091 - Fire fundamentals pt 2 - Ignition with Rory Hadden
Welcome to Fire Fundamentals pt. 2 with Rory Hadden. This episode is focused on the concept of ignition and its role in fire safety - as an event leading to fires, as something often investigated post-fire, but also as a vehicle to understand and measure general concepts of flammability of materials.
In this episode we cover:
- ignition of gases, liquids and solids
- flammability limits
- flashpoint and fire point
- open and closed cup methods for ignition of liquids
- a little bit of pyrolysis and heat transfer
Hope you enjoy this mini-series - more of those will be coming!
Wojciech Węgrzyński:
Hello everybody. And welcome to the Fire Science Show. Some weeks ago, I've had an episode with Dr. Rory Hadden of University of Edinburgh. Where we've discussed some basics of flaming combustion and flames and it has been a very popular episodes. And many of you have asked to bring more fundamentals into the fire science show. So we did. And I've invited Rory. Once again, today we are. Discussing the concepts related to ignition, which are also quite fundamental to understand the flames, spread the flammability of materials. What makes some materials more flammable than others? And what are the physical mechanisms? That leads to ignition. Uh, what are the ignition sources? So a lot of interesting things. Things that may not necessarily be directly applied to Engineering. but definitely useful concepts to understand as a fire safety. Engineer. So I really hope you will enjoy this episode. I guess there's no need to introduce this. Any more. Last episode was really wildly popular. So I really hope this one is up to your liking as well. So, yeah, lets spin the intro and jump into the episode. Producing episodes. Like the one you're about to hear is possible. Because of the support I received from my diamond sponsor of the show, the, OFR consultants. OFR consultants are a multi award winning independent consultancy dedicated to addressing fire safety challenges. OFR as the UKs leading fire risk consultancy. It's globally established team has developed reputation for preeminent fire engineering expertise with colleagues working. Across the world to protect people property in planets in UK, that includes the redevelopment of Printworks building in Canada water. One of those residential buildings in Birmingham, as well as historic structures, like the national gallery national history museum. And the national portrait gallery in London, internationally work ranges from Antarctic to Atacama desert. in Chile and a number of projects in Africa. In 2023 OFR is growing its team and is keen to hear from industry professionals. Who want to collaborate on the five safety features this year? Get in touch at ofrconsultants.com. OFR, thank you for being a patron of this show. And thanks to you. being able to make this content for everyone. And now back to your fundamentals, with Rory. Hello everybody. Welcome to Fire Fundamentals Part 2 too, again with, uh, Rory Hadden from University of Edinburgh. Hey, Rory
Rory Hadden:
hey Wojciech how's it
Wojciech Węgrzyński:
Very good, very good. Thank you. Uh, I, I'm not sure if we should call it Fire fundamentals now is gonna be advanced Fire Science . Well, let's, let's nott say that maybe someone will turn off. It's, it's fundamentals. It's gonna be great. We're going to talk about how astonishingly fireproof materials can ignite and, and ignition in general, how you like the topic.
Rory Hadden:
Uh, I think that sounds fantastic. Vo Let's do
Wojciech Węgrzyński:
Rory, so, ignition is, is a huge chunk of, of combustion science and it seems like something that should be very important or, or given critical to fire safety engineering. Yet, uh, me as a trained fire safety engineer, I, I don't know that much about the concepts regarding ignition. Of course, we did some laboratories during the school and we did, learn some fundamental methods, and I understand some basics behind ignition, but it's not a part of our, like, everyday work. I rarely work on removing or preventing ignition. I, I'm usually working on stuff that's already burning. How do you feel this concept is positioned in the fire safety engineering world?
Rory Hadden:
I think that's, I mean, it's a really interesting, observation. I think it's one that, that I've made, uh, myself around. Uh, most fire engineers start from the, the idea that there has been a fire there, the fire's already going, and you know, now you have to do something about it. You know, uh, it's kind of taken for granted that a fire will occur. And personally, I think, of course, a logical
Wojciech Węgrzyński:
Hmm.
Rory Hadden:
Um, you know, the probability of, uh, a building during its lifetime, having, a fire start, a fire being ignited in that building is probably quite high. It could be a small fire, it could be a big fire. Um, but the probability of ignition, uh, within a building, uh, is maybe not 100%, but it's, it's probably quite high that at some point something will ignite. Now this might be dealt with, you know, by somebody who's in the building. It might be that the ignition occurs and, you know, the, the intrinsic safety systems in consumer goods or whatever, take care of it. But the chances of ignition happening within a building, is a real chance. so most fire engineers, I think, don't really spend too much time thinking about it. but you know, if you are a fire investigator, you probably will spend quite a lot of time thinking about, uh, how a fire started and what the materials first ignited were, um, and figuring out, you know, what. Is most probable in terms of ignition, or indeed, trying to make some kind of assessment of the most likely thing to have ignited. So ignition is, is really at the heart, I would say of, of that kind of investigation. But just because fire engineers don't need to worry about how the fire starts, they are generally very interested in how the fire is going to grow, um, and how the fire will spread and the types of, uh, materials that, will spread flame and how fast it'll spread flame. And the logic and the, the framework that we use, uh, to discuss fire spread and flame spread is, basically almost exactly the same, as the framework that we need to discuss, ignition. So there are some very strong links of the concepts, in those two phenomena. So by understanding ignition, I think it gives you a really good way to get into understanding flame spread and fire growth. uh, but also understanding materials, a lot you can learn from, uh, a simple ignition study, about how a material will burn and what kind of risk it, it poses. So, in my opinion, anybody working in the fire space should have some, you know, solid grasp, of the, processes that underpinned ignition.
Wojciech Węgrzyński:
And I, I think, preventing ignition is at the core of fire safety. We are living in a very flammable uh, world. And the fact it has not burned down, like last time I've checked, is because. We are pretty good at preventing accidental ignition. I mean, it happens of course, how often it does not happen, and it could have happened. We have absolutely no idea because, uh, it, it, it's not happening. So, so it, it's kind of hidden there.
Rory Hadden:
Yeah, it's, it's like many things in, fire science, fire engineering or, or any safety based discipline, which is, you know, success is that nothing. So it's a little bit difficult to count this, easily. but you're right. You know, we are quite good at stopping things, catching fire. Um, you know, it's in the interests of product manufacturers and, you know, and whoever to make sure that their products are as reliable as possible and, you know, aren't going to be catching fire. know, of course we live in a world that's powered by energy, and energy always brings a ignition. Um, so we really need to, uh, manage that somehow. uh, and, consumer goods are designed in a pretty good way, I think, to, to manage that risk. there are the classic examples of the faulty tumble dryers and these sorts of things that we see a lot, but, um, you know, they're not usually the concern of a fire engineer. that's kind of comes into the fire investigation world. So understanding how Ignition happens, you know, hopefully we'll be able to do that in a relatively simple way, here. That gives enough of the, you know, gives some of the fundamentals, you know, to show that not only is it kind of cool to understand, but it's really fascinating and, and shed some light on the complexity of a lot of fire problems. And I think, you know, as an academic, somebody whose job it is to find problems, ignition is a great thing to study, but also as somebody who's practicing as an engineer, what you can learn from understanding Ignition, I think is, is really, really, uh,
Wojciech Węgrzyński:
And my last thought for the introduction, When large fire happens, like when, when Grenfell happened, everyone was talking about the, the initial item that, that triggered the fire because it ignited when a large car park burns down. Everyone's thinking about, okay, did the, did the electric vehicle ignite it? Right. So, if you're an engineer working on a fire safety, on a building, you do not really have good means affecting, uh, the ignition outside of designing the, the parts of the building that can trigger ignition. You still have to understand how it can happen to, to work around it. It's a part of the, the whole design fire, right.
Rory Hadden:
Yeah, I mean the, ignition is a key part, of understanding material flammability, the ease with which something ignites is a key part of, uh, material flammability, of course, with, you know, how much energy is released, whil, it's burning and, and all, all these other aspects. But ease of ignition is one of the, simplest ways of determining the hazard that is posed by a material or by an object or a product or whatever. So, um, I think it's really, you know, it really goes to the heart of, of fire science and fire safety, engineering.
Wojciech Węgrzyński:
Okay, let's go there. so, uh, what's this one? I guess gases,
Rory Hadden:
Yeah, sure. Let's start with gases. then we can maybe move up to liquids and then what most fire engineers will deal with, which will of course be solid materials, will end up, uh, we'll end
Wojciech Węgrzyński:
Fantastic. And, uh, from last, uh, fire Fundamentals episode, I hope listeners have a good grasp of, of the combustion processes and the flames. Uh, and we've already discussed some aspects of ignition. In, in there we've discussed how it is the gaseous phase is undergoing the combustion. So essentially to, to burn. You have to turn something into gas one way or or another, at least if we're talking about framing combustion. So how does a cloud of, of a gases ignite? Like what's happening there?
Rory Hadden:
So, uh, when we're talking about clouds of, of gases, that is perhaps the simplest, form of ignition. Um, and the ignition of a, of a gas is really all about getting the right mixture of that flammable, gas with air. Um, these flammable mixtures, uh, have been pretty well studied over, uh, the last a hundred years or so, there are huge databases, that explore, uh, flammability of gases. And most of the, the work is done. using standardized apparatuses where you introduce, a known concentration of gas into an oxidizing atmosphere. Usually for fires, it's air that we're interested in. the concentration, of fuel is, is varied. You start off with no fuel, well of course it won't ignite. You add a little bit of fuel and then you introduce a spark and you try to create an ignition of that mixture, which is usually measured by the propagation of a, a pressure wave or a flame through that mixture. if your mixture doesn't ignite, you increase the concentration and you try again, right? And you do this kind of, uh, incremental approach, until you get ignition and a big bang usually. and then you keep introducing, more and more fuel, until you get to the point where you no longer get a bang and you no longer have ignition. And what you've done there is you've found what we would call the lower flammability limit. and the upper flammability limit, for that gassier species. and these are critical, right? The, the idea of flammability limits, uh, sometimes they're called explosive limits, um, is, is really powerful in terms of understanding the hazards posed by materials. Usually flammability limits for gases are actually quite low, surprisingly low. for natural gas, for methane, the flammable range is between about 5% of concentration in air by volume up to about 15%. if you have less than 5% methane in your air mixture, it won't ignite. There's, there's not enough energy released, uh, to sustain an ignition. And if you have more than 15%, concentration of methane and air, then it also won't ignite. You've not got enough air to allow that chemical. To go to completion. this idea of flammability limits is, is pretty well established. And, you know, you can go to the SFP handbook or, or Drysdales textbook and you can find tables of this data. and you know, you can use that to look at hazards post by
Wojciech Węgrzyński:
Is it any way related to the energy of the source? Like, if I have more powerful source, can I ignite it beyond the flammability limits?
Rory Hadden:
That's a really good question. the flas are sensitive to, uh, what would be known as the ignition energy. So there's usually also presented in these tables something called the minimum ignition energy. and that is the energy that you need in a spark in order to ignite the mixture. and that can vary, quite a lot. but usually once you have enough energy from the spark, it doesn't matter if you make the spark bigger, right? kind of a, a yes or a, or a no. that becomes really interesting when, if you were, for example, do the fire investigation and looking at types of, ignition sources, and if you were signing it to an electrical fault or something, you know, is it possible to actually get enough energy in a spark to, to ignite some mixtures? uh, so I think that's a, you know, the, the minimum ignition energy thing is really interesting. The other thing though is if you have a flame, more or less a flame is capable of, of igniting any flammable mixture. that's because within the flame you've got all of the radicals and all of the intermediate species, that are formed, that are super reactive, that will, will react straight away. So,
Wojciech Węgrzyński:
Going back to the energy of the, of the ignition source, I always found it interesting why it is defined in. Energy. Like n not why not? Like in some sort of energy density or, or temperature. Like if I have a given amount of Joules but they, they, they're in a large volume. Will it cause an ignition?
Rory Hadden:
I guess, yeah, you're right. So, so this is, one of these ideas about, uh, what causes ignition. Is it simply energy or is there some other kind in there as well? And, and you're right, there is usually some other kind of metric, uh, in there as well. But this, these are energies of sparks and that is quite
Wojciech Węgrzyński:
So I this comes down to the way how it's being tested
Rory Hadden:
like any method, you know, the result is dependent on the
Wojciech Węgrzyński:
So in the spark, of course, you would have a huge energy density inside the spark because it's an arc that was powerful enough to to, make a. Piece of air glow, . So that's lots of energy.
Rory Hadden:
if you think about what the spark is there to do, basically? Yeah. The, the spark, the reason you get flow of, of electricity through the air, which is normally an insulator, because the spark breaks down the air, molecules, the, and ionizes them, and it creates, a conductive path so when you do that, you also create all those, um, weird intermediate species, the radicals, uh, and you provide energy also into the fuel molecules to help parize and, and break them down, um, as well. So the spark is doing all of that work for you, um, the, in that gas use mixture,
Wojciech Węgrzyński:
And, what if I just keep, warming my gases? Like how, how will they ignite?
Rory Hadden:
Yeah, sure. So, okay, that's a good one. Um, of all, she'd mentioned the flammability limits are of course, functions of temperature and pressure. usually higher temperatures and higher pressures widen the flammability limits. the numbers I quoted before for methane would be at standard temperatures and standard pressures. it's fair enough. Um, so if you heat it up, you, the chances of getting a flammable mixture are, are higher. Um, if you keep heating it, uh, you can of course get to, uh, auto admission, of the mixture. and it's kind of a canonical problem from the, the first half of the 20th century, where it's a very important part of understanding combustion systems was to understand, these sorts of auto ignition phenomena. And the work of, of Seminar, for example, is, is one of those, really fundamental foundational pieces of work. looking at the ignition of, of well stirred mixtures. so yeah, if you heat it up, you will eventually get to that auto ignition because instead of the spark breaking, uh, the molecules down, simply there's enough thermal energy there to start the chemical reaction because all chemical reactions have, uh, an activation energy associated with them. Uh, and really to get the reaction going, you've got to overcome that activation energy. You've got to raise the energy state
Wojciech Węgrzyński:
So, so once this energy is passed, the reaction begins and it's, it's like, then it's exothermic, so it produces more heat and it, it is going on. Right.
Rory Hadden:
Yep. If you have the right conditions, the exothermic reaction allows it to through the mixture. Yeah,
Wojciech Węgrzyński:
That's, that's cool. And, and the same effort can be, achieved by, by just squeezing it, like introducing additional pressure. And, and here we discovered this legend, I guess
Rory Hadden:
Absolutely. The diesel engine or, um, I guess, getting some engine knock on your, uh, on your petrol engine. Um, if you can press it whilst everything's hot, you can get the. ignition happened basically at the wrong time. So, I mean, a lot of the work we understand on Ignition comes from that space. You know, it comes from optimizing, internal combustion engines, to make sure you get as much power for the fuel that you're using. Um, and, and really that is a lot of that literature is where we understand most about ignition. Uh, it's from that context.
Wojciech Węgrzyński:
I wonder also in, in terms of gases, you said about this minimum energy, of the ignition source. I wonder like, for example, does a static electricity have sufficient amount of, energy inside to trigger gases? Uh, ignition.
Rory Hadden:
I mean, can
Wojciech Węgrzyński:
Okay. Okay. It's.
Rory Hadden:
that there are, some videos I've seen. I mean, of course you also take with a grain of where you can see ignition of, of gas clouds from, static, discharge. of course it depends, you know, a static can be a lot or a little right as well. it depends on the, the magnitude of that discharge. but it's not as simple as any spark will ignite any mixture. But, um, you know, we know, for example, that, um, it's much harder to ignite, a dust cloud than it is to ignite a vapor cloud. We know that, for example. uh, but beyond that, I mean, the thing is quite tricky. There's, there's still perhaps some work to be done in that area for application to a fire context. I mean, in terms. Very clean mixtures of gases, uh, and air. there's some very nice relationships about ignition energy and the, the species that you have present, but for let's say real world applications, it's not so clean.
Wojciech Węgrzyński:
Yeah. I, I also think that, uh, purely gaseous setting would be something not very, very common, for the fire safety engineer point of view, because it's, it's quite a challenging, uh,
Rory Hadden:
I would agree to a point. I mean, I think, you know, if you're working in petrochemicals or anything like that, of course, uh, that's gonna be a problem. But also, I mean, the energy transition is, is happening. people are talking about hydrogen as
Wojciech Węgrzyński:
Okay.
Rory Hadden:
we're gonna be having to deal with hydrogen, uh, systems and fire engineering needs to figure out how it wants to do that. and when you talk about hydrogen, I mean the flammability limits of hydrogen
Wojciech Węgrzyński:
Insane.
Rory Hadden:
to 75%. They're enormous. Um,
Wojciech Węgrzyński:
Yeah.
Rory Hadden:
you know, not to mention the fact that hydrogen flame is invisible, right? I mean, there's all sorts of problems, um, with this. So again, understanding, having some appreciation of the additional hazard. I mean, if you look at the flammability range of methane five to 15, and then you go four to 75, well that's a whole different potentially of, of managing that hazard, than fire engineers are used to. So I think, again, just being aware of this so that you can play a part in that, uh, in those discussions around the energy transition is super
Wojciech Węgrzyński:
Uh, I, I, actually, I take that back. I now recall we had a very strong engineering discussion on the liquid, Propan, gas fueled, vehicles in Poland, which are very, very popular in Poland. Uh, and, you know, all the sorts of discussions we, we see now on electric vehicles banning them from car parks we, we in Poland did that 15 years ago on LPG vehicles. The exact same type of discussion, the same, same type issue in a way. Is it safe to introduce, a pressurized, uh, vessel with, liquid gas into a car park? Yeah.
Rory Hadden:
uh, this is a thing I think again, why it's important to, you know, be familiar with all these terms. Cause what are the hazards, how do you define the hazards and so on. Um, so yeah, ignition of, of hydrogen, systems is, is for me super interesting. Uh, what happens with those. uh, so yeah, but I mean, you talked about liquids, l
Wojciech Węgrzyński:
Yeah.
Rory Hadden:
so maybe we I mean, maybe not to cryogenic liquids, that's a little bit different. But if we go to regular, liquids and talk about the ignition there, I think, many people will have seen, you know, these classifications of flammable or highly or combustible liquids. and I mean, those are all definitions different levels of hazard effectively. but I mean, how does a liquid burn, well, ignite, I should say it ignites in exactly the same way as a gas, The, it's the vapor phase, it's the gas phase, of that liquid that ignites. And that's an important concept, I think, to understand, which is, you know, if you have a liquid, uh, an open pool of liquid, um, then that liquid is always exchanging molecules of that liquid with the atmosphere around it. The fancy name for that is the vapor pressure. We don't really need to understand that too much. Um, we just need to recognize that, a pool of liquid will always be exchanging, um, molecules of that liquid, whether it's, you know, octane or, or heptane, acetone, whatever it might be. There will be molecules that will escape from the surface of the liquid. enter the atmosphere. and this is a way that, might be a little bit confusing to think of, uh, at first, but I mean, if you think of how a puddle evaporates in Scotland, it rains a lot. But we don't have to boil the puddles to make them evaporate, eventually just go on their own. And the reason that they, they go is because those molecules, uh, leave the surface of the liquid and normally are blown away by the wind. which means that more molecules can leave the surface of the liquid and be blown away. if we close that and we put a lid, when you close the lid of your water bottle, level stays the same, right? It doesn't evaporate. If you have a glass of water, eventually that glass of water will
Wojciech Węgrzyński:
In, in the world of fire science, that's exactly what, uh, firefighting films are doing to, uh, pull fires. That, that, that's how you extinguish them. You, you a layer that, that separates the fluids, liquids that's burning from the atmosphere, right.
Rory Hadden:
create a, um, I think that the fancy term we might use to be a mass transfer barrier, right? You
Wojciech Węgrzyński:
Oh, that's really fancy. Yeah.
Rory Hadden:
the fam liquid into the, the
Wojciech Węgrzyński:
I would say you make it astonishingly fireproof. That's
Rory Hadden:
uh, somehow. Yes. so yeah, so when you have a liquid, I mean that exchange of atoms, uh, or sorry, exchange of molecules is really what's, governing the whole process. Because as we know, flames are gas phase phenomena, so we have to get things into the vapor phase or into the gas phase in order for the combustion reaction to occur. And really after that it's exactly the same problem as with the gases. It's getting enough of the vapor. To the vapor phase so that you reach the lower flammability limit, uh, again, in order to get ignition. And most of the time with, with, you know, looking at hazards of liquid fuels, the upper flammability limit's not so relevant because you're gonna get ignition at the lower flammability limit or near that, and then, you know, you've got the flame there, you're gonna be consuming the fuel, so you'll never really get to
Wojciech Węgrzyński:
Well, If you are liquid vaporize in a, in a way that fuels the whole compartment, you're pretty much dealing with the gas problem. Again,
Rory Hadden:
Absolutely. Yeah.
Wojciech Węgrzyński:
it, it's, it's interesting when it's like a pool and it's constantly producing this fuel or, or, well, your I liquid fuel is constantly producing the gas phase at the rate that loss for, for the flame to sustain. I guess that's the challenge.
Rory Hadden:
right, and that's, there's a subtle
Wojciech Węgrzyński:
Okay.
Rory Hadden:
what we will often measure, and people might be familiar with the concept of a flashpoint, defining the hazard, uh, associated to a liquid fuel. And in general, you know, a, a lower flashpoint, is a higher risk material easier to ignite that material. one example for is hexa, uh, has a, a flashpoint of minus 22 degrees Celsius, so that's pretty low. methanol methylated spirits, it's about 12 degrees Celsius. So even for quite common fuels, we can have quite big ranges in the flammability, in, in the flashpoint, data. but the flashpoint is really defined as when the, vapor phase concentration is equal to the lower flammability limit. So when you're running the test and there are closed cup flashpoint tests, different apparatuses, for that, they're standardized in various ways. What you normally do is you heat a small volume of liquid, and then you introduce a flame or a spark into the headspace on that, uh, liquid. And what you normally see at the flashpoint is, well, a flash, right? You see a a flash of flame, propagating through the vapor phase, but then it goes out, right? The, the rate of vaporization is not sufficient to sustain the flame, and the energy feedback from the flame back to the surface of the liquid is not so, is not so high in that context.
Wojciech Węgrzyński:
What's the difference between open cup and closed cup? And don't tell me It's the, the openness of the cup
Rory Hadden:
I mean that's, that's exactly what the difference
Wojciech Węgrzyński:
Ah,
Rory Hadden:
uh, so the open cup and the closed cup flashpoint are two different ways of measuring it. The closed cup, the real difference with the closed cut method is you have, a much closer, almost perfect equilibrium between the vapor phase and and not wanting to get too much into the thermodynamics of things. And that gives you probably a more repeatable test your vapor phase and your liquid phase are in equilibrium. You can, you know, hold it in that, at that temperature for as long as you like to do the, the test that you're doing and the open cup, You don't have that equilibrium. The vapor phase, can diffuse away of the liquid. So, you have a concentration gradient from the surface of the liquid to wherever your ignition source. Which is absent closed cup. In the closed cup, you've got uniform vapor concentration. In the open cup, you've got this concentration gradient. So, different test methods, uh, and of course it'll give different results, right? the flashpoint temperature is higher in an open cup than in a closed because of that diffusion away. And the, the dilution, if you like, of the, the gases for a fixed temperature of the liquid. the nice thing about the open cup test though, is it allows you to also determine the firepoint liquid. and the firepoint is different from the flashpoint usually by a few degrees. Um, the firepoint allows you to have sustained burning. So you introduce your, your pilot flame and you get sustained burning of the and that's because you've heated the liquid sufficiently that the rate of vapor. Is enough to continuously feed, the flame. uh, and that's, that's a distinction that, you know, isn't used too much because, you know, let's be a little bit conservative and we'll use the flashpoint number to make sure that, we are gonna be, in a conservative place. you know, these things are also important and, and you've seen, you know, many fire investigations where somebody's poured lots of gasoline around in a building, to try and set a fire, waited too long, a match, put it in there, and basically created a vapor
Wojciech Węgrzyński:
Mm-hmm.
Rory Hadden:
uh, which has, you know, usually caught them by one way or another. this idea of, of flambe vapors and liquids, um, I think is really, is really interesting. but you know, again, probably not too every day, let's say for a fire, engineer, cuz most fire engineers will be working with solid materials. Guess also apply the same logic that we've just applied to gases and liquids to
Wojciech Węgrzyński:
Okay.
Rory Hadden:
So when we're igniting a solid, what are we trying to do while we're trying to heat that solid up so that we force it to undergo paralysis? Uh, paralysis is basically a fancy word to say, breaking down of the molecular chain, that forms that solid material into short chunks. Um, the short chunks are usually volatile. They're usually going to be in the vapor phase or in the gas phase. And then we can ignite, ignite them. there are loads of standardized methods, uh, for doing this. Uh, the cone calorimeter, the fire propagation apparatus, whatever. Um, and you can take a sample, expose it to some kind of heating, and then, you will be able. With a pilot flame or a pilot spark, depending on your apparatus, achieve ignition when you have paralyzed enough, material. and so it's exactly the same concept, right? It's this idea of getting the materialized, at a sufficient rate that you can get sustained ignition on the
Wojciech Węgrzyński:
But, but, it's not about just igniting the, the phase. It's about getting to that equilibrium with the sufficient energy that, that can initiate the process. In a way, the process is, is ongoing on its own, right?
Rory Hadden:
Ah, so this is quite an interesting thing about how we do ignition in this, in the solid phase is, anybody who's run a cone calorimeter test, um, or even somebody who's, you know, really paid attention while starting a, a campfire or a barbecue, you'll quite often see flashes on a solid surface or near the solid surface before you get. A strong sustained ignition. and what those flashes are, it is kind of similar to the flashpoint of a liquid fuel, which is you're producing flammable gases but not really yet enough,
Wojciech Węgrzyński:
Mm-hmm.
Rory Hadden:
rate to sustain a, uh, a flame, at a given position on the surface. So, that process is quite complicated, right? I, I think you can probably see when you've got gases or vapors being evolved from the surface of the solid and then the burning in the gas phase with a pilot flame there to get that ignition going. So actually what fire science has done, when it comes to understanding ignition is to like cancel the gas phase, right? We've decided that coupling solid phase and gas phase in ignition is too complicated.
Wojciech Węgrzyński:
Hmm.
Rory Hadden:
so what we're gonna do is just get rid of the gas phase, uh, and turn ignition of, of solid fuels into a solid only problem.
Wojciech Węgrzyński:
Okay.
Rory Hadden:
know, I think that's really useful because what that allows us to do is to come up with the idea. Of the critical heat flux ignition, um, which is, you know, the minimum heat flux that you need to supply to the surface of a solid fuel to get it to ignite. The number most people are common are, are familiar with is 12 and a half or whatever. It's something on the order for, building separation, um, calculations, uh, 12 and a half kilowatts per square meter. interesting thing about that is, that doesn't recount for the gas phase that's piloted ignition. So in this case, we always we're, we're forcing the experiment, uh, or the test to give us, ignition, but 12 and a half kilowatts. I mean, many things have a critical heat flux around that, whether they're synthetic polymers or natural polymers. and the reason for that is because we test it in a standardized apparatus. You know, the, the sample dimensions are prescribed. The, uh, the way you heat it is prescribed. The boundary conditions are all prescribed. So, you know, this is, let's be clear, these results just like the flashpoint, just like the flammability limits are situation and test dependent. but what we've done, okay, let's, let's go back to solid, uh, ignition, and we've got the idea of the critical heat flu. The other thing that people will be familiar with is, I suppose an ignition
Wojciech Węgrzyński:
Now, wait, wait, I, I, I'm gonna stop you before we go into, into that. then I do my experiments with, timber structures, and I see the surface after the char is formed. I can see flames on the surface. I understand what my heat ffl is on this surface, and I know it's, uh, astonishingly high even though it's, uh, astonishingly fireproof material. It, it, it ignited and burned and then I'm having very large heat fluxes and. the flaming combustion stops on, on the surface, you know? Uh, does this mean I run out of the, the face that could go into gas phase and I'm left only with, uh, with basically cold. That must smolder.
Rory Hadden:
uh, no. Uh, so that's, um, how materials uh, and how they ignite. It's not so simple to draw
Wojciech Węgrzyński:
Okay.
Rory Hadden:
those two concepts. but you know, back to the idea of sustaining a flame requires a, that you produce paralysis gases at a sufficient rate. And when you have a charring solid,
Wojciech Węgrzyński:
Hmm.
Rory Hadden:
in the beginning you have pure, solid and no char. as it burns, you start to turn the solid into gases. And also the char is left behind as a solid residue, the material properties of the char are very different from the timber. and, that changes the whole energy balance around how something will burn. And eventually the energy balance, uh, is tipped into the favor that and not enough energy is being conducted into. material in order to sustain sufficient rate of pyrolysis. as soon as you don't have enough pyrolysis, the concentration near the surface of the solid drops below the flammable limit, and then it can't sustain a flame anymore. So again, the concepts of ignition and flammable limits and that kind of thing can help you understand even the burning of, materials. So,
Wojciech Węgrzyński:
was exactly the point of, of the question like is it's not just like 12 kilowatts. It's, it's, it, it's burning and will because it's, much more complicated than that. It's, it's a balance of many, many things. Production of the, of the gas phase and availability of oxygen and the heat transfer that's coming and all changing in time and space.
Rory Hadden:
Absolutely. And I mean, I think, burning in flame spread, very happy to, uh, have another, uh, one of these on those topics, uh, as well because that's a whole level of, interesting stuff on, under those categories as well. Um, but the idea of of producing enough pyrosis gases is key. And, and I think, you know, people often forget about that when it, when we talk about, the burning or the ignition of solids because, because of the way we've constructed the problem as fire engineers, of the way we've tried to cancel the connection between the gas phase and the solid phase, for good reason, right? Because that's really
Wojciech Węgrzyński:
Yeah, yeah, yeah.
Rory Hadden:
Um, so how do we do it? So we get rid of that because we put a pilot flame so we can be sure. As soon as we get that flammable mixture, it will.
Wojciech Węgrzyński:
So we have this energy density we need to start. We have something that will trigger that as soon as the conditions around our
Rory Hadden:
So you can, put a heat flux onto the surface of the solid, and you can, when you find the critical heat flux, which is the minimum level of heating that you can put and still get ignition, you can do some fancy maths and from that you can calculate an ignition temperature. But that ignition temperature is truly a, a construct, uh, a mathematical construct. It doesn't really have any physical meaning, in my opinion. Right? This is potentially, other people have different opinions on this, but for me, the ignition problem isn't defined by the surface temperature reaching some threshold. It's defined by, Creating a flammable mixture in the But because we decided to cancel the gas phase, it was too complicated. The, we, you end up having these surrogate variables like ignition temperature or critical heat flux, uh, ignition. now, uh, I think that what would be more sensible to talk about if we want to keep things focused on the solid phase would be a kind of critical mass loss rate
Wojciech Węgrzyński:
Okay.
Rory Hadden:
instead of, heat flux instead of a
Wojciech Węgrzyński:
And how would you define that?
Rory Hadden:
you would define it in exactly the same way. You would weigh the sample as you heat it. And then when you get ignition, you would take that data point of the mass loss rate. Um, now we've been trying that, uh, it's not actually so straightforward. there are one or two problems, uh, with doing that measurement. but that is, that's a more fundamental, uh, approach in my, in my opinion. and of course, know, the, the other part here that I've always found a little bit. I suppose is the idea that, you know, if you run some thermo grabmetric analysis, can identify a pyrolysis temperature for your solid. if you run a cone cal study and you calculate the ignition temperature, you get a different answer. and of course, pyrolysis is, is a key process, right? We have to have pyrolysis before we can have ignition. you know, why is there this difference between pyrolysis temperature or the onset of pyrolysis in a TGA and, the ignition temperature in a cone calorimeter or a fire propagation apparatus? And the reality is it's because the latter is a complete And of course there's problems with the former as well around, you know, the scale of the sample and whatever. But for me, the ignition temperature for a solid is when the surface reaches pyrosis temperature, or actually when sufficient volume of the material is heated. Because again, we relate everything to the surface because mathematically that's easier. But actually, We have to recognize that it's a volume that's always being heated when it comes to ignition. so I mean, all of this can get quite complicated, right, in terms ignition, the end of the day, whether it's a gas, a liquid, or a solid, you're always looking at creating flammable mixture in the vapor phase, near a competent
Wojciech Węgrzyński:
but going back to the, construct of, of the ignition temperature, What, to what extent I make an error putting that as a trigger to my flaming to start in if I do a F Ds simulations, for example.
Rory Hadden:
to be honest, I have no idea what what level of error you, you get on that. It might, uh, cause it will probably depend on many of the other that you, that you make. But, you know, I've seen, for example, if you run TGA on some materials, you will find an ignition, uh, or pyrolysis temperature. Uh, the onset of pyrolysis around 300 degrees Celsius. but if you run a Cone Cal study, you might find an ignition temperature of 400, 450 degrees Celsius. that can vary quite, quite a lot. Neith, whether that matters or not for any given, uh, application, I think is probably a little bit more nuanced than just those two numbers. but I think nevertheless, what's important is to, is simply to recognize what we mean when we say ignition temperature,
Wojciech Węgrzyński:
Hmm.
Rory Hadden:
and where that comes from, right? That isn't, it's not an inherent material property, quite the opposite. it's a material property that is entirely dependent on the test set up, uh, and the, the, boundary conditions that we're using.
Wojciech Węgrzyński:
And, at some point I was exposed to some other way to, to positioning that, and that was highly relevant to, to simulations and that was a concept of, of flu time product. Are, are you familiar with that or
Rory Hadden:
Uh, yes.
Wojciech Węgrzyński:
That's
Rory Hadden:
This is something that, uh, if I understand correctly what you mean, basically you have a, a heat flux applied for a certain duration, and the product of those two things gives you whatever. And, and I think I would call that like a dose response
Wojciech Węgrzyński:
Hmm.
Rory Hadden:
mission. And it
Wojciech Węgrzyński:
Yeah.
Rory Hadden:
doesn't work. Um, it's, it's very simplified way of doing it. It's something that I've seen a few times in, in a wildfire context looking at, know, tree mortality and whatever issue is, is that heat transfer problems don't work like that. is
Wojciech Węgrzyński:
It's not an accumulation, it's
Rory Hadden:
right. I mean, it, it could work if what people were measuring instead of the incident heat flux, was the net heat flux. So the ac the actual energy absorbed by the solid, perhaps that kind of product would work. but usually people are referring to as an incident heat flux, multiplied by a time and it, and it just doesn't work. It's one of the myths of. fire science, I would quite like to dispel if I, uh, if I had a magic wand. Um, so yeah, I, I think that that's in terms good application of science for engineering, I think that's not a good, uh, not a good way to
Wojciech Węgrzyński:
but, if you apply it with a net heat flock, you, you, you say it could have worked like, because there is a ENT component to that. Uh, like if you have a certain heat flocks, like even at a cone, some stuff ignites that 50 at 25 kilowatts in 2025, it will just take longer to ignite at, at 58 will, uh, take shorter, right? So,
Rory Hadden:
Yep. But if you look at the, uh, if you plot those data, you see it, it's highly, non-linear, you so it's not, it's just not as simple as that because when you, the longer you heat something, uh, the more time you have for energy to be conducted through the solid. So, you know, potentially more energy outta the back of the solid, on the, the face opposite the heated face, I guess. Um, then if you have heat something very quickly with a high heat flux, so your whole energy balance changes, uh, completely. and that actually leads us quite nicely into some of the other important concepts for a solid ignition that you don't see in liquids or gases, which is the idea of thermally thick and thermally thin solids. So, you know, anybody who's built a campfire knows this stuff, right?
Wojciech Węgrzyński:
Yeah, the,
Rory Hadden:
easy to ignite thin materials. Pieces of paper are quite easy to
Wojciech Węgrzyński:
and the big log will, and the big log will stand in the middle of campfire till the next day.
Rory Hadden:
the big log will stay for the next. Exactly. Um, but you know, how you ignite something where you ignite something really matters. And, and I would encourage people, you know, go to a safe place, and try and ignite a piece of paper in the middle of that piece a match underneath. Try and do that, and you'll find it's actually surprisingly difficult. to ignite a piece of paper in the middle. But of course, if you ignite the edge of the sheet of paper, I mean, it ignites immediately, right? And you have really rapid flame spread. Um, so be careful if you are gonna try that. but that again just shows how, the way you try to ignite something, how you try to ignite it, where you apply the ignition source, all of that really, really matters. even if you just have a thin
Wojciech Węgrzyński:
Mm-hmm.
Rory Hadden:
edges, corners are great places to ignite stuff, and I think intuitively we all know that, know, we try and start a fire. but, um, the concept of thermally thick and thermally thin is really important in ignition. And, you know, you have completely different relationships on the heat transfer as a result, uh, of this definition. And for ignition, you know, mostly things that are thin the order of a millimeter or less. And what do we mean by that? It we mean that you can describe the temperature of the solid basically as one number. The surface is the same
Wojciech Węgrzyński:
So one side has the other, the same as the other.
Rory Hadden:
More or less. Yeah, exactly. Those things look out really easily. but most solids that we deal with in fire engineering applications are thermally thick solids, they're much more complex, to deal with, because you have a fully transient problem, uh, you know, you heat the surface and energy is conducted from the surface into the, the body of the material. Um, and you're, you're always kind of having a, a fight between the energy that's arriving at the surface and heating up the surface, driving the pyrolysis and the energy that's lost out, through the back. So again, I mean, if you're looking around, you know, for what are present, might be hazardous, you know, the, the thickness of the material is, is important. All that means it's gonna take longer. So to go back to the, you know, the log analogy, you know, of course it's very easy, to ignite small logs and small branches and twigs. Um, but it's also pretty easy to ignite a big log or a big branch if you have enough time, right? All you've got to do is have a bit more time to heat up, uh, that material. So basically the, the conductive losses. So I think that's, you know, when you see as often you do, somebody applying, uh, a below torch onto the surface of a material, uh, to say, look how, look, how,
Wojciech Węgrzyński:
Fire resistant. This
Rory Hadden:
well, it is or how not ignitable it is, you know, a very localized heat source, even if it's a massive blow charge flame. But putting that on a small area, really an ignition test at all, right? Because, uh, the ability for a material to conduct energy away from the surface is enormous. Um, you know, everybody, I think underestimates how much energy you can move around by conduction. It's huge amounts of energy you can move by conduction. so, know, I think these sorts of tests, and again, just as a, as a fire engineer, that that's not a great test to look at the ignition of a material or to look at the fire performance, uh, of a material. so yeah, so when it comes to, you know, defining, the hazard of ignition, uh, in solids, of course it all comes back to, creating a flaming mixture, uh, in the gas phase, um, as it does for liquids and, and as it does for gases. But because of the coupling between the salt and the gas phase is not very easy to do with liquids. It's great. We rely on the vapor pressure very nice, and we can that. We can work with that quite easily. solids not so easy because this whole pyrolysis phenomena gets in the way and makes things a little bit complicated. So instead we remove the gas phase and we have this, concepts of critical heat flux, uh, and, the concept of, the ignition temperature. But the one thing that we haven't really spoken about is the time to ignition. and the time to ignition is also, it's a function of the heat flux. Um, and probably some of the most famous plots in material flammability are, you know, you plot one over the square root of time to ignition, as a function of the instant heat flux, and you get this beautiful straight line, uh, as predicted by, um, by the mathematical theory. And from that you can calculate the effective thermal inertia. And, the thermal inertia is again, a really good way of understanding the hazard posed by material. Even if you know nothing of the chemistry of the material provided its combustible. Um, a material with a low thermal inertia, so something that has a low conductivity, a low density, or a low heat capacity. the product of those three terms, the thermal inertia will, will determine, uh, to a great extent the speed with which something will ignite. And so low thermal inertia will ignite quickly. Materials with a higher thermal inertia will ignite more slowly. So low thermal inertia, things are commonly foams or, or products, you know, expanded products one form or another. Higher thermal inertia. You know, if you've got sheets of, PMA or if you have, you know, sheets of polycarbonate or those sorts of, of polymers, they will be of a higher thermal inertia. And it's a very good way of, of understanding the hazard. I mean that it's gonna con thermal inertia will control the rate of heating of the solid surface. And, and, know, therefore it will determine how quickly you reach the pyrosis temperature, how quickly you can produce those flammable gases. So even knowing nothing of the chemical composition of the material, just knowing the thermal conductivity, the density and the heat capacity, you can get a handle on, uh, the time to ignition.
Wojciech Węgrzyński:
so by understanding this, this fundamental physics that you, you've been describing, these are essentially the, the tools that, the industry of, improving materials in terms of fire resistance, uh, can work with either dissipating heat, uh, increasing these thresholds at which certain things happen, changing the termin.
Rory Hadden:
Yep. Uh, I mean, certainly for, you know, reaction to fire or material mobility classifications, manipulating these things is all what you know you're trying to do in order to improve the, the fire performance in air quotes of your material. and, you know, in the end it's, it's not so many variables that you have to uh, and, and normally the optimization process fire is only a tiny part, of that. So, you know, it's unlikely that you're going to be allowed to double the density of your material in order to reduce the time to ignition. So you might have to take other means. You might have to start adding things in, you know, here we get into the debate of, of fire retardants and how they work. But basically a fire retardant is going to do, one of a small number of tasks. It's either going to decompose in such a way that it will, dilute the paralysis gases produced to make it harder to reach a flammable mixture. will absorb a lot of energy. Uh, so basically you put something in there that's just a big heat sink, get them to absorb lots of energy, uh, and basically keep this, the, the material cooler for longer. the third way, um, that it's going to act is actually chemically in. Either the gas phase or the solid phase, perhaps promoting char formation or inhibiting gas phase reactions. so you know, you can start manipulating, uh, the chemistry. Manipulating the physical properties is, is really not so, not so easy know, a piece of wood has a density within a very small range. A piece of polycarbon has a density in a very small range. so yeah, so, you know, understanding those things and how they come into being, uh, in the ignition problem, uh, I think is really powerful for fire engineers, especially when it comes to understanding the hazards posed by materials. I mean, it's almost impossible to understand, you know, from first principles, the hazard of every single material or product that you can come across. But by asking, you know, what is a thermal inertia a, converting material B, you might be able to make some informed decisions about, you know, the relative, uh, risks, uh, of each.
Wojciech Węgrzyński:
For the end, we need to talk about more things that happen in, in, in a salt phase that are specific to that, uh, type of materials. And, and very interesting as well. That is, uh, self ignition. And, that is, uh, the, the ignition, uh, that leads to smoldering, not flaming. Uh,
Rory Hadden:
Yeah, absolutely. uh, one of the, I mean, it's one of my favorite things to talk about because it is a, a slightly mind-blowing concept, um, that if you, under the right conditions, many materials, and it's quite a big list of materials, will actually spontaneously ignite. Um, now it's important to say that this is not spontaneous human combustion that is bs to be honest. but, you know, spontaneous ignition of solids is a thing that can happen usually. what happens there, is you have large quantities of material. That's kind of the underlying theme for for spontaneous ignition. So, you know, either large accumulations of material being stored somewhere or during transport, you know, bulk transport on ships, spontaneous ignition is a big problem. what is the process of spontaneous ignition is quite straightforward, really. Um, it's basically a feedback loop. the time chemical reactions are happening around us. Um, so oxidation is happening everywhere. Oxygen from the atmosphere is reacting, with things. And, you know, if you cut an apple, it goes brown because of oxidation. Um, as a chemical reaction, if you, ride a bike and the chain will go rusty, that's a chemical reaction with oxygen as well. same thing happens with, lots of carbon-based materials. you know, grain biochar, uh, activated carbon, huge list of things they will start to oxidize. Um, now oxidation reactions are generally exothermic. Um, so, the bike chain is oxidizing, but it's not producing a lot of heat. And all that heat is lost to the atmosphere, um, almost immediately. But if you've got a large, massive material, if it starts oxidizing in the middle, it's gonna release some energy. But the thermal conductivity of that pile of stuff is gonna be quite low. So, that energy can't really move anywhere. It can't escape from where the region, where it is generated. Um, so it kind of stays there and it heats up the material. but. hotter material is going to then be able to undergo more reaction. And all chemical reactions are temperature dependent, So if you heat up, uh, the material, the reaction goes faster. So my material oxidizes releases a small amount of energy. The energy can't be dissipated, so it heats up the material. So that means the, the material is hotter so the chemical reaction can go faster. So in the next time step, if you want to think of it like that, more energy is released more quickly and, that heats off the material even more. And eventually you get this feedback process that keeps going, keeps going, and you get, ignition of the material. Um, and because you've ignited this in the middle of a massive, usually porous material, you can't have a flame, okay? A flame can't exist that context. So you have a smoldering. And a smoldering fire is one, uh, that you've talked about before on the podcast. Um, but basically a fire that is, uh, heterogeneous. So the oxygen from the air reacts directly on the solid surface. It releases quite a lot of energy, or it can do, um, under the right conditions, but that smoldering fire that's in the middle of your massive will propagate, in all directions, in a kind of a spherical way until it reaches the surface. And then you will potentially get, ignition. we do in our undergraduate, uh, labs. We use milk powder. it's a very nice one for doing this. uh, it smells of like burnt sugar, uh, afterwards. Um, but we can do that and, and, uh, we do it in the lab. And the reason we can do it in the lab is because we.
Wojciech Węgrzyński:
Mm-hmm.
Rory Hadden:
so instead of doing, spontaneous ignition, ambient temperature, we do spontaneous ignition, elevated and there are some beautiful theories out there. again, develop, I guess in the first half of the 20th century, uh, the Frank Kaminesky theory, uh, that allows you to do small scale temperature, small scale high temperature tests and extrapolate back down to, room temperature kind of conditions. and I mean, it's a really fascinating mechanism of ignition because, um, it leads us to all sorts of interesting things like the transition from smoldering to flaming combustion and all these kind of unknown parts of fire signs that are still, you know, on the periphery to be explored. Um, so I think. the idea of spontaneous ignition is, is one that is super interesting and actually quite relevant. There's a lot of, um, fire start in, in manufacturing plants. Uh, you know, food processing is another one. High risk of, of spontaneous ignition. hotel laundries, hospital laundries, where you've got big stacks of, of towels and bed linens and, and that kind of thing. you know, these are all places where that is a, a real threat and, you know, we have ways of dealing with sometimes you'll see if you are near power stations, uh, you'll see huge machinery a pile of coal and like moving it, you know, two or 300 meters away. The reason they're doing that is to stop the material from spontaneously igniting. You break down the pile, you let everything cool down in the middle, and then you reconstruct the pile because spontaneous ignition, although it sounds terrify. Takes a long time to happen. That feedback process starts off very, very, very slow. so, you know, you've usually got days, weeks, months, sometimes in order to, catch a, a spontaneous submission before it goes into what we call thermal runaway. Um, so it's a really important part of ignition of solids, but not one, I guess that's really related directly to most fire engineers day-to-day work, which is much more around, material classification, reaction to fire, flammability, uh, and that sort of thing. Um, but yes, it's, it's a fascinating topic
Wojciech Węgrzyński:
Absolutely, especially if you have a pile of, of coal to, to secure. And actually, uh, securing, uh, large volumes of materials is something many Fire safety engineers do. and it is a huge challenge to deliver, the safety when you basically have a huge amounts of material you, that is difficult to control and, uh, you don't really have any good, action to mitigate that, that, because you basically have just a pile of material,
Rory Hadden:
it's one of the things I, I, I remember reading, and I don't know if it actually came into fruition or not, maybe somebody can, can write into the podcast or let you know, but, um, when they were converting one of the huge coal-fired power stations in the uk when they were converting it from coal to biomass, they store loads of biomass. So they built these huge domes, filled it through the biomass, but to avoid the hazard of spontaneous ignition, um, they constantly flown. Through there's a huge cost, a huge overhead associated to doing that. but I guess it works out economically, for them. but yeah, it just shows that this hazard is, you know, it's, it's everywhere, um, that you, when you look for it.
Wojciech Węgrzyński:
And, you just cannot pour water straight because then you will promote biological processes that, uh, will, will, will make it challenging very.
Rory Hadden:
Well, absolutely. I mean, uh, once these things have ignited, I mean, one of the most common applications for this is, uh, in bulk transport on ships. and actually extinguishing one of these, spontaneously ignited fires on in a ship's hold is really hard because. Uh, you know, you can pump in carbon dioxide, but the carbon dioxide has got to get to the right place. You know, there's no good just, uh, having it randomly in the hold. You've gotta get enough in to really flood the hold full of carbon dioxide. , you might slow things down, but the chances of stopping it, because once you remove the carbon dioxide and you let oxygen back in, it will restart, flooding the cargo hole. But you can't normally do that on a ship because you lose the stability of and all sorts of other risks. So actually fighting these fires is, is really, really difficult. Really the only thing you can do in the end, think, is remove the fuel, you know, start excavating. of course that has its own problems because you're excavating burning material. And I don't wanna write that risk
Wojciech Węgrzyński:
Well, understanding how ignition happens and, and, uh, the chain of events too that leads to that, uh, especially if it takes weeks or months to, to ignore it, is, is a pretty decent, uh, strategy for fire safety. And here we made a, a full circle why fire safety engineers should learn about ignition, because sometimes you reach problem in fire safety that can be solved only by. Reducing ignition. And if with whole certainty you are able to remove the ignition from the equation, your solutions far safe.
Rory Hadden:
Absolutely. Uh, I think, we have gone full circle. It's very nice. Um, I mean, I al I always caution though, against relying on removing the risk of ignition because there's always the risk of the unknown. Um, so it's good to have, you know, more than one, level on your fire, uh, safety that. but certainly if you can remove ignition, that's the easiest point to prevent your fire becoming a big problem.
Wojciech Węgrzyński:
Rory, thank you so much. Uh, that was another, not a very introductory lecture, I guess, well, that maybe one day we need to do like introduction to introductions or, or something. But I really enjoy this fundamentals, uh, episodes and, and it, it's really. Nice to, to learn this, important and, and challenging concepts that, uh, really in the end help you do the engineering. Like understanding fire is the first step to, prevent fire and prevent fire damage. And that, what most of us would do, uh, for living. So yeah. Thank you for sharing that
Rory Hadden:
No, thank you very much, Wojciech for having us on. I think I, I fully agree, you know, if, if you're in this, in this business, I think, um, you know, the more you know about this stuff, it can only be helpful. Uh, so hopefully it has been helpful.
Wojciech Węgrzyński:
indeed. so, thanks a lot and I hope to see you here next time with, uh, some, another . Interesting. Uh, I, I could actually give you a. Part of the show, , we did this. It's, I, I really enjoyed this. it's brilliant and the audience loves it. So let's do it again. Thanks so much Rory for coming to show and, and see you again.
Rory Hadden:
No worries, Wojciech thank you very much. Take care.
Wojciech Węgrzyński:
And that's it. I hope you've enjoyed the fundamentals with Rory. Perhaps they owe you an explanation for the running joke in the episode about the astonishingly fireproof materials. Uh, just before we recorded this session with Rory. The day before some journalist. Has published a. piece on LinkedIn about timber being astonishingly fireproof. And we have literally went on the crusades in social media, which Rory against that guy. It was quite funny and well funny and sad at the same time because journalism. dumb bins down, some facts of fire science and that's potentially dangerous and something we would not like to see. But I just could not, resist calling. Calling stuff. The fireproof in the podcast episodes. Please, excuse me, my bad jokes. Anyway, regarding the fire fundamentals. Once again, if you want more of those, please let me know. I'll, I'll try to ask him. He seems to be enjoying this and I am certainly enjoying this. If you are enjoying this, then why not to make more of those episodes? It's brilliant to learn. Fire science from some of the world's best educators. Uh, not many people have the privilege to be able to do that. At least if you're not living in Edinburgh, you probably have a much worse access. Those academics. So by. The means of this podcast, I'm trying to democratize it and bring access to brilliant minds like Rory to everyone. I hope. Uh, it's a thing we can achieve in the fire science show. I certainly enjoy learning the basics, from guys. Rory. It's always nice to refresh and sharpen your mind. And, talk about basics and basics are once you go very deep on them, they are not basic at all. There's always something hiding. Behind the corner of that. Uh, you did not know. So. Ah, great experience for me and I hope enjoyable experience for all of you. Not much to add in here. Ignition is certainly important. Part of fire science, not a huge part of fire engineering, I guess, but it's a mean to understand. Fire spread flammability in all the concepts that are fundamentals for four engineers. So a very important skill to, to have the knowledge of how things ignite. That would be it for today's episode. Thank you for being here with me and the see you here next Wednesday. Thank you. Bye.
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