping to do is to take the controlled experiments data that have been published and the work that we have done for Lahaina and the publishing those reports is to kind of extend that research to connect again from the controlled experiments to the real world, which we've seen several of those for again, some of the Nain fires, the Camp Fire, the Marshall Fire, looking at these dam systems and what we can contribute in that space as well.
Wojciech:Also, like connecting the damage that you observe in the lab versus what you observe in the field allows you to backtrace the design fire scenario at the community scale to really grasp how big the fire was and where it went. It could be also very interesting like kind of a forensic reconstruction of the fire growth.
Dan Gorham:So one of the other aspects of doing these reviews analysis of real world incidents is there are factors that are outside of our control. Right, for our controlled experiments we try and account for repeatable and reproducible fuel load, but in the real world that's not always the case. One of the other factors that we don't currently look at in our experiments is the effect of defensive actions. Right, so this is oftentimes an attribution of why a structure is damaged but not destroyed. In the rural world that might have been a homeowner that stomped out that small fire or pulled away the welcome mat, that charred the siding but didn't fully ignite it. And some things that we've seen in the rural world and have done some controlled experiments are things that homeowners and emergency responders can do if they have the time and the resources to protect structures from these exposures.
Dan Gorham:And looking particularly at windows, we understand and recognize the vulnerabilities of windows, the glass and frames, but if the fire is approaching and it's an hour or minutes away, we don't have time to replace that window. But there are things that could be done, like covering that window opening with a protection. So we have done some old experiments, similar setup as the windows openings, with that source compartment exposure. And we've seen in the real world where people have deployed ad hoc window protections or even purpose-built window protection, deployed ad hoc window protections or even purpose-built window protection. So these are kind of again continuing the pathway of recognizing the components, the window opening, as being a critical pathway. What can we do in the construction phase, building with materials and assemblies, but also what can be done in the days and hours before or even during a fire to reduce the vulnerability and increase the potential that a hole not ignite and not be destroyed from one of these fires.
Wojciech:That's a really good high-level overview of the further goals. So, Gavin, can I ask you for a high-level summary of how does it look from your perspective overseeing this? Is your board happy with the research directions they've set onto? The research directions they've set onto that's an insane amount of experiments and trial burns out there that gave us a lot of knowledge that we did not have. So I hope this continues?
Gavin Horn:Yeah for sure. Our board has been actively engaged with us throughout the development of the program. As we started this conversation we realized that FSRI has been involved in this work for really about four to five years. That moves from concept to the point where we're doing some of these analysis and, as Dan mentioned, where we're seeing they're directly related to some of the impacts that we're seeing out into the world, where we can understand what some of the exposures might be on structures in these large-scale fires, so we can help to understand what those pathways are into the structures and fill in that gap. So we've had excellent support from our board, some great ideas on some future work that we might continue down this path.
Gavin Horn:But there's so many more questions that we still have left to address here in terms of the different failure mechanisms that windows may experience. Dan mentioned Dan, joe and Becca all just mentioned a few of those and we've got more work that we need you to understand those realistic exposures that they might face. But also what can we do to help reduce those risks? Can we translate this into a standardizable exposure system or a standardizable exposure system or standardizable exposure that we can use to test the windows that might be installed in some of these WUI areas, particularly when we have high density housing. What we need to understand from all of the work that we've done, as well as other great work around the world, is we're talking about systems, we're talking about assemblies. So Dan talked a little bit about we had a non-combustible outer surface, a non-combustible siding. But if the sheathing behind it was combustible, that system still allows a pathway for fire to enter the structure. It is certainly more resilient and more resistant than a combustible sheathing on a combustible or a combustible siding on a combustible sheathing. It helps us to improve some of the fire resistance, but it's not impermanent.
Gavin Horn:We see again is joe and his beck have talked about where we have double pane tempered glass. It does a great job of reducing the impact of that thermal exposure, but it's also not perfect. There's more pieces to it the frames, the components of the, which we'll get into a little bit more in the paper that Joe was talking about. Those components that attach the frames to the sashes have an impact and many times those are plastic. Even we think about the system of how a window is put together in terms of what is the fill gas in between them. Or if you have one that's tempered and one that's plain. The order matters the same two paint types of glass, but the order in which one is tempered and which one is a plain glass. That matters Once it gets installed into a system, once we look at the entire assembly.
Gavin Horn:So we have to start thinking about all of these things as assemblies. There's a wall assembly, there's a window assembly. So we have to start thinking about all of these things as assemblies. There's a wall assembly, there's a window assembly, and when we look at the outside of structure, those assemblies come together in a further assembly.
Gavin Horn:So this research is hopefully helping us to understand each of those individual component pieces and, as you mentioned, we're really just looking at one component of the overall exposure. We're focusing on radiant heat exposures and direct flame contact once we have this very close separation distances. But those then open pathways for embers to address, for other things to come in. So we're starting to pick apart these hazards. We're starting to pick apart where the building envelope may start to break down in hopes that we can help to reduce some of those risks. But I think it's also important for us to understand when we get to these very close separation distances. When we're 1.8 meters apart, when we're six feet apart, we have limitations on what we can expect the built environment to be able to withstand.
Wojciech:There comes a point where, even with the best wall, with the best window and as good of a construction as we can possibly have, we don't have a way of completely making the buildings fireproof within the systems that we, where we were studying in these experiments yeah, and I believe, tracing those limits like, uh, you know you've just finished this, these pieces, you've uh, published your papers and here comes the fire for which it perhaps was the most relevant to you know, and I mean the lay fires, where this was evident, this was evident and I hope with research like this we can guide our communities to safety so tragedies like that are hopefully not happening realistically, are less common and we can protect our citizens even better. Thanks once again for this comprehensive review of your research on external fires A huge gap with a good closure by your team. So congratulations to FSRI for your ambitious fire research that you're carrying. The scale is amazing, the amount like I highly recommend everyone to go through the papers the number of experiments. Perhaps we did not give the justice to the number of data points that you've created, but they're all in the papers, so I can only refer the audience to look into those and I'm looking forward to hear more from FSRI on this topic. Thank you guys, thank you, thank you, and that's it.
Wojciech:We're well over the length of average fire science show episode, but I think this was still worth it. So much knowledge and recommendations in one single episode. It's unprecedented, so much actionable knowledge. Actually, that's very important because those experiments are not just interesting from the perspective of fire science, they are just damn really good for engineering. They answer important questions. They showcase what happens at a very wide range of heat fluxes, and those heat fluxes can be related to a lot of realistic fire spread scenarios. So it's not just burning a few houses, a few facades and a bunch of windows. It's about creating a really important and useful data set that allows us fire safety engineers to work with. I'm not going to summarize this any further.
Wojciech:I think if you are still interested in this research after hearing this podcast episode, your next step should be to read the papers, because they're good and you will find much more details in the papers. Well, that that's what papers are. They're extremely detailed. Explanation of what has been done by the researchers. Podcast is just an introduction and a high level overview of what has been done. So if you're interested, next step is in the papers. They are open access. You can. You can find them now. Right now they're in the show notes. So be my guest, go take a read and let me know what you've learned from them. For me, that's it for today. Thank you very much for being here with me in the Fire Science Show. It's Easter time, so happy Easter holidays if you're celebrating that, and have some rest with your family. And guess what? Next Wednesday we're coming back to the fire science show with another fire science episode. Thanks, bye, bye.