Oct. 8, 2025

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

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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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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 - Space Fire Safety Returns

02:59 - Why Fire Risks Dominate Spaceflight

07:40 - NASA Calls, History, And Prior Experiments

12:15 - SOFT—Solid Fuel Focus And Goals

18:20 - Atmospheres, Oxygen, And Pressure Tradeoffs

23:45 - Why Rods, Not Flats Or Spheres

28:15 - The Combustion Integrated Rack Constraints

31:55 - PMMA As The Benchmark Fuel

36:10 - Microgravity Flame Physics 101

41:20 - Extinction Limits And Surprising Thresholds

46:05 - Opposed Vs Concurrent Flame Spread

50:20 - Measuring Heat Release Without Gravity

54:40 - Inside The ISS Test Apparatus

59:30 - Live Operations, Links, And Dead Zones

WEBVTT

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Hello everybody, welcome to the Fire Science Show.

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Today I'm taking you to the space and we're gonna do space fire safety, space fire science once again.

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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.

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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.

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Can this burn and can this keep burning in conditions that are present?

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It's about little flames, little fires.

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So it's about really testing out the flame behavior at the incipient stage of a fire.

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If you have followed Fire Science show, we already had um space episodes.

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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.

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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.

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And if we understand how the fires grow at early stage, we may be better at detecting them and removing them.

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So while it is a fundamental research, it has also a lot of practicality to it.

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And it is just so much fun to run your experiment in the space.

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If you ever wondered how it looks like to set up a fire on the International Space Station, Michael will tell you how.

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So that's the episode today.

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I hope you will enjoy it.

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I loved it as a space geek.

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It's always uh fun to discuss space fire safety.

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And I I hope you share the passion and you share the same views.

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Uh let's spin the intro and jump into the episode.

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Welcome to the Fireside Show.

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My name is Voyage Viginsky, and I will be your host.

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This episode is brought to you in partnership with OFR Consultants, the UK's leading independent fire engineering consultancy.

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Start your journey with OFR and help shape the future of fire engineering.

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Hello everybody.

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I am joined today by Professor Michael Gollner from Berkeley.

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Hey Michael.

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Hey, how are you doing?

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All good, all good.

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Let's let's fly to the spaceman with your crazy experiments.

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I'm really happy that again on the podcast I'm able to talk about uh spacecraft fire safety and general fires and microgravity.

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It's a thing that's uh very interesting to me as an amateur astrophotographer and a space nerd in general.

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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?

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Maybe that's an interesting thought.

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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.

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I hope we're going to twist his arm to get on here someday.

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

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But yeah, so he he's been leading microgravity experiments with NASA for many years.

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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.

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You can touch them, you can see them.

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So there's a lot of history.

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He led the smoldering experiments that were done on the space shuttle.

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There's still the samples, I believe Jose Torrero and many others worked on those.

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So there's a long history, and even this current experiment, the material ignition and spread test, it has a long history, right?

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Like it, I was not around when it was initiated, and so it's been going for quite a long time.

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It it's not easy to actually conceptualize, put it in the thing, have it planned, and actually getting it up.

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It's this incredibly long process before it actually flies and is run.

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That's exactly why you are on the podcast because it just summed up the contents of this podcast episode to come.

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Tell me, tell me all about it.

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So, first let's talk about the idea.

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Does the idea come from the needs of NASA, or is it something you as a researcher come with an idea to NASA?

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Is there an open bid for like, hey, anyone wants to do a space stuff?

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Uh both, both, right?

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So spaceflight, there's been a need for fire safety research.

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When you talk about the hazards that you have in microgravity, fire is one of the greatest.

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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.

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The same thing for re-entry, a damaged tile can lead to destruction.

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But I think in terms of current space flight, fire is one of the most risky hazards that are that are out there.

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And so they're very concerned about fire safety.

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And fire behaves differently in microgravity, which we'll talk about.

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But because of this, there's always been this research program going on the side.

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So I think going in NASA Glen, and David Urban, you know, who runs that program would know better.

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But I believe he said like the drop tower started for microgravity research.

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So they got like a five seconds of microgravity drop, started around the Apollo program.

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And there were a lot of other things they were testing too, and they started to look at fire safety.

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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.

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So there were door failures, and then there was this fire and led to their death.

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Fire safety has always been an issue since then, or at least it's been highlighted.

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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.

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And we still don't understand everything about microgravity, fire safety, which is why the research program continues to emphasize.

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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.

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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.

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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.

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I actually had David in the podcast a long, long time ago, uh, 2022.

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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.

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So there are calls.

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Do they I wonder how it is awarded?

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Like, uh do they have favorite people to work with or or do you fight for it?

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Like, I'm really curious about the the technicalities of that.

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Yeah, so I came on as a co-PI after this was already started.

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This so typically NASA has calls for proposals.

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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.

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The NSF, the National Science Foundation, the US, has had small experiment additions.

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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.

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And so we never got to do any new things.

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But this program was long before I was a faculty.

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Uh, they had a call for experiments.

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It actually goes back further.

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I believe a lot of this idea originated.

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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.

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And that experiment was planned.

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I think Sarah McAllister did her thesis on it and some others.

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And then it never went to space flight because of changes in the administration in the government.

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So that program was canned, and then a new program later came where MIST was proposed.

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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.

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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.

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So this call was for material ignition, and all of the experiments are solid fuels, so solid fuel experiments.

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And the real change in our experiment missed from all the others was that heat is added.

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So if you're anyone working on material inflammability, external heating is like a core of fire science.

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That's what we always do.

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But you pretty much don't find that ever on the space station.

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It's pretty hard to add here, and there's lots of problems with it.

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So that's something unique that was added in this experiment.

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There were a series of other investigations in the same lineup, not all of which have completed.

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But that addition of external heating is supposed to make this somewhat unique compared to previous experiments.

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Although it's no longer the flat configuration from Fist, this one is a cylindrical configuration.

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So, you know, depending on the requirements, things change, but there's a lot of things that can be investigated.

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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.

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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.

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Yeah, so Sophie's main research question, right, is to look at solid fuel flammability.

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You talked about long duration spaceflight, and we know that flammability and microgravity is a little different.

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And some of that's because buoyancy is gone, and so that makes things interesting, but there's still some airflow.

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There's HVAC or heating ventilation air conditioning on the space station.

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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.

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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.

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It's an interesting mix.

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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.

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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.

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So we like our one atmosphere, 21% oxygen at sea level.

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Um, in space, if you want to go into a spacesuit at that pressure, it doesn't move.

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So you want to reduce the pressure, but then you don't have enough oxygen to breathe.

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So just like going up Everest, you pump in more oxygen.

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So you have a higher percentage of oxygen.

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That potentially adds a high risk.

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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.

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So you can really speed things up by keeping lower pressures and higher oxygen concentration on what's called the normoxic curve.

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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.

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Even at a lower pressure, you're gonna have a higher percentage of oxygen.

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So your body gets enough.

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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.

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You're also gonna have to have less material for the structural integrity of the spacecraft.

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So there's a lot of reasons and it makes space flight easier.

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But potentially, even though lower pressures and microgravity make things less flammable in general, higher oxygen makes it more flammable.

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So this experiment for all the investigations varies pressure, oxygen, and then each one does a little bit different flavor.

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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.

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And then, as I mentioned, the really unique aspect compared to any of the other investigations is we do add external heating.

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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.

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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.

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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.

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And I think the unique part about the mist experiment was that we get to do this with external heating.

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What's about the shape of the fuel?

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Why a rod?

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Is it like experimental setup specific?

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Is it like a real-world representative for space fuels?

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It's a great question.

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I don't know the true answer.

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You know, I'll tell you, I don't know.

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And I'm not saying the rod's a problem, there are lots of different ways to configure this, right?

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So the cylinder is not perfectly uniform everywhere.

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So I get why the sphere would be very nice in the very fundamental aspect, but it's very impractical.

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A flat piece would be good, though that was already proposed on the fist and then canceled.

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Not sure if that could be done again.

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I don't know how much that's the reason.

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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.

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There's complications in that, but then there's some benefits that you sort of get more thermal thickness testing.

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The other thing is with a flat sample, I mathematically prefer the flat sample a little bit.

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Maybe I just don't like cylindrical coordinates on an issue.

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Oh god.

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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?

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Okay.

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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.

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And then they'll do the switch out a week later and we do another set.

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So that way they don't have to sit there for eight hours while we're trying to run it.

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It's all being done robotically, controlled by Earth.

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And it's pretty hard to do that with a flat sample and fit that in the apparatus.

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And I maybe you should talk about the constraint.

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There is um fabulous apparatus called the Combustion Integrated Rack, the CIR.

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This apparently flew on the space shuttle and has been on the space station for years.

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It did all the droplet experiments like Flex with the cool flame discovery.

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It's done the previous Spire investigations.

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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.

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And they were quite large, right?

00:16:16.480 --> 00:16:17.360
For the space stuff.

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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.

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And I we we may have been the last in that apparatus, which is a little sad.

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It has been shut down.

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I don't know if it'll be turned back on, but you know, ISS is getting towards retirement.

00:16:38.159 --> 00:16:43.279
But we're constrained by how much space, how much gas, how much resources can be put in there.

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And so that also constrains a lot.

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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.

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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.

00:17:09.519 --> 00:17:18.640
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.

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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.

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We did a round last year and another round this year.

00:17:32.240 --> 00:17:35.279
We just concluded a couple weeks ago, and it was pretty neat.

00:17:35.279 --> 00:17:40.880
We were actually able to ignite fires in space, watch them, see it extinguish, learn something new.

00:17:40.880 --> 00:17:43.200
It was amazing to get that opportunity.

00:17:43.680 --> 00:17:49.039
I I would just send a gas burner, but my career in space uh science would end very quickly, I guess.

00:17:49.359 --> 00:17:57.519
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.

00:17:57.519 --> 00:18:00.240
Um that burner, they used a burner in space.

00:18:00.240 --> 00:18:03.200
That was if you're Quintiria, you're allowed to use burner in space.

00:18:03.200 --> 00:18:04.240
Hey, I'm not.

00:18:04.240 --> 00:18:06.319
It was very tiny, right?

00:18:06.319 --> 00:18:12.480
I remember I was in Maryland, you know, watching the grad students and calibrating the tiniest heat flex gauge in there.

00:18:12.480 --> 00:18:13.920
It was it was still cute.

00:18:13.920 --> 00:18:29.119
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.

00:18:29.200 --> 00:18:37.440
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?

00:18:37.440 --> 00:18:40.079
Polymethylmethacrylate, of course, right?

00:18:40.400 --> 00:18:42.559
Hooper's anything else than fire.

00:18:42.559 --> 00:18:48.319
Yeah, but the most realistic fire of them uh of them all, like the default uh fuel, you know.

00:18:48.319 --> 00:18:56.160
So there are arguments before and against, and you know, my PhD, I use PMMA too, so yeah, that sweet methyl methacrylate smell.

00:18:56.160 --> 00:19:11.440
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.

00:19:11.440 --> 00:19:21.440
It bubbles and vaporizes and burns, it doesn't char, it doesn't tend to release any toxic gases, which is nice.

00:19:21.440 --> 00:19:30.160
It is uniform, it's accessible, it can be made in different shapes, it can be made in different colors without affecting its properties.

00:19:30.160 --> 00:19:36.480
It's just a really nice material to work with, and it tends to just you know continuously.

00:19:36.480 --> 00:19:45.039
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.

00:19:45.039 --> 00:19:46.640
And so I like that.

00:19:46.640 --> 00:20:04.000
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.

00:20:04.240 --> 00:20:14.000
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.

00:20:14.160 --> 00:20:19.759
Uh so uh yeah, I mean there's better there's better solid-phase kinetic models for for PMMA.

00:20:19.759 --> 00:20:22.640
Not that that's been used an awful lot in this work.

00:20:22.640 --> 00:20:35.519
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.

00:20:35.519 --> 00:20:39.279
So everything we did was done on the ground and in space.

00:20:39.680 --> 00:20:44.079
Okay, well, here you talk here you take one of the questions I had for later, but thank you.

00:20:44.079 --> 00:20:46.400
Okay, another another question about fuels.

00:20:46.400 --> 00:20:54.480
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?

00:20:54.559 --> 00:21:00.640
Or no, I mean, not that they don't have fire hazards, but that wasn't part of this uh experiment.

00:21:00.640 --> 00:21:07.599
You know, the real goal of these experiments was to look at those extinction limits and particularly oxygen extinction.

00:21:07.839 --> 00:21:08.160
Yeah, yeah.

00:21:08.160 --> 00:21:09.759
Let's move there.

00:21:09.759 --> 00:21:10.960
I I like this.

00:21:10.960 --> 00:21:19.839
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?

00:21:19.839 --> 00:21:22.720
What exactly do you mean by by different behavior?

00:21:22.960 --> 00:21:23.359
Sure.

00:21:23.359 --> 00:21:28.079
In space, we're dealing with tinier flames, right?

00:21:28.079 --> 00:21:29.599
If you let's start with a candle.

00:21:29.599 --> 00:21:33.039
Candle on Earth, you get tall yellow flame.

00:21:33.039 --> 00:21:34.480
Why is that happening?

00:21:34.480 --> 00:21:38.880
The wax diffuses up, vaporizes.

00:21:38.880 --> 00:21:47.839
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.

00:21:47.839 --> 00:21:50.319
And it doesn't mix perfectly, it's not pre-mixed.

00:21:50.319 --> 00:21:55.920
So that diffusion flame generates soot, which glows yellow and orange, and you get a nice flame.

00:21:55.920 --> 00:22:00.480
In space, there's no buoyancy, no stretchy, no pull.

00:22:00.480 --> 00:22:02.799
It's a bubble, it's a beautiful blue bow.

00:22:02.799 --> 00:22:04.480
And it's interesting.

00:22:04.480 --> 00:22:23.440
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.

00:22:23.440 --> 00:22:25.519
And pop, there it goes.

00:22:25.519 --> 00:22:29.839
So we see that with a droplet flame experiments, you can do it with a candle.

00:22:29.839 --> 00:22:31.839
So in space, it's different.

00:22:31.839 --> 00:22:32.720
It is different.

00:22:32.720 --> 00:22:37.200
The feedback process, I mean, all the physics is the same, but you remove gravity.

00:22:37.200 --> 00:22:43.359
If I also took a flame in space, I could I could take and ignite that flame and then I could blow on it.

00:22:43.359 --> 00:23:03.759
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.

00:23:03.759 --> 00:23:08.480
So there are there are two limits for extinction that are gonna occur in space.

00:23:08.480 --> 00:23:12.640
And the big thing is that is that they're they'll be a little different than on Earth.

00:23:12.880 --> 00:23:21.039
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.

00:23:21.039 --> 00:23:31.440
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.

00:23:31.440 --> 00:23:32.559
Is that what you meant?

00:23:32.799 --> 00:23:33.119
Right.

00:23:33.119 --> 00:23:40.319
So that is what's going to happen unless we are giving it a little bit of wig.

00:23:40.319 --> 00:23:41.119
Okay.

00:23:41.119 --> 00:23:49.440
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?

00:23:49.440 --> 00:23:52.960
You need oxygen in there, and there's no buoyancy to keep it going.

00:23:52.960 --> 00:23:54.240
So there's always small.

00:23:54.240 --> 00:24:04.000
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.

00:24:04.000 --> 00:24:09.680
So that is going to provide some velocity over the fuels, but not much.

00:24:09.680 --> 00:24:12.480
But there isn't the buoyancy that we have here.

00:24:12.480 --> 00:24:14.960
These extinction limits happen on Earth.

00:24:14.960 --> 00:24:22.400
So, like a tiny flame, buoyancy can almost help blow itself out on Earth, which won't happen in space.

00:24:22.400 --> 00:24:30.000
It can just creep and creep and creep along very small, where it would never be stable on Earth.

00:24:30.000 --> 00:24:41.440
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.

00:24:41.440 --> 00:24:47.519
So the true limits of flammability are different in space than they are on Earth.

00:24:47.519 --> 00:24:58.160
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.

00:24:58.160 --> 00:25:05.759
And as we know, when you kick up external heating, that changes the flammability of a material too.

00:25:06.160 --> 00:25:11.759
We'll go to the the heating uh in a second, but uh there's a lot of physics we still need to cover.

00:25:11.759 --> 00:25:16.640
There's not many opportunities to talk about physics in space, so I need to be thorough in this.

00:25:16.640 --> 00:25:18.880
The the the concentration of oxygen.

00:25:18.880 --> 00:25:29.839
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.

00:25:29.839 --> 00:25:35.440
Usually, you said that in the space it's not about percentage really, but about partial pressures.

00:25:35.440 --> 00:25:37.519
Could could you tell me how that actually works?

00:25:37.519 --> 00:25:43.759
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.

00:25:43.839 --> 00:25:56.079
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.

00:25:56.079 --> 00:26:02.880
So this this with you know, when I was mentioning this, it depends it's really important when we talk about breathing.

00:26:02.880 --> 00:26:06.720
You need enough oxygen in the air uh to breathe.

00:26:06.720 --> 00:26:20.000
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.

00:26:20.000 --> 00:26:23.680
Those lower pressures require higher oxygen for people to breathe.

00:26:23.680 --> 00:26:42.400
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.

00:26:42.400 --> 00:26:52.400
The oxygen concentration to keep you breathing, having that higher oxygen concentration actually affects the flame more strongly than the lower pressure does.

00:26:52.400 --> 00:26:55.279
Like lower pressures are gonna make the flames weaker.

00:26:55.279 --> 00:27:01.119
When we want to mimic microgravity flames on Earth, we lower the pressure in the chamber.

00:27:01.119 --> 00:27:01.519
Okay.

00:27:01.519 --> 00:27:07.599
It will make them bluer, it will make them rounder because there's less gas, so there's less buoyancy effects.

00:27:07.599 --> 00:27:17.359
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.

00:27:17.359 --> 00:27:23.680
So the higher oxygen concentration has a big influence uh and is very important consideration when we talk about flammability.

00:27:23.680 --> 00:27:32.720
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.

00:27:32.720 --> 00:27:36.880
Just the same as if you do that in aircraft or if you do that in spacecraft.

00:27:37.359 --> 00:27:42.400
Now I need some fire engineers from Colorado to discuss the high-altitude fire engineering.

00:27:42.400 --> 00:27:50.799
I found a very interesting uh write on uh Engineering Berkeley about the NASA funded projects and uh by Marnie Ellery.

00:27:50.799 --> 00:28:01.519
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%.

00:28:01.519 --> 00:28:09.680
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.

00:28:09.680 --> 00:28:17.839
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.

00:28:17.839 --> 00:28:24.000
So the fact that you have higher oxygen concentration doesn't translate to that more vigorous fires, or maybe it does.

00:28:24.319 --> 00:28:29.359
Well, so first off, the experiments on on mist are not all on the normoxic curve.

00:28:29.359 --> 00:28:39.119
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.

00:28:39.119 --> 00:28:45.359
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.

00:28:45.359 --> 00:28:53.359
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?

00:28:53.359 --> 00:29:01.200
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.

00:29:01.200 --> 00:29:16.960
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.

00:29:16.960 --> 00:29:19.279
It's just it's not happening.

00:29:19.279 --> 00:29:22.319
Um, but it does happen in microgravity.

00:29:22.640 --> 00:29:25.519
And have you had a short on explaining why why that is?

00:29:25.519 --> 00:29:28.880
Is it like a heat transfer phenomenon, radiation?

00:29:29.279 --> 00:29:33.119
I think the majority of this all centers around the buoyancy, right?

00:29:33.119 --> 00:29:41.279
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.

00:29:41.279 --> 00:29:44.160
We actually interestingly found two limits.

00:29:44.160 --> 00:29:55.119
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.

00:29:55.119 --> 00:29:59.759
And then there's a second limit where it actually stops burning and goes out.

00:29:59.759 --> 00:30:00.400
Out.

00:30:00.400 --> 00:30:03.519
And you know, limits are complicated.

00:30:03.519 --> 00:30:08.480
It there's fluid mechanics occurring and the flow because it's it's a cylinder geometry.

00:30:08.480 --> 00:30:12.640
There's the heat transfer effects, which depend on the thickness.

00:30:12.640 --> 00:30:14.240
That's why we have different thicknesses.

00:30:14.240 --> 00:30:17.759
We don't change materials, but the thickness makes a big influence there.

00:30:17.759 --> 00:30:24.240
And then there's a chemical kinetic effects, which is going to affect the temperature of the flame and the heat feedback.

00:30:24.240 --> 00:30:26.079
So these are all coupled.

00:30:26.079 --> 00:30:31.200
So none of the results are perfectly translatable to everything.

00:30:31.200 --> 00:30:41.200
But universally, it's it's fairly universal configuration and fuel that we would then expect this to happen to most other materials, right?

00:30:41.200 --> 00:30:43.279
The limits may be slightly different.

00:30:43.279 --> 00:30:48.400
There may be even more, but we're trying to understand that influence and we see that pretty strongly.

00:30:48.720 --> 00:30:50.799
I wanted to ask about the flame spread.

00:30:50.799 --> 00:31:04.240
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.

00:31:04.240 --> 00:31:07.440
Do those things change in microgravity as well?

00:31:07.440 --> 00:31:08.960
They do and they don't.

00:31:08.960 --> 00:31:09.359
Okay.

00:31:09.599 --> 00:31:09.920
Right?

00:31:09.920 --> 00:31:12.799
So opposed flame spread is what we're doing.

00:31:12.799 --> 00:31:17.680
Um, and maybe after this, let's let's focus on the and I'll walk through how the experiments run.

00:31:17.680 --> 00:31:20.640
So opposed flame spread when it's going against the flow.

00:31:20.640 --> 00:31:34.720
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.

00:31:34.720 --> 00:31:41.200
And so a lot of the heating tends to be radiation from the flame or it could be conduction through the solid.

00:31:41.200 --> 00:31:50.160
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.

00:31:50.160 --> 00:31:57.119
Concurrent flame spread is where the flame laps over the area that hasn't burned yet and heats it.

00:31:57.119 --> 00:32:00.000
So concurrent flame spread is faster.

00:32:00.000 --> 00:32:06.640
It's very dominated by buoyancy or by flow, and where you see the flames in front.

00:32:06.640 --> 00:32:10.559
So upward flame spread or wind-driven flame spread, that's concurrent.

00:32:10.559 --> 00:32:12.720
And it's almost always flat faster.

00:32:12.720 --> 00:32:14.880
It's also acceleratory, right?

00:32:14.880 --> 00:32:19.920
So it doesn't ever get linear unless it's through a very thin fuel.

00:32:19.920 --> 00:32:26.319
And yeah, so countercurrent flame spread is much more fundamental.

00:32:26.319 --> 00:32:33.599
It goes back to like John DeRis in 1969's paper with the first theory for a post-flow flame spread.

00:32:33.599 --> 00:32:43.039
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.

00:32:43.039 --> 00:32:51.920
Sapphire did some concurrent flame spread, but for these small experiments, you really need to work with the small countercurrent flames.

00:32:51.920 --> 00:32:57.920
Hypothetically, if you have no flow, like well, what would it look like?

00:32:57.920 --> 00:32:59.920
In microgravity or on Earth?

00:32:59.920 --> 00:33:00.720
In microgravity.

00:33:00.720 --> 00:33:06.319
In microgravity, if we had no flow ignite at the tip, uh, it is possible that it could spread.

00:33:06.319 --> 00:33:08.720
It could be way slow, right?

00:33:08.720 --> 00:33:10.960
Because the flame wouldn't grow as much.

00:33:10.960 --> 00:33:17.440
We would probably have a very small burning region that would propagate.

00:33:17.440 --> 00:33:27.359
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.

00:33:27.359 --> 00:33:31.519
Ultimately, when we think about flammability, there are a lot of parameters that are important.

00:33:31.519 --> 00:33:36.160
Ignition, which is not something studied as much here, because we're not controlling it.

00:33:36.160 --> 00:33:39.440
You have uh flame spread, the rate at which the fire grows.

00:33:39.440 --> 00:33:42.720
You have the heat release rate, which is also something that we capture.

00:33:42.720 --> 00:33:48.079
Uh, and then you you have sort of like the, you know, in this case here, extinction suppression.

00:33:48.079 --> 00:33:52.640
So those are different aspects of flammability that would be tested.

00:33:52.960 --> 00:33:54.720
How do you capture heat release rates?

00:33:54.720 --> 00:33:56.720
Do you have oxygen colorimetry in the experiment?

00:33:56.799 --> 00:34:00.160
Or there is a lot of oxygen sensors throughout the experiment.

00:34:00.160 --> 00:34:08.239
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.

00:34:08.239 --> 00:34:21.599
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.

00:34:21.920 --> 00:34:24.480
Yeah, that's that's probably true.

00:34:24.480 --> 00:34:29.679
I mean, but as a trade-off, you don't need any sample holders.

00:34:29.679 --> 00:34:32.400
You do, you can what's time?

00:34:32.800 --> 00:34:34.239
Can we talk about like how this works?

00:34:34.239 --> 00:34:35.119
Yeah, yeah, yeah.

00:34:35.119 --> 00:34:38.000
So if you go online, you look at the experiment.

00:34:38.000 --> 00:34:46.079
So the the experiment is in this big cylinder, and inside is essentially stuck a little square, uh, rectangular wind tunnel.

00:34:46.079 --> 00:34:50.880
And so it's a very simplistic wind tunnel, and it can blow faster.

00:34:50.880 --> 00:34:53.440
What size is like shoebox, uh bigger?

00:34:53.440 --> 00:34:57.199
It's like two shoeboxes, maybe two and a half.

00:34:57.199 --> 00:34:58.559
It's not super big.

00:34:58.559 --> 00:35:10.719
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.

00:35:10.719 --> 00:35:18.400
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.

00:35:18.400 --> 00:35:27.440
Okay, so inside that apparatus are three holders which are robotically controlled, and then there's an arm that has an igniter.

00:35:27.440 --> 00:35:46.719
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.

00:35:46.719 --> 00:35:52.320
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.

00:35:52.320 --> 00:35:59.199
Do we have like a live view of that happening or sort of so you have a live view while it's in range?

00:35:59.199 --> 00:36:11.199
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.

00:36:11.199 --> 00:36:17.679
So there's a series of satellites around the earth that are bouncing off of the space station and then beaming it back.

00:36:17.679 --> 00:36:26.639
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.

00:36:26.639 --> 00:36:33.599
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.

00:36:33.599 --> 00:36:35.199
Wait, no, it happened in 15.

00:36:35.199 --> 00:36:35.920
Oh, let's go.

00:36:35.920 --> 00:36:44.400
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.

00:36:44.400 --> 00:36:48.960
But we you're on pins and needles waiting, hoping this works.

00:36:48.960 --> 00:36:51.119
But they have a real system for this.

00:36:51.119 --> 00:36:59.920
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.

00:36:59.920 --> 00:37:05.360
Of course, every time an astronaut opens up the chamber, they reinstall stuff, everything shifts a bit.

00:37:05.360 --> 00:37:09.280
So you've got to readjust everything and hope it all fits and how it lines up.

00:37:09.280 --> 00:37:21.360
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.

00:37:21.360 --> 00:37:26.880

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

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