083 - Fire fundamentals pt 1 - Combustion and flame with Rory Hadden
Let's start another mini-series! This time 'fire fundamentals' where we are going to learn some basics from the world's best. It is usually fascinating to do that! Not sure how you feel about it but I would kill for a chance to listen to the principles of fire science from Quintiere or Drysdale, even though I give these lectures on my own...
In this first episode, I've invited dr Rory Hadden - an emerging legend of fire from the University of Edinburgh, to discuss some basics of flame and combustion. We have covered the following topics:
- diffusion flame;
- flammability limits;
- role of heat transfer in solid and liquid phase fires;
- ignition sources and ignition energy;
- fire retardants;
- effects of scale in flammability;
- and the ways to measure the fire.
Quite a lot for a first lecture, and it is a little longer than the usual Fire Science Show episode, but I'm sure it is worth it. Let me know what you think about this mini-series and send me ideas for future episodes.
I also promised to link to three masterpieces you need to read as a fire engineer, these are:
- An Introduction to Fire Dynamics, Third Edition by Dougal Drysdale;
- Fundamentals of Fire Phenomena by James Quintiere;
- Enclosure fire dynamics (recently revised!) by Bjorn Karlsson and James Quintiere
Learn more about the Fire Engineering Science MSc at the University of Edinburgh here.
Wojciech Wegrzynski:
Hello everybody! The welcome to the fire science show. Happy new year. Welcome to year 2023. I hope it's a great year for you. For opening this year, I have an interesting episode. I was recently asked to create some more introductory level content in the podcast. To, to help those, to transition into the fire safety engineering. But. Also to help all other fire engineers. Around a level, their knowledge base. And, I did record such an episode. I say, I would consider myself. Fairly advanced fire user. Uh, however, I still thoroughly enjoy talking about basics. So I am completely sure everyone can enjoy this type of content. I like mini series. I may actually frame this into some sort of introduction to the fire mini series and I hope in this form, it will be easier to find it and benefit. From it. And my first guest is Dr. Rory Hadden or University of Edinburgh. Rory's a very, well-known a world-class Firestar, he's an expert in combustion expert in one wildfire dynamics. He's an investigator. He is very all around Mr. Fire engineer. So I'm was very happy that he took my invite, especially that he's a very good academic and. He students absolutely love him. So he's also very well fit to talk about the basics and yeah, we wanted to talk about combustion and flames and stuff. That's related to the chemistry of combustion. Rory's chemist actually. So, uh, that's the subject we've started with we've ended up, uh, we've ended up in very different places about. Uh, they're all connected to fire and fire engineering. So, yeah, I think that's it, it doesn't need them any more introduction. Let's just spin the intro and jump into the episode. Hello everybody. Welcome to the Fire Science Show. I'm here today with Dr. Rory Hadden from University of Edinburgh. Hey Rory. Good. Thank you. And we're gonna talk about some, fundamental stuff in the fire science, uh, discipline. I've been asking a recent survey to prepare more, introductory material for ones who entered the discipline from various ends of the world of science and engineering. And as we all know, nobody becomes a fire engineer, by their will, but they come here as an accident. Rory, what's, what's your story, how you became a fire engineer?
Rory Hadden:
a long story. mean, I guess it, I trace it back to, um, when I was in high school and we had to decide what career we wanted to have. and I told my chemistry teacher that I was going to do the special effects on James Bond movies.
Wojciech Wegrzynski:
was
Rory Hadden:
and Nice. was shot down as not really a viable career.
Wojciech Wegrzynski:
Um
Rory Hadden:
then I, uh, applied to be a chemical engineer and studied that at university because, I came from Aberdeen and we had lots of oil in those days, so that seems like a very sensible thing to do. then as I was finishing that degree, I took a class, in Fire Dynamics with Dougal Drysdale, which was great.
Wojciech Wegrzynski:
Okay.
Rory Hadden:
loved that. but by this point had kind of thought, well, there's no way that's going to be, a, a viable career for a chemical engineer like me. and then a few weeks later I got email from Guillermo who I think is known, uh, to this community, saying Hmm. are PhD positions available and if we were interested in doing a PhD in fire science, then we should go and talk to him. so I did. And then the rest is history, I guess from that point.
Wojciech Wegrzynski:
yeah. Nice. Another one in the club of, switching, professions and, and coming to fire science. So even better, uh, put yourself in a mindset like what you would love to be told when you switched from chemical engineering into, into fire safety engineering or, or let's just, read out loud Drysdales quick because that's, that's probably a viable introduction to the discipline as. most people, I think. Yeah.
Rory Hadden:
most people I think Yeah
Wojciech Wegrzynski:
Actually in the end of this episode, the, in the shortness of the episode, I'm gonna try to list some reading, , resources because there are some really great introductory resources and, not everyone is aware of that. And, it certainly helps. So today I would, I would love to cover the aspects of flames and combustion and, and like the fires. How, we define some things related to that. what are the, the, definitions of, things that we meet every day. And I, I would start maybe not that easy one, but, but the flame, like what exactly is the flame? Like how, how do you define it as a fire engineer and how, how you define it as a chemist.
Rory Hadden:
I mean for me uh, this is a very interesting question and it's one that I ask at the start of my, second year, class, defining what a flame is. Everyone I think is familiar with it, right? You see it, it's this kind of, maybe it's yellow, maybe it's a little bit blue. when you start looking at actually what's going on there and you start exploring, the structure of the flame and why it looks like it looks, it becomes quite obvious, I think, what a flame is. It's really Hmm. than a volume in space where you have some kind of chemical reaction occurring. and what you
Wojciech Wegrzynski:
Hmm.
Rory Hadden:
as, as the flame, is maybe separate from the chemical processes that are going on. So I think it's useful to separate those two things. so Okay. reaction is simply the reaction between the fuel, uh, that is generated somehow from either a, it could be a gas directly, it could be, a liquid that you have to vaporize. It could be a solid that you have to pyrolize and maybe we'll talk about some of those words, uh, later on. But basically you have to get the fuel, uh, into a gas phase. then it mixes with air from the ambient environment that's surrounding the fuel, um, when those fuel and air are in the correct proport. The chemical reaction can occur if you have an ignition source nearby. Um, and that ignition source could of course be a spark or another small flame. the chemical reaction then proceeds, um, and as it proceeds, it generates energy. and that energy heats up that volume of, of material, the air and the fuel.
Wojciech Wegrzynski:
and
Rory Hadden:
as the, the fuel heats up, the chemical reaction goes faster. Um, and we end up generating quite a lot of energy. And what we see, uh, as the flame is Hmm. manifestation of all the energy that's generated. The yellow stuff are little soot particles, so tiny little balls of carbon, uh, that are heated up to the point where they. and that's what we see as a yellow part of the flame, the blue part. If you've got a flame that's blue, Hmm. seeing there is actually the molecules themselves of the fuel being heated up to the point where they begin to, not so much glow, but release blue light. Uh, I guess, so process is simply, it's a volume in space for a chemical reactions occurring. And what we see as the flame is kind of the manifestation of the energy that's released by that
Wojciech Wegrzynski:
reaction. but, um, if you have a flame inside, it is, it's hollow like inside, there's fuel. Outside of it is, is oxygen. And they react fairly small space, right?
Rory Hadden:
an interesting point that I've I've been speaking about, I guess what we commonly would call a diffusion flame. the, the fire science world separates things into two categories, I guess, of diffusion flames and premixed flames. and that's a useful distinction to be able to make. And one, I guess most people will be
Wojciech Wegrzynski:
mm-hmm
Rory Hadden:
chemistry classes in school where you have the bunsen burner, and if you open that little hole at the bottom of the bunsen burner, you get the blue. And that's a premixed flame because the Mm-hmm air are mixed before they react. Um, if you close that hole at the bottom, you get a yellow flame, like you would from a match or whatever.
Wojciech Wegrzynski:
Okay
Rory Hadden:
flame. and it's called a diffusion flame because the process that controls the, the dynamics of that flame, the structure of that flame is the diffusion of air from the surroundings into that jet of fuel. and that diffusion process, really governs, I mean the, the shape of the flame, uh, govern also the temperature of the flame. and it's really quite, I think, a fundamental part of fire science to understand like, what is that diffusion process and how does that result in the types of flames that we see? In most fire scenarios, we don't have the convenience of a premixed flame. That's something that a combustion scientist might be lucky enough to be able to study. but that's not something that as fire scientists, we have the privilege of dealing with. We have to work with slightly more, I dunno, dunno, more complex. It's just different, isn't it? The different physics of a
Wojciech Wegrzynski:
diffusion flame. I guess the flow patterns play a significant role in how these flames unravel and behave and, like it. You have fuel generated from something, you have oxygen that technically is everywhere around, but in reality, it's not. The, the fuel burns the, the oxygen around. So it needs to be replaced and replaced and replaced Conveniently. It, it generates, uh, hot temperature gas, which has lower density than surrounding air, which creates a movement of its own. It's like, I dunno. Did you ever define a fire as a we, we thought about like, it's, it's a nice, um, concept to show fire as a pump. It sucks the air, it burns the, the fuel and releases gases and, and it's like a system like in an engine
Rory Hadden:
the, the kind of fire is a pump, uh, analogy works pretty well in, for example, a compartment fire analysis where you have, um pretty well defined flows, of air entering a space, and then the hot smoke and gases leaving, uh, leaving the compartment. All of that is driven by, yeah, the size of the fire. And, sorry, the average temperature in that compartment. And I think that that's quite an interesting point well when it comes to looking at, at flames. Cause one of the questions that, you know, we often get asked is, is the temperature of a fire? And that's a very tricky
Wojciech Wegrzynski:
Oh yeah
Rory Hadden:
to answer. one of the nice things about a diffusion flame is because the diffusion. It's controlled by the, literally, by the diffusion of oxygen into the fuel. the range of temperatures that you get from a diffusion flame doesn't really depend on what's burning. It really only depends on this diffusion, concept. and therefore the flame temperature, I don't know, more or less 1200 Celsius, maybe 1500, something like that. It's not going to vary,
Wojciech Wegrzynski:
too.
Rory Hadden:
Um, but that is not, but when you start talking about the temperature of the fire, well what do you mean by that? If you have, you know, if you're burning something in a Yeah maybe you mean the average temperature of the room, or do you mean the temperature of the flame? and that's one of the things I think a lot
rory:
of,
Rory Hadden:
people who come into the field are get a little bit, confused by or, I dunno, that sounds a bit harsh perhaps, but, you know, it's one of these ideas that's a little bit tricky, I think, to wrap your head around. And we see it quite often, you know, being expressed in kind of a colloquial term, oh, that was a very hot fire, or that was a very cool fire
Wojciech Wegrzynski:
Yeah
Rory Hadden:
think that that goes back to this whole concept of what is a fire, what is a flame? And it's about the physical manifestation of the combustion process. So
Wojciech Wegrzynski:
Mm
Rory Hadden:
is a very subjective thing. And as scientists and you know, as mm I think it's really important for us To talk in, you know, quantitative terms, not, not subjective, uh, terms. So the fire might feel really hot, but that doesn't mean that if you measure the temperature of that flame, it's any hotter than another fire. There's something else is usually
Wojciech Wegrzynski:
on I think that's, uh, a moment in, um, development of a fire safety engineer when they go through one of the earliest and biggest like, paradigm shifts in their perception of what they're touching. Like, a flame is a flame and, and, it's separate from, from the fire. And, and, and the fact that you have a, a flame inside your building, it doesn't mean it, it's gonna destroy the ceiling. Like a candle flame is pretty hot, and if you put it against the ceiling, it's uh, not gonna do a much of impression on the ceiling. But, if you have a thousand candles, there's a different story and Right
Rory Hadden:
of I mean the difference between temperature and heat, right? Is kind of what you're, what you're getting at there. Yeah of just because something's hot doesn't mean it's going to necessarily impart a lot of energy, onto something else. and I think Hmm that is probably one of the things that, certainly I remember learning, you know, through the study of heat transfer and whatever, that that's a pretty important, thing to wrap your head around and this, this, that the idea of temperature and heat flux are completely, separate,
Wojciech Wegrzynski:
concepts. I would like to go, uh, further into the chemistry of flames. So if you release, gas into environment, it's, it's not gonna always, like burn because there must be a certain like, uh, ratio of the fuel to the oxidizer in your environment. So, let's talk about how we define them and how important they are for the fire engineering problems.
Rory Hadden:
I guess when we are defining the, I guess, the hazard posed by, a, a fuel, we usually would define that in terms of the flammability limits. So, as you've mentioned, you, Hmm to, not any mixture of air and fuel will burn. You have to get them in the, the right proportions in order, to basically sustain the chemistry. You know, if you've got, too much fuel and not enough oxygen while your, your reaction isn't going to work, and, and vice versa, if you have, too much oxygen, not enough fuel, you're not going to be able to generate enough energy. So this idea of, of the flammability limits is, is pretty well established and, you know, for more or less any fuel, uh, nowadays you can loop these up. The thing that I think is usually quite surprising to people, Is that the flammability ranges for most hydrocarbon fuels are the most common things that burn, are usually quite low. You know, you're usually, uh, in the region of Hmm a few percent, you know, two, 3% as the lower flammability limit. So you don't need very much fuel, in your air for it to burn. But once you get above, I don't know, maybe six or 7%, then for a lot of fuels it will be too, what we would say too, fuel rich in order to burn. There's too much fuel to sustain the reaction. of course of our exceptions, the flammability limits of hydrogen are, are massive. Now, off the top of my head, I don't remember, five to 75% something like this. methane is from
Wojciech Wegrzynski:
It must have been. Yeah
Rory Hadden:
of methane in air, will burn. but Yeah into perhaps more common fuels, you know, your, your liquid hydrocarbons, and those sorts of things, you're down in this range of the lower flammability limit being around. You know, two or 3%, and then the upper flammability limit being around seven or 8%. it's always in, in these sorts of ballparks. And that's a really useful thing, to know for identifying, the hazards posed by mixtures of fuel and air, um, and how can look at whether or not, you know, it's possible to generate flammable mixtures. because from that concept, the concept of the flammability limits of fuel gas in air, uh, you can define the hazard posed by liquid fuels through the flashpoint, and the hazard posed by solid fuels through the, critical heat flux or the, the surface temperature and ignition. So all of those ignition phenomena are linked back to this idea of
Wojciech Wegrzynski:
limits. I, I acetylene may have the, the, the widest, I think it has some crazy why, like 2% to 80 as well, like similar to, to hydrogens. But this are not your common fuels. Like, like you've said, many of them would have very narrow. So when there's not enough oxygen, does it mean that that oxidation reaction is not happening or it just, uh, happens, but at the not, quick enough rate to to sustain it?
Rory Hadden:
both, I guess, Um, at some point it stops happening. Okay if you, can encourage chemical reactions to happen more by heating them up, or by increasing the pressure. So Hmm um, if you think of a chemical
Wojciech Wegrzynski:
Ah-huh
Rory Hadden:
when two molecules kind of bash into each other or collide, then you can increase Hmm of that happening. If you the temperature of your mixture so the fuel and air molecules are moving more
Wojciech Wegrzynski:
hmm
Rory Hadden:
or you can increase the pressure. So you're just forcing them to be closer together. And both of those things, effectively increase the probability of collisions. So the flammability limits we've just, we've just spoken about are all at, know, standard conditions at pressure, 20 hmm Celsius If you increase the pressure or you increase the temperature, then the flammability ranges typically widen, um, and you'll be able to Okay reactions to, to propagate.
Wojciech Wegrzynski:
Makes sense. Yeah, and I guess also in oxygen reach, like I had an episode by about spacecraft where they would have an increased oxygen concentration. You would have a a different limit again
Rory Hadden:
flammability limit you always have to check, you know, is it in air? Is it in oxygen, is it by volume percent, mass percent? So there's, there's a few details in there. but in principle, I mean, one of the things we are quite lucky about in fire science is most of our applications. Atmospheric pressure and, know, 21% oxygen in air
Wojciech Wegrzynski:
Yeah
Rory Hadden:
yet that's true stuff, high oxygen concentrations and high pressures to the, the clever people who do microgravity combustion.
Wojciech Wegrzynski:
Un unless you're doing fire safety engineering in Denver then, or Mexico City, then . It's, it's more tricky. Uh, okay. now on next on my list, we've discussed, the, the stoichometry of the, of the reaction, like how concentrations of, fuel and oxygen, allows the, the combustion to happen. Now, I, I'm wondering about the ignitions. You've said, uh, that there's a spark or there's a, a pilot flame that can ignite the, the mixture. Like, what are the ways, how the mixture can be ignited? I think that that's an interesting concept
Rory Hadden:
course if you have, even a flammable mixture of fuel and air within a, a volume, within a room, whatever. that will not necessarily immediately ignite, right? You have to put an ignition source there. the ignition source, for mixtures, I mean, can be, I mean, many things. You could have a small flame. Um, and a decent rule of thumb Hmm that, any flame will be capable of igniting a flammable mixture. you can use a spark. Okay are a little more complicated. usually there's a concept known as the minimum ignition energy, which is basically the energy spark has to contain, in order for it to ignite the mixture. You could just heat the mixture up. Um, so quite a lot of combustion, uh, work is done simply by putting a flammable mixture in a vessel and increasing the temperature of that vessel until you get ignition. Other things that can cause Hmm would be, you know, hot particles, hot surfaces. Um, and these are often, you know, if you are looking at fire hazards and processed plants or, or whatever, those are very often the kinds of hazards that you're most, I guess alert to. so ignition sources are very plentiful. And I think one of the nice things that, fire engineering has done and process safety does, is we kind of assume that there will always be one, right? So, we
Wojciech Wegrzynski:
of Mm-hmm
Rory Hadden:
have the conditions where there's a, a flammable mixer, we will get ignition. uh, and that's, I think that's pretty fundamental to how we study a lot of these problems. so, when you, when it comes to other modes of ignition, I guess, what we trying to do is try and divide them into, two categories. Uh, we have the piloted ignition, um, so that's where we, you know, physically put something there to, to start the, the combustion reaction. Um, or we have so-called spontaneous or auto ignition. well, so the, the piloted cases are quite nice because we can very easily define the ignition process. we heat up a, liquid or, a solid fuel usually, uh, and we get to a certain condition where the, the pilot flame that's there, or this pilot spark that's there will ignite the flammable gases that are evolved. When we look at auto ignition, it's a little bit more complicated because we have to understand much more. the processes that are going on in the solid phase and also in the gas phase. So we have to understand how the gas molecules are absorbing energy, how they're heating up, what is the temperature of that gas mixture. And that's, it's kind of an ugly problem to try and solve. so fire science from more or less the beginning took that ugly problem and said, we're just not going
Wojciech Wegrzynski:
deal with how convenient
Rory Hadden:
and we're gonna focus in
Wojciech Wegrzynski:
world
Rory Hadden:
because then when we're dealing with liquids and with solids, we can more or less ignore everything that's happening in the gas phase. We only have to worry about what's happening in the condensed phase, in the solid or in the liquid and that's a very, very powerful thing to be able to do. Right. but it does, or hide some of the complexities around the ignition process, which is the ignition is a gas But when we talk about it in terms of, of defining the hazard, we talk about things that are related to the solid or to the liquid. You know, the flashpoint is a property of the liquid. The critical heat flux is a property of the solid. Um, and I think quite often we forget. I think that that's what we're talking about. You know, and, and that in the end, the ignition process Hmm nothing more than heating your solid or your gas to the point where the mixture above the surface of that solid or that liquid is at the flammable low flammability limit. And if you've got a spark or if you have a pilot flame, then that's all you're doing, right? The conceptual leap is always the same, which is the flammability limits are what define flaming ignition. And, the rest of it is some kind of way to try to express that hazard.
Wojciech Wegrzynski:
it's, it's super funny that you say that fire science is conveniently uh, taken out and focused on liquids and gases. Where in the today's fire science, like what are the sexiest topics We have, uh, timber in civil engineering, of course, that's solid phase facades. Well, welcome to solid face, but in awkward, uh, configuration again. And, there. There's no escape from, uh, solving this. It's, well, there, the solutions exist, right? And
Rory Hadden:
the solutions exist. I think the, the issue, with a lot of this stuff is we understand pretty well, I think for individual materials, We've known, I mean, even before timber, in the built environment became a sexy topic, we knew how wood burned reasonably well. There's still many questions Yep fully have resolved, but, you know, before, that kind of started, you know, there's a very nice chapter in the Introduction to fire dynamics. There's a nice section there on how wood burns, how it ignites, you know, everything was laid out, before. Cause wood is not
Wojciech Wegrzynski:
Mm,
Rory Hadden:
material We have to you know, bear that in mind. yep engineer timber does not burn differently from regular wood, right? I mean, the laws of physics are the laws of physics. So, what I think is, is interesting about it is that once you start trying to apply that knowledge in the engineering design, I think that's maybe the difference that has happened in the last, I don't know how many years it is now, 5, 6, 7, 8 years I've been around doing this stuff. it becomes quite difficult to apply that knowledge and, and if you don't really understand where it all comes from and why piloted ignition theory exists in the way that it does, can see that it becomes a relatively complex, thing to try and understand, but the burning of all of these solid phase materials, as you say, whether it's facades, whether it's timber, or whether it's just, you know, the stuff that surrounds us, uh, in day-to-day life, you know, the compartment fires are governed by solid fuels. I mean, that's how it goes. Um, we need to, we need to understand that process of ignition, of solids. And I think, unfortunately for fire engineers, we're, we're able to remove some complexity from our lives. But the burning of solids is probably amongst the most complex problems that, science and engineering can, can try and solve just because there are so many very strongly coupled phenomena, um, which is why I love doing it right, is why I
Wojciech Wegrzynski:
it really interesting. Yeah. tell me more. if, if you can just list like how this phenomenal couple, I think it's, it's fascinating to understand how much complexity there is in a burning log of timber
Rory Hadden:
of timber is a pretty good example. I mean, if you think about just the processes that are going on, right? We've got to heat the thing up. So we've got heat transfer processes, conduction, radiation, all playing a role, uh, in the burning of a piece of, of timber. we've then got the chemical reactions. We've got the pyrolysis process. Pyrolysis is the decomposition the solid fuel into flammable gases. Uh, and in the case of a piece of timber also leaves behind, a solid char. Okay? So we've got, Mm-hmm reaction that is, turning a solid material into gases. Maybe you can also get some tar there as well, so into some liquids. Um, and then we still have this solid char left behind. So we've got all three phases,
rory:
of
Rory Hadden:
matter.
Wojciech Wegrzynski:
Mm-hmm
Rory Hadden:
got chemical reactions that are occurring, on very complex molecules. You know, the, the composition of wood is. It's reasonably well known, but the, the decomposition of that, of those molecules is not so easy to figure out. That will be temperature dependent. and it'll also depend probably on the oxygen concentration, which brings us to the next part, which is we've got to get oxygen from the environment to the fuel. Um, so we've got a mass transfer problem, um, and we've also got the fluid mechanics because we have hot gases rising up, and that's creating, a whole sort of buoyantly driven airflows. So I mean, we've got heat transfer, fluid mechanics, chemical reactions, mass transfer. Uh, we've got the whole suite of things that are complex to solve the complex to solve. because very often we don't know is actually what it is, right? We've got all these intermediate stages, you know, what is the exact composition at this position beneath the surface at this time, and how does that change Hmm chemical processes? actually is the concentration of oxygen near the surface of the log, cuz that will change how the char oxidation occurs. So it's spatially difficult to resolve, temporarily difficult to resolve, and never really have enough information. And also, I don't know how you could even get some of that information. I mean, it's, I think that's one of the tricky things is, you know, the, you can't just stick a probe to measure everything because then you will change the whole system again. So me the, the ignition and the burning of, of solid fuels is, so complex and so fascinating that, I think it does a disservice very often to overly simplify it. Although, you know, there are, I think simplification is of course gonna be required if anybody wants to, to apply this in kind of a, an engineering context rather than just a study as a scientific context. so the question then becomes how do you simplify? And to do that, you have to know what are the most important steps there, you know, is the most important step. The heat transfer is the most important step of oxygen. Cause if you know what the most important steps are, you can design, a tool or a method to help you, simplify, I should say, the problem, uh, such that it can be applied, but you have to go into all of the details, I think
Wojciech Wegrzynski:
you can
Rory Hadden:
just, that, make that, uh,
Wojciech Wegrzynski:
simplification. Man, this was supposed to be an introductory epi and it's already crazy. I , I'm sorry to everyone who came here to, to figure out the, the definitions, but, that's the beauty of fire science. Like that's the reason why it's such a complicated science and, why we are not getting out of our jobs anywhere soon because that's, it's, it's, yeah, it's not easy
Rory Hadden:
and and in some levels, you know, why should it be, right? I think very often,
Wojciech Wegrzynski:
Yeah
Rory Hadden:
people have a perception that, uh, I've seen fires, you know, I've built campfires. I, you know, have a wood burner at home. I have a, a coal firer at home. and, and there's this kind of everyday familiarity with fires. And one of the things I see, you know, as my job, um, when I'm teaching, you know, undergraduate students or MSC students, is to try and break down that, you know that. comfort with the phenomena of fire and trying to introduce all of these complexities because, I think I've said it before, but the, one of the best bits of engineering in my house is the fireplace. You know, it's extraordinarily simple, but every single time I light a fire there, I get a more or less consistent result. You know, the, from how the chimney operates Hmm air flows in, through the, the bottom of the fireplace to how the heat's radiated into the room. It's an extremely efficient piece of engineering and something that we engineered before we really understood all of these,
Wojciech Wegrzynski:
Hmm
Rory Hadden:
so think, the complexity and things, I think we have to acknowledge that they're there. as we go through um
Wojciech Wegrzynski:
these
Rory Hadden:
problems.
Wojciech Wegrzynski:
I think, uh, another breakthrough in in your personal pathway as a fire safety engineer comes when, for the first time you experience, a really large fire. like when you take a piece of, I don't know, polyethylene, uh, and you put it into bomb to measure the heat of combustion, in the end you get a slightly hot water and, and a number. You put that thing in a cone calorimeter okay, it's gonna burn quite nicely. But it's not a very, very impressive thing uh, if you take a larger piece of that and somehow ignite it, it's, it's interesting to observe how it ignites. And if you put that thing on a facade, it's a raging inferno it's nothing you've seen in your life. Like someone opened a portal to hell and, For me, it was a huge lesson of, I, I didn't even know, know the world. Like it, it was really interesting to see how much the scale changes the fire. And once you heat a particular large scale with a very bad material, how bad and how quickly it can, evolve, and once you first time in your life experience that, uh, when you see a results from cone color, okay, this one has like 20% more heat release rate than the previous one. that doesn't seem like a, such a huge deal, but it is in the end. It it is. Same when you observe compartment fires. So I I wondered why in larger scale, these bad fuels are even worse? Why? Why these fires can so tremendously accelerate and, uh, Why we have such a hard time slowing that down, like making these materials slow down are um
Rory Hadden:
are uh all about feedbacks The thing that you often don't see in a small scale test, is really the, the way in which those feedbacks occur. And that's usually because a test has been designed in some way to try and eliminate those, right? Because they're difficult to control and whatever. But once you start building up, you know, big assemblies, um, and, and you let the fire, experience or certainly let the materials experience those feedbacks then you get really rapid or you can get really rapid fire growth. And I think that that is a thing that takes most people by surprise, certainly takes me by surprise. Um, now and then when you are doing a large scale test and you know, it's these, it's these transitions, uh, that the fire go through. The most famous one of course, would be the flashover in a compartment fire. But even just if you've got, you know, a spreading wildfire or a, a spread on a facade as the flames you know, they get larger, you're burning more fuel. You start to get things like the effects of char oxidation if you've got charring materials. Playing a role, uh, external variables, you know, the flow. All of these things, generally act to enhance the fire spread. And we don't often see that in a small scale
Wojciech Wegrzynski:
in a laboratory,
Rory Hadden:
because we don't have, you know, we're not releasing enough energy to create huge buoying flows, and we don't have the external influence of wind, for example. So I think for me, the, the way of, of measuring the size of a fire, is always one that's a bit tricky. And then I'm gonna try and pull this back onto a learning point if we can. uh, is, you know, when we measure the size of a fire, we don't do it based on how tall is the flame or how wide is the thing that's burning. we always measure it in terms of the energy that's released. And, you know we would call that the Hmm rate, or the energy release rate or, or what have you. But the rate at which basically the, the, the fire's producing energy, and that is measured in, it's a unit of power, right? So it's, um, measured in watts, maybe kilowatts,
Wojciech Wegrzynski:
megawatts
Rory Hadden:
uh, some some proper
Wojciech Wegrzynski:
going. which is jewels per second, like the amount of energy generated per second of of the process Right
Rory Hadden:
per second, you know, in a fire you can go from something, I don't know, a candle flame is on the order of, I don't know, 10 watts, something like that. but you can have very easily, a compartment fire that's on the order of megawatts in size. And if you look at some, uh, extreme wildfire behaviors, they will be measured. It's usually measured in terms of megawatts per meter, right. And that's meter of the, the width of the fire line So
Wojciech Wegrzynski:
uh, I, I just had Kevin McGrain on the show when we were discussing World Trade Center. Listeners know that you don't know that , but, uh, listeners know that there was a Kevin on, on the show and, from their assessment, uh, size of the fire in the World Trade Center was approximately 2000 megawatt. So it was in the gigawatt range. So, so that's that's impressive Yeah
Rory Hadden:
you start putting these numbers in context, I mean, it's, you try to find something to Yeah a two gigawatt fire. I don't know what, you know, what is that? Is that a nuclear power station? Is that the output? I mean, I, I don't even know. You start, it's getting handle on this and what it feels like is quite, is quite tricky. And I, I Hmm people who haven't, been able to do this is to, you know, try and find a lab somewhere that will let you come in and see what a fire looks like. Because, in our lab we can run fires of up to, around a megawatt, depending on who's looking maybe a little bit more. and you know, I think the first time somebody sees a fire that's of that size, it's eyeopening, you a one megawatt fire is Mm think many people would feel comfortable dealing with or being near
Wojciech Wegrzynski:
Mm
Rory Hadden:
uh, so getting, and it's difficult to put, you know, sizes on this, you know, waste paper, basket fire, what's that? A hundred kilowatts. I mean, maybe something in that. In that order, maybe a little bit less. so it's difficult to, I think for, because of the way of the units are, are given, you know, this, this idea of power, it's quite difficult for people to get a sense of that, think. but, you know, hmm relate it, you know, the, a kettle is, you know, three kilowatts. Right. But does that help? I don't
Wojciech Wegrzynski:
know Right. You a hundred kettles per second. That's not, not a great unit of measure Right
Rory Hadden:
of the things that is a bit tricky and until you, you see it, you know, the, it's quite a difficult measurement to get to wrap your head around. but the useful thing about measuring heat release rate, is you can use it to track the fire growth. So fires don't normally start
Wojciech Wegrzynski:
Hmm
Rory Hadden:
release rate, right? Normally fires grow in some way. They start small and they get. and the nice thing about heat release rate is you can track the fire growth, using this, this measurement. and we've got different ways we can measure heat release rate, which is I think, quite useful. Um, but uh, we can talk about them Hmm a minute, but nevertheless, tracking the fire size, um, as a function of time is really, really useful in terms of how we understand the burning of individual materials, but also how we understand the burning of objects. so it's one of these kind of concepts that unifies uh, a lot of things in fire science. So, if you're running a small scale test in the laboratory, for example, using the cone calorimeter, which is, a device that basically allows us to impose some heating onto a material. the heating is by radiation that increases the temperature of the material. eventually we will reach the point where we will have a flammable mixture, as the material decomposes into the Mm-hmm A flammable mixture will exist above the surface of the fuel. We have a pilot flame, sorry, pilot spark, in there that will ignite those Hmm and the material will burn. Once the material starts burning, we can measure the energy release. And if we have something like, a common plastic polyethylene was an example you used before, that will burn in a way that basically very quickly it reaches, uh, kind of a, a maximum steady value and it'll burn like that. Um, releasing more or less a constant amount of energy until we consume all of the material. Um, and then of course, there's no fuel left, nothing to burn, so the heat release rate drops back to zero. materials if you've charring materials, so things like, timber. Um, or any kind of, uh, cellulose kind of derived product, they're typically all charring. Um, that will, that means that the, once the sample is heated, we produce the flammable gases in exactly the same way as before. We then ignite those gases. and in this case we can track the energy release as we do before. And what we'll see is the energy release, uh, immediately reaches some kind of maximum value and then decreases as the material burns. and it never reaches really a steady it's always kind of decreasing as the material burns. And that's really useful information because now we've got information that, um, is telling us how much energy these materials are releasing and also how they're releasing, that energy. And the thing about heat release rate is, I mentioned before about feedbacks. It's one of the main things that The energy that you release from the fire will, determine how much energy you have available. To go back to the material to heat it up some more, to keep it burning, to spread the flame to grow the fire that way it will also determine the airflows that you get around. So if you have, a larger heat release rate, you'll generate more, uh, more buoyant airflow. Um, larger airflows typically will again, be a positive feedback, uh, into a, a fire system. So by tracking that evolution, by understanding how, different materials burn and how they release the energy as they burn, you can learn a lot about how things might uh
Wojciech Wegrzynski:
might manifest I, I have another observation, another change in the life of a fire safety engineer. so the fact that something is difficult to ignite doesn't mean it doesn't ignite, and it doesn't mean it burns it, it just means that this particular setting of these feedbacks that you've described is slightly different than from material. Let's, let's say an easy to ignite. So if you have polyethylene, it's, let's say easy to ignite. So you need lower heat feedback. It can self sustain the combustions simpler, quicker, easier, and just, just burn off. And if you have, let's say, strongly fire retarded polyethylene. where someone has engineered modifications to this material. So it is harder to ignite. It doesn't mean it does not, it, it just means this whole, feedback loop is on, on a quite a different level. But if you reach that level and you, you get net positive heat, loop in there. So by by burning it, it, it generates more energy than it needs to ignored and keep burning. So, so it's not positive. It'll eventually grow. And, and I, I think that's something that, that we observe in, in, in this faucet were brought as an, as an example that you can put a very good materials from our, for our standards, like very high euro class materials. And because of this specific way how. Facade is constructed. That enables a lot of interesting feedback loops. Inside. You may still be in the regime where, okay, it's very hard to ignite, but after you do that, it can self sustain and, and propagate
Rory Hadden:
uh, people often ask what it is that I do. a fire scientist, you know, what the hell is that? And, you know, my, my response sometimes is a bit flippant, which is, you know, I, I take things that obviously burn and show that they don't, and I take things that shouldn't burn and show that they do. and you know, as long as something's got some carbon in it, I think, you know, we can usually find the way, to make it burn. And, and you're absolutely right. You know, this is the process of something burning, is all about these feedbacks. And actually the, the, is, you know, there's quite simple expressions, uh, for that, you know, I won't recite the equations now, but, you know, there's quite simple ways to conceptualize, that problem. And basically, Just because something is hard to ignite doesn't mean it won't burn. And I think those are concepts that often
Wojciech Wegrzynski:
Hmm
Rory Hadden:
sometimes a little bit misused. You know, something is fire retardant, well that means it will still burn. Right? You know, like it means it might be harder to ignite it, but it will still burn. And under some, you know, you also also have to ask the question like, what are the conditions that show that this is harder to ignite because, uh, you know, I can guarantee Hm know, a non-fire, retarded piece of wood and a fire retarded piece of wood in a compartment fire, the fire retardants aren't gonna be massively effective, uh, once you start having a heat flu of, you know, a hundred kilowatts per square meter. So, so you have to be a little bit careful about How you evaluate these things. But, but in the end, you know, the, the energy balance is what we're looking at. And if you're burning something, you have the heat feedback from the flame to the surface of the, the material that will keep it burning. and you will have some heat losses. And the heat losses can be, in many different forms. due to, surface reradiation, they can be due to conduction in depth. They can be due to, um, literally removing mats. You know, so if you're materials melting and dripping and flowing away, um, there's lots of ways to manipulate this, this energy balance. But in the end for something to burn, as you point out, you have to have more energy arriving at the. Then you need to pyrolize the next piece of
Wojciech Wegrzynski:
material
Rory Hadden:
I think this concept of fire retardants and, and whatever is, is one that, is, is quite complex to understand, in the end, because, you know, the, the chemical formulations can all sound a little bit tricky, but in the end, what you're basically doing is modifying that energy balance somehow. You could be doing it, by also, um, changing the properties of the flames so you can make the flame release less energy. Uh, you can also delay the formation of flail mixture by producing, inert gases. So things decomposed to form water or carbon Hmm All of those things, uh, can have an impact on the, the burning of the material. But it is at the end of the day a feedback. and if you can
Wojciech Wegrzynski:
Yeah
Rory Hadden:
energy in your system, then you can make, you can make something burn. yeah
Wojciech Wegrzynski:
and, um, to the fire safety engineer who's listening it's not that they don't work or, or they are useless. It, it's not about that. It's about understanding the purpose of these engineers changes to the materials. If the purpose is to, make it harder to ignite by introducing these ways of, of additional heat losses and moving the, the balance away from the, the point you're changing the regime in which the fire can even start. And I guess that was like a case of, ignition of a mattress by cigarette. where, uh, Eventually engineered the material in a way that energy carried by this source is insufficient to ignite, which it's not a huge change from grand scheme of things. Uh, perspective if there's a flashover in there that compartment, that sofa will burn as, as vigorously as as another one. But you've changed the amount of fires that can happen because suddenly the common ignition source is enabled to, to cause a fire. It's enabled to, to pass from just ignition to the fire Right
Rory Hadden:
that's exactly the role of a fire retardant. It's to make things harder to ignite and perhaps to, you know, then slow down those early stages of, of fire development. So, you know, you, you basically, you, you buy time, in order for people to evacuate and you know, all of these things to happen. and, and there are multiple ways of doing that and I think, you know, there are lots of statistics that show that that is successful, in terms of reducing the number of fires. but, the key thing I think to remember is that that's happening in the early stages of the fire. So if you're interested in that and you're looking at an Hmm calculation, for example, then I think, the fire retardant issue in material selection and material choice. But the question of does the fire retardant work at the scale of a compartment fire, of a sad fire, a wildfire, those are different And you know, you probably need different mitigation techniques, uh, to address that. There's no, no silver bullet in this. Uh, you know, there's not one, one Yeah
Wojciech Wegrzynski:
for everything I would also like to point out that cigarettes changed a lot and modern cigarettes carry much less energy as an ignition source. Actually, from a lab fire laboratory perspective, that's quite a problematic, I think the last batch of cigarettes used for the test we had to purchase in Ukraine. Cause the polish ones were, were not, uh, burning vigorous enough. y you are also known, uh, as the, the wildfire scientist. I wonder like we, we've talked about solid fuels like timber and stuff. now loo looking at, living fuels, like, it, it, there's many, many differences. one that for me is the most obvious is, is the, well two, two are obvious to me. One is the moisture content in the fuel and the second is it's porosity. So how does change this fundamental behavior? I guess the the the science is the same is
Rory Hadden:
I, you're absolutely right. This, for me, the way I look at this is that the science is the same. Um, you know, it's the same heat transfer processes, the same fluid mechanics processes, the same mass transfer issues, the same, uh, chemical reaction problems. So in many senses, I see way more similarities in differences, and I think. You know, one of these things that, I get a little bit of a, a b in my bonnet about is, you study, you know, structure of fires or wildfires. Well, why not both, right? You know, you're an experiment or a not both right? And I think these sorts of artificial divides that we've kind of created, our, in our community the
Wojciech Wegrzynski:
community the Tribes
Rory Hadden:
something that I find quite frustrating. I think, you know, the best work is done at the interface of all of these things. and you know, I think that Hmm a lot that, fire scientists can bring to the table, in wildfires and in the discussion around that, and that is happening. Um, don't get me wrong, that's definitely happening, and I think that's extremely positive. and vice versa, right? There's a lot we, need to learn as fire scientists, about wildfire behaviors and, and the ecological aspects and, you know, all those other parts that play
Wojciech Wegrzynski:
role in this
Rory Hadden:
problem. So, what I prefer to try and look at this problem is one or more of, of commonalities than, than differences. now of course, that brings challenges. When you start getting to the, the kind of application edge of this. If you want to build a model to predict wildfire spread, then you make different assumptions. And if you want to build a model to predict, you know, fire spread, in microgravity or fire spread on a facade or whatever, and that's normal, I think. But the, the fundamental Hmm approach to studying this, and the, the approach that, that I've tried to take, in the work I've done is or been involved in is to, you know, how much can we apply the techniques and the methods of fire science into these, wildland fuels, that the moisture content is super important, but that in a way is, is it's not simple to deal with, but you can view that as an, an energy sink. So you've got an energy part of the problem, uh, with the moisture, and
Wojciech Wegrzynski:
you've got the fluid A actually, sorry. It's, it's, it's very similar to what we've just discussed as, as fire retardant. Another way to, to dissipate the heat that doesn't go into heating up your fuel
Rory Hadden:
there are in in terms of some of the, the, the moisture content problems, that is a very nice way to think about it as, as more or less a heat sink. Some of the other, work that's going on in your should, it's a little bit more complex in the sense of, you know, is it free water or is it somehow bound? And, and
Wojciech Wegrzynski:
Mm-hmm
Rory Hadden:
implications does that have? And I'm not sure we've fully resolved, that there's some re nice work going on around it. But, in the end, for some fuels, for example, if you have dead fuels aren't living, that simplifies the problems hugely. Um, and we spent a Hmm with, with dead fuels, um, because of that simplification. But of course wildfires don't only burn in dead fuels, they also burn in these live fuels. So we need to think. that. So there's huge similarities there in terms of the porosity, issues. I think that's something that, is perhaps less well, uh, understood. there's again, really nice work around that, I think is now becoming more, mainstream perhaps, you know, work in the US Forest Service that's looking explicitly at linking the burning of wooden cribs to poorest fuels. And that goes all the way back to the kind of genesis of some of these wildfire models, which were all kind of developed using, wooden cribs or these sort of like manufactured synthetic porous materials. and for me that, that's something that's really interesting cuz it, it also puts you on. The edge of having a flaming fire and a smoldering fire. uh, as soon as you bring in this ity, so you change also the, the mode of burning, as well But we don't shift it into a world that we don't understand. I mean, we've been studying smoldering combustion, you know, since the 1950s, uh, if not since before then. and we understand all these things. So for, for me, wildfire and propagation of wildfires, if you look at it through the lens of fire safety, engineering, there's a lot you can, you can contribute. And, you know, it's, it's not the only way of solving the problem. I, I, I'm wise enough, uh, and old enough to recognize that, you know, there's more than one way to skin a cat. but there's a lot that we can do. And I think that, that for me has been one of the, uh, the most interesting, parts of my, my career so far is, is looking at how far you can push that. which of our fire engineering techniques, make the most sense in these different settings? You know, measuring the heat release rate, for example, that's still a pretty good way to go to try to understand, the Hmm or moisture content on, on the burning of fuels, measuring the mass loss rate. You know, these are things that we do all the time, in fire science that help you to understand, um, how these different materials are gonna burn. So from my point of view, there's not really a difference. I mean, I, I, I wear these two hats because I feel like I'm, Hmm made to wear these two hats. when you talk to people, you know, or wildfires are somehow different from structure fires, but I don't know, it's the same hat and just turn backwards,
Wojciech Wegrzynski:
guess. Okay. I, I had an episode with, with Sarah McAllister on the podcast, and we were talking about de combustion different scales, and at some points we also ventured in this weird place where I was talking about opening factors in combatant fires. She was talking about foresting Cris, and we've realized it's essentially the same thing in the end, how air can penetrate your source of fire. So, so, uh, it, it, it also reaffirms your, your view that it, it's the same thing. It's just just a little different, scale or different, application of, of the knowledge, um, for, for the end, something that was mentioned here many times, uh, measuring fires. I, I think that's, uh, that's also a fascinating thing to understand how does one actually measure fire? I, I think maybe, uh, you'll agree, but I, I think. The moment where fire scientists achieved ability to measure fire in terms of it release rate was, uh, one of the biggest turning points in the history of the discipline. Like we've finally received a tool that can, quantify the fire itself, not the consequences of it
Rory Hadden:
Uh yeah, I mean, I think The ability to measure the energy that's released by a fire. I think it did our way to look as a paper, by Babrauskas isn't there? That says, you know, heat release rate is the most important variable in fire science or something like that. It's, is the title. And I think that goes back to the conversation we were having before about how the energy release drives so much of the feedbacks and the other processes um, that are going on and the ability to measure know, came I suppose once, uh, the diagnostics had become sufficiently advanced I guess in the seventies and, and in the, the early 1980s, in order to measure it using the technique of oxygen consumption, Caltrate, which, is, you know, it's a pretty, uh, robust method, of measuring Hmm Um, that's based on an understanding of the chemistry, at one end, and then the ability to measure the amount of oxygen that has been. Consumed by the reaction, uh, on the other end. So if we tackle the chemistry bit to begin with, that's pretty fundamental in terms of how this works. is that, you know, for most things that we burn from a chemical point of view are pretty similar, right? They're made of carbon, mm-hmm hydrogen. sometimes they have some oxygen in there as well. Of course, we have exotic things that will have other stuff. You know, PVC will have some chlorine in it and, and, um, you know, polyurethane will have some nitrogen in there, but mostly these things are made of carbon, and oxygen. and if you understand the way that energy's released in a fire, I mean, it's made by breaking bonds, for which you have to put energy in. Um, and then bonds reforming, um, to make new molecules in the case of a fire that's usually carbon dioxide and water,
Wojciech Wegrzynski:
Hmm
Rory Hadden:
uh, the reason that a fire, can spread and can grow is because it releases more energy than it requires to break those bonds. So, if you think of Hmm terms of those chemical, uh, terms, you know, you've got fuels that are. Broadly, quite similar products of combustion that are basically always the same. You know, carbon dioxide, carbon monoxide, maybe some water. and, and what we're actually looking at are the, the ratios of bonds, right? How many bonds do I break? How many bonds do I form? and once you start breaking down to that level, you can see, well again, there's more similarities and differences between the fuels. and, you know, some work was done. I think actually the first work was done like a really long time ago. Um, and I can't remember, the, the paper
Wojciech Wegrzynski:
but some um, was by Thornton Thornton
Rory Hadden:
Um and he found that basically you always get the same amount of energy per, kilogram
Wojciech Wegrzynski:
of oxygen. That's like 1920s. That's, that's really a hundred years old Uh piece of work
Rory Hadden:
it took, the guys at NIST a little while, I guess, to figure out, um,
Wojciech Wegrzynski:
to make the diagnostics work on How exactly.
Rory Hadden:
and,
Wojciech Wegrzynski:
Yeah
Rory Hadden:
so in the 1970s or so, once we had the ability to measure oxygen concentrations, in a relatively simple way, we were able to develop this idea of the oxygen consumption calorimetry. and really, I mean, you simply, you measure how much oxygen you have in the air, which is normally always 21%. And then you ignite something and you keep measuring the air, And as you burn the object, you reduce the amount of oxygen that's in the exhaust stream. And, you know, by doing some calculations to turn concentration into a mass, you can figure out how much energy, is released. the magic number that you need to convert, between all of this is something that you hear fire scientists talk about a lot. This so-called 13.1 megajoules per kilogram, of oxygen. it's an average. I mean, some materials it's a bit higher. For some it's a little bit lower. but in terms of ability to make the measurement, usually that's good enough and it's also really powerful Mm we don't have to worry about what we're burning anymore. if you're burning individual pure materials, then fine, you can go and look up, you know, is it 13.1, 13.2, you know, is it 12.9? Whatever. But if you're burning something like couch or you know, something that
rory:
is
Rory Hadden:
a, a composite or made of many
Wojciech Wegrzynski:
Bagel.
Rory Hadden:
13.1 number is, is then very useful. it also means that, you know, we have to take these measurements in that context, you know, there's may be no sense
Wojciech Wegrzynski:
Mm-hmm
rory:
places
Rory Hadden:
the heat release rate of your fire. but technique is so powerful in letting us.
Wojciech Wegrzynski:
some
Rory Hadden:
handle on that, that fire size. there's a lot of tricks in there though. The, the, the process is not one that is super easy to follow. And, you know, I would encourage people to go and look at the original work and, unpick that calculation. there's a lot in there that is, translating from the general concept that I've just described to implementing it, to making those measurements Hmm technologies um, that's not quite so straightforward. Um, but that's the jive of it, I think, you know, is, is finding these devils in the details. the other way to measure heat release rate that I think is really powerful as well is just by measuring the weight of the thing that's burning And if you measure the mass of it, and we know roughly the heat of combustion, that gives you a separate way to try and, evaluate the energy that's being released. Um, again, that can be quite complex if you're burning. not pure materials because what is the heat of combustion of a couch? I mean, I don't know. but you know, it can give you a sanity check, uh, on these numbers.
rory:
and
Rory Hadden:
I think the nice thing about the mass loss technique is, is that something that you can, deploy at different scales, right? Um, and it's relatively easy to do that. So one of the things, Hmm coming back to my time in, the wildfire world, one of the things I've been trying to do there is, you know, which of our usual techniques can we take out of the lab and into the woods? uh, we can't put a giant, extraction system on top of the forest that we would need to Yeah heat release rate by oxygen consumption color imagery, but we can maybe put a load cell, uh, underground, you know, build a platform and put a load cell there. So the mass loss technique, I think. It's pretty useful. from that point of view, uh, it's, it's a little bit more adaptable. It's a little bit more robust. You know, you only need to make one measurement. There's only one piece of hardware that you need. so I think, you know, looking at, at the techniques and, asked the question of, of, our, um, ability to measure fires has improved massively. Um, which it totally has. Um, but I think the other thing we have to remember as scientists is you know why do we want to make the is going on here? And, Hmm it comes to measuring fires, I always think that, there's two levels of the measurement. There's like the global measurement, so that could be the heat release Hmm Um, for example, uh, in a wildfire it might be the rate of spread in the wildfire. Um, and mm really things to characterize a fire, but then always interested in the next level down. You know, why is that the spread rate that we have? Why is that the heat release rate that we have? And that's where we we're able to kind of pull back on all those ideas we talked about in terms of, know, what is the flame, uh, understanding the, the processes that drive a flame, understanding the heat transfer mechanisms that result in the feedbacks. So we're, we live in an age where, you know, people before us made it easy to make these measurements. Now what I think the Hmm we're living in is the, is the why. You know, why is that the heat relief rate, why is that the rate spread of a wildfire? Why is that the rate spread, um, on our facade? You know, why is that Hmm growth rate in my timber compartment? And I think those questions are much more interesting Forms of question than just, you know, how big or how fast or whatever. because once you know the why, you can then actually start to engineer systems and products and materials much much better
Wojciech Wegrzynski:
There, there's one more way, which is extremely hot, but I know there was an attempt, like technically it's a release of so by solving the complete heat transfer of your whole thermodynamic system of your compartment, you can do that. And there was this Edinburgh Tall Building, uh, experiment. I think Juan made a quite a decent attempt on figuring out from heat transfer, but, but that, that's hardcore, uh, right. It's, it's not easy to solve that
Rory Hadden:
I think we have to think carefully about what measurements do you want to make and why, you know? Cause if you want to solve Yeah that way, you need to make a very different set of measurements then, if you want to solve it in a different way. And this is for me is now the hard part. Cause we do have a lot of toys at our disposal. You know, we've got lots of different Yeah things, you know, mass loss, temperature, heat flux, uh, energy release, you know, whatever we can, we can do it. Right. The, you know, we can even shine lasers into flames
Wojciech Wegrzynski:
look at the structure. you can see where the, uh, ions are in the flame. Exactly. Like, oh, age group, where is it? And you, you can actually map that in, in real time It's amazing
Rory Hadden:
question I always end up coming back to is, do you want to do it how does it help you to take a step forward? Because, you know, sometimes I think the most difficult thing is having lots of data and then not being able to see the wood for the trees. Right. So I think bit of experience that I've, uh, developed over the, the years is,
Wojciech Wegrzynski:
is
Rory Hadden:
really hard ahead of time about the measurement that you want to make, make that measurement really well, and then try to compliment that measurement, in the context of your problem. Because these days, yes, we can measure everything. question is, is it desirable to do that? You know is it going to actually help you? Um, do you have, you know, three years to spend crunching through all that data or whatever. So I think, you know, we, we've moved on from the age how to make the measurements. Now I think as I've said it's about
Wojciech Wegrzynski:
about what do those measurements. Why? Fantastic. that was a fantastic journey. It might be my new, one of the favorite episodes, . Thanks Rory for that. I would like to, place an advertisement on your behalf. Uh, I know that University of Edinburgh is starting a new masters in, f you already had a structural one, like you are very well known for a structural curse. So maybe you can, uh, tell anyone listening who, who would like to, to pursue a formal education in fif engineering. Uh, what what's in the offer from Edinburgh Nowaday
Rory Hadden:
you as you said, yeah, we've, had an MSC since the 1970s. um, the MSC started by, uh, Doug Drysdale, professor Rasbash and, uh, Eric Merchant. and we have a long history of teaching fire, um, in Edinburgh. uh, what we've launched for, students starting in 2023, um, is a new, version of that MSC that I think, reflects more the needs, of fire engineering today. the MS. C focuses on really delivering, a solid, grounding in the basics of, of fire science. the, the MSE is called fire Engineering Science. So it's, um, really trying to put at the forefront of fire engineering the, the concepts and the scientific principles that underpin the discipline. Um, so, you know, we draw on, know, areas of, of combustion heat and mass transfer, and of course the fire engineering itself, you know, how you apply, uh, these sorts of things.
Wojciech Wegrzynski:
of things
Rory Hadden:
uh, we also have, as, as part of the, the class as, as part of the degree, practical work in laboratory as well. So, you know, being exposed to making the kinds of measurements you've been speaking about, understanding the complexities of that, understanding the value of some measurements, um, under different contexts, looking at standardized test methods, as well, you know, and, and analyzing the data from them. So, hopefully, an exciting kind of, broad, uh, education in fire engineering science. , so the graduates can
rory:
go
Rory Hadden:
into careers where, you know, they're talking about, the important concepts of fire science that underpin the issues around, whether it's timber, buildings, facades, wildfires. Really the idea is to try and create the broadest possible, spectrum, uh, for fire engineers. And so we're excited about it. Um, we'll make sure that the link is in the, podcast episode somehow. Um, if people are interested in finding out more or applying or, or they can of course feel free uh to get
Wojciech Wegrzynski:
to get in touch And, yeah, you heard the man, the masters, program is, is this exact podcast episode by, but spread out over two years and filled with amazing content just
Rory Hadden:
year. Just yeah
Wojciech Wegrzynski:
yeah. one year. Okay. Rory, thanks for doing this. It was amazing, talking to you
Rory Hadden:
Alright
Wojciech Wegrzynski:
And that's, it's a very brief introduction to combustion in the flame for fire safety engineering. I hope you've enjoyed that. Let me know what you think about this type of content. And I'll, we'll try to bring more if you like it. There's so many subjects that could be covered in this way with, uh, some, all stars of the fire discipline. I always found it. Very interesting to learn the basics from the best. It's usually very interesting experience to actually try and listen. What the world's brightest minds have to say about the most fundamental phenomenon. You always learn something. As I said, I have learned lots during this interview and I have enjoyed talking to Rory a lot. So I hope that this type of content can be interesting for any type of fire engineer. I don't think there's much to add in here. Um, outside of three books debts, you definitely should have on your, on your bookshelf. I'm going to link this, uh, titles in the show notes. That's an introduction to fire dynamics, Bali duel. A little Drysdale and absolute classic. There are fundamentals of fire phenomenon by Quintiere and Enclosure Fire Dynamics by Quintiere and Karlsson three magnificent books that cover. So many aspects of fundamental fire engineering. And if in your career path, you've never had the chance to go through them. I absolutely recommend that because there's no many other places in the world of fire science where you can learn as much as reading through this masterpieces. Anyway, I won't prolong this too much. I'm still recovering from my flu. Has every good employee I took my week off after Christmas. And. And Colton nasty flu. So I spend most of it in bed. It's still recovering, but It's going good. so yeah, I'll go back to rest and, hope to see you here back in next Wednesday. And there's another episode waiting for you and next week's going to be quite interesting for the podcast. I think. So you rather don't want to miss that. Cheers. Bye.
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