Fire Science Show
Fire Science Show
196 - Fire spread through external walls pt. 1 with FSRI
In this podcast episode, we host Rebekah Schrader, Joseph Willi, Daniel Gorham and Gavin Horn, all from the FSRI, to cover their recent experimental research on fire spread through external walls. This is part 1 of the interview - the background, rationale and context. In part 2, we cover the experiments themselves, findings and actionable guidance from the experiments.
This research is conducted within the context of structure-to-structure fire spread, potentially in urban conflagration scenarios. The subject is most relevant, as when wildfires meet urban areas, they transform into something far more destructive – "wildfire-initiated urban conflagrations." These events devastate entire communities as fire spreads rapidly from structure to structure, overwhelming firefighting resources and leaving widespread destruction in their wake.
The Fire Safety Research Institute has embarked on a comprehensive research initiative examining exactly how these conflagrations develop and spread. What started as a response to their advisory board's call to action in 2018 has evolved into a groundbreaking exploration of the complex interactions between wildland fires and the built environment.
We break down the three primary mechanisms of fire spread – radiant heat, direct flame contact, and firebrands – while highlighting specific vulnerabilities in modern construction, particularly windows and cladding systems.
What makes this research particularly valuable is how it bridges traditionally separate disciplines: wildfire science and structural fire engineering. The team explains how they've translated complex wildfire scenarios into controlled laboratory experiments that yield actionable data for improving building codes and community design.
Whether you're a fire safety professional, community planner, or homeowner in a wildfire-prone region, this conversation offers crucial insights into how we can create more resilient communities in the face of this growing threat.
In the next episode, we will cover in depth the details of three experiments mentioned today.
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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Hello everybody, welcome to the Fire Science Show. My mission in this podcast is to curate a listening list for you covering the most important interesting research happening around the world, and my attention came to a very interesting and big piece of research recently that is constantly published by Fire Safety Research Institute, fsri, and their research orbits around the topic of external walls and fire spread between buildings, fire spread through external walls and different aspects of that fire spread. And when I've looked into the papers, it was immediate to me that this is a fantastic piece of research. It's a piece that covers a very important knowledge gap that we have in fire safety and, what's even more interesting, it does not just cover the fire spread on its own. It puts it in the context of wildland, urban interface, fires entering urban habitats and fire spread like the ones that we've seen, perhaps, in LA Palisades fire recently. You know the urban configuration, types of fires that are really the most threatening ones, the ones that we really worry about the most. So, beyond just studying fire physics, beyond just studying compartment fires, beyond studying fire spread, this research literally bridges two disciplines wildfires and compartment fire science, and that makes it really, really interesting, and therefore I've started digging, started connecting myself with the colleagues at FSRI and organized this interview, and boy, this project is much bigger than I thought. So what you're about to witness is a two-part episode. Actually, in this first episode published today, we are covering the background, the rationale, the why, why are they pursuing this massive research set, what questions do they try to answer and what's the scientific context of the considerations. And in the episode that will be published in the next week, we will go more in-depth into the experiments performed, the experimental setups, results of those experiments, how they interplay together, what we've learned new from those experiments and how fire engineers can use that. My guess first time, I'm doing an interview with four different guests at the same time. So those are Rebecca Schroeder, joseph Willey, dan Gorham and Gavin Horn, all from FSRI, all involved in this magnificent external wall research project. So what else to add, you'll figure out yourself. Let's spin the intro and jump into the episode.
Wojciech Węgrzyński:Welcome to the Firesize Show. My name is Wojciech Wigrzyński and I will be your host. This podcast is brought to you in collaboration with OFR Consultants, a multi-award-winning independent consultancy dedicated to addressing fire safety challenges, established in the UK in 2016 as a startup business of two highly experienced fire engineering consultants. The business has grown phenomenally to eight offices across the country, from Edinburgh to Bath. Colleagues are on a mission to continually explore the challenges that FHIR creates for clients and society, applying the best research experience and diligence for effective, tailored solution. In 2025, there will be new opportunities to work with OFR. Ofr will grow its team once more and is keen to hear from industry professionals who would like to collaborate on fire safety features this year. Get in touch at OFRconsultantscom.
Wojciech Węgrzyński:Hello everybody, I am here joined today by quite a crowd from the Fire Safety Research Institute. Hello guys, I'll start with Rebecca Schroeder from FSRI. Hello, rebecca, nice to meet you. Hi, nice to meet you On my screen. Next is Joseph Willey hey, joseph, how's it going? Dan Gorham hey Dan, okay. Yeah, nice to meet you On my screen. Next is Joseph Willey hey, joseph, how's it going? Dan Gorham hey Dan, okay. Yeah, good to see you. And Gavin Horn Welcome back, sir.
Gavin Horn:Thank you, great to be here.
Wojciech Węgrzyński:Oh, and really amazed that we've pulled this over, and I'm really happy to record this podcast episode. So, to go straight into the important stuff, you guys are inside of a very interesting project related to external walls, heat exposures, fire spread into the buildings from the buildings, all rotating, revolving around external walls of our buildings in in the most interesting context, combining a wild and urban interface with built environment civil engineering. I love it, love it. I love the way how you are applying this. So, before we start talking nitty gritty about your experiments and the setups that you've done, tell me what made you start this work, because I assume it was not just a random coincidence that you run into this massive undertaking. So what was the initial trigger to go into this research, joey, would you like to start?
Joseph Willi:So at FSRI we have an advisory board that we kind of consult with, filled with fire experts from all different types of fields whether that's the fire service or fire protection engineers or fire researchers and they kind of help guide our research.
Joseph Willi:And so we have an annual meeting where we tell them, get them up to speed on the kind of research we've been doing over the past year, and then we have a session where we ask what do you think our next topic should be? What are some spaces we're not exploring that we should explore? And so we had one of those meetings, and was it 2018,? I think that we should explore. And so we had one of those meetings, and was it 2018? I think. And by far the number one issue that we hadn't been addressing was wildland or WUI fires, and that makes sense. It's been a hot topic, especially over the last couple of decades, as these fires increase in frequency, severity and size. So, based upon that, we started planning out what our research would look like, what we would focus on, and our first goal was to kind of look at structures. We've always focused on structure fires. Fsri started with the fire service and looking at fires inside of structures. So our idea was we would be looking at fires outside of structures kind of exterior fire spread into the structures. And so a part of researching that, our first round of experiments we conducted in a large-scale fire lab in Northbrook and we had three different phases of experiments.
Joseph Willi:Our first phase was looking at different types of building material, construction materials, samples, when they're exposed to a well-characterized heat source in the form of the heptane spray burner and kind of how they would react. So we set them at distances that gave us approximate heat fluxes of 10, 20, and 30 kilowatts per meter squared. And we were looking at materials from roofing materials, siding materials, decking materials and then small window samples with glass panes in them. So we looked at how they reacted at those different levels of exposures. And then we also wanted to kind of characterize what the heat flux exposure from a compartment fire would be. So the second phase was looking at a compartment fire that had an attached facade to it with different siding materials to see if the different siding materials would contribute to that overall exposure from a compartment fires. And then our third kind of experimental phase was okay, we have the compartment fire that we characterized in the second phase what happens if we put a target facade across from it at a separation distance that you would see in a community with a high population density, and how would that target facade react to this compartment fire exposure?
Joseph Willi:So we were looking at different types of siding materials on the target facade. We had two double-hung, double-paned windows mounted in the target facade. But then a third thing we were looking at is the fire spread between them and what type of potential fuels could you have in between two structures that would kind of initiate fire spread from the compartment to the target facade? So we ran three experiments with three different types of what we referred to as ladder fuels. We looked at the impact of a car in between two structures. We looked at the impact of an attached deck attached to the target facade, and then we also examined a shed small shed in between the two structures. And so, based upon these three sets of experiments, we decided that we would plan our next experiments to be a bit more focused and look at the impact of different siding materials or exterior wall assemblies, as well as look more into window failure.
Wojciech Węgrzyński:So you said it started like 2018. What did the environment, like scientific environment, in this regard look like? Was it like a blank spot? Where did you find the biggest gaps in knowledge in solving those problems? Because I think 2018, I would say that was already the wildfire. Research was already pretty intense.
Dan Gorham:I think one of the things that makes the WUI fire, or community conflagration fire, that a challenge is because of the complexity, the spatial scale is because of the complexity, the spatial scale. If we talk about a high-rise building that's 20, 50, 100 stories tall, you can think about them as individual structures, but you have that primarily vertical component, whereas at the community scale we have this horizontal component. In addition to the vertical component we have multi-story residential structures or commercial structures component, have multi-story residential structures or commercial structures, and so it really is that complexity of oftentimes it's not a single fire scenario, it's oftentimes multiple fire scenarios. So that might be your immediately adjacent structure that has burned from a kitchen fire or some other typical fire problem, but in a community conflagration event, where the fire transitioned from the wildland into the built environment, oftentimes it's multiple structures. So it's your neighbor next to you and across the street and three houses down, and so now we have multiple thermal exposures for multiple vectors. There's also the complexity of fuel continuity. Joe was talking about that in some of those initial experiments looking at the intermediate or ladder fuels between structures.
Dan Gorham:If we think of structures and buildings as the primary things in the built environment, that being damaged or destroyed is the biggest loss. There are all the things in between and the residential communities. That can be cars, that can be ornamental vegetation, that can be your kid's play set. So there are a lot of these complexities that differentiate this WUI or G&E conflagration problem from other fire safety problems. But that is.
Dan Gorham:It has also created an opportunity to learn from and lean on the experience and the knowledge base that we have in that space to translate it over. But we have to add compounding factors like that sprawl, that spatial component, the ambient factors like temperature, relative humidity and wind. And then another important component of FSRI's research is fire service intervention. When we think about structure fires or fires within the compartment, we oftentimes think about ventilation limited and water suppression. But in these configuration events, water supply is oftentimes limited. There's oftentimes more fires than there are resources, whether that be engines or responders, and so this is why the fire safety problem is big and something that FSRI is compelled to address safety problem is big and something that FSRI is compelled to address.
Wojciech Węgrzyński:FSRI is known for giving good fire safety considerations to the firefighters. A follow-up question, going from a general weave problem or even urban conflagration problem into actionable research items. It's not something you just simply sit down and research. It's too big, so you had to narrow down. So how did you come up with this research program in which this, I understand, there was a preliminary research, but how does it tie Like why, in particular, this fire spread through the external walls, why this was the gap that you've tried to fill out.
Joseph Willi:So, as far as windows go, there've been post-Wooey fire investigation that have identified windows window failure as a potential point of fire spread to structures. Once a window fails, there's now an opening for hot gases, fire and embers to get through and ignite interior contents. However, there has been some research in the past that looks at window failure. Some of that is more than 20 years old and windows have developed since then then. But also there's not a whole lot of research out there that's more on the full scale side. So that's one gap that we were trying to fill with this research so with the modern technology I also.
Wojciech Węgrzyński:I think window technology and in general, facade technology is perhaps one of the biggest innovative areas of civil engineering and construction. Is it also the case for uh, private housing and dwellings and smaller?
Joseph Willi:developments I would say so. I mean, you know energy efficiency has become a large thing over the last few decades, so with that you have kind of ever-changing window technology.
Wojciech Węgrzyński:Yeah, and the other aspects. You started listing them. I interrupted you.
Joseph Willi:Yeah, yeah, no, I was just going to mention that. The other thing, specifically with reference to codes and standards that are used in the united states. So there's kind of three primary documents. There's nfpa 1140, chapter 7a of the california building code, and iwc. That are wii based codes and within them they address windows, but in a limited fashion. They're typically focused on the glazing or paint assembly and they make no mention of other window components such as frames. And then when it comes to the, the glazing or the glass, they have some variation between them. So for iwec and nfp 1140 they require either a tempered pain assembly or a multi-pain assembly. But with the multi-pain assembly they don't specify what type of glass should be used, so you can have a double pain, just plain glass assembly.
Wojciech Węgrzyński:And then with chapter 7a they require a multi-pain assembly with at least one pain tempered, but they don't specify which of the two or more pains should be the tempered pain did the preliminary research also guide you towards which, which are the most, I don't know, often found to be failure in wii scenarios, or was something that you only unraveled during your experiments?
Joseph Willi:yeah, we saw. So we weren't. We were only looking at double-pane plain glass assemblies during those initial experiments. But with the phase three, with the target facade we had, like I mentioned, we had two windows. One of those windows had a low E coding on it and so we kind of based on our analysis of the data, saw interesting things with the window failure itself. We saw frames start to deform and whatnot, but also different types of failure with the panes, and saw maybe an indication that a low recoding could have may or may not have an impact on glass failure.
Wojciech Węgrzyński:If I understand correctly also this whole research, it was not just that the structure is a target of wild and urban interface fire, so you just understand how the structure responds to the fire, but you were also looking into a structure being a source of exposure to neighboring structures, also those interactions from in between. So it also kind of progresses to the influence of those external walls and how we build them as a factor that could contribute to an urban configuration scenario. I I would say like, if you ask me, uh, if you asked me, like last year, uh, about urban configuration, I would say, there, they, they don't seem to happen recently, but after what I saw in la uh just a few months ago, I'm not so sure if the age of urban configurations is gone. So, and you've started this in 2018. How did it look back then? Was it a part of your interest?
Joseph Willi:Absolutely so. The best way I've heard these events described are as wildfire-initiated urban conflagrations. So it may start out as wildfire, but once it enters areas that are more populated, with a higher structure density, then all of a sudden there's a new fuel load introduced in the form of structures and the fire kind of spreads structure to structure throughout these communities. And that's where you see a lot of times the large amount of loss and devastation that's associated with those events is due to that time when the fire enters these kinds of communities.
Wojciech Węgrzyński:Is there also any specific context in how the structures are built, the distances between the structures?
Joseph Willi:Was it also something that you've looked into? So we based our structure separation distances on kind of the worst-case scenario, or the highest population density areas or not the highest, but on the higher end and what kind of structure separation you'd see between there. So particularly we looked at anywhere from 1.8 meters to 4.3 meters separation distance.
Wojciech Węgrzyński:And in case, if there was a lot of fuel in between, did you also put the fuels between the structures and investigate that, or that was just preliminary, preliminary yeah, just during the preliminary.
Wojciech Węgrzyński:Okay. Now of course, in hindsight uh, looking at that, la fires was put up. It's obvious that this structure to structure fire spread was something you could expect in hindsight. Events like that did you observe? You must have went through the literature and and the previous fires. Have you observed events like that and how big part of your research plan was investigating fire behavior like we'd later observed in the lake?
Dan Gorham:Yeah, and you know, when you look at the history of fire, particularly in the North American United States but across the world, I mean events like the Peshtigo Fire the same night of the Great Chicago Fire, I mean so many of those urban fires from the 1800s to the modern day.
Dan Gorham:I mean over the past decade, the state of California alone has had some of their top 10, most destructive by structure loss count the Tubbs Fire, the Camp Fire, other parts of the country, the Marshall Fire and then just a couple of years ago now in Maui, hawaii, they had a series of fires. These were initiated as wildfires but in the case of the town of Wahaina, that brush fire or wildfire transitioned into the built environment, very similar to what we observed in the Marshall Fire in Colorado and many others around the world. And it's this transition from a wildfire or vegetation fire or a brush fire which has its ecological purposes, but as it enters into the built environment, it's that again, that fire safety or that fire phenomenon transition from a fuel that maybe needs burning, whether it be the vegetation or the shrubs, to the built environment where we have our homes and our communities that we don't want to burn, and that's the fire problem that transition from the wildfire into the built environment.
Gavin Horn:Yeah, and to bring this introduction full circle, this is how FSRI became engaged in the Wildland Interface research.
Gavin Horn:Our colleague, derek Alconis at the time was the chief of the Air and Wildland Division at LA County Fire Department and was on our advisory board and he'd been responding to these fires that Dan just mentioned and including the Woolsey Fire and others that were there in Los Angeles County and year after year they were seeing these events that were occurring and were looking for answers on how they can better prepare their firefighters, prepare the citizens and be ready to respond to these fires but also make sure that the citizens themselves are as informed as possible and codes could be updated as well as possible.
Gavin Horn:And because FSRI sits at a unique area where we were born from the firefighters St Jude Research Institute right, the firefighters have long been our core citizens, our incredibly important core audience for us, where we can take this full-scale research and address those concerns that exist. So after we saw a series of those fires in California, we began this program and identified, as Joe had just mentioned, windows as being one of the key vulnerabilities that there's some research that we can do at a scale that can help to fill in this gap and hopefully reduce some of those challenges that the fire department's facing, so citizens can have their structures prepared as best as they possibly can, and the firefighters can then respond as efficiently and as effectively as possible. So that's really how we really got to the area that we're at right now from a research perspective.
Wojciech Węgrzyński:Yeah, I'm pushing and chipping you to tell me the story, how you came into that. Because, like you guys are FSRI, you are the people who burn things down and do that in lab. That's like a normal Friday for you to burn down the house. I'm a fire researcher as well. I'm doing my time in the lab. Heat flux on my skin is not something I'm very unused to and, uh, in some odd way, you know, doing this research and doing all of those endeavors is our normal everyday's life.
Wojciech Węgrzyński:But there are hundreds of people out there fire safety engineers, civil engineers, architects who now have this problem of whole communities burning down, who wonder how do we solve the problem? And I would love people to understand how we, as scientists, how we figure out a high-level problem. In your case that's wildland-urban interface, initiated urban conflagrations. I love it because it nails down the problem. But here's it's a high level objective and by investigating, going through the history, going through the previous research, investigating evolution of the market, solutions, technologies, the ways how people build houses, looking into firefighters, reapers, you start narrowing down that big high-level problem into something that could be a window pane or a gasket or a facade technology and then in your laboratory, you can very precisely tell what makes the difference in this problem. That's the way of thinking that I want our audience to really understand, because if you understand the research process, one, you understand the research better. But two, if you have good ideas, you can send them to people like FSRI or me and we'll perhaps follow on that.
Wojciech Węgrzyński:But anyways, sorry for getting sidetracked, I just really had to say that and also admire your work a lot. Anyway, we know why, but one thing we still need to clean out. It was previously said that those fires spread through firebrands. We also mentioned heat fluxes, we mentioned ladder fuels, so fires in between the buildings. So perhaps let's clean out how the fires can enter the building and how fires can exit the building. I don't know, dan, maybe you can start.
Dan Gorham:Yeah, so thinking about exterior fire or fire outside of the box, outside of the enclosure, and oftentimes we think about the box, the enclosure, the house, the building, the structure as the property or as the asset that's most important. And again, a lot of times when we think at these historical fires, what comes to the top is the acres burned, the unfortunate number of fatalities and structures damaged and destroyed. And so how do structures get damaged, how does fire initiate from the exterior into the building and then, ultimately, how can that cause it to be destroyed? So when we think about that fire progression, you know there are lots of ways to kind of from first order fundamentals, but one framework to think about it is the building ignition mechanisms. We can think about that as radiant heat, and so this is that heat transfer that doesn't require any form of medium. So whether it be from a crown fire, you know large, 100 plus foot flames causing radiant heat transfer to a structure fire, similar magnitude flames, no direct contact, but enough heat transfer via just radiation to cause material to ignite.
Wojciech Węgrzyński:How really, like I don't fully understand. Well, I understand it but I don't fully feel it. So if you have a crown fire and let's say it's 100 meters away, which is approximately 300 feet in your units, how big the radiant heat flux could be from such a crown fire? Is it really high enough to ignite? Or how close the house has to be to the crown fire for radiant heat to be really like a direct hazard?
Dan Gorham:Yeah, no, that's a good point that you know that radiant heat transfer. You know Jack Cohen's work. Looking at crown fire, you know we can see from the fundamentals that radiant heat transfer decreases with the distance right. So the amount of heat transfer required would be very, very high. You'd need so much radiant heat transfer required would be very, very high. You'd need so much radiant heat. But an important factor that radiant heat plays in this space is that while it may not be that tipping over the straw that broke the camel's back to cause ignition, it can be the prelude to cause materials to rise in temperature, to dehydrate, to maybe evaporate some of those components that would reduce the time to ignition. So that radiant heat may not be the tipping point. But I think in a lot of cases, and again in these conflagration events, radiant heat plays an important role in that fire spread, in that building ignition because of that back and also, if you have a structural fire next to your structure, then we're talking about completely different heat fluxes.
Wojciech Węgrzyński:And if you have a structural fire next to your structure, then we're talking about completely different heat fluxes. And if you have a ladder fuel in between and that ladder fuel burns, then again we're talking about completely different radiant heat flux. So again, this way of thinking about just a single house ignition versus, you know, a whole scenario in which, house by house by house, they start going off. I guess the mechanisms, the mechanisms, the prevailing mechanism can also shift. So radiant heat flux, that's one. What are others?
Dan Gorham:Yeah, another mechanism. You just mentioned how these oftentimes are not in isolation. I think in almost every case, barring some exceptions, there's some combination of them. And the next that I would think about is that direct flame contact has that radiant heat component but also has that aromantency. So we think about the convective heat transfer. And so this is where we start to think about the fuel connectivity and the horizontal and vertical components, about how it's not just the structure separation but it's also the fuels in between.
Dan Gorham:So let's put ourselves in a scenario, maybe a typical suburban or urban community. My home and your home are separated by, let's say, 30 feet, but between our homes I have a privacy fence that connects to the property line. On the side of my home I have some combustibles, like a garbage can and maybe my parked car, and you have the same. So now we have a scenario of the fire spreading perhaps from my structure to the fence, to the vehicle, and now it's not just the radiant heat from my structure and all those intermediary fuels, but now those fuels very close to your home can cause that direct and intermediate clean content.
Wojciech Węgrzyński:You said convective. How big a part of that is wind.
Dan Gorham:Yeah, I think wind plays a really important role in these exterior fires and the convective how big part of that is wind? Yeah, I, I think wind plays a really important role in these exterior fires and the convective heat transfer. So if you think about, you know the, the gas temperatures it's superheated and if you're in that plume. But convective heat transfer can also play a role in cooling right. So we know about wind eddies and it's not always a straight line constant wind flow and oftentimes in these um, you know these urban communities, there's eddies and there's vortices and it's not constant. So convection plays both a heating and a cooling role. But I think when we talk about, you know that direct contact or, in the line of the plume, the convective heating. I think it's probably more dominant radiant. But convection is important enough that we shouldn't neglect it and firebrands.
Wojciech Węgrzyński:I think a lot of research I see recently is around firebrand ignition and how they can penetrate structures, so obviously that's a pathway right.
Dan Gorham:Yeah, absolutely, firebrands, or embers or you know whatever you want to call them, these glowing or burning particles that are one generated by fuels, whether they be from the wildland or wildfire vegetation, as well as in the built environment.
Dan Gorham:So once structures start to burn, once cars and RVs and kits placed that start to burn, they generate these particles.
Dan Gorham:And one of the components of embers is they can travel beyond the kind of fire perimeter so they can travel distances reported of more than a mile, but even short range distances of tens of twenties of feet or, you know, tens of twenties of meters that can cause spot fires. Additionally, those firebrands can enter into the structure. So a lot right now we've been talking about kind of the, the building, the structure as a, as a, as an encapsulation, a force field if you will, and the flames and the radiant heat having to penetrate it. Well, these embers can penetrate into small little open. That might be through vents, into your attic, your crawl space. That might be through a window that hasn't failed from the heating mechanism but might have just been left open because people have their windows or some natural convection. So embers penetrating into the building or causing spot fires around the building can be that third, and oftentimes a large portion of building ignitions play a role in kind of three in combination of the mechanisms.
Wojciech Węgrzyński:So how does one turn a wildfire scenario or an external fire exposure scenario into laboratory-controlled exposure? Like, how do you go from wildfire into laboratory unless you're having a wildfire-sized laboratory? In that case it's perhaps easy, but how do you create this design exposure?
Joseph Willi:let's say Well, really, whenever you're talking about fire exposure, there's a lot of different variables. With wildland fires especially, there's many including size of the fire, wind, etc. And so to kind of help control this, we came up with a scenario of a compartment fire that's venting out of an opening, the compartments flashed over, and that exposure from a fire venting out of an opening is not, it's going to be based on the opening size. If you have a compartment that's flashed over, just given ventilation to the fire, and we can replicate this exposure, and then, as far as what your targets are, we can have a matched target facade wall that's the same size as the wall attached to the compartment across from it, and so this kind of simulates fire spread from one structure out of event opening and how it could potentially spread to a adjacent structure.
Wojciech Węgrzyński:So this would be structure to outside or structure to structure.
Joseph Willi:It's structure to structure. So we're imagining a scenario where there's already a structure that's involved with fire and a vent or large window opening. In this case it's approximately the size of a sliding glass door, and we designed it that way not just to replicate a sliding glass door, but also so we could get an even exposure to the target facade, which I'll highlight later about why that's important. But yeah, so the scenario of fire venting out an opening of roughly that size.
Wojciech Węgrzyński:And the scenario where the fire is primarily outside of the structure and, let's say, attacks the interior of the structure. How do you come up with representative scenarios for those exposures Range of radiant, heat fluxes, firebrands, convection how do you manage?
Joseph Willi:those. This kind of goes back to different variables and mechanisms of fire spread, but we're primarily looking at the impact of radiant exposure. So these experiments did not involve firebrands, but rather they just involved the radiant exposure from an adjacent structure fire.
Wojciech Węgrzyński:In your papers you also cover how structures respond to that and there was a term in your papers called the structure hardening as a key strategy to mitigate this building destruction. And I also understand this was some also previous research carried. Before you go into exposing and testing your hypothesis, rebecca, can you tell me more about how the structures were prepared to wildfires and, again, how looking into those structures allowed you to craft this new experimental program?
Rebekah Schrader:Yeah, so looking at once, we identified that structures are a key source of fire spread during these complications, looking at what different materials of the structure can we focus on to see if there are better designs that might make those materials more non-combustible and help to increase the chance of a home surviving during a complication. And so one of my first projects at FSRI while I was still an intern was doing a large literature search on what research had been done in the wildland urban interface space, and a lot of that focused on modeling, also looking at vegetation fires, not including the structures. But from that we were able to identify key components of structures that are especially vulnerable and need to be addressed, and from that we came to the conclusion of starting to study cladding or windows more in depth.
Wojciech Węgrzyński:Yeah, and how about have you looked into things like I don't know? Ventilation openings or a roof structure is something that comes to my mind as an extremely complex, like if I was an ember, I would like to land in the joint between the roof and the house, or the windows were so apparent. That is the main research gap today.
Rebekah Schrader:Yeah, that's the main research gap we focused on. Roofing materials are definitely also identified as a vulnerable part of a structure. We haven't really gone into too much depth in that area yet.
Wojciech Węgrzyński:And the evolution of windows. What did your literature study tell you about the changing threads of the Windows? Is it something you can identify from the statistics, looking back into the fires, that, for example, we are more or less vulnerable today than we were, I don't know, 20 years ago?
Rebekah Schrader:We definitely have more designs of Windows, and the designs of windows have evolved and changed. Now we have double pane windows are more common, as Joe mentioned earlier. There's the low E coatings on the windows, different gas fills and double pane windows that are typically used to increase energy efficiency. To this research, there hadn't been much research conducted on looking at how those different design choices can impact how a window responds when it faces an exterior fire exposure.
Wojciech Węgrzyński:Yeah. One more question in general to the whole project is we are talking about the fire spread through the wall, whatever is a part of that wall. But is it like binary? If the fire has spread, you consider the structure lost at that point, or you still consider how bad is the spread? How much is ignited? What's being ignited inside, or is it irrelevant, because as soon as it spreads there's no way to respond? Also, this is an interesting firefighting consideration angle, because if it's just one house at the edge of the forest then probably they can put all their focus on it, but if there's a thousand in a neighborhood, then it must be a different story.
Dan Gorham:Yeah, thinking about the kind of the binary nature oftentimes we think of for fire, impacting these configuration events is a combination of factors, like you said, and during these events a lot of times it's more fires than local resources firefighting resources can respond to and kept capacity to, like water supply. There's also oftentimes factors like the wind and the rate of spread that drive other incident priorities like evacuation. So you know, a fire engine might drive past three or four structures that are just igniting to get to a location where they can help for evacuation. So there's, you know these are large scale, oftentimes large scale events that have lots of different factors. But if we just kind of think about it, even from a control setting, when fire transitions from the exterior into the structure and it's sustained, it's not intermittent, it's not self-extinction, it's a sustained ignition of the structure, a lot of times that will transition to being destroyed. And this is just the fact of, you know, I think, a lot of building constructions and building science fire from the exterior to the interior. We have a lot of construction practices that limits fire spread from one compartment to another on the interior, like gypsum walls and fire barriers, attention.
Dan Gorham:I think that this highlights the need to both better understand it from a research and a phenomenon perspective, as well as translating that knowledge to implementation, whether it be at codes and standards level, whether it be as guidance or best practices for designers, engineers, architects. But kind of coming back to the question, fhir need not be binary, but the accumulation of factors, weather, resources, other priorities. Oftentimes we think about that if a structure ignites and it sustains that ignition, it's most likely to be destroyed. There are a few structures that are ignited and damaged but not destroyed, but in most cases that not transitioning to destruction is attributed to suppression or defensive actions by firefighters or others. So, again, thinking about it from a fire science or fire phenomenon perspective, the goal is to reduce, to limit the potential that a structure or fire transitions from the exterior to the interior, so that it doesn't require a firefighter or someone to suppress it.
Joseph Willi:So one thing that makes this scenario different than your just typical structure fire or even have one, maybe two structures on fire and you can have enough resources from the fire department respond that they're focused on those structures is that now, instead of just one or two structures on fire, you have 10, 20 more structures on fire and more structures in danger of being on fire. So pretty quickly, resources become quite limited and fire departments have to triage and there's a chance that they are not going to get to a structure that's already ignited and be able to suppress the fire. So one of the goals of this research is looking at different construction methods and building components and what can you incorporate to have a home that can resist ignition.
Wojciech Węgrzyński:This is so far probably the longest buildup to an experiment I've ever had in the podcast, but it's well well worth it.
Wojciech Węgrzyński:However, let's maybe try to summarize the rationale part of of this podcast and in in the next episode we'll go deep into how does one translate from a wildfire scenario into laboratory scenario and we'll go deeper into your experiments on heat transfer through windows. We'll go into the window pane fallouts and also external fires and residential structures. So there's a lot to uncover from this work that the Nits and Bits of their research. But perhaps let's try to build a concise summary how the field has changed over the years and what a fire safety engineer should consider in designing a fire-safe community from this perspective of historical knowledge that we have on urban configurations or wildfires transferring it, what was omitted in fire safety engineering previously and how they can. If someone is charged with designing a community, let's say because fire safety engineering previously, and how they can. If someone is charged with designing a community, let's say because fire safety engineering for communities may perhaps be a job for the future.
Dan Gorham:So I think, when we think about wildfires, wildfires often get a lot of highlight in the news, whether it be hundreds of thousands of acres burning in very remote areas, but more oftentimes when that wildfire or brush fire transitions into the built environment and so that wildfire initiated. Complication, I think, is where fire safety engineers need to play a role. Wildfires in the wildland has traditionally been addressed by foresters and those in the land use space, but fire safety engineers have a long and trusted history of understanding and appreciating the impact of fire and developing smart and innovative design solutions, whether it be materials or components, or structures altogether, to address them. So I think that that's again where fire safety engineers really need to play a role. There's a lot of opportunities to do that. I mean we can take learnings from industrial fire safety engineering to spread hazards out, to produce the potential for fire spread.
Dan Gorham:So we think about the assets that we care about, the homes, how can we spread them out.
Dan Gorham:Sometimes that's not always possible, so we can think about how do we harden structures and harden assets. So buildings and homes are accumulation of the components, the roofs, the vents, the walls, the eaves, all of these components, the windows through them, and so designers need to recognize that it's not just one component Having a fire resistant roof, say, or having ember resistant vents isn't necessarily good enough because fire will find the path of least resistance and then also really recognizing that it's multiple mechanisms and combinations of the radiant heat and direct flame contact and fiber into embers that oftentimes result in structure ignition and that, different from traditional structure fire protection, a lot of times we won't have or there will be limited emergency response. So acknowledging these limitations and putting them into the design criteria at the front documents and recommendations and codes and standards begin to improve, referring to them and incorporating them earlier on instead of just as an afterthought, I think is an important role that, again, fire safety engineers need to and can play in this space.
Gavin Horn:Yeah, fire safety engineers have a very important role to play in this. As communities are being planned, there's a lot of different inputs that come into that and fire safety has not traditionally always been one of those key pieces that have been raised to the forefront. There's a lot of effort and cost and focus put on energy efficiency, and energy efficiency is a great thing for us and it can impact fire safety some ways for the good and some ways for the bad, depending on how that energy efficiency, how the insulation, may perform in terms of its fire safety. There's also, particularly in the western United States, a large focus being put on reducing urban sprawl. So what often that's doing is a lot of communities being planned out here are being put as close together as possible.
Gavin Horn:While that makes sense from many different perspectives, what we also see is that's how we see a lot of the structure-to-structure fire spread being driven in these large-scale events where you have very close spacing on the order of two to three to four meters worth of spacing between each of these structures, and that is going to continue to grow and drive some of the communities that are being developed out in the western United States.
Gavin Horn:So the fire safety engineers have to be able to have a seat at that table also to identify. These are the concerns that we have, that we have to build with more energy efficiency as well as fire safety in place. At the same time, we're doing this in order to reduce that risk for structure-to-structure fire spread by continuing to understand the trade-offs in the materials in terms of how well they provide insulation, how well they protect from the environment, but also how well they work. When we have very near fuels right next to each other, including another structure that might be right next door, how we can start to understand that fire spread and how we can help to work with the communities to make sure that these are structures that can survive within the environment that they are designed for, but also are sustainable engineering solutions so that they can continue to be there for several years into the future. Perfect.
Wojciech Węgrzyński:Let's move into the experiments, and if you're listening to this, this part is coming up in the next episode and that's it. If you reached this far, I don't have to advertise the next episode for you. It's full of actionable knowledge really data sets, experiments, conclusions of those experiments, how those experiments interplay together, what new knowledge was unraveled through this experimental program and how we can take actions based on what fsri was researching. I think big projects like this require massive spotlight on them. It's very rare that scientists try to solve such a big problem like urban fire spread, and it's not possible, you know, with a small research project. You really need to attack those things with good budget, a lot of experiments, good research outline, and that's what I wanted to show you in this podcast episode. How do researchers who are the best in what they're doing in the world, how do they come up with those experimental programs, how do they plan their next steps, what factors influence their research choices and how those interesting research concepts, research ideas, become a reality? In the show notes of the episode, you will find multiple reading materials from the project that we were discussing today, so it's not just a podcast episode. There's much more for you to unravel, and feel free to reach out to those materials, which are readily available.
Wojciech Węgrzyński:Fsri makes sure that everything is open access. Fsri publishes a lot of auxiliary material that follows up the research projects. They really really put a lot of effort on making data and knowledge accessible for the society, for firefighters. I had an episode with Steve Kerber from FSRI on why this is the core of their philosophy. So podcasts like this and materials produced by FSRI are definitely the greatest source of fire knowledge that you can have, and from those materials and the next podcast episode you will learn a lot on the exact things that were studied in their project on the fire spread through external walls. So that's it for this podcast episode. Thank you for listening and next week, some more great fire science coming your way. You know exactly what to expect, so I hope to see you then. It's really worth it. Cheers, bye.