Fire Science Show

221 - Fire experiments at the ISS (SoFIE-MIST) with Michael Gollner

• Wojciech Węgrzyński

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Fire doesn’t play by Earth’s rules once you leave gravity behind. In this deep dive with Professor Michael Gollner, we unpack what the recent experiments at the ISS called SoFIE-MIST taught us about solid fuel flammability in microgravity—how tiny ventilation, oxygen levels, and pressure shifts determine whether a flame spreads, stalls, or vanishes. The details are surprising: blue “bubble” flames, two distinct extinction points, and sustained burning at oxygen levels that would fail to ignite on Earth.

We walk through the entire setup: PMMA rods chosen for clean, uniform burning; a compact wind tunnel inside the ISS hardware; ceramic heaters delivering 1–3 kW/m² to probe incipient behavior; and a control strategy that often lets the flame’s own oxygen consumption carry the chamber gently to extinction. Along the way, you’ll hear how constraints drive design—why rods beat flats, why halogen lamps didn’t fly, how crew time is minimized with robotic runs—and how data is captured without weighing anything. Opposed-flow flame spread becomes a window into fundamentals: radiative preheating, thermal thickness, and the delicate balance between convective loss and feedback when buoyancy is gone.

The implications stretch to future habitats and vehicles. As spaceflight moves toward longer missions and more commercial operators, safety will hinge on accurate flammability limits under low ventilation and non-Earth atmospheres. We connect the dots to normoxic choices, partial‑g research on the Moon and Mars, and the growing need for space fire engineering that’s grounded in real data. If you care about spacecraft safety, materials selection, and the science behind early fire detection, this conversation is right for you.

If you want to learn more, do it here:

Cover image credit: NASA, Igniting a 12.7 mm sample at 21% oxygen under 100 kPa ambient pressure in microgravity. From article https://engineering.berkeley.edu/news/2024/12/nasa-funded-project-offers-new-insights-into-fire-behavior-in-space/

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Wojciech Wegrzynski:

Hello everybody, welcome to the Fire Science Show. Today I'm taking you to the space and we're gonna do space fire safety, space fire science once again. I've invited Professor Michael Gollner from Berkeley to discuss some recent fire experiments that have been carried at the International Space Station called the Sophie Mist. So uh well, we'll talk more about what that acronym means and what goes into the experiments, but the general overview is that they are testing the flame extinction limits in different conditions in microgravity to answer a very, very simple and fundamental question. Can this burn and can this keep burning in conditions that are present? It's about little flames, little fires. So it's about really testing out the flame behavior at the incipient stage of a fire. If you have followed Fire Science show, we already had um space episodes. I had David Urban in the podcast from NASA, and we've discussed about how big fires look on spacecraft, and we had unfortunately we had some in the past and they were all catastrophical, and uh yeah, we're doing everything we can uh to not have fires in the spacecraft and space station. Therefore, studying uh the incipient stage of fires is the highest importance because if we can detect it early, if we can understand when something burns, we can perhaps create conditions at which it cannot. And if we understand how the fires grow at early stage, we may be better at detecting them and removing them. So while it is a fundamental research, it has also a lot of practicality to it. And it is just so much fun to run your experiment in the space. If you ever wondered how it looks like to set up a fire on the International Space Station, Michael will tell you how. So that's the episode today. I hope you will enjoy it. I loved it as a space geek. It's always uh fun to discuss space fire safety. And I I hope you share the passion and you share the same views. Uh let's spin the intro and jump into the episode. Welcome to the Fireside Show. My name is Voyage Viginsky, and I will be your host. This episode is brought to you in partnership with OFR Consultants, the UK's leading independent fire engineering consultancy. With a multi-award-winning team and offices across the country, OFR are experts in fire engineering committed to delivering pre-eminent expertise to protect people, property, and the planet. Applications for OFR's 2026 graduate program are now open. If you're ready to launch your career with a supportive forward-thinking team, visit OFRconsultants.com to apply. You will join a worldless organization recognized for its supportive culture and global expertise. Start your journey with OFR and help shape the future of fire engineering. Hello everybody. I am joined today by Professor Michael Gollner from Berkeley. Hey Michael. Hey, how are you doing? All good, all good. Let's let's fly to the spaceman with your crazy experiments. I'm really happy that again on the podcast I'm able to talk about uh spacecraft fire safety and general fires and microgravity. It's a thing that's uh very interesting to me as an amateur astrophotographer and a space nerd in general. Anyway, let's perhaps start with uh I know that there's a long history of Berkeley doing work with NASA, so maybe you can introduce the listeners about how the NASA collaboration began at Berkeley and how did you turn into the current round of experiments? Maybe that's an interesting thought.

Michael Gollner:

Well, I definitely don't know the whole history, but um, you know, Professor Carlos Fernandez Pello, who fortunately, you know, has not been able to join the podcast. I hope we're going to twist his arm to get on here someday.

Wojciech Wegrzynski:

The more people twisting, the easier it's gonna be.

Michael Gollner:

But yeah, so he he's been leading microgravity experiments with NASA for many years. Actually, you know, for anyone that comes to our lab, which I'm running now, it's it's really cool because we have at least two or three apparatus that have all been on space shuttle, been space hanging around. You can touch them, you can see them. So there's a lot of history. He led the smoldering experiments that were done on the space shuttle. There's still the samples, I believe Jose Torrero and many others worked on those. So there's a long history, and even this current experiment, the material ignition and spread test, it has a long history, right? Like it, I was not around when it was initiated, and so it's been going for quite a long time. It it's not easy to actually conceptualize, put it in the thing, have it planned, and actually getting it up. It's this incredibly long process before it actually flies and is run.

Wojciech Wegrzynski:

That's exactly why you are on the podcast because it just summed up the contents of this podcast episode to come. Tell me, tell me all about it. So, first let's talk about the idea. Does the idea come from the needs of NASA, or is it something you as a researcher come with an idea to NASA? Is there an open bid for like, hey, anyone wants to do a space stuff?

Michael Gollner:

Uh both, both, right? So spaceflight, there's been a need for fire safety research. When you talk about the hazards that you have in microgravity, fire is one of the greatest. Obviously, in launch and in re-entry tend to be the highest risks because there's a lot that can happen that goes wrong during launch, and we've seen those critical failures. The same thing for re-entry, a damaged tile can lead to destruction. But I think in terms of current space flight, fire is one of the most risky hazards that are that are out there. And so they're very concerned about fire safety. And fire behaves differently in microgravity, which we'll talk about. But because of this, there's always been this research program going on the side. So I think going in NASA Glen, and David Urban, you know, who runs that program would know better. But I believe he said like the drop tower started for microgravity research. So they got like a five seconds of microgravity drop, started around the Apollo program. And there were a lot of other things they were testing too, and they started to look at fire safety. You know, Apollo one was this critical failure and disaster on the pad where high oxygen environment, which makes some things easier, and we'll talk about that, led to a spark, which which then the astronauts couldn't get out. So there were door failures, and then there was this fire and led to their death. Fire safety has always been an issue since then, or at least it's been highlighted. There's been an accident on Mir, there's been a lot of close calls, the space shuttle and even space station, you know, nothing really severe has happened, but that's also because a lot of effort is put into mitigating these hazards. And we still don't understand everything about microgravity, fire safety, which is why the research program continues to emphasize. And so I think you see NASA, well, they rarely have calls for spaceflight experiments, but when they have for combustion, there's been like fundamental combustion and then kind of fire safety, and then fundamental combustion and then fire safety. And so it is a big priority beyond just the science for us to actually try to make sure that you can do long-duration spaceflight safely.

Wojciech Wegrzynski:

On uh Sophie Mist website, it even says that it's kind of triggered by the future missions to moon to the Mars, which are very long-duration events, and of course, uh a fire could be a catastrophical failure in such a mission. I actually had David in the podcast a long, long time ago, uh, 2022. And oh that I'll link the episode in the show notes if if the listeners have not have missed it one, it's joy as well, uh, one of my favorite all-time episodes. So there are calls. Do they I wonder how it is awarded? Like, uh do they have favorite people to work with or or do you fight for it? Like, I'm really curious about the the technicalities of that.

Michael Gollner:

Yeah, so I came on as a co-PI after this was already started. This so typically NASA has calls for proposals. I mean, this there may not be any more given the ISS's retirement coming up, but they have calls basically when there's openings for experiments, and then there's some things that have come through what's called cases, which is like a sidearm into kind of commercial operations. The NSF, the National Science Foundation, the US, has had small experiment additions. And so uh I've had I've had some that were approved by that, but then they came back and said, Ah, actually, we don't have time. And so we never got to do any new things. But this program was long before I was a faculty. Uh, they had a call for experiments. It actually goes back further. I believe a lot of this idea originated. So there was a an older experiment, the flame ignition and spread test, Fist, which used heaters on a sample uh as it was blowing. And that experiment was planned. I think Sarah McAllister did her thesis on it and some others. And then it never went to space flight because of changes in the administration in the government. So that program was canned, and then a new program later came where MIST was proposed. And as I recall, it may not have been this one, but one of the other projects, the one that Jim Quintiri worked on with the um fuel emulator, I think Carlos and Quintiri, uh Jim Quintiri worked on together, but it wound up that only one PI was, you know, Jim was leading it. Um, but in this case, it was sort of like an adaptation of what was going to happen on Fist, but adapted to the new call. So this call was for material ignition, and all of the experiments are solid fuels, so solid fuel experiments. And the real change in our experiment missed from all the others was that heat is added. So if you're anyone working on material inflammability, external heating is like a core of fire science. That's what we always do. But you pretty much don't find that ever on the space station. It's pretty hard to add here, and there's lots of problems with it. So that's something unique that was added in this experiment. There were a series of other investigations in the same lineup, not all of which have completed. But that addition of external heating is supposed to make this somewhat unique compared to previous experiments. Although it's no longer the flat configuration from Fist, this one is a cylindrical configuration. So, you know, depending on the requirements, things change, but there's a lot of things that can be investigated.

Wojciech Wegrzynski:

Yeah, I have some questions regarding the details of the experiment, but first let's maybe give a far field introduction to the uh missed experiment itself and maybe the SOFI program, in which it's it's a part. So if you could give a high-level summary of what SOFI was missed, and what is the first uh and main uh research question in those.

Michael Gollner:

Yeah, so Sophie's main research question, right, is to look at solid fuel flammability. You talked about long duration spaceflight, and we know that flammability and microgravity is a little different. And some of that's because buoyancy is gone, and so that makes things interesting, but there's still some airflow. There's HVAC or heating ventilation air conditioning on the space station. We assume it's about 10 centimeters per second, so it's pretty slow, but it's there, and that can cause conditions potentially for materials to burn where they couldn't on Earth. They're not going to burn as intensely necessarily, but creeping flames that keep growing still present a huge hazard and can grow over time. It's an interesting mix. So Sophie is designed to look at the fundamentals of that, and in particular, a lot of the experiments are focused on the ignition and extinction limits. So this also ties into another interesting question, which is that we don't always keep the same atmosphere in space as we have on Earth. So we like our one atmosphere, 21% oxygen at sea level. Um, in space, if you want to go into a spacesuit at that pressure, it doesn't move. So you want to reduce the pressure, but then you don't have enough oxygen to breathe. So just like going up Everest, you pump in more oxygen. So you have a higher percentage of oxygen. That potentially adds a high risk. And it takes time for for your body because of the way you know the nitrogen bubbles were, it's gonna take time to adjust to the higher oxygen environment. So you can really speed things up by keeping lower pressures and higher oxygen concentration on what's called the normoxic curve. So it's basically says you have to keep the same partial pressure of oxygen, you have to keep enough oxygen for your body to breathe. Even at a lower pressure, you're gonna have a higher percentage of oxygen. So your body gets enough. And if you start, you know, with a lower pressure but higher oxygen, you're gonna have a lot less time to get into and out of a spacesuit. You're also gonna have to have less material for the structural integrity of the spacecraft. So there's a lot of reasons and it makes space flight easier. But potentially, even though lower pressures and microgravity make things less flammable in general, higher oxygen makes it more flammable. So this experiment for all the investigations varies pressure, oxygen, and then each one does a little bit different flavor. So in mist, we're looking at flame spread along a rod, and then we look at extinction limits as well as the flame spread process for different rods. And then, as I mentioned, the really unique aspect compared to any of the other investigations is we do add external heating. So there's already like Jim Tien uh led an experiment uh with a cylinder where they're looking at ignition extinction, and it's a really nice, very fundamental flow. So you can get like one D in the tip of the cylinder, and so there's a lot that you can learn from that. And then for modeling, Sandy Olsen from NASA led another, and that you know, so there were there are a bunch of investigations, each taking their angle. And I think the unique part about the mist experiment was that we get to do this with external heating.

Wojciech Wegrzynski:

What's about the shape of the fuel? Why a rod? Is it like experimental setup specific? Is it like a real-world representative for space fuels? It's a great question.

Michael Gollner:

I don't know the true answer. You know, I'll tell you, I don't know. And I'm not saying the rod's a problem, there are lots of different ways to configure this, right? So the cylinder is not perfectly uniform everywhere. So I get why the sphere would be very nice in the very fundamental aspect, but it's very impractical. A flat piece would be good, though that was already proposed on the fist and then canceled. Not sure if that could be done again. I don't know how much that's the reason. But also part of it is by doing a rod, you can do 360 heating and you can do different size rods, so we can get thinner and thicker, and we do do three different diameters. There's complications in that, but then there's some benefits that you sort of get more thermal thickness testing. The other thing is with a flat sample, I mathematically prefer the flat sample a little bit. Maybe I just don't like cylindrical coordinates on an issue. Oh god. But it but an issue with the flat sample is that how do you ramp up so that you can do three of them in a test? Okay. So the way it is actually designed is that they put the astronaut refills the gas canisters, clean things, closes it up, and then we run three experiments in a row robotically. And then they'll do the switch out a week later and we do another set. So that way they don't have to sit there for eight hours while we're trying to run it. It's all being done robotically, controlled by Earth. And it's pretty hard to do that with a flat sample and fit that in the apparatus. And I maybe you should talk about the constraint. There is um fabulous apparatus called the Combustion Integrated Rack, the CIR. This apparently flew on the space shuttle and has been on the space station for years. It did all the droplet experiments like Flex with the cool flame discovery. It's done the previous Spire investigations. Maybe the only exception would be Sapphire, which was was pretty cool, and I'm sure David Urban talked about where they they used the resupply craft to do some bigger experiments.

Wojciech Wegrzynski:

And they were quite large, right? For the space stuff.

Michael Gollner:

Like they were they were they were when it was not attached to people, so that's how they were but in terms of something attached while people are on board, the CIR has been the main vehicle for doing that. And I we we may have been the last in that apparatus, which is a little sad. It has been shut down. I don't know if it'll be turned back on, but you know, ISS is getting towards retirement. But we're constrained by how much space, how much gas, how much resources can be put in there. And so that also constrains a lot. Another thing, for instance, we were planning on higher heat fluxes, but you can only burn something so much, and halogen lamps, which would provide higher heating, sound like a real safety risk when the flight engineers take a look. And so they had to switch to more ceramic heaters, which don't achieve as high heat fluxes, but should be better surviving on launch. And so that was and they they did survive, they put they broke once, they flew new ones, but the halogen lamps obviously, you know, they're worried about floating like broken glass. So there are there are unique constraints to running these experiments, but the missed experiment was this next round in in Sophie, where we actually got to test the rods. We did a round last year and another round this year. We just concluded a couple weeks ago, and it was pretty neat. We were actually able to ignite fires in space, watch them, see it extinguish, learn something new. It was amazing to get that opportunity.

Wojciech Wegrzynski:

I I would just send a gas burner, but my career in space uh science would end very quickly, I guess.

Michael Gollner:

Hey, you know, you Jim Quintiri led that experiment, Peter Sutherland and the group, and then John DeRist joined like was ever everybody was on that. Um that burner, they used a burner in space. That was if you're Quintiria, you're allowed to use burner in space. Hey, I'm not. It was very tiny, right? I remember I was in Maryland, you know, watching the grad students and calibrating the tiniest heat flex gauge in there. It was it was still cute. Um, but they that was it, it was a really neat idea to use a gas burner to emulate solid fuels, and that whole experiment, the acne project was focused on gas burners, and that everything was configured for gas, and then this is all configured for solid fuel.

Wojciech Wegrzynski:

Yeah, uh, in in terms of materials, what what the roads were made of, did I or you just use PMMA as as just one single material? Polymethylmethacrylate, of course, right?

Michael Gollner:

Hooper's anything else than fire. Yeah, but the most realistic fire of them uh of them all, like the default uh fuel, you know. So there are arguments before and against, and you know, my PhD, I use PMMA too, so yeah, that sweet methyl methacrylate smell. So one, you know, you can argue, well, they make make windows out of it, there's some plastic, but I think a reality is one, we have a large data set of PMMA already, and two, it is a really fundamental good material to work with. It bubbles and vaporizes and burns, it doesn't char, it doesn't tend to release any toxic gases, which is nice. It is uniform, it's accessible, it can be made in different shapes, it can be made in different colors without affecting its properties. It's just a really nice material to work with, and it tends to just you know continuously. There is a little bubble layer which is slightly off, but otherwise it it's a pretty uniform material which makes it easier to model, easier to work with. And so I like that. I understand why we use that, and when you have so few materials that you're actually able to test in space, it's good to test on something you know, and then we're focused more on other aspects happening in the gas phase and that interaction rather than this material property, that material property.

Wojciech Wegrzynski:

Also, I I assume because it's studied so much, you also have easy access to the best numerical models for for that uh compared to other complex fuels.

Michael Gollner:

Uh so uh yeah, I mean there's better there's better solid-phase kinetic models for for PMMA. Not that that's been used an awful lot in this work. We're looking more at this uh at well, extinction limits and spread, but it enables everyone to go back and model this and compare it to years of studies on the ground and in space. So everything we did was done on the ground and in space.

Wojciech Wegrzynski:

Okay, well, here you talk here you take one of the questions I had for later, but thank you. Okay, another another question about fuels. Uh perhaps uh well, you're clear that it's just PMMA for mist, but were like foam materials, porous materials also tested in in space?

Michael Gollner:

Or no, I mean, not that they don't have fire hazards, but that wasn't part of this uh experiment. You know, the real goal of these experiments was to look at those extinction limits and particularly oxygen extinction.

Wojciech Wegrzynski:

Yeah, yeah. Let's move there. I I like this. When you you say that fire behaves differently in space, could you like give uh again a high-level summary to a fire engineer who's just interested in that? What exactly do you mean by by different behavior?

Michael Gollner:

Sure. In space, we're dealing with tinier flames, right? If you let's start with a candle. Candle on Earth, you get tall yellow flame. Why is that happening? The wax diffuses up, vaporizes. Gravity, because it's lower density hot air, hot gases, pulls it up as it reacts with the air, and you get that long stretched flame. And it doesn't mix perfectly, it's not pre-mixed. So that diffusion flame generates soot, which glows yellow and orange, and you get a nice flame. In space, there's no buoyancy, no stretchy, no pull. It's a bubble, it's a beautiful blue bow. And it's interesting. If I took a candle and I made that beautiful blue bubble and it grew and it grew and it grew, eventually the heating from the blue flame would not be sufficient to keep vaporizing the fuel, and we'd reach a radiation-dominated extinction limit. And pop, there it goes. So we see that with a droplet flame experiments, you can do it with a candle. So in space, it's different. It is different. The feedback process, I mean, all the physics is the same, but you remove gravity. If I also took a flame in space, I could I could take and ignite that flame and then I could blow on it. And if I blow and blow and blow fast enough, I at high enough oxygen concentrations, the flame's gonna get thinner and hotter, and eventually there's gonna be insufficient like convective feedback, and there's gonna be too many convective losses on the surface, and it's gonna go out, and that's gonna be kind of like a thermal or kinetic blow-off limit. So there are there are two limits for extinction that are gonna occur in space. And the big thing is that is that they're they'll be a little different than on Earth.

Wojciech Wegrzynski:

Yeah, but but still, like uh you maybe not have buoyancy, but you're gonna have like thermal expansion of the gas because of change in density. So the fumes are not like escaping this area of the of the flame or or or the region of the they'll just stay there and create a growing bubble. Is that what you meant?

Michael Gollner:

Right. So that is what's going to happen unless we are giving it a little bit of wig. Okay. And that's what really happens on any human spaceflight, is that there's always some ventilation because you need the air to mix, right? You need oxygen in there, and there's no buoyancy to keep it going. So there's always small. We it they say it's about like 10 centimeters per second that the HVAC system is blowing air through the space station or other spaceflight vehicles. So that is going to provide some velocity over the fuels, but not much. But there isn't the buoyancy that we have here. These extinction limits happen on Earth. So, like a tiny flame, buoyancy can almost help blow itself out on Earth, which won't happen in space. It can just creep and creep and creep along very small, where it would never be stable on Earth. And that makes an interesting situation where in theory you can have flames that exist and persist in microgravity that wouldn't exist and persist on Earth gravity. So the true limits of flammability are different in space than they are on Earth. And if you are designing protection systems, if you're picking those materials, you can get into a safety scenario where you think something is safe and non-flammable, but it is. And as we know, when you kick up external heating, that changes the flammability of a material too.

Wojciech Wegrzynski:

We'll go to the the heating uh in a second, but uh there's a lot of physics we still need to cover. There's not many opportunities to talk about physics in space, so I need to be thorough in this. The the the concentration of oxygen. In my uh boring earthly systems, uh in the terrestrial fire engineering, I I do 15% oxygen concentration, and I'm pretty much done if I want to protect the space. Usually, you said that in the space it's not about percentage really, but about partial pressures. Could could you tell me how that actually works? Because I'm I'm so used to the concept of just you know concentration and everything that uh it's it's it's kind of uh yeah.

Michael Gollner:

Well, it does change with pressure, but it you know, we we still often call it like a limiting oxygen concentration, but it's it's actually like a limiting oxygen volume fraction, would be a more proper term. So this this with you know, when I was mentioning this, it depends it's really important when we talk about breathing. You need enough oxygen in the air uh to breathe. And so there are issues when you're lowering the pressure, which is done for those reasons for external vehicular activities, EVAs, and um just the structure of the spacecraft. Those lower pressures require higher oxygen for people to breathe. And the higher oxygen concentration, even though even though you have the same volume fraction, which is what you need to breathe, the flame has a higher percentage in terms of this limiting oxygen oxygen concentration, and and it it's going to behave differently. The oxygen concentration to keep you breathing, having that higher oxygen concentration actually affects the flame more strongly than the lower pressure does. Like lower pressures are gonna make the flames weaker. When we want to mimic microgravity flames on Earth, we lower the pressure in the chamber. Okay. It will make them bluer, it will make them rounder because there's less gas, so there's less buoyancy effects. But it's actually fascinating that just the little bit of oxygen in there extra, even at that lower pressure, does tend to overcome a lot of those pressure effects. So the higher oxygen concentration has a big influence uh and is very important consideration when we talk about flammability. So if you're designing a hotel, you know, in the Himalayas, and you want everyone to breathe nicely, you're gonna have a big flammability problem. Just the same as if you do that in aircraft or if you do that in spacecraft.

Wojciech Wegrzynski:

Now I need some fire engineers from Colorado to discuss the high-altitude fire engineering. I found a very interesting uh write on uh Engineering Berkeley about the NASA funded projects and uh by Marnie Ellery. And uh in that text, there's like a quote from Car from Carlos who says in normal gravity the limit oxygen concentration, which materials are flammable, is approximately 18%. But we're finding that in uh the spacecraft environment is about 15, and then there's uh we're expecting that it would be lower, but not that low. So I understand uh okay, the partial pressure, so so you keep it more or less like on in the end, it's more or less like in normal atmosphere. So the fact that you have higher oxygen concentration doesn't translate to that more vigorous fires, or maybe it does.

Michael Gollner:

Well, so first off, the experiments on on mist are not all on the normoxic curve. Okay, we methodically change the pressure and the oxygen concentration to understand the process, which some hit on the normoxic curve and some don't. So it's not like we've done papers and things where we just follow that curve, but that that's not the case here. It's not only following that curve because we really want to understand what's more strongly influencing is it the pressure, is it the oxygen, is it the heating? And we can only do so much because we're limited in the number of experiments, but yeah, we've had experiments that are lower than 15. So the limit is getting close to 14 oxygen concentration, which you just uh you just won't find PMMA burning at 14 point something oxygen concentration on Earth. It's just it's not happening. Um, but it does happen in microgravity.

Wojciech Wegrzynski:

And have you had a short on explaining why why that is? Is it like a heat transfer phenomenon, radiation?

Michael Gollner:

I think the majority of this all centers around the buoyancy, right? So uh the buoyancy is not blowing off the flame, some of it's geometric in the way the flow is going around and where it's centered. We actually interestingly found two limits. So there's a first limit, which is a little bit higher oxygen concentration where the flame stops spreading, and then it sits there and it burns still, but it no longer spreads. And then there's a second limit where it actually stops burning and goes out. Out. And you know, limits are complicated. It there's fluid mechanics occurring and the flow because it's it's a cylinder geometry. There's the heat transfer effects, which depend on the thickness. That's why we have different thicknesses. We don't change materials, but the thickness makes a big influence there. And then there's a chemical kinetic effects, which is going to affect the temperature of the flame and the heat feedback. So these are all coupled. So none of the results are perfectly translatable to everything. But universally, it's it's fairly universal configuration and fuel that we would then expect this to happen to most other materials, right? The limits may be slightly different. There may be even more, but we're trying to understand that influence and we see that pretty strongly.

Wojciech Wegrzynski:

I wanted to ask about the flame spread. So if anyone wants to learn about flame spread, there's like Jose on Princeton lectures, and somewhere between the fifth and ninth uh hour of lecture, there's like two hours on opposed and concurrent flame spread and everything about it. Do those things change in microgravity as well? They do and they don't. Okay.

Michael Gollner:

Right? So opposed flame spread is what we're doing. Um, and maybe after this, let's let's focus on the and I'll walk through how the experiments run. So opposed flame spread when it's going against the flow. So it's flowing one way and it's trying to go the other, um, is more similar in microgravity than and Earth because it is focused on the small-scale effects from the tip of that flame where it's anchored, and it's heating the material surface ahead. And so a lot of the heating tends to be radiation from the flame or it could be conduction through the solid. The flame isn't extended to unburned materials, it's centered over what's already burning and then heating what's not burned, and it propagates. Concurrent flame spread is where the flame laps over the area that hasn't burned yet and heats it. So concurrent flame spread is faster. It's very dominated by buoyancy or by flow, and where you see the flames in front. So upward flame spread or wind-driven flame spread, that's concurrent. And it's almost always flat faster. It's also acceleratory, right? So it doesn't ever get linear unless it's through a very thin fuel. And yeah, so countercurrent flame spread is much more fundamental. It goes back to like John DeRis in 1969's paper with the first theory for a post-flow flame spread. And theoretically, it's it's easier to deal with, it's also smaller, and so for configuration like this, that's kind of what you want to do. Sapphire did some concurrent flame spread, but for these small experiments, you really need to work with the small countercurrent flames. Hypothetically, if you have no flow, like well, what would it look like? In microgravity or on Earth? In microgravity. In microgravity, if we had no flow ignite at the tip, uh, it is possible that it could spread. It could be way slow, right? Because the flame wouldn't grow as much. We would probably have a very small burning region that would propagate. So it would look a little more like the extinction limit, which, you know, could still be interesting in some ways, but it's not going to achieve that kind of flame spread over time. Ultimately, when we think about flammability, there are a lot of parameters that are important. Ignition, which is not something studied as much here, because we're not controlling it. You have uh flame spread, the rate at which the fire grows. You have the heat release rate, which is also something that we capture. Uh, and then you you have sort of like the, you know, in this case here, extinction suppression. So those are different aspects of flammability that would be tested.

Wojciech Wegrzynski:

How do you capture heat release rates? Do you have oxygen colorimetry in the experiment?

Michael Gollner:

Or there is a lot of oxygen sensors throughout the experiment. And you know, in the past that wasn't being done on Earth, so we added oxygen concentration measurements on Earth so we can do heat release there. But you know, PMA, again, going back to simple, it's all about timing because you're measuring oxygen in different parts, but you you you can get the heat release rate, and yeah, you can't weigh it, there's no gravity.

Wojciech Wegrzynski:

Yeah, that's that's probably true. I mean, but as a trade-off, you don't need any sample holders. You do, you can what's time?

Michael Gollner:

Can we talk about like how this works? Yeah, yeah, yeah. So if you go online, you look at the experiment. So the the experiment is in this big cylinder, and inside is essentially stuck a little square, uh, rectangular wind tunnel. And so it's a very simplistic wind tunnel, and it can blow faster. What size is like shoebox, uh bigger? It's like two shoeboxes, maybe two and a half. It's not super big. I mean, the plastic samples are you know seven centimeters-ish, something like centimeter wide, and then there's three diameters up to what uh was it nine millimeters. So they're not they're not that big because we can't get that big of a fire and heat it and do everything we want to it. Okay, so inside that apparatus are three holders which are robotically controlled, and then there's an arm that has an igniter. And so on a test day, we start off and we have they the we don't do this, but while we're talking to them, the you know, contractors that that run this are then positioning the sample in the duct and then positioning the igniter and the wire close to it. And you gotta be really careful because if you knock it, you're gonna break the igniter or you're gonna bend something, and then nothing will work. Do we have like a live view of that happening or sort of so you have a live view while it's in range? So this gets to a fun part where when you're running an experiment, they're prepping the day and they're gonna predict when they have signaled and internet, but then sometimes things are out. So there's a series of satellites around the earth that are bouncing off of the space station and then beaming it back. There are dead spots and there are good spots that are sending the internet back, and sometimes some of them the connection breaks, and they're constantly working on this. And so it's really interesting where you go and you're like, okay, we got a window for an hour and they're positioning and then oh, they're like, okay, next window in 20 minutes. Wait, no, it happened in 15. Oh, let's go. You know, so they know a lot more about this, and they're constantly in contact with Johnson Space Center, which is controlling the ISS um to manage this. But we you're on pins and needles waiting, hoping this works. But they have a real system for this. When you see the live view, we have multiple camera angles, we have all the sensors, and so they're they're fiddling with this to see where it is. Of course, every time an astronaut opens up the chamber, they reinstall stuff, everything shifts a bit. So you've got to readjust everything and hope it all fits and how it lines up. And it can be challenging, it can take them hours to twist around and rearrange without breaking because if you hit a wire, you break something, no one's you know, astronaut time is the most valuable commodity. So we can sit for two hours repositioning and it's hard. Once it's all positioned, that igniter comes up to there and basically heats up. We usually sometimes we do it on a lower flow, depending on what the oxygen and the pressure is. So, like low pressure, low oxygen, be really hard to ignite. Lower flow means there's gonna be a bigger buildup of gases, it's easier to ignite. And then you you ramp up the wind and you can like blowing on it like a fire, right? You shield it from the wind, you get it going, then you blow on it. So there's some fiddling and playing to get it ignited sometimes, and then that flame is gonna spread against the wind, so a post flow from the tip across. And what's really unique, the experiment was first designed that we were going to take the oxygen concentration and we were gonna pulse nitrogen in to drop it and see at which nitrogen concentration it goes out. When we've built a mock wind tunnel here in the lab, so originally our wind tunnel, the lab, blows whatever pressure and oxygen concentration you want through the sample, and we have a little straightener and wind tunnel in the lab and a pressure chamber, and we can test the samples here, and which is great. It's closed, it is it's it's sealed, and we realize that we were always testing where we're just blowing it the whole time. So we tried sealing it and using a fan, and you realize the oxygen concentration builds up pretty quick, which is fine. You can add the nitrogen, you can pulse it. But it turns out the way in which you purge over pressure kind of tweaked the experiment. The whole plan originally was that we're gonna add nitrogen and then we'll bleed a little bit of gas from the chamber to keep the pressure the same. But the rate at which you add nitrogen and the rate at which you bleed is not perfectly timed, and so it winds up having kind of step and the pressure jumps up and down, and then it's really hard to find an extinction limit because you're like affecting the flame. And just by testing it, it turned out if we just let it burn, CO2 builds up really quickly in the chamber, and oxygen goes down, and oxygen goes down, and it puts itself out. So on some things where you start on a high oxygen, yeah, you can pulse nitrogen once or twice in the beginning, and then you bleed a little bit to keep the pressure right, and then you can just let it go. The most important thing is at the extinction limit that you're not adding impulse in which might wiggle and might affect the plane, and then at the end, you can get really close, and then actually the accuracy of that extinction point you can get to like a 0.2%, 0.1% rather than like a single percent, because that change in pressure was really affecting it.

Wojciech Wegrzynski:

How do you maintain pressure while doing that? Do you have some relief?

Michael Gollner:

Uh I mean, I assume the error is a relief valve on the space station. It's it's you know, I believe it's relieved in space. So there's only so much you can do at a time, and it has to be controlled, and those limits make it so that it's like, you know, when you open it, it does it and it closes, and it's just it's just jerky for our experiments.

Wojciech Wegrzynski:

Once you ignore it, you you can only sit down and observe pretty much like any fire experiment. Or do you do you get to do things to it?

Michael Gollner:

We do get to do things to it. Okay, they really hate if we don't tell them what we're gonna do in advance. Yeah, they're wonderful. It was it used to be called Zinn, now I think it's part of Sierra Lobo or something, but there's a company in Ohio that supports this experiment, built the apparatus that was flown up, uh, and they're just wonderful to work with. And then there's folks from NASA Glen, and they're all on site at NASA Glen in Ohio, um, running it, and we're remotely logged in. I mean, there's some of them where some of us uh flew in to join with them. Most of the time we're remotely directly connected, and we also have the same live stream when it works, um, viewing the cameras and viewing all the instrument data. And we have options to do things like we can say, Oh, pressure's getting high. Can you please bleed it for a little bit? You know, and that they can do that live. They can change the camera angle, they can change the lighting. We started at the very end to position the sample during the burn. We didn't do that in the beginning, it was never in the plan. Um, but one of the students, there's two two students, grad students, who who helped prepare most of these experiments when it was in space, Christina Liverto and Jose Rivera. And Jose came up with the idea. He's like, wait, we're always positioning, and sometimes the flame starts spreading away from the heater. Can we just scooch it to the heater? Why not? You know, then it stays heated longer because sometimes it just burns longer than we expected. And that was me, because then when you get closer to that lower 14% extinction limit, um, because it stays heated. And there are things we can do, they just they like to know a little bit in advance. There are limits depending on how much gas is prepped and what we're doing, but it's it is a live process.

Wojciech Wegrzynski:

Do you have like a mock-up of the like you said, you have wind tunnel, but do you have like an exact copy of the experiment in the space in your lab to like play fine-tune or no?

Michael Gollner:

We don't have an exact mock-up. I think uh I think the lab at NASA Glen or the Zen team has a mock-up because they calibrated the wind tunnel using that, uh, but we do not.

Wojciech Wegrzynski:

And uh do the people so so well, technically you can fiddle, but it's true a third-party engineers. Like, uh, what's their comprehension of experiment? Do you have to brief them of on what you're doing, on the science of it? Like how how how much do they know?

Michael Gollner:

I mean, they know a lot, but they're not the scientists. It's interesting. So they do have a lot of experience, which is great because they've done a lot of microgravity experiments and they're very close to the NASA engineers. So, this you know, the planning for this project goes back many years. I, you know, Carlos originally did the application. I was actually part of the first science review team. So when I was a new professor at Maryland, I was unaffiliated with this, and they asked me with a bunch of other much more well-known um people to come and evaluate the science and whether they were ready. And this was the projects were already selected, like in the grant. But is this ready to like go for space? Um, which it was, you know, we made some suggestions and changes, like, oh, add this too. Why aren't you doing this? Or, you know, and then there was another review whether it was technically ready. Is the design, does everything sound like it's feasible to do a space? Cast this was baby, like it felt like 10 years ago. I don't know exactly, but it was it was a while ago till it's actually flown and and done. But it was only years after that process that then Carlos was talking to me about joining the project from my work on flame spread and needing help. But this was after I was you know, all the reviews were over. It takes a long time to make sure that everything comes together, and there are many changes along the way because you have to fit what's going to happen in there for all the different investigators over time, stay within budget, and there's a lot of NASA rules, right? For you can use this, you can't use that, this camera's allowed, that's not, it hasn't been certified. They have to pass a flame spread test, these sorts of things.

Wojciech Wegrzynski:

So does your PMA pass a flame spread test?

Michael Gollner:

Uh I wouldn't think it does. So the NASA actually adds a flame spread test. It's uh what is it, NASA 6000, like 6001 test. It's an interesting standard, but it's it's basically you know a rod, you ignite it in whichever pressure oxygen and see whether it yeah it's or not. It's it's not very advanced.

Wojciech Wegrzynski:

Uh another question. Uh the heater. So the twist in this experiment you said is is the heat feedback. So given the previous experiments, what does the heater change? And and how how did you introduce the heater to the to the experiment? I assume it's 360 degrees, it's like uh a tube to which you put the sample? Or how the how does it work?

Michael Gollner:

Don't be wish. No, okay. Uh it's three rods, three row rounds. Okay. Um, originally there were more, but there were three that were allowed. Um and there are reflectors, rounded reflectors on the back to try to even that out as much as possible over the sample. It's not perfectly uniform, but it's not that bad. Um so yeah, the apparatus, the rod is pushed into that wind tunnel, and around are the three heaters. Okay. Ceramic rod, or whether not ceramic, they're ceramic, they're like flat rectangular heaters with a that shiny foil reflector behind them to try to then reflect that over the surface so they overlap a bit. And they're they're it's fairly good. It's not perfect, but it's a fairly good coverage. Originally it was supposed to be halogens, which are much more controllable, but there's issues with power and with that chattering. So when we run the heaters, so the first set of tests last year was without heaters, and this year, it's not that we really got to an incredibly new lower oxygen concentration. Um, but generally the experiments could achieve lower oxygen concentration. You know, so it's not like the back's limit changed, but the same conditions that were not getting down are getting lower with additional heating. It it hasn't been a dramatic change. I I should caution too, the heat fluxes are one to three kilowatts per meter squared. Okay. Sunny day. It's uh very three kilowatts is is a little more than a sunny day, but yeah, it's very sunny day. Yeah, so it is not the 20 kilowatts per meter squared that we think of in fire testing on Earth, but these are very tiny flames, and we're doing them in space. And I mean, there is a change. If three kilowatts per meter squared, you see longer flames and it spreads faster, and it it changes because it it's heating the sample. Countercurrent spread, those those flames take time, and heating up the sample is also going to help it spread faster. So there's a lot of effects that are kind of all tying it together.

Wojciech Wegrzynski:

How does this relate to real engineering problems on the spacecraft? Wouldn't you expect like much higher heat focuses? Or it's actually quite representative because you have this very sophisticated smoke detection with the with the suction. Like, I guess it's very early detected the fires in space. You don't like wait until it's a megawatt, it would be the disaster, right?

Michael Gollner:

Right. So, I mean, it's not representative of everything going awry where things are spreading and falling apart. This is representative of the early incipient stages, and I think that's where the goal is is that you don't want things that can get to that stage and propagate further. So it really is focused on the early stage fires and the ignitability limits. Could this really burn and keep burning? And we're trying to understand those limits, and that's the focus. I you know, for long duration of space flight, there's a different level of safety. I mean, astronauts wear cotton shirts and people freak out on the safety end, but they're still gonna allow it because it's just something the astronauts really want for their comfort, but at the same time, most other things are held really stringently to just not allow a lot of flammable materials in living spaces. It's just really trying to reduce that as much as possible to lower the risk. It's a different kind of safety considerations.

Wojciech Wegrzynski:

I wonder what like I mean, observing the the space market, let's say, I wonder how it's gonna evolve because perhaps one day we'll you you'll have like a cargo missions which will be tolerating a larger level of risk but both needing oxygen on boards, and you could just send a bunch of stuff there, and you could have like this VIP uh passenger vehicles, which would be crazy control, like like uh early detections and stuff. Do you think uh that there will be uh work for uh space fire engineers? I wonder if that's gonna be a thing in the future.

Michael Gollner:

I I do really worry about what is going to come when things are a lot less regulated, because things have been so regulated. It's just, you know, I it's not like, oh, this is the specific risk, but obviously, you know, we worry about how an unregulated environment for something that is traditionally very risky and unique, and how that's going to change the the system. I think I think we do worry about that, and I don't think we know exactly how that's going to change. NASA, for all aspects, has had that approach of just super over-engineering design within limits to try to be as safe as possible. We've already seen that change in the space flight industry, you know, it's evolved with the NFTA on the spaceport safety standards, and that kind of evolved because we're now taking the off of a military base and we're putting it into a you know private thing, where now a county inspector is inspecting. And what did they do? That's really complicated. Yeah, it's gonna be the same in space flight, but right now I think NASA maintains a lot of the inspection and a lot of the safety rules, but you know, it might change. So it's the space flight's never routine.

Wojciech Wegrzynski:

Yeah, one more question that I that I had in mind before uh I forgot to ask. You said the astronauts' time is the most expensive commodity. How much do astronauts really physically do with those experiments? It's not that an astronaut is sitting and observing your flame through a window, but what's actually their part on the experiment?

Michael Gollner:

Yeah, I mean, I think they spend, you know, an hour to a few hours. So when we would typically run once per week, be an all-day test day, unless something went wrong, we have a makeup, and we'd do three test points to prep for that, or at the end of that, an astronaut would come in, they'd open it up, they'd replace some gas cylinders, they might replace a filter, they take the fuel rods out and they'd replace them every other week. So we'd re-burn them if they weren't too badly damaged. They might replace an igniter tip. You know, these extra materials were flown up with the experiment, and then they close it all up again. So they the contractors would give them a list of what to do, and they they were trained and they went in there and did that. And you know, it's always neat to see the pictures back when you see like the but it used to be on Twitter. Now you see it on their LinkedIn, yeah. And uh, you know, so like Johnny Kim, who's a famous astronaut, is is in our apparatus, you know, going changing our experiment, putting things in.

Wojciech Wegrzynski:

And the communication with the astronauts, it goes through the third party. Did you uh have to train them, or you just made an explicit instructions on what's gonna happen, or that's the the company from Ohio doing that.

Michael Gollner:

The company and then NASA are doing most of that coordination. Obviously, NASA Johnson Space Center Mission Control is doing the direct communication with the astronaut. This is very interesting the way this process works as the PIs, you know, we're proposing and we're planning. We work together with the NASA scientists who are fabulous. I mean, their experience, you know, so was Sandy Olson and Paul Stracool and Dennis Stalker are always someone is always there supporting us. And they've done decades of experiments, and they actually see you know the company as they're building it, and they're like, no, no, no, no, no, you know, so so they are very, I mean, we're involved too, and we're constantly in calls and checking, and we're flying at, but but not to the level that they are. Um, and they do have a lot of experience. It's not the first fire experiment they built, they built a lot of them, and so that's you know, and they know what astronauts can do, what they can't do. We have no idea about that, and so it helps tremendously. That's really just part of that process. And NASA contracts with them to build it. We just run the science part.

Wojciech Wegrzynski:

The decades of experiments, I guess you can say it never gets old. And I can I can I can only imagine like the joy of a student who gets to do their master's or PhD like experiment in a space station, like like we had a you know, so you know, Mari Thompson worked on this.

Michael Gollner:

There's another student, Andy, it's a postdoc Charles and Luca all worked on MIST. And it hadn't flown yet, it was going to, it was delayed and delayed and delayed and the delayed, you know, right? They got rid of the spatial, they moved to the space, and then this happened, that happened, and then yeah, Jose and Christina just and me lucked out flying. Like, wow, this is happening. I didn't believe it was ever gonna happen, you know, and then um and then we spend weeks getting the computer to connect through Alabama to the space station so you can see the video, and then we, you know, I mean, like we spent months getting the IT stuff so that we could see it in real time. I had to get my NASA ID so I could install it. Like there's silly little things to make it happen, but it was a really neat experience.

Wojciech Wegrzynski:

I I guess uh you would do it again. Like you look like someone who would do it again if if if got the proposal tomorrow.

Michael Gollner:

Yeah, yeah, of course. I mean, you know, we've applied for other things, but I'm afraid that a lot of the programs are gonna be are gonna be shutting down now, which is sad. I I looking at the emails, you know, the folks who supported us, you know, they put out some nice commemorative kind of like posters about everything that ran in the combustion integrated rack and the kind of like a good buy. Because they've been supporting it for well over a decade, and um, and I guess we closed it out. So it's a little sad. Maybe it'll come back again, but yeah, at the moment, I don't know if anything else is planned.

Wojciech Wegrzynski:

I I hope that after uh some downs there comes the ups, and uh like you understand everything about fire in space. Well, there's still fire experiments on the moon to be done, fire experiments on Mars to be done.

Michael Gollner:

There are now there are some, there are some planned. I know, you know, NASA Glen and I think, and um Ya Ting Lao, I believe, at Chase Western. Uh she's part of a group. I believe they are planning a small experiment on the moon. That partial gravity will be really exciting and interesting at the moment. The only way to do it is while dropping in a drop tower for five seconds and spinning it. So you got a lot of distortion effects. And actually, you know, some of the previous studies have shown that partial gravity may be riskier than you're on Earth.

Wojciech Wegrzynski:

Well, in that case, uh, we will not run out of topics uh for the space fire science show uh episodes in the future. And I am really looking forward uh to hear some news uh from from this industry. Anyway, Michael, well, I didn't even notice, but it was it's already an hour. Wow. Uh thank you, thank you so much for coming to the fire science show and sharing all of this. It it was a pleasure, and uh my uh space geekness is satisfied right now.

Michael Gollner:

I'm glad it was you know, I I have to say it uh one of the coolest things was not just I mean it's amazing seeing your first ignition and watching it might because it always happens at a weird way too early or late. You know, my kid was there, was like, you know, then an extent, you know, everyone was we were all excited, cheering, you know, watching it through a screen. And but when you realize the level of support for even any of those experiments, you know, you've got support staff, people are doing things in a lab, but to put something in space, I mean, there is a massive team supporting space station, but just for this experiment, there is a huge group of those contractors who are designing the experiment, checking, someone's making sure the data is working, someone's making sure the arm is working, someone's watching the gases and doing that. There's NASA scientists there checking. We're doing that. Someone at Johnson's making sure the astronauts had all this prep, they had to do it. It's such a massive undertaking for those few moments of you know gathering science. It's it's really incredible. And uh it's it's just an amazing privilege to be part of it. And I'm hoping that there'll be more opportunities and more researchers in the future get to do this because it it's a it's really a neat experience, and it provides some valuable information that you just can't get on Earth, and the discoveries are not done. We just finished a couple weeks ago. We've got mounds of data to go through, and we're just starting all the analysis. So we're gonna learn a lot in the next year from all of that data that we collected.

Wojciech Wegrzynski:

And that's it. Thank you for listening. So much stuff we still don't know, uh, so much stuff that we still need to learn about uh fires in microgravity and fires in space in general. And at the same time, it's not that we can learn those things uh at the surface of Earth. So, yeah, still plenty of uh science to do in space. I hope uh the world ends up a little bit more optimistic than uh Michael is worrying about. I hope that those experiments in space continue and we find new ways to put interesting stuff at uh representative scales in the space environment and get a little more fire researchers to get this excitement of having you know their first ignition outside of uh planet Earth, I think. That that that must be a thing, right? To start your first first experiment in the space. I can just imagine the amount of joy and excitement that that accompanies that. If we look at the practical side of things, you know, fire engineers, I I think there is some space for fire engineering in space pun intended. I think uh maybe. It's not gonna be a huge industry. I mean, if you look at aircrafts and air travel, there is a lot of foreign engineering to be done in relationship with aircrafts and in the same way as we have space travel. I mean, when I was a kid, you know, there was NASA, there were Russians, they were sending stuff to space with those governmental funded rockets through governmental companies. That was it. And today you have those billionaire big boys who are playing with rockets, and there's more and more companies that actually go into this industry as a commercial project and they're actually building very large vessels, very large vehicles, like SpaceX is running the biggest vehicles right now. So it appears that once we enter the era of interplanetary travel, maybe more missions to the moon, perhaps missions to Mars. If what Elon Musk says he means that we will be able to send a whole fleet of ships to the Mars. In not so far from now, maybe 20, maybe 30 years, who knows? But but it's definitely in the foreseeable future that we we should have the capacity to do that. At that point, you will need a lot of fire engineering to make those missions safe and to to figure out ways in how you provide those people amenities for months of travel in the space, and you will need to find ways to to make uh their destination safe, you know, the Martian colonies safe, the lunar colonies safe. We've already had a brainstorm in the fire science show some episodes ago. I think it was a very interesting episode where we've just sat down and and thought like if we want to make a Martian uh Martian-based fire safe, what would it look like? It was a very interesting and exciting task, and I highly encourage any fire site engineer to actually do such a brainstorm. How would you make a Martian-based safe? Because it opens up some pathways you wouldn't think they exist. So yeah, I would I would highly recommend it. But anyway, a lot of fundamental science and a lot of practicality that I see in in research like that, and I hope you've seen that as well. Thank you very much for being here with me in the fire science show. And next week I'm gonna bring you more fire science, terrestrial fire science this time. So see you here next week. Uh same same time, same place. See you there. Bye.