Fire Science Show
Fire Science Show
202 - Designing fire safety with firefighters in mind
The gap between fire safety engineering and firefighting operations creates a profound challenge that affects building safety worldwide. Even experienced fire safety engineers - myself included - face uncertainty when designing for firefighters without being firefighters themselves. Yet many building codes explicitly require engineers to account for firefighting operations in their designs.
This examination dives into the timeline analysis essential for effective firefighter support, from notification (when firefighters learn about the fire) to arrival at the building to actual intervention. Each phase contains complexities often overlooked: fire alarm systems might be delayed by human verification, architectural complexity can significantly slow down firefighters reaching the fire, and building conditions upon arrival dramatically affect intervention capabilities.
The assessment of design fires represents one of the most challenging aspects of this engineering work. At what fire size will firefighters begin their intervention? The fire might be growing, steady-state, limited by compartmentation, or controlled by active systems. This crucial but uncertain consideration fundamentally shapes how we design for firefighter safety.
Through computational fluid dynamics modelling, we can evaluate the building conditions firefighters will face. Rather than using simple pass/fail criteria, experienced engineers look for smoke layer behaviour and clear access paths. The gold standard is providing smoke-free routes from the building entry to the fire vicinity. When this isn't possible, we must carefully evaluate the conditions through which firefighters must navigate.
Fire safety systems - from sprinklers to smoke control, information displays to architectural layouts - all dramatically influence firefighter effectiveness. Yet perhaps the most important principle is creating systems firefighters trust. Overly complex designs may be disabled by firefighters who don't understand them or don't trust them with their lives.
The most effective approach combines rigorous engineering analysis with direct input from firefighters themselves. By understanding their actual needs, which might surprise you - we can design buildings that truly support those willing to risk everything to save others. What would your building design look like if you asked firefighters what they really need?
Listen to the entire episode with Szymon Kokot here: https://www.firescienceshow.com/051-fire-science-in-eyes-of-a-firefighter-with-szymon-kokot/
Want to know what happens in the building after a fire alarm? Find out here: https://www.firescienceshow.com/136-fire-fundamentals-pt-6-the-fire-automation-in-a-building/
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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 Fire Science Show episode 202. This time there is no science fiction in the episode, but it's not going to be a hardcore fire science either. Well, it is fire science, but from the research perspective I'm going to share some fire safety engineering, my own fire safety engineering today, and I must say it's quite a challenging part of fire safety engineering. I've picked a topic that perhaps is a little bit difficult, but I guess it needs to be talked among fire safety engineers as it's a big part of our everyday practice. So today we're going to talk about firefighters and fire safety engineering, and I do not mean teaching fire safety engineering to firefighters, I mean firefighters as the part of fire safety engineering.
Wojciech Węgrzyński:For some of you the concept may be odd, but in my law system and I know in many European law systems there are specific clauses of your building code, of your technical codes, that refer to firefighters and providing them with some stuff safeguarding firefighters. In my Polish system I have to account their ability to firefight in my design of smoke. I have to account their ability to firefight in my design of smoke control systems, for example.
Wojciech Węgrzyński:So there's a direct clause of the law that pretty much tells me you need to account for firefighting in your fire safety engineering and how the heck I do that? That's a big question. Of course I'm not a firefighter, so I have to figure out something and I'm never sure that it's the best thing, but I'm trying my best and this episode is about destroying your best. I'm not going to give you answers of what firefighters want, because if you want to learn that, you can really ask them. I think for most of the problems, communication is the answer them. I think for most of the problems, communication is the answer. However, if you're burdened with having this consideration in your fire safety engineering analysis of some sort, I'll at least share with you some ideas of how I, in my own personal fire safety engineering, account for that. And we're going to go through different aspects, one being how soon they will be on the site, so all the timeline aspects of firefighting operations. We'll touch a little bit on design fire concepts. I think it's highly relevant and highly critical to understand the conditions in which the firefighters will operate. We will talk a bit about the conditions in the building and assessment. So this whole assessment for me is a part of my CFD calculations or computer modeling of fires in buildings, so I have to account for that in my modeling. Therefore, we will talk about how to do that in computer modeling and in the end, I will share some opinions about some tools of fire safety engineering not software, but more like devices, sprinklers, smoke control, etc. And how they influence fire safety operations in the building fire and rescue operations in the building. I hope this will be an interesting one for you, so 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. 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 pre-em independent fire risk consultancy. Ofr'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 plant. 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.
Wojciech Węgrzyński:And now back to the episode. Okay, let's go. This episode is really making me uncomfortable. Okay, let's go. This episode is really making me uncomfortable and I have quite a big moral dilemma whether I should talk about this or I should not talk about this subject. You know, accounting for firefighters in my engineering is not something I would like to do because I'm not a firefighter. I'm not. I'm simply not a firefighter and it's very hard for me to grasp what exactly a firefighter would like to have in a fire. I've quenched some fires I would not say I've battled fires but I have some experience on putting water into fires, even large fires. I have experience in trying to control fire with firefighting operations. I have experience with ventilation, vast experience with ventilation. I understand the smoke flow and et cetera. I understand compartment fire dynamics, but I'm not a firefighter and I thought maybe I should not talk about this because it just feels wrong. But then again, my everyday engineering, the building code, does not clarify I'm a firefighter the technical guidances that tell me to account for firefighting.
Wojciech Węgrzyński:they don't distinguish whether you're a fire safety engineer who by chance is a volunteer firefighter or who, by chance has professional firefighting experience. The system doesn't identify that.
Wojciech Węgrzyński:You are just supposed to account that volunteer firefighter or who by chance has professional firefighting experience the system doesn't identify that you are just supposed to account that someone put a clause in the law, and perhaps for better. They put the clause in the law because it makes us reflect on what we're doing and it just forces us for this thing, this aspect, this inclusion of firefighting to be a part of firefight safety engineering. Perhaps it's better, perhaps that's a good thing, perhaps if we were not forced to that, we would be too uncomfortable to do it on our own. So maybe this for the better. Therefore, I think it's fair to discuss, as I'm doing this anyway. We can as well discuss on how I believe to do it the best I can, and that's the spirit of this episode. So in this episode, I'm going to have to put a disclaimer. This is not an outcome of any research project. This is not something I would call an unbiased fire science. This is very biased fire safety engineers opinion about their craft. This is me, wojciech, a fire safety engineer, talking with you, fellow fire safety engineers and fire scientists, on how I do my engineering, and there is a good chance someone can do it better, someone can do it in a different way, someone can achieve their goals in a different pathway than mine. Uh, that's pretty fine. That's that's really good and I would love to share. I would love to learn from you.
Wojciech Węgrzyński:Anyway, let's let's move on and discuss on how to include, for, uh, firefighting operations in the building. First, what does it even mean? Like what does it even mean that I account for firefighting in my building? Do I make provisions that allow firefighters for firefighting and, if so, what kind of provisions would that be? Do I control the fire in some way until the firefighters arrive? Am I supposed to protect the building in some specific way that allows for firefighting? I think it can go pretty deep and I think we're going to touch most of those layers in the podcast episode. But let's start with the rival. Let's start with firefighters getting to your building.
Wojciech Węgrzyński:And I must say in Poland I'm not personally doing that in my engineering, but I saw many consulting companies would do that. They would try and estimate the time to arrival, the time to arrival of firefighters into their buildings and put a number in their report. It takes 14 minutes for firefighters to come from the nearest fire station to this building and they put this as a number. You know, that defines the timeline, defines at what point the firefighters will be able to fight fire in that building as always. I'm comfortable with that, and there are multiple reasons. One is that fire station location is I mean it's pretty stable, but at the same time it's temporary. We design buildings to last for 50, 100 years. You cannot assure that a fire station that is there at some specific point where you design the building will be there for the next 100 years. There's no kind of social contract you can sign to make sure that the conditions at the day of design will be unchanged for the entirety of the life of the building. So that's one uncertainty that I'm very uncomfortable with. Another thing is the time itself, how long it takes the firefighters to come, and I would distinguish like three specific periods of time that I think should be considered in this part. One is how long it takes to successfully notify the fire brigade that there is a fire in the building. The second one is how long it takes them to arrive to your building. And the third one is how long it takes from their arrival to a point in time in which they efficiently can apply water. So first, how long it takes them to be notified, this largely depends on the types of systems you have in your building.
Wojciech Węgrzyński:I'm mostly dealing with larger buildings in the ITB in the work that we're doing, so I'm used to working with buildings that are already very well equipped with different fire safety systems, and having a fire alarm system is kind of prerequisite for us to be on the building. Even so, we pretty much never work with buildings which would not have fire alarm systems and therefore I can to some extent rely on the fact that a fire alarm will be triggered by the fire. Therefore, at the early stages of fire, I can assume that the fire will be detected in the building. Now what's going to happen after a fire is detected in the building? I have a whole episode about what happens in the building after a fire is detected in the building. I have a whole episode about what happens in the building after a fire is detected. You can listen to that if you want to understand more about fire automation and all the sequence of things that happens.
Wojciech Węgrzyński:But once the fire is detected in building, multiple things can happen due to the action of the people inside the building. So even if you have a system that will automatically transmit the alarm to the fire brigade, it will only do so if the fire is confirmed and the fire can be confirmed by manual operation of the people at the building. It can be automatically confirmed if you, for example, have a second detector going into alarm and you have a program that tells you, okay, if two detectors come, this means it's a confirmed fire. It can also be confirmed if sufficient time passes from the first detection to, let's say we call it times T1, t2. They refer to the operations of the crew at the building. So there's a specific amount of time that the team at the building has to confirm or decline a fire. And if they do not take any action and this time simply passes, then the fire is also considered confirmed. If someone pulls a manual alarm after automated alarm is also confirmed. So multiple ways you can confirm an alarm.
Wojciech Węgrzyński:But there's so multiple ways you can confirm an alarm. But there's also multiple ways you can delay this. The people who are working at the building. They can cancel the fire alarm. They are able to ignore it for some period of time At some point. It's probably impossible to ignore it if it's a large fire and it triggers multiple sensors. But if it's a small fire and it's in see. But if it's a small fire and it's in sepian stage. It's possible to delay that by manual operations of the people inside the building.
Wojciech Węgrzyński:Now, if the building is unmanned in terms of fire alarm central, then it's going to be automated and I assume at least in our system, most of the buildings would be fit with transmission devices which would send a signal to the fire brigade and inform them that there is a fire in this building. Sometimes it would even inform them in what relevant part of the building the fire is, if such a distinction is put in place. If there is a crew in the building, I assume the automated information also passes through. But there will also be a human contact with the Far Brigade, telling them what's happening and probably guiding them. Now, this timeline to notification. It sounds like immediate, but it can really be a long time which we have to address. So we cannot ignore it. It's not like 60 seconds in the fire. The fire brigade already knows it may take quite a long time for them to be notified about the fire, and the better the fire automation systems in the building, the better the fire alarm system in the building and the higher trained the people staffed in the building, the shorter this time will be. The second one is time to arrival, and here I don't really have that much to comment. I know that the firefighters operate very quickly, so as soon as they will be notified, you can expect the team to be dispatched in literally minutes and they will come to your building as soon as possible. Some people try to establish that with a simple Google map directions from the fire station to the building. How long it takes? It is an approximation, I guess, and perhaps not even the worst one, so you can pretty much say how much time can pass from the firefighters leaving the fire station and arriving to your building. And the third thing is what's going to happen when they arrive to your building. I think this is very, very interesting.
Wojciech Węgrzyński:So here I would like to jump into an episode of podcast that I've recorded. Three years ago it was episode 51 with a good friend, szymon Kokot, and Szymon is one of the most well-known FAR instructors in the world, I guess Definitely the most known in Poland. A good friend of mine and I had this podcast episode with Shimon about looking on fire science through the eyes of a firefighter, so really doing something like in today's episode, but talking to an actual firefighter. And I've asked him Shimon, what happens when a fire brigade arrives on the scene? What are the things that you consider? So I would just like to play a short response of Shimon to that question, because he's a firefighter, he knows what he's saying. So I want you to hear the commentary from Shimon, and then I'll probably enhance this with some thoughts of my own. So let's play the sample. Let's go to the car park. Let's tell the fire engineers what the firefighter does when they get a call that the car park is on fire and it's underground. We already agreed that. Okay, multi-level underground car park.
Szymon Kokot:So, based on experience, there is a PDA predetermined attendance. That's probably a very British term.
Szymon Kokot:Like a minimum of vehicles and personnel that absolutely has to be dispatched to this kind of event as a minimum. First, let's say serving, and then, when the commander is on scene, he or she will decide if it's enough or will they need more. Now this decision is based on multiple factors. They need more Now. This decision is based on multiple factors. If this is a building that was in the area for some time, there is an increased chance that they know the layout of the building. If it's a new one, maybe there was just one visit or maybe there was no exercise yet. We have operational planning that envisages going to all major or complex buildings you know frequently, or at least try to put them on the list and check them one after another, because it's a maze, the problem like whatever. When I sometimes teach the firefighters in the factory, I tell them the difference. You know what is your advantage. You know the buildings, you know exactly the building. So next, you know what is your advantage. You know the buildings. You know exactly the buildings. So next time you just are walking around, you know eating your donut, chatting with your friend, just have a look around. This is your great advantage.
Szymon Kokot:When we are attending a fire, we basically don't know where we are going. That's one thing. The second thing we take into consideration what is the time of the day? The second thing we take into consideration what is the time of the day? If it's evening till morning, the car park is mostly full. If it's the other part of the day, it's mostly empty.
Szymon Kokot:So fire load, fire load, but also the ability or the easiness to travel around it without being disoriented, because obviously you have to throw in limited visibility. If it's limited visibility, it's smoke. If it's smoke, it means breathing protection. Breathing protection has limited time. So, depending on also depending on another, let's say, science, which is ergonomics, you have to be able to assess it's not entirely the case of the fire commander, because every firefighter has to know this for themselves how much air they are using. Is it 50, 60, 70, 80 liters per minute, based on different types of work moderate work, heavy work or so on, or, more practically, they have to just read the gauge of their BA pressure frequently enough and be able to communicate, if we want to communicate.
Szymon Kokot:There's a problem with concrete floors which blocks the signal, so there's a number of difficulties. What is the average ability of a firefighter to combat fire, be it cool smoke, be it attack the seat of the fire, and if I'm having today an average firefighter, a very good firefighter or a poor firefighter? It's a great set of variables.
Wojciech Węgrzyński:So there's many levels of constraints. You have to take into account the time you can send people for a certain amount of time until their breathing apparatus stops working, and probably you need to secure the logistics how to exchange them, pull them out early enough so that they don't work.
Szymon Kokot:yeah, they don't work on the reserve, because it's basically being in the danger zone, working on reserve, but also being able to send in someone in exchange so that we have a continuous firefighting operation.
Wojciech Węgrzyński:Then you mentioned communication, which also can be blocked by the building itself. It can.
Szymon Kokot:Then visibility Do I have thermal imaging cameras? Now, that's a piece of scientific equipment, you know, like reading thermal radiation from emitting objects, which, by the way, is also. They need to understand. This is not a thermometer, this is an assessment. If it's heavy smoke, there's a lot of soot.
Wojciech Węgrzyński:You will not be able to see through it okay, I'm back and, uh, it was fun to revisit episode 51 with shimon. I recommend you listening to that one because it's a firefighter speaking about firefighting, so he's much more fit than me to talk about it. Anyway, the things that shimon mentioned were not first things that came to my mind when I imagined what a fire brigade may do at the site, and there indeed is a ton of considerations to be done at the site. What I wanted to achieve with this walk down memory lane and bringing back Shimon into the podcast episode is to highlight that the fact that firefighters arrived in your building does not mean the fire has stopped. It does not mean that the water is on the fire and immediately the action is being taken. And, depending on how complicated your building is, how large your building is, it can take considerable amount of time to reach the location of the fire. That's the problem with Mastimber, for example. We highly rely on firefighters' intervention in Mastimber. They literally have to be there because the structure is participating in the fire. Therefore, it must be actively battled, and if they have to climb 30 flights of stairs, it's going to be difficult. At the point when they reach the fire they will be already exhausted and that their job has not even started yet. Therefore, there's a lot to be accounted for. Firefighters appearing in your sight does not mean that they have started fighting fire. Perhaps I'll invite someone from FSRI to discuss this in a much deeper state, because FSRI is working a lot with firefighters and they have prepared those great considerations for firefighting, so maybe we will be able to narrow down the timeline a little bit better. For me, the important thing is that it just can take a lot of time, and the bigger, the more complicated building I am designing, the more time it's going to take and more reliant on my fire engineering those firefighters will be to reach the point where they can fight fire.
Wojciech Węgrzyński:Okay, the other thing is, the fire brigade was notified, they were dispatched, they've arrived to the scene. At the same time the fire was growing. Kind of right, we have a fire developing in our building. So now, if I try to do any sort of engineering assessment, what would be the conditions when the firefighters arrive or when the firefighters start their firefighting operations? This is what my clause of the building code tells me to do. I have to account for that. So I have to in some way assess in what conditions, they will be able to start their firefighting operations in the building right. So if I want to do that, I need to understand how big the fire is at that point. And it's quite intriguing because many people do not realize that.
Wojciech Węgrzyński:But in some design fires you already have that as an integral part of your design fire, for example, the TNO fire for vehicles, one that I've praised a lot of times in this podcast and I like it a lot. But it kind of assumes that around 20th minute you will have an intervention and this is the reason why the fire stops growing, because there's a firefighting intervention. And indeed those firefighting interventions can be very, very efficient. In car parks, bre experiments, for example if you go back to them you will see that experiment, one the one with three vehicles, very huge growth fire, very large fire in a very small space. But as soon as they applied water it really dropped the heat release rate and they controlled it very quickly. So we also know that those interventions can be very efficient.
Wojciech Węgrzyński:But okay, what state the fire will be when those firefighters can start their work? And now it's pretty uncertain. Of course, like everything in fire safety engineering, fires are growing. We mostly consider growing fires, some kind of alpha-thisquad fires. That's a relationship that fairly well captures the growth of fires in most types of buildings that we deal with.
Wojciech Węgrzyński:But fires can also be limited. Fires can reach some sort of steady state or quasi-steady state, and if they reach a steady state the job becomes easy because you just assess what the steady state fire science is, then look for the conditions in that steady state. The steady state can be reached through different ways. To be honest. One is when you have a fire confined to a small compartment, your fire size will be highly related to the openings and ventilation in the compartment. So it's classical compartment fire dynamics. You can tell the maximum size of a fire in a compartment knowing what kind of openings the compartment has, and you cannot skip physics. It's not going to be larger than that. It could be larger, but outside. So perhaps if your compartment is lined with timber or you have some just ridiculous amount of fuel inside your compartment, the fuel will burn out outside of that compartment when it gets oxygen in the exterior conditions. That's a different thing, in some cases highly important, in some cases not that relevant. But in terms of the compartment itself, the size of the fire, there is a maximum limit to that. That comes from physics. That's it. It can also be limited by availability of the fuel. So every compartment fire until there's a flashover is basically a collection of single items burning or groups of items that are burning, and if you have a vehicle parked in the middle of a car park and there is no other vehicle around it, the fire cannot spread. That's it. If there's no fuel package to which the fire can jump, then the fire is not able to spread.
Wojciech Węgrzyński:Now, this is pretty tricky to design for, because you have to understand the exact location of the fuel in your building and the type of fuel if you're building, and the conditions at which the fuel may ignite or may not ignite, and you probably also need some sort of control over that. This exact fuel will be in the building. So if you are designing a car park, you really hope there is not going to be a garage sale or something in the building. So if you are designing a car park, you really hope there is not going to be a garage sale or something in the car park, because that's a completely different hazard than the one you designed for. Vincent Brennan once told me that if there is a space you have to consider a wedding being placed there and people would put weddings into most ridiculous spaces. So I can actually imagine a wedding in a car park. So that's a hazard I usually do not design for.
Wojciech Węgrzyński:But in your classical case the fire can spread through, of course, direct flame contact. That's probably the easiest, and if it happens it will most likely spread to any type of combustible material. It can spread to radiation. That one is a little bit more challenging because you really need a lot of radiation to ignite things, and the radiation from a flame to its surroundings, if it's fairly small flame, is actually not that intense to ignite at high distances. Of course, if you have like 10 megawatt fire it can ignite a lot of stuff around. But if it's a few hundred kilowatts, one megawatt really, the distance at which you're unable to ignite is pretty small. But you may also have radiation from the smoke layer and that changes the dynamic a lot. So yeah, it's something you can account for. It can also ignite through convective heating, some sort of firebrands or flamelets that are flying parts of your burning item that are falling apart from that item and flying through your building. They can also ignite very easily. A classic new example is lithium ion batteries, where you start having your individual cells flying around your building and igniting stuff at different locations. This is a pretty crazy fire scenario but yeah, it can happen like that.
Wojciech Węgrzyński:But anyway, if you assume that the fire cannot spread and you put a limiting size of your fire because of that, you have to be really confident in the design and you probably have to have some sort of way to execute that, to really enforce the fact that the fuel packages in your building will be exactly what you've just described in your fire safety engineering or your fire strategy. In some cases, when you have large spaces, open spaces, the fire will turn into a traveling fire, and that's something we've discussed with Professor Guillermo Reyn in the podcast. In a traveling fire, basically, the concept is the fire is continuously spreading, but it's not so fast that it takes the entire compartment within a minute or two. Therefore, some of the fuel burns out and eventually you have one front of fire spread. That fire spreads to the nearby objects and moves through your building and the second front of decaying fire, where it's just burning away the fuel package that it just consumed. Therefore, it cannot burn anymore and overall it looks like the fire is traveling through a building.
Wojciech Węgrzyński:I remember when we were doing first Obora X1 experiment and it was supposed to confirm or disprove the hypothesis that traveling fires exist and that the fires can travel through the fuel package. And I remember I was burdened with securing the perimeter with a good friend, francesco Restuccia. So we were at one part of the building and we were putting water on the roof structure outside of the building because the fire was venting through open windows outside and we had the roof structures that we really did not want to lose. Therefore we were applying water and we had this fire know, fire spread front, move in front of us. So our perimeter was burning and, uh, quite some minutes later we see, you know, this fire decaying and, kind of, you know, going down, moving away from us, and we're like, oh, thank god that fires travel, because I'm not sure how long more we could handle this perimeter. So it was good that fires traveled.
Wojciech Węgrzyński:You may also have the fire size limited by firefighting operations. So if firefighters arrive off the scene, they start applying water to your building, to your compartment, the fire size. You can consider that. That's the point at which the outcome is very uncertain and highly reliant on the firefighting capabilities. So therefore I don't see any point to grow the fire anymore beyond that point. But you really have to have in mind the time at which they will come. So you really need to understand at what point of alpha T squared fire. The T is the time where the firefighters intervene and my growth stops. The growth may also stop because you have some kind of system in your building that simply limits the spread of the fire, like a sprinkler system, like water mist system, like foam system.
Wojciech Węgrzyński:Any fixed firefighting system should, by design, prevent the spread of fire or limit the spread of fire. So if you have one of those in your buildings, I think it's a fair assumption to find some kind of steady state fire size and design for that. And I would put forward that you could potentially slow or stop the spread with smoke control. Not always, in some circumstances you could and it probably would be very difficult, but many people say you could not. But I would put forward that you potentially could significantly influence the spread of fire in your building through smoke control, especially if you're able to remove the heat from your ceiling and you prevent the smoke layer to radiate on the fuel packages. I think it's a considerable action of smoke control and could be accounted for, but again, highly uncertain. So, as you see, the design of fire is quite a problem because it really is an uncertain consideration. It really is From my perspective.
Wojciech Węgrzyński:All the fires are growing and for the perspective of assessing the conditions for firefighters, I need to know a number, I need to have a number of the size of the fire at which they have started their intervention, to assess what's happening in the building. And it's probably some of the most challenging fire safety engineering decisions that I'm taking in my professional career. At what level? I stop the size of the fire and I assess and I say this is the fires they will fight. Therefore, I'm assessing their ability to enter the building. Well, we'll just go in there in a minute, but I just stop at this fire size and I do my fire safety engineering for this Design fires. What a funny problem, what an interesting concept and what a huge challenge for fire safety engineering. Perhaps there should be a design fire podcast or something where we would discuss how things burn and what kind of design fire they lead to Maybe a spin-off. Maybe I'll do that one day, we'll see.
Wojciech Węgrzyński:Anyway, now let's move to a part that I thought that will be the main part of this episode. It kind of ended a smaller chunk at the end and this is what can we assess and how to assess if we have a design fire, if we know for what kind of heat release rate we'll be designing the systems and what kind of fire we will expect at the time when the firefighters come into a building, when they come. So you've assessed your timelines and you're fairly comfortable with them. Now how do we assess what's happening in the building when they come? And this is something that exactly is required by the building code in here. So I have to do exactly that. I have to assess the conditions in which the firefighters will operate. How do I do that? Of course I do it by fire modeling, and by fire modeling I mean CFD, and for me it's a simple choice. I would just use CFD method as my preferred tool of choice, and I think that's not a very controversial statement, that that's how the fire safety engineering is practiced worldwide today.
Wojciech Węgrzyński:And in CFD you have ability to measure or estimate different variables, conditions that define the environment in the building inside. The most basic ones, of course, temperature, radiation, visibility these are the most common variables and probably you will end up working mostly with those. So when I look at my fine safety engineering analysis on my simulations, what I'm trying to find in them? First of all, what is extent? So I'll probably change the way of thinking. So there's no easy way to do this. There is no easy way that says okay, you know, if the temperature is below 120, we're good. Or if the visibility is above 10 meters, we're absolutely fine and the conditions are beautiful and they can just work. It's not as easy as that. It's not binary, it's a spectrum and therefore it's an assessment and in some buildings some conditions may be okay. In some buildings the same conditions may be critically wrong. A lot depends on what you are designing and how complicated it is going to be to get to that location and how uncertain you are about the design fire, how uncertain you are about the timeline of the intervention itself. All those things will matter in the assessment and what you're looking at. For me it's never a simple binary exercise 10 meters, check. 120 degrees check, we're good. It's more than that.
Wojciech Węgrzyński:So I'm trying to look first of all on the extent of smoke in the building. So how much of the building is filled with smoke? One thing that I'm looking into is the layer behavior. So is the smoke in a well-defined upper layer in my compartments or does it fill the entire space of the building from the floor to the ceiling? Because those are two completely different conditions. If you have a layer, in some cases it doesn't really matter what the visibility in the layer is, because if you're on your knees you can see through the building and you have a really good chance to identify where the fire is. Of course, if you have a simple open plan compartment, it's much easier than if you have a labyrinth built in. The architectural structure of your building also influences how easily one can define where the fire is and effectively fight it. But a layer is something that I look for, and if my systems can maintain this stratification of layers and I can maintain some sort of free layer height, that's a good sign that then I'm already very pleased with the outcome.
Wojciech Węgrzyński:If I cannot, then the visibility will start to matter a little bit. A little bit, because I don't find it as a definitive criterion. There will be more podcasts on visibility based on the current research that we're doing, so I'll probably go there in those podcast episodes. But one thing is like imagine you have 11 visibility and you have a smoke filling your entire compartment, which is, let's say, 1000 square meters. Even if I had 11 meter visibility, which would be something that's fine with my tenability criteria, still I can't see anything in that building. So it's not really helpful that the tonnability criterion was maintained when the smoke filled the entire space, and also the uncertainties related to this assessment. You know the suit yields of materials, the combustion efficiencies and so on. So I rather like to look at it whether I had smoked somewhere or not. That's the information that I'm rather certain about and the parameters of that smoke. That's a challenging one.
Wojciech Węgrzyński:So definitely layer behavior visibility in some conditions I would look into that. But really what I'm looking is is there a smoke-free access path? That's really a thing that I'm looking for. Is there a pathway? Because if I design a smoke control system, I would like the smoke control system to work in such a way that it creates a smoke-free access to the compartment. That kind of connects the point of access with the fire itself. And I like to justify it for myself and perhaps, if I'm wrong, my firefighter friends. Please correct me, but I assume that if firefighters have ability to enter a large compartment on fire imagine a car park If they have a good point of entrance and I always make the gates of the car park point of entrance I never allow to extract smoke through the gate point of entrance.
Wojciech Węgrzyński:I never allow to extract smoke through the gate. I always use the gate as my main air supply location, because then the firefighters will always have a chance to enter the car park through the external gate, which is the most convenient way to access it. So first, is my access point free of smoke? If it is, it means they can enter the space. Now, if there exists a smoke-free path between the entrance point and the seat of the fire. It doesn't have to be directly the fire, but let's say 10, 15 meter perimeter around the fire. I assume that firefighters can take a look into the building and immediately see where the smoke or flames are and conveniently approach it and start feeding water, because the discharge distance of water is actually quite large. So you can fight fire from 10, 15 meters. So I assume if they have this smoke free access, they're very good, in a very good position. In some cases it's not really feasible or possible to provide that kind of access and in those buildings we look into the conditions of the smoke through which they will have to move to get to the fire. And here we go into those visibility ratings, the temperature of the smoke. We like to keep it as low as possible and to give them a chance. Of course firefighters can take higher temperatures than your normal people because they are wearing full personal protection systems and those suits are very high quality nowadays. They can take a lot actually. So we know that they can take a little higher temperatures and radiations than general population.
Wojciech Węgrzyński:The question what is the magic number that you should look for is a difficult one. Is it 120 degrees. Is it 5 kilowatts per square meter? Is it 2.5 kilowatts per square meter? I don't feel like I'm in a position to tell you what the value is.
Wojciech Węgrzyński:You probably have to discuss this with the firefighters in your location. The authority having jurisdiction so we call it in fire safety engineering that's the person you need to talk about this. But we have the numbers that we use and we assume that if those conditions are there, they simply can enter, use some sort of thermal imaging to identify the direction at which the fire is and slowly progress towards that fire. Of course it's a completely different progression than if you have a smoke-free access. It's completely different conditions, but we just assume that it's a completely different progression than if you have a smoke-free access. It's completely different conditions, but we just assume that it's still possible. And if the conditions in the car park are extreme, like I have a 400 degrees average temperature of smoke or I see the conditions inside the compartment are promoting a flashover in that compartment or fast growth in that compartment, I just assume I cannot provide anything to firefighters and I have to either change my design fire affect what's in the building or I have to change the systems that I have in my building. Perhaps that sprinklers? That would be the first and most immediate choice.
Wojciech Węgrzyński:Now let's move to the tools of fire safety engineering. I've already mentioned sprinklers. I think any type of fixed firefighting system in your building is already the best thing you can have in relation to the firefighting operations. Simply, it's best to have your water applied to your fire as soon as possible. I think this will universally make the life and job of firefighter easier and by far safer. So there's nothing that can be fixed. Firefighting systems, whatever kind you are using for sure.
Wojciech Węgrzyński:Smoke control yes One. It's going to decrease the temperatures of the smoke. It just removes the energy from the building, from the compartment system, therefore limiting the radiation, the hazards related from the temperature to the smoke. To some extent it reduces the hazards related to toxicity. But keep in mind that the firefighters would be operating in breathing apparatus, so these hazards are not as much directly to them as to your normal population, excluding hydrofluoride, which is a nasty stuff and comes from some of the EV fires. So let's say that that's a different story. But for most fires the breathing apparatus allows them to proceed, even in the clouds of gases of smoke.
Wojciech Węgrzyński:Smoke control is also capable of providing the smoke-free access. And I think in here especially the pressurization systems, the systems that you use on your horizontal pathways, like corridors. You can do a lot of those and you can do a lot of engineering with those. You can really create great conditions to make sure that the compartment that's on fire, that's the only place in the building where the smoke and fire is. The smoke doesn't spread through your corridors, staircases and so on, because if firefighters approach a building, the fire is on the 10th floor and there's already half of the building filled with smoke. You have to perform rescue operations, save lives. It really makes firefighting extremely challenging, orientation in the building extremely challenging, firefighting extremely challenging, orientation in the building extremely challenging. It just makes everything slower and less efficient there than it could be and I believe through my engineering I shall make their life as easy as possible.
Wojciech Węgrzyński:Another thing is information. Firefighters need information and if you can design a clever interface that indicates where in the building there is a fire, where in the building there is smoke, which access path is smoke-free, how many people you have in the building, the procedures that are easily outlined, which floor has been evacuated, where do we have places of safety in the building, how this building deals with helping evacuation of disabled population. The information is kind of critical because it also will make decision making on the site easier for firefighters and I'm a huge supporter of visual aid systems that have a map of the building that just show you, you know, with LED diode, here is the location of the fire, you are located here. It really makes life easier if you can communicate such an information and I don't think enough value is placed on systems like that in fire safety engineering. I think those information systems are perhaps as important as active means to suppress the fire or extract smoke and heat from the building.
Wojciech Węgrzyński:Earlier I've mentioned fire alarm systems and automated alarm transmission devices. For me it's kind of prerequisite. I don't really do fire engineering in buildings that do not have them because we're typically involved in large buildings, but definitely if this is something your building does not have, it will make this transition into firefighting easier. It will just help issuing signal to firefighters that there's a fire in your building. It will shorten the timeline. So definitely a very important system lifts and lifts for firefighters. So vertical transport of heavy equipment is extremely difficult. If we can provide them with lifts that are safe in case of a fire, that are at a higher degree of safety that they can trust. I think those could be great things.
Wojciech Węgrzyński:I've mentioned trust. This is an important one Really. Whatever system you're designing, the firefighters have to trust it. I've had those discussions with firefighters where I was designing a very complicated smoke control strategy that, in my eyes, was beautiful for the building. It's really great. But the first thing that I will do when I arrive, I'm going to turn this off. I do not trust this. I do not understand this and I do not trust this with my life and this was like a red light for me. I cannot make my systems too complicated. I need to make systems that can be understood by firefighters and that they can use to their own benefit, because they will also take actions in the building.
Wojciech Węgrzyński:If you think about smoke control, smoke control works in a very well-defined set of boundary conditions inlets, outlets you know what the flow path is. But if they put, let's say, smoke curtain in an inlet that you consider your makeup air inlet, they're going to change everything. If they use positive pressure ventilation outside of your building, they can change the flow path. They will affect how your systems work and the better they understand the systems, the less chance is that the final outcome of your system working and their intervention. There's less chance of failure in that case. Therefore, I think making systems easy to understand and obvious in how they operate and trustworthy is a key component in here.
Wojciech Węgrzyński:And finally, a big factor is architectural complexity, and it's something you can also think about when designing buildings. What are the view paths from the points of entry? How much you can see from the point you enter a compartment or a floor? Is it easy to navigate that floor or is it very difficult? Is it possible to just enter a floor and immediately see all ends of it, therefore making identification of the location of the fire easier, or is it a labyrinth? You can't just go above that. It has to be part of your considerations. You have to account for that, and any good fire strategy or any good fire safety engineering analysis must be aware that different architectural complexities will lead to different firefighting operational procedures and, different times, different timeline of operation. I think a good fire safety engineer should consider that. One challenge is that we sometimes, for example, office buildings, we often would do fire safety engineering for shell and core design and then when a tenant comes there, they would come with tenant design, which would be completely different thing. So for shell and core, I just provide means that someone eventually the tenant can design with those means a system that will work for them. It's probably challenging to account for firefighting means when you have a shell in core stage, but but still I think it's.
Wojciech Węgrzyński:Anyway, this was a lot of talking about how we account firefighters and I think one thing that you can notice in this episode is how insecure I am about this. It's kind of really uncomfortable. I like to think about myself as an expert. I've designed a few hundred buildings like probably like 500 of them, and in each of them. I've designed a few hundred buildings probably like 500 of them, and in each of them I've considered the fire safety operations of firefighters. Therefore, it's something that I routinely do every day, but I do it because I have to, and every time I'm doing it I remind myself I'm not a firefighter, and one thing that really helps me doing this job is talking to firefighters, having firefighters included in the design and seeing what their expectations are. I would not say it's possible on every single project, but when you design a tunnel, when you design an airport.
Wojciech Węgrzyński:It's very easy to reach out to them and they are very interested in participating in those discussions and they can tell you exactly what you want to know, and you may be surprised with the things they want. You would think they want smoke control, but no, they may want better water supply. They may want a better hydro network or more access points to water. They may want a safe space in which they can rest and, you know, reorganize their safety operations at the 20th floor of your building. They may want a space where they can change their oxygen bottles or a sort of a system that will automatically change them. These are the things that they often want and, as a fire safety engineer, you probably would not consider them up to a point when you are forced to do that. They may want communication systems in place, better radio antennas in your building to support their radio communication. Those are things that you would not think as a fire safety engineer until you talked with firefighters, which I highly advise you If you want to design your building to support firefighters.
Wojciech Węgrzyński:Firefighters are the people you should talk with to assess what they need and I'm pretty sure as soon as it's clear what their expectations are, and as soon as you clarify some key components of your designer, such as the timeline, the design, fire, and so on, your designer, such as the timeline, the design, fire, and so on you will be able to create a building for which you will be able to say yes, I have accounted for firefighting operations in this building in my engineering design and that's how I would like to conclude all my engineering and this is how I would like to conclude this episode.
Wojciech Węgrzyński:I hope you will have a good time designing buildings. I hope you will be able to design fire-safe buildings and you will be able to account for the needs of firefighters. They are awesome people. They are people willing to risk their lives to save others. I have the greatest appreciation to the firefighters and I would simply like my engineering to be useful to them. Thank you very much for listening to this Fire Science Show episode and I hope to see you here again next Wednesday. Thank you.