262 - Fire Fundamentals pt. 22 - Optical diagnostics in fire with Elizabeth Weckman

Why Firelight Is Also Data

Wojciech Węgrzyński 0:00

Hello, everybody. Welcome to the Fire Science Show In today's episode, we're trying to take you into the world of diagnostics we are using in fire experiments and more specifically optical diagnostics that are used in the world of fire. Imaging fires is a fantastic thing. Everyone enjoys a good, uh, video of flames and fires and, uh, of course, it's mesmerizing. But actually, while you're collecting pixels of light, uh, shooting an image of a fire, you're at the same time collecting data because the light that the fire emits carries a lot of information with it. And as we get better in deciphering this information, we get better in understanding fire phenomena. It's, it's kind of beautiful what can you see within the fire today, not just, you know, the external shell, the, the light and the flame, but you can really pick into the flame, understand the reaction regions happening inside the flame. You can remotely measure temperatures, remotely measure velocities, calculate entrainments, et cetera. It's a beautiful world and a whole, whole array of devices and tools that allow us to literally see into, into the flames. And for this, I have a fantastic expert on that, uh, Professor Elizabeth Weckman from Waterloo University Beth has covered that on her recent plenary lecture at the IAFSS conference, which I have witnessed. It was fantastic. And also I've just learned that, uh, she was, uh, given the Arthur B. Guise Medal from the SFP Foundation This is, for recognition of eminent achievements in the advancement of fire science and technology. So that's, that's fantastic. That, that's... Congratulations, Beth. I, I didn't know that you're the recipient of this award and, the timing seems now really, really perfect. Really happy for you and, uh, very well-deserved award. Anyway, Beth has much more to tell about the optical diagnostics than I do. So how about we just spin the intro and jump into the episode?

Sponsor Message From OFR

Wojciech Węgrzyński 2:32

The Fire Science Show podcast is brought to you in collaboration with OFR Consultants, a multi-award-winning independent consultancy dedicated to addressing fire safety challenges. OFR is the UK's leading fire risk consultancy that this year celebrates its 10th anniversary. As experts in fire engineering, they are fully committed to delivering preeminent expertise to protect people, property, and the environment. With over 30 chartered engineers and a team of fire researchers at their core, they continually explore the challenges that fire creates for their clients and society so that the best research, experience, and diligence can be applied for effective tailored solutions. In 2026, OFR will grow its team once again and is keen to hear from industry professionals who want to collaborate on fire safety features this year. Get in touch at ofrconsultants.com. And now back to the episode

Defining Optical Diagnostics Clearly

Wojciech Węgrzyński 3:33

Hello, everybody. I am joined today by Professor Elizabeth Weckman from University of Waterloo. Hey, Beth.

Beth Weckman 3:39

Hi, Wojtek

Wojciech Węgrzyński 3:40

Good, good to have you too in the podcast finally. I'm really happy that, uh, that you took the invite. I've really enjoyed your plenary talk at the IAFSS, so I really hope we do a great job in, in here

Beth Weckman 3:52

Looking forward to it

Wojciech Węgrzyński 3:53

Yeah, and, I need to find a title for this episode, so you need to tell me in the broadest sense what kind of diagnostics are we talking? What, what's the broadest term you could put on the measurement techniques that we're about to d- discuss in this episode?

Beth Weckman 4:11

I think the broadest term for those would be a set of optical diagnostics.

Wojciech Węgrzyński 4:16

Okay

Beth Weckman 4:17

a lot of people call it advanced diagnostics, but I, I prefer the term... The majority of them are based upon the interaction of light in some way with, the process that we're trying to measure

Wojciech Węgrzyński 4:29

I love the name advanced. if we find a new technique, we're gonna call it more advanced and then super advanced, mega advanced, like this doesn't work well. Uh, w- w- what about intrusive, non-intrusive diagnostics? Because that's a term that you were al- also using a lot in the, uh, plenary talk.

Beth Weckman 4:46

Well, basically non-intrusive means that you don't disrupt the physical or chemical phenomena you're trying to measure. In some sense, many of the optical methods are still a little bit intrusive because you're sending molecules from one energy state to another in order to make the measurement. So, while they're called non-intrusive in comparison to sticking a probe into a flow and having the, flow have, to, go around your measurement sensor, they are-- they still suffer from, uh, interfer- some interference effects

Wojciech Węgrzyński 5:23

why do we need, uh, other diagnostics? Why, why, why are you n- not happy with my thermocouples? I like my thermocouples.

Beth Weckman 5:30

several limitations to probe-based methods. Uh, one is that you can only put them in certain discrete points, and so while they may be relatively robust in a fire in comparison to some of our other techniques, we can't get the spatial distribution of measurements that we might want to truly understand something in a little more depth.

Wojciech Węgrzyński 5:54

Mm.

Beth Weckman 5:54

The other thing is that in making that thermocouple measurement, the fire may be causing errors in the measurement itself due to secondary radiation effects or local effects of heat transfer around the, around the sensor

Wojciech Węgrzyński 6:11

Although thermocouples are probably the easiest ones. Like, I mean, if you're lucky enough to put them exactly in the place where you want to measure the thing, which is not necessarily given, but thermocouples are not the worst. But, uh, as soon as I move into measuring, uh, flow with, bidirectional probes, for example, that's a mess. And when I go to gas sampling, oh boy, that's a challenge. Like it's, it's not a probe you stick into the stuff. You need to sample, you need to clean it, cool it, remove the moisture.

Beth Weckman 6:43

Exactly. And so any, any probe-based method really, has additional characteristics or additional factors that in a hazardous fire environment where there's also, there's heat, there's soot, a mix of, of chemicals, a chemical soup, so to speak. When you start to try to, deconvolute that using, a probe-based sampling technique, it becomes quite difficult to interpret what you-- the, the value you finally get

Wojciech Węgrzyński 7:14

And, and finally the scale itself, because if you talk about compartment fire, a thermocouple is a, is a point in space, like almost nonexistent. But if you want to talk about the sheath of the flame, which is microns thick, the thermocouple may be giant, right?

Beth Weckman 7:31

Yes. So you've always got what resolution of measurement probe do you need for the process that you're trying to measure? and that may govern as well what level of diagnostic approach you go to,

Wojciech Węgrzyński 7:46

Mm-hmm.

Beth Weckman 7:46

dependent on the, on the finer or coarser level of detail that you need, whether you want a global measurement or a more localized time-resolved measurements. So probe-based methods also tend to be somewhat slow in comparison to some of the scales of the flow within fire situations, and that can be, um, it causes a, a time-averaged effect or a bit of a smearing effect in time. So again, if you're trying to follow the dynamic scales, you may have to go to a more advanced optical technique.

Why Thermocouples Are Not Enough

Wojciech Węgrzyński 8:23

But it's also like not that, you have a, a simple device that you just point in and that gives you remotely all, all the stuff you would like. Maybe one day we, we'll get it, but the-- it takes some work. I like that, uh, in your plenary at the end, you said that, "Okay, it all sounds very complicated and the names are long, and there's awfully lot of lasers in them." But, it's just a technique once, once you learn it, once you get in, you, you start to build that, that skill set that, that's necessary, and that's also something we try to do right now. Um, I'll choose the table from your paper. The paper is obviously in the show notes for all the listeners. you kind of listed some primary non-intrusive optical diagnostics there, and they go by sections. There's section on flow visualization, uh, gas species concentrations, temperatures, then s- then there's a section on, on soot and particulates and, and finally on velocities. I think we, we could, uh, to give this episode some structure, we could perhaps go through that. So you start in your paper with, with simple techniques of photography, how much you can learn through shooting videos of a fire or fire phenomena in a broad sense?

Beth Weckman 9:34

You

What You Can Learn From Video

Beth Weckman 9:35

can learn a tremendous amount from shooting videos. In fact, I usually recommend that as the first step in doing a fire experiment. At the very fundamental level, it tells you where to put your other measurements. Um, at a broader level with, uh, with advancements in computer-- well, camera technology as well as computer technology and ability to light in different fashions, you can do all kinds of digital image analysis and actually boil down the structure of fires to fairly small scales. we go to the side of looking at smoke flow, for instance, then, visual discernment of the contrast between a smoky environment and a clear environment gives you a wealth of different opportunities for trying to estimate how, how is that evolving even a large-scale compartment fire situation

Wojciech Węgrzyński 10:30

Uh, in your experiments with the, with the couches in a house, you've reported these different layers of smoke with-- which were observed through the camera. So even like attempts on quantifying the properties of the layers, maybe just, you know, by, by calling them thin and thick layer, but already like seeing in-depth physics in there. That, that's, that's something modern cameras can do. They're pretty good actually

Beth Weckman 10:55

Yeah, the other thing we saw in those fires that was very interesting was smoke actually rising from the landing up towards the ceiling. And the reason for that was because in the particular fire scenario, the smoke remained f- relatively cool compared to what we think of as fire smoke, and so it wasn't buoyantly flowing all the way up to the ceiling, and it gave us a whole different picture of some of the hazards that could occur during a house fire in terms of occupants and occupant safety

Wojciech Węgrzyński 11:27

How much preparation do you take to, to set up an optical system for, uh, an experiment? I mean, you can drop some random cameras every now and then, but if you want to have like maximum outcomes of that, how, how do you approach that?

Beth Weckman 11:40

Well,

Calibration Workflow And Camera Survival

Beth Weckman 11:41

with any piece of measurement equipment, uh, you should calibrate it. And so calibrations of cameras typically are- require some kind of a contrast board or a color board, depending upon what level you wanna go into, the same as if you were, trying to calibrate your computer screen, for instance, for color work. Um, it's the same kind of a concept. so that's before the experiment, you would run calibration, series, and then during the experiment, your lighting and various other things can change. That's a bit harder to take account of.

Wojciech Węgrzyński 12:14

Mm-hmm.

Beth Weckman 12:15

and then at the end, of course, you, you apply any corrections that you may need to your data as well. So the whole process, depending upon the level of accuracy you want, can, can be relatively time-consuming. best to get a standard procedure for doing it, and, uh, and then it becomes a lot, a lot easier

Wojciech Węgrzyński 12:37

My, um, experiences with, with cameras are, well, you need to put a lot of them because some of them tend to die. But, uh, o- one interesting experience was when Imperial were doing the, the first large traveling fire experiment in Poland, and, uh, we approached the project with, uh, you know, a set of cameras ready for the experiment with a, a nice, protective, boxes that were supposed to, to protect them. And, you know, we, we set the experiment. It was quite a large fire in the end. And, cameras got destroyed. The, the, some of the data was recovered, but n- like a, a very few of that. But a lot of people were on the side. We were shooting pictures with our phones, a lot by like 20, 30 people. So Egle, the, the lead researcher at Imperial, Egle Varakauskaite, she took all this, data, and she mapped them in time and space from which location the picture was taken and where it was taken. And she was able to reconstruct the experiment from a scatter of random pictures taken by random people in no synchronization. And actually, from that collection of scattered data, we, we got some really useful data points on the movement of the fire within the structure. As it was the traveling fire experiment, so we're kind of interested in where the hell the fire is, you know? So uh, of course, it would be better if we had all the fancy cameras we've prepped for the experiment on that day. But still, this forensic recovery, that, that was a hell of a beautiful job, Beth, really.

Beth Weckman 14:18

Well, really, I mean, with cell phones that you have timestamps, right?

Wojciech Węgrzyński 14:22

yeah. That

Beth Weckman 14:23

if you're running a master clock on an experiment, which we typically do on our large scale experiments anyway just because we have so many different systems running, then the cell phone pictures are invaluable. We likewise use video cameras. We tend to use security cameras 'cause they're actually amazingly robust in fires and

Wojciech Węgrzyński 14:43

Security cameras. Okay, that

Beth Weckman 14:44

replace. and so we run them until they die, but they're all piped back, so you record up until the point when the camera actually dies. but after that, we use all the cell phones that students or, or other people at the experiment actually, actually take pictures with and, and do the same kind of thing of compiling the images together at the end

Wojciech Węgrzyński 15:07

Yeah. Uh, uh, FSRI also uses, security cameras if I'm not wrong, and then a hilarious thing is that they start recording by pressing a panic button. There's literally a button that says panic, and it's supposed to f- at this point, like record everything in it from all cameras. Just I, I just kind of find it hilarious. So sorry.

Beth Weckman 15:27

No, no. That, that's one thing with security cameras, but the other is that actually they will, if you get the night vision kind,

Wojciech Węgrzyński 15:34

Yeah

Beth Weckman 15:35

as the light dies down or in different parts of the fire environment where there's low light, they will actually continue to record a, an interpretable signal, because they're intended for use in, in low light conditions. So you can get some really good images using some of the cheaper cameras.

Wojciech Węgrzyński 15:53

in our experiments, we tend to use, like, the cheapest sport cameras you can buy, and they're like full HD 60 frames a second, and they cost like 25 bucks, maybe 30 bucks. Like, like really the cheap kind. Not, not, no GoPros, no fancy like... I mean, GoPro is fantastic. It's just, it has a ton of image processing within itself. It has a very clever, um, lens, but it's a very advanced lens, so you're gonna have a lot of distortion, which makes it, uh, and you need to remove it. And when it dies, it costs a lot, and it's gonna die. It's like the lifetime of a camera in a fire lab is not particularly long

Beth Weckman 16:36

No, we've come a long way since, uh, my early days when we were putting real video cameras into divers' cases to try to keep them alive in, in fires.

Wojciech Węgrzyński 16:46

I think a, a lot of people like tend to start with like really nice GoPro. I have one at my desk, but I'm not using this for fire experiments anymore. that, that, that's the starting point, and once you learn the, lifetime of those, it's, it, it goes, it goes slower and slower.

Infrared Imaging And Emissivity Pitfalls

Wojciech Węgrzyński 17:02

Um, how about infrared imaging? Because that's something we also have access to, for very long time, but I, I feel like when I joined the lab, my first infrared camera was really huge. It was like a beamer size. It was clumsy. Now the camera is like little. You can literally have a FLIR add, uh, uh, add on to your cellphone.

Beth Weckman 17:23

phone. That's

Wojciech Węgrzyński 17:24

how small they are. So, so what's the value of those as an, as a measurement technique in, in, in fires?

Beth Weckman 17:30

Well, those are absolutely critical as well because they give you the distribution of the thermal energy at worst temperature if you can calibrate them against a known source and are confident that your calibration coefficient for the emissivity of that source is, somewhat accurate throughout the life of the fire. but in general, they'll give you an excellent complementary map to a visual picture how the, how the heat is distributed or the thermal, thermal energy is distributed throughout the fire environment, whatever it is that you're looking at. can also use them to look at in-depth, heat transfer into objects, or you can put them on the cold side, an unexposed side of an object and see how long it takes for that to reach some threshold value of temperature. so again, very handy depending on the type of measurement and, and the situation that you're looking at.

Wojciech Węgrzyński 18:28

But if left uncalibrated, if left without, in-depth knowledge about the emis- emissivity, potentially misleading. I, I find that a challenge

Beth Weckman 18:38

Correct. That's absolutely right, and a lot of people don't take the time to properly calibrate their infrared cameras for especially changing emissivity through the course of a fire.

Wojciech Węgrzyński 18:52

Mm-hmm

Beth Weckman 18:52

So one process that we've used if we're looking at surface temperature, so not gas temperature, but the surface, a surface temperature, is to potentially use a, paint that we know the emissivity of. We know that emissivity doesn't change as, as it heats until such point as the paint may totally fail.

Wojciech Węgrzyński 19:14

Mm-hmm

Beth Weckman 19:14

and then that, gives a higher level of certainty of what you're looking at in terms of the surface temperature of the item that you're trying to measure

Wojciech Węgrzyński 19:23

W- w- what kind of paint is it?

Beth Weckman 19:24

it's Pyromark black paint, so

Wojciech Węgrzyński 19:26

Okay.

Beth Weckman 19:27

it's a calibrated paint

Wojciech Węgrzyński 19:29

okay. So you're...

Beth Weckman 19:30

given emissivity. You can also measure the emissivity using a black body radiation source, right? Some people do that and they then look at, they expose a surface to different levels of temperature, different levels of heating, and recalculate an emissivity under each condition. it again depends upon level of detail or what level of accuracy of temperature you're looking for. If you're looking for changes in your parameters, then highly detailed calibration may not be as crucial in some instances, although you do have to be a bit careful 'cause with temperature things go as the fourth power if you're looking at radiation. so you can get yourself into trouble

Wojciech Węgrzyński 20:14

I, I mean, it's not that, other techniques are free of that because if you use plate thermometers, there's, there's also an issue of emissivity that changes and

Beth Weckman 20:22

Correct

Wojciech Węgrzyński 20:23

you need to use an old one that was already pre-burned, et cetera. I found, uh, as an amateur hack, you know, I, I found a black paint you can use for, chimney doors.

Beth Weckman 20:33

Mm-hmm.

Wojciech Węgrzyński 20:33

Like, there, there's a very black matte paint that you use for chimneys. It, it at least doesn't change the color in very high temperatures. I cannot, like, guarantee it doesn't change emissivity at all, but it, it feels like way more stable than just not having anything. So a good-- That,

Beth Weckman 20:49

Yeah

Wojciech Węgrzyński 20:50

still better than anything. Um, what about-- I mean, there, there's, uh, there's not everything in, in the, world of, optical, uh, diagnostics, based on visualization.

Schlieren Imaging And Measurement Geometry

Wojciech Węgrzyński 20:59

There are also techniques like, uh, Schlieren, uh, measurements. Can you, can you tell a little bit more on, on that?

Beth Weckman 21:06

So in Schlieren measurements, you're looking at the-- light refraction due to the density or temperature gradients that are naturally occurring in a fire. again, a complementary technique to say flow visualization, where if you have strong enough differences in temperature, say between your fire and your ambient air, you can mark the edges, if you will, of the high temperature zones. where it also comes into play is if you're interested in where combustion is taking place on a global scale rather rather than a detailed, reaction type chemistry-based scale. You can look at, okay, where are my highest temperature zones? Does it make sense that those would align with my combustion within

Wojciech Węgrzyński 21:50

嗯。

Beth Weckman 21:50

scenario? and back out again, back out, information that allows you to better interpret what it is that you're, you may be looking at

Wojciech Węgrzyński 21:59

Though this is not necessarily correct assumption which we will reach at the laser induced fluorescence in a few seconds, I

Beth Weckman 22:05

Correct.

Wojciech Węgrzyński 22:07

We're, we're getting there, we're getting there. But I have one more question to ask ab- about those measurements because you also mentioned the types of measurements. You mentioned planar, line of sight, uh, tomographic. Could you put some, you know, comments on, on, on what does each of those mean in, in, in relationship?

Beth Weckman 22:24

So basically we-- let's start with a point measurement.

Wojciech Węgrzyński 22:28

Yeah

Beth Weckman 22:28

you think of your thermocouple, the bead of the thermocouple is where the temperature is measured. That's a given point, in space. And then if you look at how the temperature at that point changes with time, that would be the spatial resolution of your, thermocouple or relate to the spatial resolution of the thermocouple. If we go from a point and want to make measurement across a plane, then we generally have to look at, generating some kind of a thin sheet, usually of light in the case of optical diagnostics, expand that sheet into the size of plane that we want to do our diagnostics over, and that would be what we would call a planar measurement. If we're looking at a line of sight technique, what that means is that you, you're passing a beam usually, again, in optical measurements, passing a beam through a length in your fire environment. So there's, the path of the beam. the measurement that you make is basically integrated then over the path that that beam takes through the scenario. So if something changes along that path, the temperature changes, the chemistry changes, whatever you're trying to measure changes, then essentially you get a smeared value for your output value based upon how long a path you've used within the, within the measurement volume

Wojciech Węgrzyński 23:56

And, uh, what about the tomographic? How does that work? What does it mean?

Beth Weckman 24:00

In the case of tomographic, what you're typically doing is looking at multiple planes and then reconstructing it is that you saw in a spatial sense. So it's similar to what you described with the videos and reconstructing the videos in

Wojciech Węgrzyński 24:16

Okay

Beth Weckman 24:16

but tomographic techniques typically are done in space. And

Wojciech Węgrzyński 24:20

All right

Beth Weckman 24:21

make multiple measurements, usually across different planes, and then try to reconstruct the three-dimensional, field that you were actually looking at. So there's a lot of math and potential assumptions involved in a process to that level

Wojciech Węgrzyński 24:37

But you can get the three-dimensionality of the phenomena once you do it correctly.

Beth Weckman 24:41

Correct

Wojciech Węgrzyński 24:42

Uh, uh, but when I'm shooting a picture with a camera, it's kind of a two-dimensional plane, but I cannot guarantee everything is in one plane because, like, obviously stuff is gonna be in different, uh, levels. So there's also something you, you have to take, uh, into account

Beth Weckman 24:56

And that's very true with smoke movement because you often get smoke right near the plane of your lens is obscuring what's happening further back in the field of view of the camera. And so you have to be a bit careful in, in interpreting what you're looking at to ensure that you at least think about the potential of something like that happening

Gas Chemistry Measurements With Light

Wojciech Węgrzyński 25:19

Well, luckily there's, PIV techniques which we're gonna talk at the end. Let's move to, uh, to gas species concentration and temperatures. Okay, I shoot the pictures of my fires, that's great already, a lot of information. I can trace the movement. I can perhaps, you know, cast a shadow and see, uh, the differences in, in refraction. Uh, maybe be able to see a little bit more of the structure of the, of the fires. But, how do I know what's actually happening within a fire with non-intrusive diagnostica?

Beth Weckman 25:52

So the non-intrusive diagnostics are meant to make relatively detailed measurements of the chemistry and physical processes that are going on in the fire. So that can be charted using temperature, that could be charted using the chemical composition or the distribution of a particular marker chemical as we call them. Um, it might be a flame zone marker like OH, which I realize is coming up when we talk about

Wojciech Węgrzyński 26:20

Yeah

Beth Weckman 26:20

laser-induced fluorescence, or it could be CO, which would be one of the toxic gases, HCN, another of the toxic gases. depending upon the purpose of your experiment, and I spent some time in my plenary lecture indicating that you have to match the diagnostics to the objective of what it is you're trying to measure, then there are a, spectrum of diagnostics that allow you to access the chemistry and/or temperature of the gases that you're looking at

Wojciech Węgrzyński 26:50

But just shooting a picture of, of a fire, this does not yet allow you to, to create this spectral,

Beth Weckman 26:57

No.

Wojciech Węgrzyński 26:58

yeah

Beth Weckman 26:59

within that picture, you have to pick a point of interest, and that may be your fire plume, it may be your combustion zone,

Wojciech Węgrzyński 27:06

Hmm

Beth Weckman 27:06

may be somewhere further afield that something is happening in, and you then tune your diagnostic method to look at that. If you're shooting planes, you have larger areas that you can take measurements across. and so if we use a plane of laser light, for instance, and use a camera, a high resolution camera image that plane onto, then it's the pixel resolution, but we can map in space what's, what's actually happening

Wojciech Węgrzyński 27:38

W- what kind of physical phenomena allow us to investigate those chemical substances within the plane through those optical measurements?

Beth Weckman 27:48

So typically we're looking at a molecular phenomena, so it's the interaction of the light, whatever wavelength of laser light we have, with a particular molecule that we select. And by shining at a certain frequency into our field, we match the frequency of the light to what's called a molecular transition of the molecule. So if we step back a piece and think of molecules vibrating and rotating, as we probably learned in high school chemistry, then what you're doing with your laser diagnostics is you're trying to tune your laser frequency to one of the vibrational or rotational frequencies of that particular molecule and excite it so that you can then look at how does the molecule respond the interaction with that particular frequency of light. From that, you can back out using quantum physics and all kinds of other things, you can back out temperatures or concentrations

Wojciech Węgrzyński 28:50

I, I've learned you can kind of do it in two ways. Like, you can either shine a, a range of, of wavelengths and then, uh, use something like Fourier transform infrared spectroscopy to, like, figure out which, frequencies are eaten by the particles in, in your gas and, uh, are missing and how much is missing. And based on, like, kind of fingerprint of each of the particles, you can say, "Uh-huh, in this smoke, there's probably a lot of this substance, a lot of this substance, and we don't see a fingerprint of this substance in the spectrum, so it's likely not there." So that's one thing where you have a lot of different, species in your gas, and you basically excite them all and just see what's the outcome. And the other way where you, you basically know, "Ah, I want to look at a, a particular radical like a OH radical," so I have to pick very narrow source and then a very narrow filter that just looks at this kind of frequency, and then out of-- everything else is gonna disappear and I'm just gonna see that. Do I, do I got it right?

Beth Weckman 29:58

Yes. So there's a bit more than that even.

Wojciech Węgrzyński 30:00

I can imagine.

Beth Weckman 30:01

the first technique you described sounded, uh, is probably an absorption technique where we shine a broad band of light into a molecular soup, and then we look at what lines of that light were observed, which ones weren't, and depending on the, you said, rightly said, the molecular fingerprint of our soup, then we can back out what was in the soup.

Wojciech Węgrzyński 30:27

Uh, y- maybe, maybe, uh, so we can give people some kind of, like, idea where this is used. So wh- wh- where would this be used in fire science, like, every day, let's say?

Beth Weckman 30:36

in measurements of, basically emissions from fires.

Wojciech Węgrzyński 30:41

Yeah

Beth Weckman 30:42

whether you're talking about wildfire emissions or whether you're talking about looking at the heating of a material and what pyrolysis gases are given off by that material or potentially what toxic gases would be given off if that material was burned, then you get into the techniques like FTIR, Fourier-transform infrared spectroscopy. what that is, is it's an infrared light beam that's absorbed, that's sent through your gases, and depending upon which lines are absorbed and which are not absorbed, then you back out what was actually the composition of those

Wojciech Węgrzyński 31:18

W- I, I, I've learned in our lab that you can couple it with a cone, you can couple it with like a, a Purser tube furnace, et cetera, to, to really have a quick assessment of, of the gases. So very, very useful technique, and I, I think a lot of people are already using that just as, you know, another device you put directly on your train of, of, of devices in, in experiments.

Chemiluminescence To Find Flame Zones

Wojciech Węgrzyński 31:41

Uh, what about those emission, uh, techniques?

Beth Weckman 31:43

So then the emission techniques are a bit more difficult. In that instance, what you're looking at is, you're looking for a specific wavelength, so you're trying to pick up... A, a typical one is chemiluminescence

Wojciech Węgrzyński 31:57

Mm-hmm.

Beth Weckman 31:57

of a molecule. Typical molecule might be excited, um, CH, which is a marker of where your combustion zones are. If you think of hydrocarbon fuels, you have H and you have C. As those fuels break up into little bits, you end up generating CH that has very strong emission lines at temperatures and in situa- combustion situations. And so what we do is we tune our optics, if you will, to look at that wavelength specifically, and then by marking where the highest from that wavelength is in our field of view, whatever we're looking at, then we say, "Okay, that's where our flame zones actually are situated." So you can use that for things like looking at flame spread phenomena over surfaces, for instance, because you can then track where the flame is moving relative to where you might have a heating and not so much, of that particular molecule produced or produced at a different rate

Wojciech Węgrzyński 33:02

I just mentioned the the FTIR, that it, it can be a part of a cone. For this, is not a simple diagnostic that you can take with you to a field experiment and do, or, or can you?

Beth Weckman 33:13

No, in this instance, what you would be doing is setting up what we call a canonical experiment, most likely somewhere in a lab with controlled conditions where you've defined that I want to look at flame spread processes over a solid surface, for instance. Then you would set up your diagnostic system in order to be aligned and tuned to looking at certain regions within your, experiment, and from there interpret the data that you obtained, accordingly. So chemiluminescence can be done in a fashion where you get more than a single point at a time, so you can chart actually areas of, of interest within a, a flame zone as well.

Wojciech Węgrzyński 34:01

But, the true, like, benefit of that is that with this, if you pick the correct radical that you're looking for, you take a picture of a flame and suddenly you remove all the light, all the heat from the image, and you only see-- It shines only where the reactions are, so really where the chemistry happens. So y-

Beth Weckman 34:20

That's right

Wojciech Węgrzyński 34:21

yeah, so y- you see exactly like interior body of flame, like in, in detail that, that's un- unbelievable with any other method

Beth Weckman 34:30

That's right, and, and that's effect- that's usually what it's used for, right? Is to highlight where is the burning, where's the combustion actually taking place. And so even in a fairly complex fire-related situation, you can say, "Okay, combustion is taking place here, but w- I don't see as much over here." And so then you back out to your experiment and say, "Why was that the instance?" So if you combine a technique like that, say, with looking at suppression, fire suppression, you can actually see how a suppression droplet, a water might interact with a flame in order to understand, okay, how is this actually putting the flame out? And if I use a field of water droplets, then I should see how is that distributed, as it interacts with a, with a fire situation. So lot of these techniques start their life, if you will, in the, in the fire science applications with these canonical or controlled laboratory experiments. But that's not to say they can't be transported to full-scale fires.

Wojciech Węgrzyński 35:41

W-

Beth Weckman 35:41

there were a number of examples in my plenary as well of very, very-- of them being applied in very, very large-scale situations, and it's, again, a case of, experimental design, how successful or not that might be.

Wojciech Węgrzyński 35:59

I'm, I'm also, uh, already talking with, Dr. Gupta about his work in this field, also related to his previous work at the University of Sydney with, uh, with what you've just described. So, uh, I, I have a feeling there's gonna be a very long and in-depth episode on water mist, quenching, flames in the non- non such a far future in the Fire Science Show. So I hope people are looking up for that. Um, but there are more. The, the chemiluminescence, that's just one. Uh, you also mentioned fluorescence and phosphorescence methods.

LIF Phosphorescence Raman And CARS

Wojciech Węgrzyński 36:31

how does that work?

Beth Weckman 36:32

So laser-induced fluorescence is where you're essentially still looking at an emission characteristic, but in this case, you're exciting it using a laser beam.

Wojciech Węgrzyński 36:41

Mm-hmm.

Beth Weckman 36:41

So you now need the laser beam as a source, and you tune that laser beam to the frequency that you need to excite a molecule, often applied in fires to the OH radical, which is hugely again, in combustion, in hydrocarbon combustion situations. And you look at the emissions from that,

Wojciech Węgrzyński 37:05

Okay.

Beth Weckman 37:06

the OH, s- and again, mark, typically mark flame fronts

Wojciech Węgrzyński 37:10

So, so in the previous one, you would just observe the effects of the, of the flame with a specific filter on your camera,

Beth Weckman 37:18

Correct

Wojciech Węgrzyński 37:19

and here you add a source that additionally excites those molecules to make it more stand out, I guess, from the, from the noise

Beth Weckman 37:26

Yes, and also look at, potentially different aspects of the chemistry depending upon which, which radical you actually look for, right? you can see, different things, different happening, related to the combustion chemistry or the fire chemistry, depending upon exactly what technique you choose

Wojciech Węgrzyński 37:48

And phosphorescence, I perhaps heard, uh, some time ago that you can measure temperatures with that, which, which was very interesting to me

Beth Weckman 37:56

Yeah. Again, phosphorescence is another in a similar family where you actually lay a, um, a coating on a surface, a fine coating on a surface, and then by looking at the interaction of that coating with, again, with light, tuned for the process that the coating requires, you can look at a distribution of, of temperature, say, across the entire surface. So they all, they all work together in one sense, but they're independent techniques as well

Wojciech Węgrzyński 38:28

in this group, the final ones are, uh, scattering techniques, Raman and CIRS, RS. So, so w-w-what do those do?

Beth Weckman 38:37

So CARS and Raman techniques again require a laser excitation. In this

Wojciech Węgrzyński 38:42

A lot of lasers.

Beth Weckman 38:43

yeah. Hey, fun with lasers.

Wojciech Węgrzyński 38:45

Yeah, I mean, that's like, that sounds like a fun job. Like, fire was already a fun job and you're like putting so many lasers into it.

Beth Weckman 38:53

But on that note, as we discussed previously, the technologies of using a laser to excite molecules are common across many of these techniques. So once you've got into learning it for one of the techniques, then applying it to a different technique also becomes incrementally easier, right?

Wojciech Węgrzyński 39:14

Yeah, yeah

Beth Weckman 39:15

so in CARS and Raman, what you're looking at is essentially exciting the molecular vibrations of the molecule. So rather than looking at an emission spectra, you're looking instead at actually tuning a laser to excite a molecule, and by, again, looking at the intensity of the signal from that molecule. In this instance, in CARS and Raman, you can measure both temperature and concentration. And so you can, um, typically get good signals, but the difficulty in application is also higher and much more difficult, generally point measurements, because you need a very intense laser beam for probing a species where there's not a high concentration of that species because your output signal depends directly on the concentration of the material that you're trying to look at

Wojciech Węgrzyński 40:11

And I assume in this case we're also talking about canonical problems brought to a laboratory in a very sophisticated setup

Beth Weckman 40:18

Well, CARS has been applied in one-meter diameter fires.

Wojciech Węgrzyński 40:22

One meter diameter fires. Okay, that's, that, that counts. That, that counts like, uh

Beth Weckman 40:28

um, not without, not without technical challenges, but certainly, you know, any of the... I, I maintain I'm an optimist, I guess. Any of the techniques with appropriate design of the probe systems, and use of optical fibers and the lasers, the diode lasers, and the new types of lasers that are now on the market, any of these techniques can be applied in larger scale situations. It's a question of, designing the system such that it works in that situation

Wojciech Węgrzyński 41:01

I would say the B- budget and courage. That's, that's

Beth Weckman 41:07

Well, you know, budgets for these techniques used to be millions.

Wojciech Węgrzyński 41:11

Yeah

Beth Weckman 41:12

now with cheaper lasers, cheaper high-powered lasers, certainly that-- budget questions have reduced significantly over what they used to be, even for good cameras, right? If we think of camera technology and how it's changed. Um, in the situations where you can use say, new CCD or CMOS camera technology, you can also get extremely high speeds, which are helpful when you're looking at fires, which tend to, be driven by very dynamic changes at times. so sometimes it's worth it. I-in terms of the effort, that one's more difficult

Wojciech Węgrzyński 41:50

Yeah.

Beth Weckman 41:50

will

Wojciech Węgrzyński 41:51

A-a-a-and courage because like it's not--

Beth Weckman 41:54

yeah.

Wojciech Węgrzyński 41:54

we just, we just talked about how easily the cameras die in the fires, so you perhaps don't want to put your, uh, most expensive, uh, laser, uh, diagnostics in a place where it's exposed. do, do you think LED diodes will, will, uh, eventually be useful in that types of diagnostics where you could just, you know, buy a simple-- Like I can build a, like the light extinction meter for five bucks today, like literally. Uh, we're gonna just talk about them in a second, but I, I can do that. I can buy a cheap diode, I can buy a cheap photodiode, that's it

Beth Weckman 42:26

So the diode lasers are maybe tens of thousands,

Wojciech Węgrzyński 42:30

Hmm?

Beth Weckman 42:31

you know, and, and they can certainly be used in things like tunable diode laser absorption spectroscopy, right? TDLAS, which was, uh, in line with FTIR, similar types of techniques. So again, you can, use these technologies for multiple purposes. When you get into, the molecule-specific optical methods that require a certain concentration to achieve the resolution you need, then it becomes more difficult to, to get the cost down because you need significant power in your input beam in order to generate a signal to begin with

Wojciech Węgrzyński 43:11

Yeah.

Soot Diagnostics Beyond Light Extinction

Wojciech Węgrzyński 43:12

Okay, let's move to soot and particulates in fire. Why, why did you put it up as a separate section? Is it because, uh, the, uh, combustion people hate soot that much, uh, in their canonical fires? Uh, what, what's the reason?

Beth Weckman 43:24

No, it was actually because when I started to sort these, I was, I was trying to think of how do I sort the different methodologies, and I had a series of gas-based methodologies above that. So soot being a particulate, I

Wojciech Węgrzyński 43:39

Okay. Okay, that's it.

Beth Weckman 43:41

soot in a category by itself, even though it's again, um, laser-induced incandescence is again a laser that's generating a process, an interaction with the soot particles in order to measure the temperature, right? So it's not a, it's not a totally independent or different technique from the ones that are used in gases, but our light is now interacting with the soot particles in order to allow us to, measure soot particle fraction or s-- uh, or temperature

Wojciech Węgrzyński 44:13

S- soot is very interesting. I, I, I like, playing with it, uh, you know, for, for the-- with the remit of, of studying visibility in smoke. it's also a well-established technique in, in fire in general because we tend to measure light extinction coefficient of smokes, which we then, you know, kind of associate with specific amount of soot being present there. And, that's quite a shortcut, but that's a, a very well-established measurement technique. Shine the light, measure how much is gone, drop a logarithm on that, you, you're good to go. how much more, how much more do you learn by introducing that laser-induced incandescence or, or other like more advanced, uh, tools to the same problem?

Beth Weckman 44:57

So it would be used in slightly different applications.

Wojciech Węgrzyński 45:01

Okay

Beth Weckman 45:02

So if you're trying to figure out, let's say in a wildfire,

Wojciech Węgrzyński 45:06

Mm-hmm

Beth Weckman 45:06

you're trying to figure out what are the local particulate, what's the nature of the local particulate versus the aged particulate that our atmospheric lidar systems are looking at, then you might do measurements that are close to the source of some kind of an experiment where wild biomass fuels were burning and look at what's the ear- it's often called the early soot formation

Wojciech Węgrzyński 45:30

う ん。

Beth Weckman 45:32

which allow you again to, by, by looking at a slightly higher level of detail, it allows you to get a sense of, okay, how is the soot forming and aging time in these kinds of fires, and what does that tell us about if I have a slight variation on this theme, what might I expect in, in a slightly different fire situation? The other place where particulates are becoming more prevalent is in some of the newer technologies, right? So if we look at batteries, for instance, there there's a particulate, flow, effluent of particulates. You can use some of the diagnostics to examine what do those look like? How are they coming out? What are the, what are their temperatures? What might be the composition of them, for instance?

Wojciech Węgrzyński 46:23

I find this v- very interesting and especially, you know, this, uh, time resolved manner because with the light extinction, I can tell you the light extinction at this point of time, but it, like it-- I must make up at least two other numbers to make, uh, sense out of this number, which I have no, like, real, you know, way to, to verify. But if I want to, like, see how it evolves over the time, I have to resort to probing, and probing soot is not that easy. Uh, you have to capture it, but you have to know when you captured it, how. The way how you capture it is a l- can already break it in a way.

Beth Weckman 47:03

Mm-hmm

Wojciech Węgrzyński 47:04

so, so it's a real-- Like even if I have access to intrusive diagnostics for that, which we have just done with the colleagues from, uh, from Jülich, uh, uh, which was amazing that they were able to do that. That was a huge, huge effort to do that

Beth Weckman 47:19

Well, that's right. And the other thing is that your extinction measurements are a significant line of sight,

Wojciech Węgrzyński 47:26

Hmm?

Beth Weckman 47:26

right? I mean, they're, they're a long path through the fire, so you're, you're getting a global-- a very global measure of what that soot field actually looks like relative to something that's slightly more resolved. Um, or if you use LAI in a planar sense, you can get maps essentially of the distribution of, soot in different planes throughout the whole field

Wojciech Węgrzyński 47:53

I mean, if I am worried about the visibility in smoke, which also is kind of a line of sight problem, that's perhaps not bad. But even in this field, even in this type of measurements, we already have a lot of development with the LED, uh, smoke, uh, uh, techniques, LEDS, uh,

Beth Weckman 48:11

Letzte, ja

Wojciech Węgrzyński 48:12

yeah, it's, it's awesome. Like, we, we've built one. It, it's really, really cool to be able to, to, to finally have something like kind- more than one-dimensional, more than one line of sight that allows, that allows you to do a lot of interesting things.

PIV For Velocities In Fire Flows

Wojciech Węgrzyński 48:24

Um, finally, we reach the flows, and, uh, for me that, you know, the first time I've heard about PIV, I immediately felt in love with the idea of, of doing, optical measurements in a slice. Like slice your plume with a laser and measure what's inside. That, that felt like a brilliant idea. And what followed was 15 years of not being able, to do it because no one allows me, to put my flame near enough of that beautiful, uh, experimental device. So I'm in a love-hate relationship. I would love to do it, but no one allows me to, to put PIV close enough to my fires

Beth Weckman 49:07

Oh, wow. Okay. 'Cause we did it in one meter diameter

Wojciech Węgrzyński 49:10

Oh, well, that's a small fire. No, just kidding. That's, that's awesome. That's awesome. I, I was never able to, to reach that point. It's not that I've tried very, you know, hard on that. It j- j- just was a dream that was always in- inachievable for me

Beth Weckman 49:24

So ironically, you were asking me about why I separated out soot. Well, if we look at PIV again, it's a pa- particle scattering

Wojciech Węgrzyński 49:33

Yeah

Beth Weckman 49:34

right? Um, so you're relying on those particles to actually follow the flow field, and that's sometimes the largest challenge if you're looking at the fire itself as opposed to the plume of the fire. because in the combusting regions, the particles tend to migrate to the hottest temperature zones, thermophoresis, just like you have when you're trying to sample soot with a,

Wojciech Węgrzyński 49:58

Mm-hmm.

Beth Weckman 49:59

a physical probe. And so i- if particle image velocimetry was typically based initially upon uniformly seeded flow and that those particles were nicely following the flow, um, and keeping their uniform seeding throughout the whole field, um, there's since been, uh, improvements in the processing technology that allow you to back out the velocities regardless of the uniformity of the seeding. um, but there are still challenges in applying a technique like that in fire. Now, when you get it working, it opens up huge possibilities for looking at the flows through doorways, through openings, for instance. That's one of the, really interesting areas where I've seen it used, as well as, uh, again, interactions between, say, sprays and fires or particles, um, coming from fires and where they may be flowing to after they get ejected from a battery, for instance

Wojciech Węgrzyński 51:02

Yeah, so, so, so in this case, w- what you're doing is you have to put a lot of stuff like particles in the air basically, then you put a sheet of laser light through that space, and then you observe how those particles shine in that sheet of light with you being able to tell each particle independently and track them in space basically

Beth Weckman 51:28

you basically have a quickly gated set of ca- camera that you take two images in quick, very quick succession, and that freezes the particles. But from image to image, you see movement of the particles, and from that you can back out the velocities by the distance the particle has moved over the time between your images. So you have to get the timing as well as the spatial resolution of your field of view correct in order to be able to track the individual particles

Wojciech Węgrzyński 52:01

How, how little are the particles? Like flour little? Like, uh, sand? No, they must be sm- smaller than sand

Beth Weckman 52:08

So they're typically, um, the ones that we've used are titanium dioxide or magnesium oxide, so they're very, very, very

Wojciech Węgrzyński 52:16

like dust

Beth Weckman 52:18

type People have done it off the naturally occurring soot. The problem with

Wojciech Węgrzyński 52:24

Oh

Beth Weckman 52:24

tends to agglomerate, so it becomes a little difficult to know what you're looking at. but as long as you aren't looking over long periods of time, you can sometimes get transients by using very high-speed camera Um, so there's different ways you can or modify many of these techniques to away from their theoretically best application, if you will, much as we do with thermocouples or bidirectional probes or any other method, um, in order to allow you to get information about a fire situation

Wojciech Węgrzyński 53:03

And now the real magic when you start coupling them

Beth Weckman 53:05

That's correct. That's where you can start to probe the true physics and chemistry of what's happening. So if we can catch the flow dynamics as well as changes in the chemistry in space over time, then we can begin to really understand what's driving the characteristics of that fire

Coupled Measurements For Model Validation

Wojciech Węgrzyński 53:25

I mean, it's really inspiring to see how far we collectively, uh, not that I've done any of it, we got, uh, in, in, in this. And like Professor Mercy mentioned in his, uh, Emmons lecture, this is not just, you know, knowing what's happening in the flame, this is validation techniques. This is our-- us improving our models, our predictions. This is us, you know, moving beyond, uh, what has been possible 20, 30, 40 years ago,

Beth Weckman 53:55

Absolutely. And, um, if we look at the history of these techniques in the pu-purer combustion or the controlled combustion field versus the fire field, they've been used in large scale combustion processes for some period of time. with that in mind, the transition to use them in the, in the fire sense, is a logical one. And knowing that we need the coupled data to be able to continuously refine our fire models, they're one way that, I mean, again, as I say, I'm the optimist. They're one way that allows us to access the type of detailed information in both space and time that we need for the, fire models we're, we're currently working on

Wojciech Węgrzyński 54:43

when I was a, a little child, I was fascinated by the concept of black hole, you know? And just the concept of that thing existing was blowing my mind. And, uh, I remember I then, I've read, uh, in a, in a book that, uh, yeah, they exist, but we're never gonna be able to see one. Like, we're-- we'll never be able to see how it looks like. N- it's, it's just too far and too small. And, and then, you know, 30 years later, some researchers, uh, turn, uh, Earth into a giant radio telescope, uh, linking, uh, radio telescopes from South Pole with China, with US, transferring data by jumbo jets filled with hard drives, and, and they figure out a way to, to shoot an image of, of a black hole. And, uh, it, it's just amazing how far people can get when, when they are given, you know, uh, chance, ability, they have enough passion and, uh, and cleverness. And, and it's the same thing I seen here. Like, you know, i- if I shoot a picture of a flame, that's, that's beautiful. But y- you can now shoot a picture of reactions happening in the flame a- and, you know, have this resolved, uh, temperature field within your PMMA that's creating the, the pyrolyzed gases in that flame, and at the same time capture the entrainment and flow of air around that with a set of beautiful techniques. It's, it's, it-- I think it's, it's beautiful, uh, this part of science. I, I can imagine w- why you really enjoy this field so much.

Beth Weckman 56:21

Yes, and I mean, it could be very simple, like the

Wojciech Węgrzyński 56:24

Yeah

Beth Weckman 56:24

who thought to use blue light and look at charring

Wojciech Węgrzyński 56:27

That's

Beth Weckman 56:28

through the

Wojciech Węgrzyński 56:29

good

Beth Weckman 56:29

right? That was, that was amazing. or it can be much more difficult, like applying CARS in a, in a large-scale fire situation and having to develop a method by which you can set up, design the probe as well as keep the probe from burning up while you, while you make the measurements. So really, there's lots of different entry points for fire researchers, in the diagnostics space, dependent upon what do you wanna learn, what techniques will apply to your particular situation, and then what can, what can we see with those? It's, it's amazing.

Wojciech Węgrzyński 57:04

I actually mentioned blue light and that reminds me there's a whole episode, uh, with Matt Hoechler from NIST about visualization techniques they were developing from, uh, blue lights to Bob, which is a, a, a underwater camera that we should--

Beth Weckman 57:19

Yeah

Wojciech Węgrzyński 57:19

I love Bob. I built one, but it died very quickly along with my very expensive 360 camera, so that also happens. Um, Beth, is there like one technique that you enjoy the most or you like the most? If you had to pick, w-what's your favorite? What's your like, pet peeve, optical technique that, that if you, if you get to play it, it puts a huge smile on your face?

Beth Weckman 57:44

Oh, wow. That's a, that's a tough question.

Wojciech Węgrzyński 57:46

you, you let go of them

Beth Weckman 57:48

I generally like the field of diagnostics, so I've used, um, a fair number, probably less the absorption type techniques like FTIR than, than some of the others. most challenging would've been the application of planar laser induced fluorescence and PIV in the large helium plumes that are part of the MAC FP, uh, project. but now even, even good photography and image processing and the amount of information you can see from that, continues to blow my mind, if you will, in terms of what we can understand about, about fires and, and the flows

Wojciech Węgrzyński 58:28

it's a beautiful world and we have so many more interesting ways to- Mm-hmm uh, shoot the pictures and probe the world, uh, in a non-intrusive manner, slightly intrusive manner. Um, Beth, thank you, thank you so much for coming to the "Fire Science" show and, uh, and showing the, the listeners, uh, the, the fantastic world of, of optical diagnostics and fire

Favorite Techniques And Future Directions

Beth Weckman 58:48

Oh, you're welcome. My pleasure.

Wojciech Węgrzyński 58:50

And that's it. We've went through a whole range of techniques from simple imaging through infrared thermal cameras, uh, methods based on emission and scattering of light all the way through PIVs and, you know, advanced coupling of those methods. So the array of tools that are in the hands of researchers and, and engineers today is unbelievable. Of course, they come with their own challenges, with their own complexities. Some are as easy as setting up a camera and pointing it towards the dir-direction from which you want to record up to very complicated sets where you need to have a very strong coherent light sources that are pointing exactly in a little tiny fraction of space where you're looking for your chemistry to happen. Uh, they of course come at different costs, at different challenges, different entry-level points. But as, again, I'm gonna say that as Beth succinctly pointed out, uh, once you start playing with them, they're very much iterations of similar techniques, uh, some more advanced, some less advanced. But they usually require you to provide a very strong lighting source which you control very precisely and just image that with a camera that you also control very precisely. You can learn that. I've actually learned a lot of that by doing astrophotography and, and shooting images of sky because, uh, it's, it's very similar in some of the techniques where you have to, uh, chase specific wavelengths to take your pictures. So I resonate very well with what Beth is saying and, uh, I think the setups are quite manageable. Anyway, that would be it. Uh, I think it's a good "Fire Fundamentals" episode that gives you an overview of, of what can be done and what can be measured remotely in fire with those advanced methods. Uh, more in-depth episodes will come and, um, I really need to invite Vinnie to talk about the magical water mist stuff they've done because it's, it's really fascinating how they've looked into the phenomena of extinction at the micro scale and other optical techniques. I know there's ERC grant in Spain on optical techniques. David Morrissette has also been doing great things on optical diagnostics. So there's, uh, plenty to talk about those things in the future "Fire Science" episodes. Now I feel you are prepared for those to come with this, uh, you know, overview, of the

Final Wrap And Goodbye

Wojciech Węgrzyński 1:01:13

methods. So thanks for being here with me today, and I hope to see you in the "Fire Science" show next Wednesday. Cheers. Bye.