Aug. 27, 2025

216 - What do we measure and how? with David Morrisset

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What happens when we stick a thermocouple into a fire? The answer is surprisingly complex and has profound implications for fire safety engineering. In this deep-dive episode, Dr. David Morrisset from Queensland University joins Wojciech to unravel the science of fire measurements that underpins every experiment, test report, and dataset in our field.

The conversation reveals a critical truth often overlooked by practitioners: measurements don't capture reality directly - they capture the interaction between our instruments and fire phenomena. When a thermocouple reports a temperature, it's actually measuring its own thermal equilibrium, not necessarily the gas temperature we assume it represents. This distinction becomes crucial when using experimental data to validate models or make engineering decisions.

The hosts explore various measurement techniques - from temperature and flow measurements to heat flux gauges and oxygen consumption calorimetry - detailing their underlying principles, practical challenges, and hidden assumptions. David shares fascinating insights from his research, including innovative approaches to extracting meaningful data from noisy mass loss measurements and using high-resolution temperature fields to calculate heat fluxes without traditional gauges.

This episode offers essential context for anyone who reads research papers, interprets test reports, or uses experimental data in their practice. By understanding the nuances of how we measure fire phenomena, engineers can better evaluate the quality and applicability of experimental results, recognise their limitations, and ultimately make more informed safety decisions. Whether you're conducting experiments or applying their results, this conversation will transform how you think about the data that drives our field.

I've received a bunch of papers from David to share with you, here we go:

Data smoothing - particularly around things like the MLR. This is covered in many papers, and you can start with: https://linkinghub.elsevier.com/retrieve/pii/S0379711222000893
The "blue light method" was discussed in the podcast with Matt Hoehler from NIST - I came up with the same kind of effect but with PMMA (using black light instead of blue light) - https://doi.org/10.1016/j.firesaf.2025.104425
We did some work on characterising the thermal boundary layer generated by gas-fired radiant panels. https://doi.org/10.1016/j.firesaf.2023.104013
In the flame spread work, I did use temperature data to approximate the heat flux acting at the surface https://doi.org/10.1016/j.firesaf.2023.104048

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The Fire Science Show is produced by the Fire Science Media in collaboration with OFR Consultants. Thank you to the podcast sponsor for their continuous support towards our mission.

00:00 - Introduction to Fire Measurements

09:25 - Understanding Temperature Measurements

21:32 - Pressure Probes and Flow Measurements

29:35 - Heat Flux Gauges and Challenges

39:01 - Heat Release Rate Measurements

48:40 - Mass Loss Rate Measurement

52:00 - Data Processing and Smoothing Techniques

59:54 - Advanced Measurement Methods

WEBVTT

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Hello everybody, welcome to the Fire Science Show.

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So you're a fire safety engineer, you're working on a project, you have to solve a specific fire safety case, a problem.

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You need to find a solution, you need to use some tools modeling.

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What do you put in those models?

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Usually, the golden standard would be to find an experiment that someone has done in a setting that's relevant to the case that you're studying and use the data from that experiment in your modeling, in your research, directly.

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Because, hey, experiments are the the truth, right?

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So, yeah, they.

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They are the manifestation of laws of physics.

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The laws of physics in the real world are not optional like in your simulation.

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You don't have to turn them on for them to work.

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But to have a really good value out of an experiment, one thing needs to be done correct, and that is the measurements.

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And measurements boy, this is not a simple topic.

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While it looks easy, you just stick a thermocouple into a fire, there is surprisingly, surprisingly a lot of things that have to happen.

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Well, for that measurement to provide you with the information that you are seeking and this is the easiest one there will be more complex ones that we will be talking about in this episode because, as you can imagine, this episode is all about what do we measure in fires and how we do that.

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I've invited a guest, dr David Morissett.

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David has already been in the podcast.

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We had a Far From the Moles episode together.

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Young researcher from Queensland University, a brilliant mind with a good upcoming career in this space and also someone who's very passionate about fire experiments and loves to talk about it, which you will clearly see.

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And this episode will give you a bit of guidance on how to interpret the data that you see in research papers, in journal papers, in test reports that you are supposed to use in your engineering.

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We'll talk about temperature, we'll talk about flow, we'll talk about heat fluxes, we'll talk about heat release rate, mass loss rate all the useful stuff that you will find in various data sources that guide your decisions.

00:02:12.224 --> 00:02:26.883
So I actually think this is a very important episode because measurements are things that not that many of us are carrying, but every single one of us is using in their engineering practice, and we need to understand how do they work.

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That would be it for the introduction.

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The episode is fun.

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I promise that.

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Stay with us.

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Let's spin the intro and jump into the episode.

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Welcome to the Firesize Show.

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My name is Wojciech Wegrzyński and I will be your host.

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The Firesize Show is into its third year of continued support from its sponsor, ofar Consultants, who are an independent, multi-award-winning fire engineering consultancy with a reputation for delivering innovative, safety-driven solutions.

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As the UK-leading independent fire risk consultancy, ofar's globally established team have developed a reputation for preeminent fire engineering expertise, with colleagues working across the world to help protect people, property and the plant.

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If you're keen to find out more or join OFR Consultants during this exciting period of growth, visit their website at ofrconsultantscom.

00:03:51.949 --> 00:03:54.385
And now back to the episode.

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Hello everybody, I am joined today by Dr David Morrisset from Queenston University.

00:03:59.900 --> 00:04:03.867
Hey, david, good to have you back in the podcast hey, wojciech, thanks for having me back, appreciate it.

00:04:04.661 --> 00:04:05.866
Yeah, I appreciate it.

00:04:06.020 --> 00:04:19.769
I always love to talk with a fellow FAR geek about FHIR geeky stuff, and today a topic that you have actually proposed to cover in the podcast is stuff that we measure in FAR experiments and how do we measure them?

00:04:20.279 --> 00:04:46.944
Why, as a practitioner and someone who's like always misses a thermocouple location or always has trouble with some kind of data logger and converting files and messing with all this stuff, it brings me a lot of joy that there are others who consider this a significant scientific problem, are not really exposed that much to the world of measurements and the world of how we actually quantify stuff in our experiments.

00:04:46.944 --> 00:04:49.870
A lot of people are blindly believing in experiments.

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That's my experience.

00:04:51.543 --> 00:04:56.122
A lot of people are taking experimental results and they just believe this is the truth.

00:04:56.122 --> 00:05:06.952
You know the true truth While me, as an experimentalist, I know there's a lot of hardcore work to be done to have a good experiment and measurements are a big part of that.

00:05:06.952 --> 00:05:18.536
So let's start with actually what is the act of measurement and how do you perform such an act in a scientific experiment.

00:05:18.939 --> 00:05:49.127
I mean that's a great question and a great place to start right, Because in FHIR F, fire is a unique field of study where a lot of what we do ends up being experimental, whether that's proper novel experiments trying to understand physics or a lot of complexities in fire phenomena that we reduce to standardized test methods to just actually, instead of trying to assume something about a material or assembly, we actually light it up and see how it performs.

00:05:49.127 --> 00:05:53.942
So all of these kinds of processes include the requirement for measurement.

00:05:53.942 --> 00:06:03.122
So a question that I start to see as a relevant question the more I do experiments is not necessarily how do you make a measurement, but how do you make the right measurement?

00:06:03.122 --> 00:06:18.853
The more time you spend in a fire lab, you see not only is there like a wide range of choices at your disposal to make a measurement, but there's also the more you see experiments, you get a little bit of the context behind what makes a good measurement a good measurement.

00:06:18.853 --> 00:06:26.213
So you'll see, for example, you look at something like, let's say, like temperature is something that we try to measure all the time.

00:06:26.213 --> 00:06:30.803
Now I can take a mercury thermometer, right, and I can measure temperature.

00:06:30.803 --> 00:06:34.329
Right, you can measure the temperature of, say, a beaker of water?

00:06:34.329 --> 00:06:34.810
Absolutely.

00:06:34.810 --> 00:06:42.057
Now, does that mean that I should be sticking a mercury thermometer in the upper layer of a, you know, a smoke layer in a flashed over compartment?

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Right?

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Is that the right measurement to make?

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How do we even interpret that, right?

00:06:50.021 --> 00:07:03.288
But I mean in terms of, uh, yes, there are certain things that we can use to make measurements, uh, but I think it's it's actually the context behind why we use certain instruments that gives us the insight to the true value of a given measurement.

00:07:04.410 --> 00:07:09.096
I think another element is also, measurements can be intrusive, right?

00:07:09.096 --> 00:07:15.708
So if I put a pressure probe to measure flow, right, let's start talking about different things that we might measure.

00:07:15.708 --> 00:07:18.886
For temperature, right, we might use a thermocouple.

00:07:18.886 --> 00:07:23.290
If I want to look at flow fields in a fire experiment, I might use a pressure probe.

00:07:23.290 --> 00:07:28.869
If I want to look at heat fluxes from a flame, I could use a heat flux gauge.

00:07:28.869 --> 00:07:35.264
But all of these things are physical instruments that take up space.

00:07:35.264 --> 00:07:39.932
Most of them are metallic in nature, right, and so they are.

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Naturally.

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If I stick a pressure probe into a duct that is on the same order of magnitude as the pressure probe itself, it's going to interrupt that flow right.

00:07:50.074 --> 00:07:52.242
There's going to be an intrusive nature to that.

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In the same way that if I'm taking a sample and I want to measure the heat flux acting on that sample, if the heat flux gauge that I'm using is physically a large portion of that surface, then that's going to start becoming intrusive and for some of your applications that matters and some of your applications that doesn't matter.

00:08:12.867 --> 00:08:18.310
But I think some of the intricacy of trying to set up an experiment is figuring out.

00:08:18.310 --> 00:08:25.773
How do you balance what we can practically do with what do we do to get the most value out of the experiment?

00:08:26.334 --> 00:08:29.689
I mean, you've opened so many kinds of forms in this opening.

00:08:29.689 --> 00:08:32.403
Perhaps we shouldn't have done this episode, but let's do this.

00:08:32.403 --> 00:08:36.990
I mean yeah uh one experiments versus tests.

00:08:37.030 --> 00:08:48.548
This is very valid and at some point the quality of your measurement becomes truly the measure of the fire properties of assemblies or materials that you're using like.

00:08:48.548 --> 00:08:58.561
Take a plate thermometer measurements that guarantee that you had a standard time temperature relationship in your furnace test when assessing resistance to fire.

00:08:58.561 --> 00:09:17.177
This this is fundamental and actually actually the story of the plate thermometer is exactly the story of reducing the uncertainty of a measurement and making sure that every exposure in a furnace in the world is more or less the same, because they were not at some point of time.

00:09:17.177 --> 00:09:18.826
I think this is beautiful.

00:09:18.826 --> 00:09:26.724
Perhaps we'll go back there, and I also love the question of how they actually match.

00:09:27.285 --> 00:09:32.287
How do you get a perfect experimental setup, measurement setup for your experiment?

00:09:32.287 --> 00:09:48.331
And I really like the school of Guillermo Reyn, because whenever I do experiments with him, he's never crazy about the number of measurements, because he also takes into account the capacity to analyze the outcomes.

00:09:48.331 --> 00:10:01.832
One could say a better experiment is the one that has more measurements, but more measurements means more intrusion the thing that you just said and also means like you're going to spend so much more time processing data.

00:10:01.832 --> 00:10:03.154
So much more time processing data.

00:10:03.154 --> 00:10:13.860
I remember absolutely magnificent the toll building experiment in Edinburgh where they had this three-dimensional array of thermocouples in a large open plant compartment.

00:10:13.860 --> 00:10:15.927
That was like 2,000 thermocouples.

00:10:15.927 --> 00:10:21.129
There were like 30 YouTube videos of them setting up this experiment for a month.

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Absolutely beautiful work.

00:10:23.386 --> 00:10:30.751
But it took them years to publish the first paper because the amount of data, the amount of stuff to process was so insane.

00:10:31.440 --> 00:10:37.942
So yeah, so many things but one thing, that sort of just off the building off some one of those ideas there, right is.

00:10:37.942 --> 00:10:46.462
You mentioned things like the development of plate thermometers and different kinds of methods to measure something right, whether it's temperature, whether it's whatever.

00:10:46.462 --> 00:10:56.263
But I think also, something that I think we lose sight of sometimes is to say okay, well, I'm using this device to measure temperature, therefore the output of this is temperature.

00:10:56.263 --> 00:10:59.600
It is the temperature of my compartment, the temperature of my gas, and so on.

00:10:59.600 --> 00:11:18.268
But we're always making an assumption because let's say, I just take a thermocouple, I take a plate thermometer, I take take a thermocouple, I take a plate thermometer, I take a few thermocouples, I put them in a compartment and I'm measuring the temperature right, even if each of these things are exposed to the same gas temperature at any given time, because there's fluctuations in the compartment and so on.

00:11:18.940 --> 00:11:28.702
Let's say you use a 0.25 millimeter thermocouple bead versus a 1.5 mil thermocouple bead versus, you know, a large plate, and so on.

00:11:28.702 --> 00:11:31.610
All these things are going to measure different outputs.

00:11:31.610 --> 00:11:34.549
That doesn't mean the gas temperature is physically different.

00:11:34.549 --> 00:11:35.615
If they're all you know.

00:11:35.615 --> 00:11:39.995
Let's say, in a perfect scenario all these three devices should be measuring the same gas temperature.

00:11:39.995 --> 00:11:41.461
As a function of time.

00:11:41.461 --> 00:11:42.482
They won't.

00:11:42.482 --> 00:11:48.073
That doesn't mean that, yeah, that's just a consequence of using different technology, right?

00:11:48.073 --> 00:11:55.048
So all of these things have inherent benefits and, I guess, consequences, depending on what you choose to use.

00:11:55.048 --> 00:12:06.168
Now it's up to us, as the engineers, to then interpret that and say are we truly measuring the gas temperature or are we just, we're just measuring the output of this thermocouple?

00:12:06.168 --> 00:12:10.216
How close is that to what we assume is, say, the gas temperature?

00:12:10.740 --> 00:12:12.226
I would rephrase what you've said.

00:12:12.226 --> 00:12:17.706
The thermocouple shows you what the reading is and that's my interpretation.

00:12:17.706 --> 00:12:21.951
It's not necessarily the temperature of the gas wall or whatever else.

00:12:21.951 --> 00:12:28.787
It's just an outcome of a thermal equilibrium at which this device is with the environment that you're measuring.

00:12:28.787 --> 00:12:46.774
So if you understand the heat transfer processes between those devices and the environment that you're measuring, you have a very good chance to understanding what kind of temperature of the medium that this device is exposed to will create this thermal equilibrium.

00:12:46.774 --> 00:12:50.431
On the contrary, you don't really understand those properties.

00:12:50.759 --> 00:13:05.993
You end up with a very rough measurement because, yes, the thermocouple could technically be at the temperature of the gases in your compartment If it was exposed long enough, if it was like very steady temperature, which is very unlikely in fires.

00:13:05.993 --> 00:13:09.269
Fires are turbulent, fires are chaotic in their nature.

00:13:09.269 --> 00:13:15.791
Fires are very complex in three dimensions, so it's very unlikely you will have the same temperature everywhere.

00:13:15.791 --> 00:13:25.870
But at some point those are just minuscule details and noise in a measurement and sometimes they can lead to a severe misinterpretation of the results.

00:13:25.870 --> 00:13:38.321
And that perhaps was one of the causes of the plate thermometer requirements for the furnaces, because those differences if you put a tiny, tiny thermocouple versus a plate thermometer.

00:13:38.321 --> 00:13:41.008
They could have been huge in the furnace.

00:13:41.789 --> 00:13:48.203
But also absolutely, I think, an element of that that's also really important is the context behind.

00:13:48.203 --> 00:13:49.226
What are you interested in?

00:13:49.648 --> 00:13:51.392
If you're interested at the scale of a compartment.

00:13:51.759 --> 00:14:02.642
That's very different than if I'm trying to use some sort of device to measure the temperatures of a flame on the scale of a Bunsen burner right, and so all of a sudden those fluctuations matter, right.

00:14:02.642 --> 00:14:09.673
All those things I think a big part, I guess, in terms of as an engineer or as someone using data.

00:14:09.673 --> 00:14:19.091
I guess one of the biggest things that you learn when you're in a fire lab doing these experiments is everything is highly dependent on what you choose to make that measurement right.

00:14:19.091 --> 00:14:30.847
And I really like what you said about basically a thermocouple isn't if you put it, you stick it in a compartment, it's not actually measuring the gas phase temperature, it's just measuring the temperature of the thermocouple.

00:14:30.847 --> 00:14:41.894
Yeah Right, whatever that might be, and we can maybe get to a good example of that later too in some of my flame spread experiments where we use thermocouples and you got to, is it really the temperature of the solid?

00:14:41.894 --> 00:14:51.769
Probably not right, and so we're making an assumption there, uh, and just being sort of honest with yourself, I think is a important part of that.

00:14:51.789 --> 00:14:52.712
But that's like any, any measurement.

00:14:52.712 --> 00:14:57.225
But perhaps a nice addition to this would be to explain the how the hell does the thermocouple work?

00:14:57.225 --> 00:15:03.184
I'm not sure if everyone understands, uh, that on a high level yeah, yeah, sure, I mean.

00:15:03.426 --> 00:15:11.139
The simplest explanation, right is a thermocouple is sort of the standard issue technique we use to measure temperatures and fire.

00:15:11.139 --> 00:15:18.354
Yeah, and it's basically a joint of two dissimilar metals, so a wire of two dissimilar metals.

00:15:18.354 --> 00:15:29.572
Depending on the type of the metals you'll get different types of thermocouples, um, I forget exactly what metals go into k-type thermocouples, um, but k-type nickel chromium.

00:15:29.572 --> 00:15:47.927
There you go, nickel chromium, um, they give you a very specific kind of thermocouple and basically what that does is at that junction, the through the seed back effect, basically the temperature of that joint will induce naturally a voltage and we can correlate that voltage to temperature.

00:15:47.927 --> 00:16:08.365
So basically, by measuring a voltage we're not measuring a temperature, we are measuring a voltage, a very small voltage, and then we correlate that to the temperature at the thermocouple joint, and so that effect is basically how we measure temperatures, and so that is our workhorse in fire safety for measuring temperatures.

00:16:08.466 --> 00:16:12.784
I'll ask you a question that I had to answer so many times where exactly does it measure?

00:16:12.784 --> 00:16:14.148
Does it measure at the point?

00:16:14.148 --> 00:16:21.216
Does it measure at the length, where I mean thermocouple can be a long metal rod, where, where the rod measures?

00:16:21.878 --> 00:16:29.533
yeah, yeah, so sometimes they look like a rod right, but basically it's all about where those wires are connected right and most well.

00:16:29.533 --> 00:16:36.861
I'll say with almost almost every, every single thermocouple, it'll always be the tip, because it'll be where those joint, where that joint is made.

00:16:37.283 --> 00:16:46.812
But it's all about where those wires come together exactly so it's about the connection between those two metals that creates this, this electrical current of some sort responding to temperature.

00:16:46.812 --> 00:16:52.753
So this current can only appear at the connection point between those metals.

00:16:53.461 --> 00:16:54.446
Yeah, absolutely.

00:16:54.446 --> 00:17:11.944
And again, something that you could measure, something like boiling water within the precision of 0.1 degrees C.

00:17:13.221 --> 00:17:20.026
I can give you an answer if you tell me the pressure to a very high degree based on fundamental physics.

00:17:20.441 --> 00:17:23.041
That's how we calibrate them actually many times.

00:17:23.041 --> 00:17:30.839
But yeah, in fact you're correct the bulkiness of the device, the way how it's connected, the type of the device, I mean.

00:17:30.839 --> 00:17:38.674
On one hand, it feels kind of silly to discuss what the K-type thermocouple is in the podcast episode.

00:17:38.674 --> 00:17:49.570
On the other hand, I've seen so many research papers where people would be using thermocouples that are meant to temperatures up to 400 degrees, for example, to measure fires.

00:17:49.570 --> 00:17:52.540
That's a massive error in your instrumentation setup.

00:17:52.540 --> 00:17:54.023
That leads you nowhere.

00:17:54.023 --> 00:18:02.226
That will not allow you to create a useful experimental output that could be used by fire engineers one day.

00:18:02.226 --> 00:18:06.294
I've seen them connected in the worst way.

00:18:06.294 --> 00:18:13.848
I've seen the thermocouple part disconnected from the plate because someone did not understood that there's a thermocouple in the plate.

00:18:13.848 --> 00:18:15.280
That needs to be Hell.

00:18:15.280 --> 00:18:28.711
I've seen, you know the plate thermometers hanged up with the insulative layer targeting the open space and the, the steel plate, you know, back to the wall completely opposite way and it just happens.

00:18:28.750 --> 00:18:41.824
So I think there's a there's a huge value in discussing this, yeah and I mean even things like I mean we all I know from talking to other experimentalists at conferences, but everyone's aware of these things, but you know you don't see it written down many places.

00:18:41.824 --> 00:18:59.695
But things like you're measuring a voltage so electromagnetic interference can mess with your measurements, so things you don't even think about, but uh, I mean everything that is normal equipment would be sensitive to, for electromagnetic interference can completely mess up your thermocouple temperatures if you're not careful.

00:18:59.695 --> 00:19:07.792
But yeah, just things like that, like that most people don't think about, are our important context behind how we might use these measurements.

00:19:07.792 --> 00:19:08.920
Right, what?

00:19:09.240 --> 00:19:15.311
other measurement techniques you would say are common in the fire related experiments.

00:19:15.311 --> 00:19:18.726
You have name dropped some, so let's perhaps try to make a list.

00:19:19.347 --> 00:19:19.750
Yeah, sure.

00:19:19.750 --> 00:19:21.708
So let's just, let's rattle off a few, right?

00:19:21.708 --> 00:19:26.510
So if you're trying to measure temperature, most people would use would default to a thermocouple.

00:19:26.731 --> 00:19:27.212
I think that's fair.

00:19:27.212 --> 00:19:36.567
If you want to measure a flow so let's say I want to measure velocities in a gas most people would default to using a pressure probe.

00:19:36.567 --> 00:19:47.267
Right, and you know you can go back to the original work by McCaffrey coming up with this idea of the bidirectional probe, which was more robust than like a pitot tube, but in principle it's the same idea, right?

00:19:47.267 --> 00:19:55.301
You have a probe that measures the difference in pressure over, basically, from a stagnation point in a flow and from that pressure.

00:19:55.301 --> 00:20:02.209
If we simultaneously have a temperature measurement, we can then correlate that value to flow velocity.

00:20:02.209 --> 00:20:09.608
Right, and you'll see these big, chunky steel pressure probes in many fire experiments.

00:20:10.099 --> 00:20:15.022
I would rank them very high on the list of measurement devices that I hate.

00:20:15.022 --> 00:20:16.930
There's going to be a second list after this episode.

00:20:16.930 --> 00:20:20.228
All the types of measurements that I despise.

00:20:20.248 --> 00:20:20.897
They're the worst.

00:20:21.701 --> 00:20:23.607
They're so difficult in use.

00:20:24.059 --> 00:20:28.132
But what's funny is the probe's not the problem, right?

00:20:28.132 --> 00:20:32.586
It's because you need to hook up the probe to a pressure transducer, and those are always the problem, right?

00:20:33.181 --> 00:20:34.446
So I know what you mean.

00:20:34.446 --> 00:20:42.490
Actually, for us, the transducers, they were never the issue, because we have our good ones for flow-related experiments in the lab.

00:20:42.490 --> 00:20:54.086
I find it more difficult because one it's sensitive to its orientation, so you have to be perpendicular to the flow and that means that you have to understand where the flow will be.

00:20:54.086 --> 00:21:06.666
If you do not understand where the flow will occur, there is no way you can put a probe in there in the correct orientation and there's very little you can do to change the orientation of the probe when you are in the middle of the far experiment.

00:21:06.666 --> 00:21:15.929
That's one thing, and the other thing is that because it's a pressure signal, the pressure signal travels through some little pipes with air.

00:21:15.929 --> 00:21:19.444
Basically it's like, basically like for aquarium.

00:21:20.134 --> 00:21:25.046
So those are those little nasty plastic pipes and the plastic pipes.

00:21:25.046 --> 00:21:27.601
They don't really work that well with fire.

00:21:27.601 --> 00:21:33.219
So if you have them in sensitive locations, welcome to the world of welding copper and God.

00:21:33.219 --> 00:21:41.407
It becomes really annoying to to build an array of those devices, uh, for for a large scale of our experiment.

00:21:41.407 --> 00:21:45.520
So that that's why they're high on my list of why I don't like them.

00:21:45.520 --> 00:22:02.513
They require ridiculously a lot of work to set up and unless you've done the experiments once before and exactly understand the flow field in your experiment, then there's a good chance you're not going to get any useful output of those devices.

00:22:02.513 --> 00:22:07.613
I wish there was a simple technique for measuring velocities, really like an optic.

00:22:07.613 --> 00:22:13.086
Like you know, I know piv exists but no one, no one's saying, does pav in full-scale fires right?

00:22:13.467 --> 00:22:16.242
so I wish there was we can talk about things like piv later, but, um, I think, yeah, no one I saying, does piv in full-scale fires, right?

00:22:16.242 --> 00:22:16.288
So I wish there was.

00:22:16.288 --> 00:22:23.460
We can talk about things like piv later, but, um, I think, yeah, no one, I mean it's, it's, I mean it's difficult just to say that that can be readily implemented across.

00:22:23.460 --> 00:22:26.996
Yeah, you know, especially fire testing at length scales, but I think what?

00:22:27.195 --> 00:22:39.948
What you mentioned about pressure probes, I think is an important one for the listeners to again have context behind some of these measurements where, if you're not exactly in line with the flow, right, you can get very misleading results.

00:22:39.948 --> 00:22:46.678
So we again, if you're putting this in a doorway where you know that it's going to, you basically know what direction the flow is going, that's fine.

00:22:46.678 --> 00:22:54.146
But if these are just placed in a compartment, it's very difficult to say with any certainty what flow you're actually observing.

00:22:54.146 --> 00:23:05.345
Um, so it's another important point to remember about some of the limitations and and I guess again, context is the word I keep saying, uh, behind, behind these measurements let's go further.

00:23:05.526 --> 00:23:07.819
You you've said heat flux gauges before.

00:23:07.980 --> 00:23:11.053
Let's try those uh, yeah, so I mean heat flux gauges.

00:23:11.053 --> 00:23:11.855
They're an interesting one.

00:23:11.855 --> 00:23:15.179
There are different techniques by which you can measure a heat flux.

00:23:15.179 --> 00:23:23.549
I think one of the most robust techniques that people will use are water-cooled heat flux gauges Exactly the reason why we hate them.

00:23:23.549 --> 00:23:24.631
Yeah, yeah, exactly.

00:23:24.631 --> 00:23:28.577
So you got a water coolant, which becomes a logistical nightmare.

00:23:28.577 --> 00:23:31.866
But if you see this in the literature, right, that's the device being used.

00:23:31.866 --> 00:23:38.597
That's the device being used Basically.

00:23:38.617 --> 00:23:47.527
You have a slug of material, a metallic slug that basically, as you point in the direction of, say, some sort of radiating body, you can back out the heat flux at the surface of that radiometer, right, and you can get two different.

00:23:47.527 --> 00:23:49.278
You can get different kinds of heat flux gauges.

00:23:49.278 --> 00:23:52.125
You can get some that give you a total heat flux.

00:23:52.125 --> 00:23:58.875
So, basically, what is both the combined radiative and convective heat transfer at the surface of that gauge?

00:23:58.875 --> 00:24:10.840
Again, with the water cooling, it should mitigate certain elements of heat transfer, right, but you can also, if you want to completely remove convective heat transfer from the surface, you can add things like a sapphire window.

00:24:10.840 --> 00:24:28.487
So then what you're getting is as close as we can get to a pure radiative boundary condition, and that allows you to just by choosing things like different kinds of heat flux gauges, you can sort of change what kind of heat flux conditions you want to focus on.

00:24:28.487 --> 00:24:37.063
But that becomes of course difficult too, because then you need different gauges and they all need to be water cooled and that becomes a difficult process, of course.

00:24:37.083 --> 00:25:00.904
course, but that's the sort of the tried and true default thing that people would go to for heat flux would be a water cooled gauge for for me that would be probably the one of the most useful measurements I could do in any large-scale fire experiment and at the same time one of the most difficult to actually get done, again, due to the logistical nightmare that it creates.

00:25:00.944 --> 00:25:03.318
In the laboratory you need to get the water cooling.

00:25:03.318 --> 00:25:23.054
So again, the plastic pipes or copper welding to get your water to the heat flux gauge you have like, basically the back side of it should be in non-fire exposed compartment which, uh, in some experiments your fire might switch from a compartment to compartment, for example.

00:25:23.054 --> 00:25:37.401
So you're not really, unless you're willing to sacrifice them, which is not a great idea because they're extremely expensive from my perspective, and also if you just want to use them on some sort of structure to put it near the fire.

00:25:37.401 --> 00:25:57.817
If you, for example, want to measure a heat flux one meter away from a solid structure, wrap it up in a lot of mineral wool, protect it.

00:25:57.817 --> 00:25:59.101
Basically it has to.

00:25:59.101 --> 00:26:06.303
It becomes, it suddenly becomes a really massive device that really can influence the flow field around of your structure.

00:26:06.303 --> 00:26:12.118
So it's it's not easy to put a lot of them around and I think another approach you can.

00:26:12.259 --> 00:26:15.143
You can again, like you said, these heat flux gauges are expensive.

00:26:15.143 --> 00:26:22.211
So there have been, you know, other instruments developed like a thin skin calorimeter, right.

00:26:22.211 --> 00:26:23.780
So tscs are used.

00:26:23.780 --> 00:26:40.047
If you calibrate those and you calibrate them in the right conditions, they're basically a a small disc with a thermocouple on it and, in principle, if you can, if you can set it up in a configuration where you can calibrate them, they can give you a pretty good approximation of heat fluxes.

00:26:40.047 --> 00:26:40.509
Right.

00:26:40.509 --> 00:26:44.787
Again, there's quite a few more assumptions there than a water-cooled heat flux gauge.

00:26:44.787 --> 00:26:56.356
But if you're looking at a large-scale test and you want different, high spatial resolution of heat flux measurements, a lot of people will lean towards those, just so they can get more information.

00:26:56.356 --> 00:27:02.298
But still accepting the reality that we can't just put a thousand heat flux gauges, yeah, compartment test.

00:27:02.840 --> 00:27:11.589
Arguably, if you accept the decrease in quality of your measurement and then some approximation to it, you could also live with plate thermometers.

00:27:11.589 --> 00:27:12.654
That's my perspective.

00:27:12.654 --> 00:27:28.025
You can get a lot from plate thermometers, especially if we're talking about very high temperatures, because if you're like, of course, if you're trying to get a minuscule change on a very small sample and plate thermometer, which is quite large device, it's not going to cut it.

00:27:28.025 --> 00:27:35.045
But for compartment fires, large flames, this is not high for me, to be honest.

00:27:35.366 --> 00:27:37.775
Sure, and I guess it all comes down to accepting.

00:27:37.775 --> 00:27:42.941
What is the goal of that measurement, absolutely and understanding.

00:27:42.941 --> 00:27:44.282
Am I choosing the right tool for that?

00:27:44.282 --> 00:27:45.746
What are the impacts of that?

00:27:46.386 --> 00:27:51.884
That's the struggle what I'm trying to measure and what I want to do with this measurement in the end.

00:27:51.884 --> 00:28:00.290
If do with this measurement in the end, if I wanted to give to my fellow foreign engineers as some sort of reference, do I want to use this to calibrate my modeling?

00:28:00.290 --> 00:28:02.720
Do I want to understand fundamentals of physics?

00:28:02.720 --> 00:28:05.288
Do I want to understand the novel material?

00:28:05.288 --> 00:28:09.480
Each will lead to different measurement setups, of course, yeah.

00:28:09.480 --> 00:28:11.826
So, david, what's next on your list of measurements?

00:28:11.826 --> 00:28:13.578
And I'll rank how annoying they are.

00:28:14.782 --> 00:28:15.846
So up next we have.

00:28:15.846 --> 00:28:21.983
Let's look, I mean, I guess something that we want to characterize quite frequently right is the burning rate of a solid.

00:28:22.526 --> 00:28:22.906
Absolutely.

00:28:23.898 --> 00:28:33.597
Solid, whether it's a piece of timber or whether it's a couch, right, yeah, and there's two sides of that coin, one being what is the heat release rate, what is the energy being released?

00:28:33.597 --> 00:28:47.729
And we measure that typically through oxygen consumption, calorimetry, right, where, by measuring the depletion of oxygen in your effluent stream, we can then back out basically what is the amount of heat being released, right?

00:28:47.729 --> 00:28:52.503
And, of course, there are corrections for CO generation, co2 generation, moisture, so on.

00:28:52.503 --> 00:28:55.623
But that's the principle, right, and we've talked about heat release rates.

00:28:55.955 --> 00:29:04.555
You know a lot on this on this podcast right, we should go deeper on that, because it's uh, it's easy to say you just measure oxygen concentration, but that's not everything.

00:29:04.555 --> 00:29:10.045
Like if I want to burn a vehicle in my hood.

00:29:10.045 --> 00:29:12.588
Now I'm thinking as an experimentalist.

00:29:12.588 --> 00:29:22.775
You're my client, you come in and you say I have a vehicle to burn down and you have to give me the heat release rate, which I can't provide it because I do not have oxygen chlorometry in my large foot.

00:29:22.775 --> 00:29:26.221
But if I had, there would be multiple challenges to that.

00:29:26.301 --> 00:29:37.428
First of all, I really need to capture all of the smoke, which is not certain, like it's not 100% certain, that you will capture all of the smoke in the measurement.

00:29:37.428 --> 00:29:38.897
That's number one.

00:29:38.897 --> 00:29:55.483
If you look through a lot of videos from different calorimetry experiments performed, especially in vehicles, some of them were performed with ad hoc devices which lost a lot of smoke to the environment, which means you have not captured all of that, so you've not measured all of this precious oxygen depletion.

00:29:55.483 --> 00:30:12.883
Second, I need to transport that in a reliable manner that allows me to establish how much time it takes from the fire to the measurement, which is not obvious, like it can be 20 seconds, it can be seven, depends on the flow field depends on temperature, densities and everything.

00:30:13.556 --> 00:30:40.378
I have to understand the mass that is flowing through my pipe where I'm measuring the oxygen, which is not a straightforward measurement and it either includes a complicated ventilation ducting with some sort of pressure-based measurement devices or velocity probes and temperature measurements and then you can measure oxygen and compensate for your carbon monoxide, which is.

00:30:40.378 --> 00:30:50.884
There are equations and this is arguably the easy part, but for me, from the laboratory perspective, the things that need to happen correctly, in the correct order to get to that point.

00:30:50.884 --> 00:31:00.079
Even this is a madness, even though I find this measurement, that point, even this is a madness, even though I I find this measurement.

00:31:00.079 --> 00:31:15.724
I would put ability to measure fires through oxygen calorimetry as perhaps top three things that ever happened for fire science, like seriously, like this drysdale's book and uh and fds top three for me absolutely well, let's, let's take one big step back to when we're talking about heat release rate.

00:31:15.765 --> 00:31:29.323
right, because, like you said, it is one of the singular, most important measurements that we have been able to make as a fire scientist, and the most critical for fire engineers because they need it for the design fires.

00:31:29.423 --> 00:31:37.163
Because everything, basically our framework of fire dynamics, has been set up in a way where the heat release rate becomes the input.

00:31:37.163 --> 00:31:43.969
It becomes the heat pump, so to speak, in our system, where it's the thing generating the smoke.

00:31:43.969 --> 00:31:50.760
It's the thing generating, you know, it's the input to your two zone model, it's the input to your ceiling jet correlations, it's the input to your FDS model.

00:31:50.760 --> 00:31:53.824
Right, it becomes an essential part of the system.

00:31:53.824 --> 00:31:56.483
But the measurement is inherently complex.

00:31:56.483 --> 00:31:57.858
We see it all the time.

00:31:57.858 --> 00:31:59.724
Every you know, every lab can do it.

00:31:59.724 --> 00:32:14.480
But, like you were saying, something that isn't immediately apparent when you're reading these papers that show you the heat release rate is that you have to, literally in your mind's eye, imagine the smoke being released, you know, from this fire.

00:32:14.480 --> 00:32:17.766
It has to travel into a duct, it needs to go through that duct.

00:32:17.766 --> 00:32:18.734
It's mixing.

00:32:18.734 --> 00:32:26.661
It goes quite a distance away from the fire through a duct, and then a tiny little pump will extract some of that little bit of smoke.

00:32:26.661 --> 00:32:41.307
Take that through another duct into a gas analyzer, and that's where it'll actually and it'll cool it down, it'll pass it through things like desiccant, whatever, and through all this process then it'll give you an oxygen and CO and CO2 reading.

00:32:41.307 --> 00:32:53.457
Now all that time, even if we're saying, okay, cool, now this tiny little sample, which I'm assuming is mixed and is representative, let's say that gives me the oxygen concentration In order to actually get oxygen depletion.

00:32:53.457 --> 00:32:57.200
Another big assumption is I can measure the flow through that duct.

00:32:57.200 --> 00:33:10.710
So again we run into all the issues that we just talked about, where I need to know the temperature and the pressure in that duct, and that comes up to all the issues and uncertainties that we have with thermocouples and pressure probes, because we need to be able to understand the flow.

00:33:10.710 --> 00:33:30.986
So it turns out, if you really sort of look at the propagating uncertainties in heat release rate, one of the biggest, if not the biggest, is the uncertainty in knowing our flow rate in that duct Because actually the uncertainty of the oxygen measurement we have that down pretty well, but it's actually the flow rate that becomes a bit difficult.

00:33:30.986 --> 00:33:46.685
There was a paper recently published in FSJ by the researchers at NIST looking at different ways to quantify the actual flow rates through large scale calorimeters and that becomes really interesting in trying to reduce those uncertainties.

00:33:46.685 --> 00:33:49.063
But that becomes a big part of this equation.

00:33:49.063 --> 00:33:55.498
But now let's say we have that data, let's say that we're confident in our flow rate and say we're confident in our oxygen reading, right.

00:33:55.878 --> 00:33:58.266
Then comes another assumption, right?

00:33:58.266 --> 00:34:12.911
The beauty of oxygen consumption calorimetry is that for most things that we burn, we can assume an energy constant of about 13.1 megajoules per kilogram per kilogram of oxygen consumed, precisely.

00:34:12.911 --> 00:34:20.286
So that's this beautiful number where, if we know the kilograms of oxygen consumed, we can get energy release right.

00:34:20.286 --> 00:34:23.117
But, like all things, right, that's still an assumption.

00:34:23.117 --> 00:34:25.465
Now, for most things that works really nicely.

00:34:26.135 --> 00:34:38.438
But there are lots of fuels that actually, if you look in the back of the SFB handbook, there's an entire table tabulated for energy constants for different materials, and most of them hover around 13.1.

00:34:38.438 --> 00:34:44.818
But they're even for individual materials, like things that are phenolics, even some species of timber, right.

00:34:44.818 --> 00:34:51.516
You start to deviate significantly 10, 20, 30% from those energy constants, right.

00:34:51.516 --> 00:35:03.842
And so the principle of measuring the heat release rate means I can take any material, I can throw a car, I can throw an office space, I can throw a house underneath my hood and I can measure the heat release rate.

00:35:03.842 --> 00:35:19.523
But I'm assuming that all the gases produced, all the pyrolysis process products being produced, are going to behave somewhere around that 13.1, right, if you're not specifically adjusting for it, which is the you know again, but it's something to think about.

00:35:19.523 --> 00:35:22.284
It becomes another assumption in that list of assumptions.

00:35:23.215 --> 00:35:26.219
Politically difficult question Would you apply that to a battery?

00:35:26.740 --> 00:35:27.563
Oh, that's tricky.

00:35:27.563 --> 00:35:30.081
I think we have a lot more.

00:35:30.081 --> 00:35:36.606
I mean short answer is I think there's a lot more work to continue doing on that.

00:35:36.606 --> 00:35:55.601
So we're doing battery testing at UQ and one thing that I think is continuously challenging right is to understand can we quantify enough the composition for any given particular manufacturer of battery or whatever, how it changes the state of charge, all these different variables.

00:35:55.601 --> 00:36:01.438
Do we understand the effluent stream coming out of this well enough to say yes, without a shadow of a doubt?

00:36:01.699 --> 00:36:15.170
We have the energy constants that we're assuming, and you know I'm not necessarily convinced that that's across the board yet, because the second you have say like, let's go to a simpler solid Instead of of a battery.

00:36:15.170 --> 00:36:20.724
Let's look at polyoxymethylene, right, pom, which has oxygen and you know, embedded into its molecular structure.

00:36:20.724 --> 00:36:30.375
We know that the energy constants for pom don't work out to be 13.1 right, because it in itself has oxygen embedded in it.

00:36:30.375 --> 00:36:40.681
So any kind of material that would release oxygen in any capacity through any sort of chemical reaction, that's something you got to pay attention to, it's something you got to look at right.

00:36:40.681 --> 00:36:42.239
And can we quantify that?

00:36:42.239 --> 00:36:50.688
Can we account for that and not saying that we, you know that, whether it's batteries or any other technology, not saying that we can't do that.

00:36:50.688 --> 00:36:52.262
We have the framework to do it.

00:36:52.262 --> 00:36:54.945
I'm just not totally confident that.

00:36:55.548 --> 00:37:01.206
Uh well, we're completely across every case, I would just say it's not your easiest straightforward measurement.

00:37:01.206 --> 00:37:08.929
Just drop a battery in a cone and and have the number that it shows and then praise it as the true value, right?

00:37:08.929 --> 00:37:11.179
That that's where I was leading, it's not that?

00:37:11.179 --> 00:37:12.161
It's not that easy.

00:37:12.161 --> 00:37:14.487
Um, let's talk another.

00:37:14.487 --> 00:37:35.217
I mean, if I rank things about how annoying they are, I I mean, I don't know how annoying oxygen calorimetry is, because I don't have one and I would love one and I probably would be willing to sacrifice a lot of my comforts to have oxygen calorimetry, whereas I cannot say the same about the bidirectional probes, especially for obvious configurations.

00:37:35.217 --> 00:37:48.728
But yeah, I think it's fundamental, especially if we are talking about research, if we're talking about science, if we are trying to use those experiments to build engineering on top of them.

00:37:48.728 --> 00:37:50.842
Of course, not always possible.

00:37:50.842 --> 00:37:53.483
There are other ways which we'll talk right now.

00:37:53.483 --> 00:37:55.458
What are the other ways to measure fires, david?

00:37:55.458 --> 00:37:56.461
The other ways which we'll talk right now.

00:37:56.481 --> 00:37:57.987
What are the other ways to measure fires, david, the other ways?

00:37:57.987 --> 00:38:01.981
And, and I think before I get into that, I want one more sort of comment on the battery in particular.

00:38:01.981 --> 00:38:07.164
Yeah, this actually ties really well to the philosophy of measurement right where heat release rate is amazing.

00:38:07.164 --> 00:38:16.876
Yet the default is let's try to measure the heat release rate of this thing right where I think there's for anyone who's seen videos of battery fires, right.

00:38:16.876 --> 00:38:29.936
One thing that we know is when you see a battery fire, characteristically what you're seeing is fundamentally different than a hydrocarbon fuel, like a couch fire, a pallet fire.

00:38:29.936 --> 00:38:32.543
You're seeing, you know, jet flames.

00:38:32.543 --> 00:38:36.722
You're seeing really energetic, really rapid growth rates of fire growth.

00:38:36.722 --> 00:38:39.322
So I find it something to think about.

00:38:39.322 --> 00:38:44.987
Take a step back, and the first question we asked on the podcast is is this the right measurement?

00:38:44.987 --> 00:38:47.563
Are we even comparing apples to apples here?

00:38:47.563 --> 00:38:56.764
So I think understanding the consequences of a battery fire are different, and sure, we might be able to manifest that through the heat release rate.

00:38:56.764 --> 00:39:12.143
But I think there's also more information there, because if everyone's saying that the most important reason we need the heat release rate is to use it in our engineering models, but are our engineering models, even validated for battery fires, because these flows are different, because these flames are different.

00:39:12.143 --> 00:39:17.865
It's just something to think about, right, and I think there's a lot of exciting work to be done there.

00:39:17.865 --> 00:39:23.217
But before we assume that this is the right measurement to make for every case right Is there?

00:39:23.217 --> 00:39:25.445
What is the reason we're doing it right?

00:39:25.445 --> 00:39:29.146
Does it actually capture the differences in the consequences produced?

00:39:29.146 --> 00:39:30.016
Right, anyway.

00:39:30.416 --> 00:39:37.550
But to move away from oxygen consumption, calorimetry, heat release rate, is one way to look at the burning rate.

00:39:37.550 --> 00:39:44.041
The other I kind of say like the other side of that coin, is the rate at which you're losing mass, so the mass burning rate.

00:39:44.041 --> 00:39:49.327
So they're kind of two sides of the same coin if you look at most common fuel packages.

00:39:49.327 --> 00:39:55.188
So, basically, the rate at which you're losing mass, the rate at which you're let's assume that most of that is pyrolysis.

00:39:55.188 --> 00:39:56.840
That's also an assumption, right?

00:39:56.840 --> 00:40:02.427
But let's say that most of that's pyrolysis, then that is sort of the input to your flame, right?

00:40:02.427 --> 00:40:26.322
Your pyrolysis gases feed that flame and there's a link, basically, you know, between your heat release rate should effectively be your mass loss rate times some heat of combustion, whether it's a true heat of combustion or an effective heat of combustion, some obviously that's based on combustion efficiency, but some sort of heat of combustion, right, and that kind of links the two ideas together.

00:40:26.322 --> 00:40:29.103
But already by saying that I've made a few assumptions, right.

00:40:29.403 --> 00:40:40.956
Yep, because if you actually put a solid on a load cell and you measure its mass loss over the duration of a fire, you're accounting for.

00:40:40.956 --> 00:40:43.001
The bulk of that is pyrolysis, let's say, or the release of flammable gases in some way shape or form.

00:40:43.001 --> 00:40:46.978
But it includes other things too, right, like even things like moisture loss.

00:40:46.978 --> 00:40:51.170
You will be losing moisture in that effluent stream, right?

00:40:51.170 --> 00:41:00.782
You'll be losing things like if you burn timber, eventually bits of ash will fall off right, bits of bits of timber might fall off right.

00:41:00.782 --> 00:41:06.498
So all these little finite losses of discrete mass will be accounted for in that load cell.

00:41:06.498 --> 00:41:14.760
But for most applications it's a pretty good surrogate for the rate of pyrolysis, right, which gives us a nice way of quantifying the burning rate.

00:41:14.760 --> 00:41:19.927
We just need to sort of keep in mind if there are other large sources of mass loss.

00:41:19.927 --> 00:41:23.536
Those will also be part of that measurement.

00:41:23.918 --> 00:41:28.130
For me as a laboratory, this is a measurement that I default to.

00:41:28.130 --> 00:41:28.550
Usually.

00:41:28.550 --> 00:41:32.320
I really like doing mass loss rate measurements.

00:41:32.320 --> 00:41:35.887
From my perspective, they're manageable to set up.

00:41:35.887 --> 00:41:42.469
We are very commonly designing custom load cells for our clients.

00:41:42.469 --> 00:41:49.943
We've designed like a scale on a scale so you can measure the crib inside of a building and the building structure independently.

00:41:49.943 --> 00:41:52.623
We've measured hanging CLT slabs.

00:41:54.016 --> 00:41:57.226
There's a lot of funny measurements you can do with master straight.

00:41:57.226 --> 00:42:29.088
However, one thing that you really need to be aware of, and you kind of pointed to that if I want to measure a slab and know that over 20 minutes of a steady state fire where steady state is, of course, a very big word for a fire, but a fire that plateaued on some sort of size and did not really change that much over the course of that time, I had approximately five megawatts of heat release rate.

00:42:29.088 --> 00:42:32.902
That's the type of information I can get from my mass loss rate system.

00:42:32.902 --> 00:42:46.643
If you want a detailed analysis, second by second, of what was the heat release rate every second, that's a hell of a measurement to make and I know you've done research on that.

00:42:46.643 --> 00:42:48.623
You've investigated that case.

00:42:48.623 --> 00:42:51.735
How do we, what do we get out of that measurement?

00:42:51.735 --> 00:42:54.684
Because at some stage it gets it becomes chaos.

00:42:55.315 --> 00:42:57.519
So I think I mean I for the same reasons, get out of that measurement because at some stage it gets, it becomes chaos.

00:42:57.519 --> 00:42:58.375
So I think I mean I, for the same reasons.

00:42:58.375 --> 00:43:18.878
I like mass measurements in fire because, like you said, I've done mass measurements on the scale of a entire compartment, you know, on load cells, down to you know, a tga crucible full of, you know, milligrams of powder, right, and you can see some really interesting results across scales.

00:43:18.878 --> 00:43:19.400
Right.

00:43:19.400 --> 00:43:23.067
But like you said, it depends on what you're trying to look at.

00:43:23.467 --> 00:43:31.659
So let's go back to the drawing board of what I defined the mass burning rate as like the opposite side of the same coin as heat release rate.

00:43:31.659 --> 00:43:39.782
So, yes, you, you can use a mass loss measurement to then get to a heat release rate if that's the output you want.

00:43:39.782 --> 00:43:45.181
But I also think it's really valuable using the mass loss rate for what it is right.

00:43:45.181 --> 00:43:56.246
So in some of our work we will just keep it as the mass loss rate because, let's say, I'm trying to look at the change in the rate of pyrolysis, then the heat release rate is, you know, again, it's a surrogate.

00:43:56.246 --> 00:44:07.916
But by measuring the heat release rate you're making again, you're making an assumption, that's the right surrogate, whereas if you measure the mass loss, you're actually making one less assumption and that's actually maybe the better measurement to look at.

00:44:08.436 --> 00:44:13.327
And perhaps making a mental shortcut in here, because of the role of this podcast.

00:44:13.327 --> 00:44:23.039
It connects to engineers and I see very little or even no applications of direct massless rate measurement in engineering daily.

00:44:23.039 --> 00:44:32.181
I think it would be extremely difficult to apply, maybe in some really really specific projects, whereas heat release rate every single project.

00:44:33.978 --> 00:45:02.992
That's why this is a connection in my brain that's very strongly enhanced over the years of practice I mean it's fair enough, right, and and you're right, but I also think it's worth the practicing engineers I know, like when I was, you know, when I worked before my phd I was working at an engineering firm too, right, and so, yep, having experience working in an engineering firm, I wish I I had known to look, if I looked at a paper and looking at the difference between this is actually looking at the rate of pyrolysis, right?

00:45:02.992 --> 00:45:10.465
The mass loss rate has so many significant things because it has links to things like ignition theory, it has links to extinction theory.

00:45:10.465 --> 00:45:13.706
So, looking at like, self-extinction of a timber compartment will not be determined by the release rate.

00:45:13.706 --> 00:45:15.594
Fundamentally, they not be determined by the heat release rate.

00:45:15.594 --> 00:45:20.463
Fundamentally, they'll be determined by the mass loss rate and things like that where, yes, those are subtleties.

00:45:20.463 --> 00:45:24.525
Many engineers will not be applying that in the day-to-day work.

00:45:25.275 --> 00:45:44.742
But I hope we can build tools like that in the future that require the level of understanding that there is a difference, right, and I think that's what we should be aspiring to as researchers to develop those tools that are based on the right physics and in a problem like an ignition problem or an extinction problem or those are just two I can think of off the top of my head.

00:45:44.742 --> 00:45:46.942
Those are led by pyrolysis.

00:45:46.942 --> 00:45:50.740
Another one actually come to think of it is charring, right?

00:45:50.740 --> 00:45:57.822
So charring of, say, a timber slab, that's just a pyrolysis process, that's the progression of a pyrolysis fund.

00:45:57.822 --> 00:46:02.318
So if you can measure the mass loss rate, you can get a surrogate for charring.

00:46:02.318 --> 00:46:16.235
So, actually, you know, being able to decouple these ideas I think are really important, and if we want to develop engineering tools, they need to be based on the right physics, right.

00:46:16.235 --> 00:46:20.010
So not to say that we have those tools widespread at the moment, but I do think it's worth having that, that distinction there absolutely, absolutely.

00:46:20.030 --> 00:46:23.641
Let's talk about, perhaps, the averaging, because I know that you had papers on that.

00:46:23.641 --> 00:46:27.262
I found them very interesting and they highly relate to the mass loss rate.

00:46:27.262 --> 00:46:34.141

216 - What do we measure and how? with David Morrisset

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