Nov. 9, 2022

075 - Spacecraft fire safety with David Urban

075 - Spacecraft fire safety with David Urban

Dear Terrestial Fire Engineers, let me take you on a journey that will make you experience fire engineering like nothing on our planet. Because in fact, it is the fire engineering of spacecraft for their operations in a zero-gravity environment. The environment in which the most fundamental aspects of fire engineering (think about smoke cannot go up when there is no up!) are being challenged. Where fire physics is completely different, and where things that are necessary for humans (oxygen, clothes...) become a major risk factor.

From my today's guest, Dr David L. Urban of NASA Glenn Research Centre, we will learn about the catastrophical fires that shaped the space industry. We get introduced to testing methods and fire safety engineering solutions commonly used on older and modern spaceships, and also try to take on the issue of fire safety of beyond-Earth human habitats.

I'm not sure how much practical engineering you will learn, but I am more than sure that you will enjoy this thoroughly. And maybe one day, you can pursue a career in space fire engineering...Who knows!

Additional resources:

Cover picture credit: NASA Glenn Research Centre


[00:00:00] Wojciech Wegrzynski: Hello, everybody. Welcome to the fire science show session. 75 Great to have you here. Today's a very exciting episode for me, because we're going to talk about. Spacecraft fire safety and fires in space. That's something that.

[00:00:12] Or at least the. The space travel is something that was with me through my entire life and always loved rockets and spaceships and space travel. And. Now I got to talk Someone from NASA. That's that's amazing. I've invited Dr. David Urban from NASA Glenn Research Center, who has been involved with multiple space exploration missions and fire safety of

[00:00:37] Developing a five safety of spacecraft and also researching fires in micro gravity in low Gravity environments. So you're very knowledgeable person about how does the practice of delivering fire safety to space objects or spacecraft look Amazing. And, uh, it's, it's super fun because, This would take for granted that smoke goes upward. Well, forget [00:01:00] about it. It

[00:01:01] No gravity. I loved everything about it. So I really hope you will enjoy this episode. Maybe less practical than usual Fire Science Show episodes, but definitely on the. upper boundary of excitement and interesting facts about fire science. So, yeah, very, very An hour of your time. But before we jump into the episode, I wanted to share some stuff about the podcast. So I've introduced a new, interesting thing. Uh, for you. I have opened ask me anything part on the, on the site. It's a place in the website of the, podcast at.

[00:01:36] You can actually send me a voicemail in that voicemail. You can send Either a question, a commentary, a view on something that we've discussed on the podcast. You know, I want to hear your voice. I want to hear what you have to say about what you've heard on the podcast. And maybe you disagree with something. Maybe you agree with something. Maybe some things need some different point of view, maybe.

[00:01:58] In your professional [00:02:00] experience. Uh, something works completely different. Or maybe you can tell us about how to use the technology that we have discussed on the show. And we have not covered in a, in a way that, So I'm, I'm super curious about what you have to say and what you would like to comment.

[00:02:15] I want this to be. Something that would be a monthly, let's say. No, no pressure there. I'll do it as often as you want, but let's start with a monthly. Ask me anything sessions where I will record an additional, podcast episode that will air on the end of the month. In which I will play these questions. I'll try to answer them. I'll player, either commentary.

[00:02:37] I'll try to discuss with them. If it touches some points that were on previous podcast episodes, I'll try to invite the guests. To give a short answer to the questions or commensory posed. So I think it could be quite a nice opportunity to, to have a discussion with you all. And see what you like about the show? What you.

[00:02:57] don't like about the episodes. What [00:03:00] are your points of view? Because from the letters I get You have very often very, very good points. And from the discussions on Twitter, LinkedIn, So many interesting aspects that are happening around the episodes. And of course, I'm just covering one point Uh, it's my point of view. I don't know yours. So, so here's the chance. So yours is also given then aerospace in the podcast. And if you like it, if it works. We're eventually going to increase the language of the incoming voicemails may be increased intensivity of that. I hope you like this way of participating. Oh. And if you're stressed about like sending a voicemail,

[00:03:39] As I will air in here, you can always just send me a text message through the common On the podcast website. So either way it will reach me and I'll try to work with So very looking forward to your commentary, to your questions, to your opinions. And looking forward to, to recall them this additional podcast episode for you to, to have a way to discuss [00:04:00]

[00:04:00] And, now. Well, I am as a lengthy introduction and there's a hell of a grade that both. Cause that'd be so just after that, Music so let's not prolong this anymore let's spin the intro and jump into the episode


[00:04:34] Wojciech Wegrzynski: Hello everybody. Welcome to Fire Science Show. I'm today here with Dr. David Urban, Chief LTX Low Gravity Exploration Technology branch at NASA hello, David. It's great to have you in the podcast.

[00:04:45] David Urban: Hello. It's really great to be here. I enjoy your, show

[00:04:47] Wojciech Wegrzynski: Thank you so much. I'm so, uh, so excited, overly excited, audience will, will find this disturbing, uh, the amount of extension in my voice because I'm, The second besting, after fire is, is spacecraft. And in my [00:05:00] childhood, this was probably the opposite.

[00:05:01] And I always wanted to be an astronaut. Now I'm fire scientist is a decent path of career. But boy, uh, being a fire scientist at NASA must be, very interesting path actually. How, how did you end up doing this? did you always wondered how, how it will be to set the things on fire in space or what, what brought you to the position you are today?

[00:05:21] David Urban: Well, it was, um, as a graduate student, I focused on combustion, phenomena.

[00:05:27] And, but in that case it was for oil recovery. And

[00:05:30] then my graduate work, my post, sorry, was, um, It's basically an air pollution issue with, you know, from petroleum.

[00:05:37] And, um, then I was for jobs in combustion. I had the wonderful opportunity to, be recruited by NASA Glen. And when I came on, it was primarily the focus was more on fundamental combustion, in low gravity and with a side, line of, uh, fire safety over time that shifted to. My work being primarily, uh, fire safety, basically our fire safety with a [00:06:00] sideline of fundamental combustion, I guess

[00:06:01] is the way to describe

[00:06:02] Wojciech Wegrzynski: it.

[00:06:02] But

[00:06:03] David Urban: it's always been really exciting, both the being able to contribute to the space program, but also to be able to participate in some really exciting experiments where we make, uh, what's normally a constant gravity variable.

[00:06:14] changes things, turns things on his head.

[00:06:17] Wojciech Wegrzynski: I mean, if you want to increase the acceleration on the ground, you have this spinning tools that allow you to do that. if you rotate them other way, it doesn't reduce the gravity no more. So the, the space for low gravity place to do experiments on earth is, is very limited, let's say.

[00:06:34] In the history of space exploration, fire is a part of history, also in a, in a kind of tragic way. And, I know the, the, the story of Apollo one where, um, the astronaut crew, has, uh, died during a fire on the ground actually, and I, I know these stories.

[00:06:51] Change the way how space industry works, um, with relation to fire. So maybe we can start there. How this [00:07:00] tragic even shaped the fire safety, view of, of, of NASA or, or space exploration agencies in, in general. Maybe you can bring our listeners a little closer to what happened during the Apollo one and, and how it influenced, uh, everything that happened later on.

[00:07:16] David Urban: So, yeah, it was in 1967. And, prior to that, I mean, there were some accidents in oxygen chambers that Might have given people, warning. I mean, there's a, fatal accident in the Soviet chamber, 1961, but,

[00:07:30] it's generally

[00:07:31] agreed that NASA

[00:07:31] did, didn't appreciate the hazard due to, uh, fire and enhanced, particularly enhanced oxygen. And in the rush, there's so many challenges. To do, uh, the spacecraft that, they did not have good control of the materials in the spacecraft, uh, cabin. And so then on a ground test, uh, so they were in, uh,

[00:07:51] the challenges. The, um, up through Apollo, the spacecraft were pure oxygen.

[00:07:55] Um, there in flight, in flight it was only about three and a half pounds. Uh, total pressure. [00:08:00] But on the surface, Because of the del uh, outside pressure, uh, it was fif, you know, near sea level, uh, little

[00:08:08] above sea air, uh, one atmosphere. And so then they

[00:08:12] Had

[00:08:13] a small arcing event inside the spacecraft, and, There's a large amount of, nylon

[00:08:18] netting holding uhto and whatnot in place, and it

[00:08:22] ignited that nylon netting and, uh, that fire spread rapidly. And, um, there are also issues with the cabin door, which was not readily opened with, uh,

[00:08:33] internal pressure and so they were not able to, uh, escape in any in time. And so they crew were overwhelmed by the fumes before the fire, uh, ultimately ruptured the vehicle. So it totally changed NASA's perception of the fire risk.

[00:08:46] and other agencies, did likewise have now very strict material controls and a lot of the attention is paid to, the ignitability of the materials in the spacecraft, and also the atmosphere in the spacecraft.

[00:08:58] Wojciech Wegrzynski: in essence [00:09:00] oxygen is something you need because people need to breathe. And, providing this, this pure oxygen, I guess it's for some reason, uh, optimally in, in a, spacecraft, you have it under, pressure. You, you cannot remove that. You cannot really ventilate the space.

[00:09:14] You cannot evacuate easily. That's also thing, I guess we'll touch it there later on. So you really need to control the materials. The second fire that I've, I've read on, uh, when preparing for the episode was the fire on the MIR station, the, old, Soviet station. that after sky up the second big outposts of humanity in into space.

[00:09:34] do, do you recall that fire or,

[00:09:36] David Urban: Yeah, I, I had the fortune to be part of the post-fire investigation

[00:09:40] team. Um, so I traveled to Moscow with, uh, some other people. Cause the, um, particularly, it was particularly important because that, uh, oxygen generation system, it was the BA is the backup for the IS International Space Station.

[00:09:53] Wojciech Wegrzynski: the one that burns,

[00:09:54] David Urban: Yeah, and it a system used in commercial

[00:09:58] aircraft.

[00:09:58] and in submarines,[00:10:00] it's uh, a perchlorate, in the aircraft it's sodium perchlorate and uh, that little mass pops down. There's little

[00:10:06] cartridges above your head

[00:10:07] of sodium perchlorate that gets triggered off and, uh, reacts ex etherically making oxygen. And likewise, in. The spacecraft, the, um, Russian system uses lithium perchlorate

[00:10:19] and it ends up being for mass and, long term storage trades better than oxygen tanks.

[00:10:26] and so it's very popular again on spacecraft and, uh, again on submarines and so, The problem was

[00:10:33] it's, you've got a, you know, exothermic system with producing, uh, pure oxygen. you know, one, one could never know what

[00:10:40] the actual cause was,

[00:10:41] but it's pretty clear

[00:10:43] that it was contamination.

[00:10:44] of the, materials inside the canister. And so it ignited, it was dramatically frightening, uh, vast amount of smoke and, apparently shooting. Moulton's metal

[00:10:55] out the end. we did a bunch of similar ones, but they're h one's [00:11:00] different, so one cannot

[00:11:01] be Sure.

[00:11:01] exactly how theirs proceeded, but, uh, some of the ones we saw on the ground were quite threatening if you were in a volume the size of a school bus or something

[00:11:09] with, with us.

[00:11:10] Wojciech Wegrzynski: You said the first, after the, the Apollo disaster, a lot of influence was put on, materials. So, does this mean only in combustible materials apply to space or there is certain, like how do you approach the flammability, uh, problem? You, you have your own, uh, ways to test the materials to approve them.

[00:11:28] David Urban: for, since that period, NASA settled on an upward fla abilities test, where the, uh, material is subjected, uh, in its, thinnest form. They want to use it in the worst

[00:11:38] Case atmosphere.

[00:11:39] is subjected to a very strong ignition source.

[00:11:42] And, uh, then there's a maximum

[00:11:45] distance it can burn after the ignition source burns out. that's deemed

[00:11:48] to

[00:11:48] Pretty conservative. Uh, you know, nothing change the conditions, anything will burn just about, you know, Uh, but it, uh, separates all the, uh, highly flammable objects. And [00:12:00] then if it passes that test, you can use extensively without

[00:12:04] any restrictions. If it fails that test, then strict controls are put in place and many

[00:12:09] things do fail to think clothing, towels, you know, paper all fail. And Ziploc bags. But, they're deemed necessary, but they, control how many of them you have and where they're stored, you know, And so you can't have a whole ton of Ziploc bags everywhere out.

[00:12:24] They keep an eye on that,

[00:12:26] Wojciech Wegrzynski: I, I always wondered if, uh, Scott Kelly's Monkey costume on, on SS was, uh, was fireproof

[00:12:33] David Urban: probably

[00:12:33] almost certainly not.

[00:12:34] So

[00:12:34] Wojciech Wegrzynski: was, I was that. Yeah. Yeah. Fair, fair point. Um, there's so many things, uh, I want to ask. We, we will go into fire engineering spacecraft in this episode for sure. But first one thing that, I would love to ask is the combustion in space.

[00:12:50] In microgravity. I think, uh, most people recollect this. Picture, I think it was a candle flame, uh, on a space station. This [00:13:00] beautiful circle or flame. It, it's an iconic image for, for fire scientists, I guess. And, uh, I've seen it multiple times in, in multiple different places. So, let's talk.

[00:13:10] How fire burns in, space. It must be different, like on the ground. It's, it's very driven by buoyancy, by the turbulent flow that, this, um, buoyant upwards movement of flame creates. Even in your fire test, you said it's a vertical setting, so you're also very reliant on, on convective, heat transfer from the they, I guess and, and stuff like that.

[00:13:31] But in space, wow, this, uh, gravity is zero or close to zero, so you don't have that. So,

[00:13:37] David Urban: Yeah.

[00:13:37] Wojciech Wegrzynski: Tell me the physics of, of the flame. Uh, how does it work?

[00:13:41] David Urban: so that was an, that photo was taken on the Mere Space Station by,

[00:13:44] Uh

[00:13:44] the astronaut Shannon Lucid with, uh, collaborating with, uh, Daniel Dietrich and Professor Jim t at, uh, case on that experiment. And, uh, it was really is a cool image cause it really demonstrates, you know, everybody knows on earth, a candle knows which way's up. And you turn [00:14:00] the candle, the flame always

[00:14:00] points up. It's amazing. in space. Is no up. So the shape it assumes is a blue hemisphere, and, uh, and in that case it's dominated by diffusion because there is, um, you've got a step on flow, the expanding vapor, from the, flame and uh, counter. that's what the oxidizer has to an oxygen has to diffuse inward of the product stream to support the flame. And so you. With no flow in low zero gravity, you're gonna get beautiful one dimensional spherical flames. And we have some really cool, images We've used, uh, both spherical droplet flames and um, spherical burner flames to study details of the flame chemistry that you really couldn't do easily on earth.

[00:14:39] so if there's no flow, then it becomes a pure diffusion system.

[00:14:44] but before the alarms go off in a spacecraft, there's. We always have flow to keep the air mixed up so the crew doesn't, isn't breathing a pocket of carbon dioxide, for example. And so, uh, there's a low speed turbulent flow in the space station at all times. And [00:15:00] so, in the presence of flow, then yeah, there is no, buoyant flow, but there is the force flow and it. Typical range is on the order of 20 centimeters a second

[00:15:09] in a spacecraft, which is,

[00:15:11] um, below what you'd get, uh, from a buoyant, flow in one G.

[00:15:14] And, so really

[00:15:16] you're in a different regime of burning, where the, you know, buoyant flow brings in oxygen, but it also takes out energy. And so the, it cools the flame at the same time so you can, that's, there's, a u-shaped flammability boundary where at higher velocities, uh, the flame will blow off and then you come down to the bottom and the lower side it loses, basically, um, quenches we call it where

[00:15:37] the heat loss puts it out. So, in space, the fire risk is always worse when there's the flow is on, which is before you've detected it.

[00:15:47] Wojciech Wegrzynski: And it's a pure oxygen setting or a mixture,

[00:15:50] David Urban: Well, that

[00:15:51] varies.

[00:15:52] In the, um, before the Apollo era, it was all, pure oxygen include up through the Apollo era. It was pure oxygen [00:16:00] at low pressure, uh, against the human physi physiology, response to partial pressure of oxygen, not the concentration. whereas the, uh, fires is, you know, primarily

[00:16:09] respond.

[00:16:10] to. The concentration because, the nitrogen will take away energy and will interfere with reaction progress. but humans need a partial pressure. So the, uh, it's simpler to have a one gas system than a two gas system and a spacecraft. So the poly is all, um, and four, all one gas Now,

[00:16:28] Uh, Sky Lab was a different, um, intermediate condition, but on the Space station and the shuttle system and, Mirror and the sos the target is sea level air,

[00:16:39] but it's, you know, mixed from nitrogen and oxygen. And so that, um, make is much safer condition. Looking forward, we're probably gonna be higher, uh, concentration oxygen on the lunar habitats,

[00:16:49] to, um, enable more. extra vehicular activity. The crew wants to go

[00:16:54] outside and there's space suit. The space suits. You know, very low pressure about, uh, sorry.

[00:16:59] [00:17:00] You're, uh, it's three and a half pounds, uh, partial, uh, pressure in the

[00:17:03] Wojciech Wegrzynski: Oh my God.

[00:17:05] David Urban: uh, pure oxygen

[00:17:06] Wojciech Wegrzynski: I'll recalculate that to

[00:17:08] David Urban: Yeah. So uh, I have to, I forgot, I calculate, So it's a co fifth of an atmosphere, mid

[00:17:13] 24. Yeah. and that's to allow mobility in the space suits, which are

[00:17:18] soft. And so if it's, it was at one atmosphere, you wouldn't be able to move.

[00:17:21] Wojciech Wegrzynski: Okay, and you'll probably bounce like crazy from everything

[00:17:24] David Urban: And, uh, the problem is if you go from sea level air to that condition, you can get decompression sickness.

[00:17:28] So they have to

[00:17:29] pre-brief. to prevent that, they want to have a less oxygen in the cabin, and to do so, they, I mean less nitrogen, sorry. And so the, uh, that makes it more dangerous.

[00:17:39] So it's gonna be about, uh, 37% oxygen, um, on the habitats.

[00:17:45] Wojciech Wegrzynski: amount of, the amount of science and consideration that goes even for, for this simple setting is, is mind blowing. I wanted to, uh, I, I have a follow up question about the oxygen, but I must come back to the candle for a second. Why is it blue?

[00:17:56] David Urban: well, the blue means there's no sort

[00:17:59] and, [00:18:00] uh, the, uh, that's the subject of some, um, in completely studied, I guess I would say. But in that case, uh, the, flame has slowed down enough, um, because it's just surviving on, the diffusion of oxygen into the flame.

[00:18:12] So the overall, the temperature dropped to the point where, uh, it doesn't form. It doesn't form sot and so it doesn't, the combination of tempera in residence time is not adequate to make.

[00:18:21] Wojciech Wegrzynski: I wonder is, is the flame thicker? And by flame I mean these, this exact space in which directions happen. I, many people don't know that and even fire researchers, do not appreciate the fact that that flame is a hollow inside. There's nothing inside the flame. It's just like a. I like to call it iso surface of combustion, uh, the shape of the flame.

[00:18:42] And I once tested it by putting my iPhone inside, and I've recorded it from inside and it went viral on social media. The phone survived. So I, I wonder, , I wonder if, if this, uh, spark flame, if the actual place where directions take place, is it like thicker [00:19:00] and, is it hotter than in, in, in like a candle flame?

[00:19:02] David Urban: well we didn't have good temperature profile measurements in there, but we, uh, believe it to be colder. Um,

[00:19:08] so, um, flame zone, you know, where the actual peak reaction rate, uh, region, is. Presumably thicker. And so than it would be in one G, it

[00:19:18] tends to expand, have to expand outward. It's further away from the fuel typically than in a one G situation because the flame boundary is looking for the balance of, um, fuel and oxygen at still geometric proportion. And that tends to, go further out. And then what happens is the flame gets so large that it loses energy by radiation and it. but, the, yeah, typical candle flame, the flame itself is outside the part. You can see it, the, the high temperature zone is just outside the visible bright, so region which is captured inside the flame.

[00:19:49] Uh, so, which is all very counterintuitive to people.

[00:19:51] so,

[00:19:52] Wojciech Wegrzynski: Yeah. That, the thing. The deeper you go into fire science, the, the more of that you realize. Okay, let's go back to the [00:20:00] oxygen question. you told me it's 20 centimeters per second. I did a quick, uh, back of an envelope calculations. if we just assume a square meter of space if it's pure oxygen, you would have enough oxygen transported through that square meter, which is large service.

[00:20:15] For like 400 kilowatts of fire. If it's a 38% mixture, it would be 200 ish kilowatts. And I remember in reading in one of your papers there, you were testing realistic fire scenarios for a space vehicle. And the, there was a sentence used that we have tested a large.

[00:20:34] The fire was actually 50 kilowatts. And I'm like, Wow. This from, for, from space perspective, this is considered a large fire, which is very interesting for me. 50 kilowatts is, is an ignition source, not a fire yet. You know, it's a, it's a trash bin and not very large one. And for you, uh, from your perspective, that was already a large fire event.

[00:20:56] So, it, it's a completely different perception what's dangerous, what's, what's [00:21:00] not. Maybe you can expand on how, how did you come up with, with this fire scenario, and is it really a representation of, of a large threat, a significant threat for a spaceship?

[00:21:09] David Urban: Well, yeah, we're learning that when, uh, we can be a little more, tolerant of, of fire size by modeling, but, but the, it starts from the whole perspective that if you have that fire, the burning trash can in your typical house, you can quickly make a decision. Do I double? Ham nearby lit of water on it, or do I go out the door? Uh, whereas in a spacecraft, there is no, out the door is not an attractive option. So,

[00:21:33] uh, So, um, so then you've gotta try to deal with it and you're. Can't get further away from it. So, um, you're much closer to the event. So, and you have a lot of critical systems that could be damaged, and there

[00:21:47] really, there's not much or very little redundancy on the system.

[00:21:50] and the, there's not much redundant air supply.

[00:21:53] so putting that all together, We have to be very intolerant of fire. So yes, A one G ignition [00:22:00] horse of building fire is, a very worrisome end state for a spacecraft. I mean, I think the mere fire really was, I lost my calculations for that, but the heat release was not excessive from that.

[00:22:11] But,

[00:22:11] um, it was very dramatic because of shooting out burning steel. But, uh, the net, you know, the actual energy was, uh, you know, thankfully not all that. so yeah.

[00:22:20] so we're trying to sneak up on that and it turns to get A good understanding of, um, how much of the

[00:22:26] heat from a fire in

[00:22:27] a spacecraft goes to, gets absorbed into the materials versus raising the pressure and so on.

[00:22:32] Um,

[00:22:33] Wojciech Wegrzynski: I think the pressure is super interesting aspect because, uh, we would not care about that that much on the ground. Our buildings are very imperfect. um, the amount of gaps we have in buildings in a very tightly sealed building would be very unacceptable for a spacecraft, I guess. So there's a completely different level of, Tightening the volume. So here, even a small fire can probably lead to very significant pressure gradients. And [00:23:00] that you then you have safety measures in the spacecraft to, to release that pressure. So, so I guess even small fire can have, uh, considerable effect on the atmosphere. And it, it's not that when fire happens, you, you don't open the door to to, uh, release the smoke.

[00:23:14] Right.

[00:23:15] David Urban: Yeah, no, it, it turns out they already, all spacecraft that are launched, uh, end up having positive pressure relief valves that are quite large

[00:23:24] to prevent, um, over pressure the spacecraft. And those turn out to be a very helpful in the vent of a fire. and, uh, consequently, they relieve any excess gas and heat produced by much of the heat and gas produced by a fire pretty quickly because they're designed, uh, for, Based on the launch conditions.

[00:23:42] So you allowing no more than one atmosphere delta pressure across the vehicle, uh, or not much more. So it's,

[00:23:48] uh, so then you go say 1.1 atmospheres. So when once you get into, uh, orbit, you're, if you're already at one atmosphere in the vehicle, you're very close to venting. so that doesn't take much for the pressure to, uh, [00:24:00] cause arise to cause them to vent.

[00:24:01] That will take

[00:24:02] Out, Um,

[00:24:03] excess heat. and uh, so it's very helpful in the event of a

[00:24:07] fire, in orbit. But those same valves will, uh, the vehicle has to go to two atmospheres total pressure if it's on the, which is the problem in the Apollo one.

[00:24:15] Wojciech Wegrzynski: Okay. Now, we, you are talking about these things, not just hypothetically, but I know you, or NASA with your presence has done that Exactly, uh, during, Sapphire mission. So I would love to talk about Sapphire Now, that was an series of experiments. Uh, Large scale experiments, uh, of controlled fires in microgravity, in space.

[00:24:39] before we go into the technicalities of Sapphire program, how does one get an approval to burn a fire in the spacecraft? Actually,

[00:24:49] David Urban: Uh, you know, it was a long process. I, you know, I was. Concern because, I mean, we really had no perspective of what

[00:24:58] a, a spacecraft fire would be [00:25:00] like. You know, as you know, in fire science study

[00:25:03] every occupied structure on earth,

[00:25:05] be it a

[00:25:06] type be it a building, a plane, a train in a auto automobile ship, submarine, pla you know, they've mines, they've done fire studies. And, uh, and plus we have a long history of, uh, re, you know, experience. So this huge amount

[00:25:18] of data that people

[00:25:19] know, versus

[00:25:20] spacecraft.

[00:25:21] we'd never done anything other than, um, the mere fire. And, the Apollo one Fire had not done any full scale and experiments.

[00:25:29] Wojciech Wegrzynski: Apollo was on ground, not

[00:25:30] David Urban: in

[00:25:30] Exactly. So

[00:25:31] that was a very different case.

[00:25:33] So, so MiiR was the only case in the spacecraft, and it was very informative, but there was not instrumented and

[00:25:39] so .So the uh, and uh, even the timeline is confused about this sequence. So, so. Was

[00:25:46] searching around for

[00:25:47] a spacecraft that we could do something in, and it was larger than the small. five by

[00:25:52] 10 centimeter experiments we've done is the

[00:25:54] maximum. So we, um, uh, looking

[00:25:57] around for

[00:25:57] vehicles that might

[00:25:58] be available,

[00:25:58] I looked at the Russian[00:26:00]

[00:26:00] progress

[00:26:00] vehicles, but they're really quite small.

[00:26:02] And then, um, talked to the

[00:26:05] Europeans and then ultimately, and I, I was

[00:26:07] looking at other alternatives and I

[00:26:09] got laughed.

[00:26:10] out of the room a number of times. Finally, um, a combination of circumstances. The, uh, Cygnus uh, different company at the written time, but now it's Northrop Grumman, was very interested in this possibility. And NASA, um, itself was interested. And so we had the opportunity of a habitable vehicle that was habitable, but had nobody in it

[00:26:28] would never have them in it again. So, uh, there was no risk to people. And so we just had to make sure we didn't hurt the vehicle enough, that it couldn't, reenter the way it's planned.

[00:26:39] Wojciech Wegrzynski: By reentry, you mean? Uh, happily being, decimated by atmosphere, not landing anymore.

[00:26:46] David Urban: Exactly.

[00:26:47] Wojciech Wegrzynski: a, uh, so it's like a dis responsible, uh, vehicle.

[00:26:51] David Urban: yeah. So slated for, or, you know, reentry, disposal, uh, destruction. And

[00:26:56] they, and

[00:26:57] so

[00:26:57] we, uh, so there really, there's nothing to more to [00:27:00] be done with it. So that was the great thing about it.

[00:27:01] Wojciech Wegrzynski: Good, good. That's an expensive piece of expandable fire infrastructure. But, uh, but great. So, so how did you plan the, the research? What, what was the point of it? Uh, what, what were you interested in, in, in burning in that, in that bagel

[00:27:15] David Urban: two types of questions we wanna address. We wanna, we want to learn

[00:27:18] about

[00:27:19] details about fire

[00:27:20] growth, uh, when you had a large you know, practical size material and is there, um, in one G, typically there's a T squared growth rate. and, you know, things will just keep growing almost, you know, without bound, I mean, to live very, very large. And uh, theory suggested that wouldn't grow continuously in, low G. And so we wanted to look at that,

[00:27:39] and then we wanted to get an idea. Just the way people use FDS and other codes to model the, impact

[00:27:46] of the fire on

[00:27:47] the structure and

[00:27:47] habitability and on earth. We were trying to use FDS to model the impact of the

[00:27:52] fire on the spacecraft and really wanted to get

[00:27:55] some calibration points. Uh, so make sure that we weren't, uh, [00:28:00] just going off. in the wrong direction. uh, so we wanted, so we had two, two goals. One is to just have

[00:28:05] a fire. Look how big it gets, how fast it grows, and two at the same time, have the fire impact the vehicle and see what it did to the vehicle and pressurize, temperature rise, et cetera.

[00:28:14] Wojciech Wegrzynski: And also in, in this, uh, setting where there's a constant ventilation. Right. So you would mimic the, the, the typical conditions in the space. Okay. Okay, good. And, um, what, what types of materials were you, were you burning? Uh, because I assume it was not the fireproof materials that used normally in spacecraft.

[00:28:31] It was, uh, something specific.

[00:28:32] David Urban: the, so sort of broken into two series. One was the first series where you really were pretty, very

[00:28:38] conservative and really, did not impact the vehicles much as was helpful, would be helpful later. But we are looking, so that initial series we looked at two very large, or for us very large, but it's, some would say

[00:28:50] it's a size of a tee towel, but, um, you know, half a meter by a meter. Piece of fabric. it's a cotton fiberglass blend

[00:28:59] so it [00:29:00] rip and

[00:29:00] tear. It's a beautiful reference,

[00:29:01] uh, fabric.

[00:29:02] and we did two, two flights with that at different flow rates. And then the intervening flight, we

[00:29:08] had a variety of smaller samples, nine.

[00:29:10] smaller samples

[00:29:12] of. Same material

[00:29:14] plus, uh, p a and silicon, um, rubber, and which was an interesting INFLAMMABILITY case, but trying to look at that.

[00:29:22] And those were all done, um, in Nearly sea level air. and

[00:29:26] then after that

[00:29:26] we, um, got approval to

[00:29:28] continue. we wanted to look at the, uh,

[00:29:32] higher risk

[00:29:32] atmospheres and so we lowered the pressure in the spacecraft working with the owner. After they separate from

[00:29:39] the

[00:29:39] space.

[00:29:39] station, they vent out a bunch of gas, and then we, uh, backfill it with oxygen. That we carry on board and try to bring it up to 36% oxygen. And, then we were burning a mixture of samples ranging from, again, that same fabric and, more, p a samples, uh, both simple ones, and one with a structural, you know, grooves and [00:30:00] ridges and, Nomex, which is, um, a fire retarded material used for stowage, I think is in spacecraft. and so then

[00:30:06] plus we had all kinds of other

[00:30:08] sensors throughout the vehicle. And so we, each of the flight we were trying to burn one

[00:30:12] very large sample that released as much heat as we could. And then, uh, we temperature and CO2 sensors at six locations in the spacecraft, and smoke sensors and a smoke recovery system at the other end.

[00:30:23] Wojciech Wegrzynski: So outside of the violation, uh, data, were there any like important lessons learned, uh, from, from that experiment?

[00:30:30] David Urban: so is in interesting. The fires did achieve a very, uh, spreading flames very quickly, achieved a very steady spread rate. Um, we also learned that the environment in which the fire is burning is more significant than we thought, as far as affecting the spread rate. All previous experiments were done in relatively smaller ducks, which

[00:30:50] we thought were big enough. due to the, um, Growth of the flame with respect to the volume. It, uh, there is more flow acceleration in the other. Ducks than we, [00:31:00] uh, anticipated. So they spread slower if they're in a big open environment than we, uh, had previously thought. We saw some very interesting results, uh, validating previous experience with a material like pma.

[00:31:13] Um,

[00:31:13] Polymethyl. Aate, which, uh, doesn't char and, uh, melts and paralyzes and has, um, you. breakdown in paralysis, in depth in the material, which causes bubbles and ejection. And, um, similar thing was seen in Sky Lab years ago when they were burning nylon. But basically we turned off the flow and it continued to burn

[00:31:33] for a very long time on its own. And, do supported by the, uh, heated ejecting gas from the, in, in depth in the material.

[00:31:42] So, um, that was one surprise. And the other surprise, one big question is how long, if you got a fire in a spacecraft, how long do you need to, have the extinguishing agent around it, uh, before you can turn the flow back on and, and allow people to breathe. so we saw in that case, um, it needs to be off of quite some time [00:32:00] for that, uh, that kind of material. And likewise, on another flight we had. It was really cotton, a knit cotton, like a t-shirt material, and that tended to curl and roll. And the charing, the embers, uh, persisted in the curled section quite a long time and it, it did reignited as well once the flow was turned back on. So, um, so there you can sort of have something like a deep-seated fire in low gravity, which we weren't sure of some. Those are the big fire discoveries, I guess.

[00:32:28] Wojciech Wegrzynski: so, so from just burning a cloth, like a towel or, or very small samples of materials, it's really, uh, that's fascinating where you enter a place where no one has ever been before and, and you start to touch things that no one has ever, uh, thought at the scale before. And we always, like, I'm not surprised that the scale changed everything.

[00:32:46] That's the story of fire science and, and, and, and everything we. Have you also done something with smoldering fires in that regard? I, I had Professor Rein on the podcast many times, and, he, he seemed to be concerned of, of smoldering, uh, persistent fires [00:33:00] in, space for example.

[00:33:01] David Urban: Yeah, the, um, he was a collaborator with professor, uh, Fernandez, Fernandez, Pello

[00:33:07] in Berkeley, uh, on a series of smoldering experiments we did. and found that, I guess overall in depth smolder was, um, harder to

[00:33:16] support because, in one G, uh, you have the buoyant flow. Um, pretty much, uh, will. Do enough airflow within the sample

[00:33:23] in, uh, low gi, you really, unless you really are pushing the air through it, uh, it's uh, harder to forget oxygen in depth, uh, in the sample. But we do believe that there's a significant risk for, A sample

[00:33:37] with an exposed surface

[00:33:38] for.

[00:33:38] it to sort of, uh, lodge itself in the, um, foam in depth, and then transition to flaming later when the flow kicks on again.

[00:33:45] So I think that's an area that, uh, needs more study, than it has gotten to date. And I think that's one of the residual concerns to me. And long term habitation, I'm worried about the things like the

[00:33:55] trash

[00:33:55] Wojciech Wegrzynski: we're, and we are also talking about long, term space flight.

[00:33:58] I'm [00:34:00] like, Okay, ISS is, is a long term space flight. It's very, very long term space, space flight. But, but still, if we think about exploring Mars or something, there's, uh, you don't have the. How to say the comfort of hanging, of having Soyuz aircraft that you can bored and escape, uh, if something really disastrous happens.

[00:34:19] Um, you've mentioned suppression, so let's, let's go into engineering side of spacecraft. That, that also is fascinating. I have questions about detection, ventilation, suppression, evacuation. So let's try to, let's try to touch a bit of, of everything because everything is different in space. So first of all, detect, how do you detect fire in, in space?

[00:34:38] David Urban: So that's been a real challenge. So the, focus has been on smoke. so you know, there are some aviation systems have thermal sensors, but there's uh, really not a, the mass penalty, it gets to be too heavy to have too many of those. So that's

[00:34:53] not ty, it's not been done in spacecraft. And, uh, there's not a magic species, chemical species [00:35:00] you can look for.

[00:35:01] Um, For all materials we'll emit. So there's a lot of them mimic co, but not all of them enough. And so then there's co2, but there's a high background of CO2 in a spacecraft cause of the people respirating. So Lee's really back every izing material, emits a lot of aerosols part. Uh, so we're back to. Uh, smoke particles. The only problem is in one G is everybody knows this. Um, smoke rises. You get a beautiful smoke layer, uh, where they've concentrated smoke of the ceiling in a spacecraft.

[00:35:30] Again, there's no up and you have a well mixed, slow speed turbulent flow. So you pretty much have to raise your whole spacecraft to the tax and threshold, before, um, In Detective Fire cause it's all mixed.

[00:35:42] And, um, actually at the same time, the life support system, the airflow is, taking smoke out of the system by the filtration. So

[00:35:49] it's very tricky. We don't have, um, better solution I guess. But that's, uh, so we're looking at smoke and you really have to each space corrective model individually, based on it, the vague, unique things [00:36:00] about its flow system.

[00:36:00] Wojciech Wegrzynski: But, but you don't have a ceiling to put the, the smoke sensors on the ceiling. So where do you put, So smoke sensors,

[00:36:06] David Urban: The universal answer is before the air intakes.

[00:36:09] so you have your whatever flow system, you know, you, it blows out in some areas and you suck it in in other areas. They have filters right after that point. But if you put it in front of the filters, that's, uh, you can assure

[00:36:19] that air. It's sampling the vehicle pretty well.

[00:36:22] Wojciech Wegrzynski: So it's somewhat like, in the very least, smoke detection systems where you have aspiration devices that would, uh, suck in probes of, of smoke. So here, here you use your vent system in a, in a station to, to probe the air all the time because it's constantly being, uh, recirculated to the filters and everything.

[00:36:39] David Urban: All right.

[00:36:40] Wojciech Wegrzynski: you just take the opportunity the whole area sucked through. That's opening and you detected, Okay. That's smart. And I guess flame detection makes no sense because if there's flame that's kind of late. Right. And, you probably don't want to have that anyway.

[00:36:51] David Urban: Yeah, and it's a very cluttered environment so that it's getting line of sight to the

[00:36:56] source that no one's come with a good answer. and you know, the flame ones typically work on, [00:37:00] military vehicles where there's a big flame and, and uh, rather dramatic signal. So, um, is an example.

[00:37:05] But, um,

[00:37:06] Wojciech Wegrzynski: let's go suppression. is there extinguisher on the spacecraft that, that you grab and, and extinguish stuff?

[00:37:12] How, how does that work?

[00:37:13] David Urban: you know, it's varied over time. The shuttles era, the, uh, US vehicles used, uh, halon,

[00:37:18] traditional CF3Br. the um, Russian systems used a foam. and Apollo,

[00:37:24] they used the, just a, basically a squirt gun from the water, uh, food hydration system. then, uh,

[00:37:30] now in.

[00:37:31] the space station, there's two choices on the e US segment. Uh, one is a CO2 extinguisher and the other is a, Now, more recently, they added a water missed fire extinguisher,

[00:37:40] Wojciech Wegrzynski: Why not Halon anymore? I thought, uh, it would be brilliant because you're above the ozone layer, so we have nothing to destroy with it.

[00:37:47] David Urban: Yeah, it, the problem is, you know, in the spacecraft you can't get rid of whatever you, whatever agent you release, you have to be able to live with. And, uh, so, um, uh, halons a problem because it's, uh, does

[00:37:58] Bad things to other parts of the life [00:38:00] support system. Some of the air purification beds, uh, Don't like ha on. And so they, um, so in the space shuttle

[00:38:07] era. if They,

[00:38:08] used a ha on

[00:38:08] extinguisher, they had to to in meetings. Uh, so the space station

[00:38:12] they just ruled it out.

[00:38:14] And then if you.

[00:38:14] go to the future habitats, it's not gonna work well anyway, because of the Han Oxygen concentration. Halons become flammable themselves.

[00:38:22] uh, so that's not gonna work.

[00:38:24] And CO2 is challenging because at the extinguishing concentration is not a healthy concentration for people.

[00:38:32] And that's why in small volumes, it's not really. A great choice and it gets worse if you have a higher oxygen environment.

[00:38:39] So they, uh, it's a good choice for if you got a fire inside a, an electronics rack, you can deploy the CO2 in there and you can raise that whole rack to, you know, half CO2 without, I mean, a problem with the crew.

[00:38:53] Wojciech Wegrzynski: how do you apply it? Uh, does it have like special, uh, inlet dis inside distribution system in the racks? [00:39:00] Because like, I, I assume it's not a, someone standing with a ex. I just imagine in my head someone run not normal extinguisher in the space station and they would just immediately fly away from the fire.

[00:39:11] So that's not a Robs application.

[00:39:13] David Urban: Now, So the, all the extinguishers have two choices. There's two, uh, nozzles. One is, uh, a diffuser

[00:39:19] nozzle for spraying on a fire in front of you. And the other is a, a probe that you stick into a, what's called a fire port. And all, uh, electronic systems that, aren't sealed in a way to prevent a fire from propagating.

[00:39:31] Have to have a fire port

[00:39:33] and you have to show that the fire port will, um, bite through,

[00:39:36] test, get the, gas to all the corners of your rack.

[00:39:39] Wojciech Wegrzynski: Wow, that's rocket science . That's a specific fire part for extinguisher. That's, that's interesting. And uh, and these things are operated by human or there are like parts where it would be like automated.

[00:39:51] David Urban: the space shuttle had, um, Certain sections of the, um, critical, um, avionics were, uh, could be triggered with a fire extinguisher [00:40:00] from the flight deck. But, the space station, it's all crew, extinguishment, so there are no, um, they looked at a automatic, in a centralized system, but the mass penalty was too high. It was just everything you

[00:40:12] have to weigh benefit

[00:40:13] versus how much you're gonna launch, you know, some,

[00:40:15] Wojciech Wegrzynski: And since you are sending a lot of kilograms of very well trained personnel there anyway, they can as well. I do that part. Great, great, great. next on my list, I have ventilation. So, uh, you've said that some smoke will be filtered by the life support system. So the, the smallest fires, I guess you can get away and.

[00:40:36] At, at what point you would extract the smoke from the system? I dunno. Seal a part of the, of the station and just ventilate.

[00:40:44] David Urban: yeah, the scenario, they have to, it's gonna be a real time decision. There are certain sections of the station they could, uh, then have needed, but generally that most of them, you can't. um, and we're redesigning what we call smoke eat, we call it, which is a filtration system, [00:41:00] which, um, w would be designed for a fire scenario as opposed to the. Life support filtration systems, which aren't really design, uh,

[00:41:09] fire's not their thing. Uh, main thing. So, but basically you would have a series of, um, you know, aerosol filter, strip out all the aerosols, followed by a, um, catalyst bed to convert the CO to co2 and then a CO2 absorption, uh,

[00:41:25] Wojciech Wegrzynski: Ah, and because you're designing for that anyway, for the breathing and, uh, okay. I, I guess Space Station is a little different because it's a complicated, building in a space to pretty much, while, um, vehicles, uh, would be different. So if we think about, uh, like Artemis, uh, vehicles or something, there you don't really have a possibility to ventilate because or, or you have, you would have to have the, crew wearing space suits pretty much all the time or be able to access them very quickly.

[00:41:55] Is, is that a thing, uh, is it possible to ventilate in such vehicles?

[00:41:59] David Urban: Well [00:42:00] decompress. The, the vehicle could be, is designed to be decompress in the event that they have to do emergency, uh, extravehicular

[00:42:07] activity. They can, um, Decompress the vehicle, open the hatch and go outside and fix whatever, uh, needs to be dealt with. Um, um, and the land itself, of course the door opens. but The electronics can function without air in them, so you can maintain your vehicle.

[00:42:21] Um, but generally they, and depending on the mission, they have a certain amount of a spare oxygen stores to manage both, a necessary e eva or if there's a leak scenario, they have to be able to feed the leak until they can, um, either fix it or return. Um, but that doesn't, Give you enough oxygen typically to carelessly, you probably can replace one atmo, one volume of

[00:42:43] your chamber, your vehicle. You, uh, typically wouldn't do it all at once. You'd have to vent and fill, go to the lowest pressure you can tolerate, vent, venting, and back fill. so they, um,

[00:42:52] Typically wanna

[00:42:53] manage the, products also by, um, filtration and, uh, replenishment in all those vehicles.

[00:42:59] The crew could go [00:43:00] on back in their suits and mask up and then, breathe off the suit loop, which would also, um, Provide them clean air. So that's the other option. So it, there's, it's really

[00:43:10] very vehicle

[00:43:11] specific.

[00:43:11] You've got the, NASA spacecraft and, um, and you've got the, commercial, lander vehicle, plus you've got these commercial crew vehicles and all of them have made different solutions, for the, this question.

[00:43:23] But they all have. Have some level of, uh, be able to tolerate a leak and recover, you know, manage it and re return to earth in time, and have a scenario where they can provide alternate breathing until they can get, uh, the crew to safety.

[00:43:36] Wojciech Wegrzynski: Yeah, last on my list is evacuation, but I already understand that they're not just victims of a fire, they are firefighters on their own as well. So, So I guess the procedure, to your best understanding, how do, how would the procedures look? Would they like, uh, first being formed?

[00:43:55] Intervene and in case of overwhelm, they would, escape. Who takes decision [00:44:00] about evacuating? Is it, is it the mission control or, or, the commander in the space station.

[00:44:06] David Urban: I guess I, it depends on the, extent of the fire. I and the crew has the ability to make the decision on their own, on the space

[00:44:13] station, but typically wouldn't expect the fire to be slow enough where there be time to, uh, communicate that their first priority is to get to, uh, their escape vehicle.

[00:44:23] So then they, um, There's assured return for everybody. There's a seat home for everybody, but they're not all. May not be near them. So, hopefully they're all

[00:44:33] not

[00:44:33] on separated by

[00:44:35] the fire from their. way home. But, um, so that's the Cause there isn't necessarily a properly fitted suit for them in the other vehicle, so they re there's a. Uh, challenge to get to the right place. Once

[00:44:46] they're, there, then they, begin to address the

[00:44:48] fire they put on their protective

[00:44:50] gear, grab an extinguisher, and, proceed to, cut power to

[00:44:54] the affected system, et cetera. But the first priority is to get

[00:44:57] them. On

[00:44:58] the safe side of the fire.[00:45:00]

[00:45:00] And then, uh,

[00:45:01] from then they

[00:45:02] would again, the general practice

[00:45:04] is immediately to cut the flow in the affected module and particularly the affected rack or whatever system. And that will tend to, um, dramatically weaken the fire and hope this will go out on its own. Then they proceed to use the extinguisher as a indicated.

[00:45:19] Wojciech Wegrzynski: okay. Uh, I have friends, uh, who are involved with, with Nexus Aurora projects. They, they design habitats and I would get murdered if I don't ask you some stuff about, uh, potential, uh, future exploration. But habitats may be a, a far thing ahead, but we have, uh, moon to fly soon with, Artemis program.

[00:45:39] So I, I think it's, it's very relevant. So maybe let's try discuss, uh, how does the challenge, uh, change when you go from. Earth's gravity to, let's say moon gravity. Are there any specific changes to that? Cause

[00:45:54] David Urban: Yeah, it's actually very, very challenging. I mean, first, as we mentioned it, [00:46:00] most of the near term habitats, there'll be a higher oxygen environment,

[00:46:03] so that raises the flow mobility. Second of all, now you have buoyant flow, so you can't count on turning off the flow to turn off fires

[00:46:09] and it will support fires in narrow channels and you get back to the in.

[00:46:14] Inflammability case where you have, uh, more enhanced interaction between two surfaces, uh, to support a fire that, um, so things that will fail the NASA test In one G, with another piece of material nearby will burn. For example, wood is a classic thing. One piece of wood is very hard to ignite a continuing fire on, put two near each other.

[00:46:35] You can easily ignite it. So, the, uh, similarly in space that can have similar effects with interactions. So you can, and you can have fires and narrow channels. And then on top of that, the detection is. I would describe as an unsolved problem as yet

[00:46:48] we know there's buoyancy and that's gonna push the smoke up to the ceiling, uh, but less strongly than it does in, uh, one gene. And the lunar surface dust is very hazardous. It's [00:47:00] very small particles,

[00:47:01] so it's in the, in a submicron range, uh,

[00:47:04] which is very bad for human respiration.

[00:47:06] Wojciech Wegrzynski: That, that's like the size of smoke particles.

[00:47:08] David Urban: Yeah, exactly. There's the detection issue, but on top of it, it's just a very bad respiration issue. It's, um, so they really want to get it out of the, and they're taking steps, but it's gonna come in on the surfaces of the suits, et cetera.

[00:47:21] They're gonna have to mitigate it. So, uh, the. Likely scenario is you're gonna have pretty aggressive ventilation downward to take advantage of the gravity to help push the particles to the floor where you'll suck 'em out. And so the question is, for a plausible lunar fire, will the smoke plume penetrate that, downward flow, or not? So we're still trying to model that to get a good understanding of the best, approach for pla placing your detectors.

[00:47:48] Wojciech Wegrzynski: For, for once. I, I feel like my earthly experience is somewhat relevant to the problem you've mentioned because, uh, in earthly buildings we often do hot smoke tests at the commissioning stage [00:48:00] of the, of the buildings. And here we use a fairly small sized, sources of, of fire, hundreds of kilowatts maximum to warm up the layers of smoke that we put into the, um, building.

[00:48:12] Of course, it's a , but. If we have any source of air that is like high velocity, jets of air that mixed with our smoke, you, what you get with is a smoke mixture and aerosol mixture, that is at the ambient, uh, temperature. So it loses its buoyancy, so suddenly it just moves, you know, uh, more like in.

[00:48:34] Inertia flow, it's not even dispersion anymore. It's like with inertia of the flow that it got trapped into and you end up with this very persistent mixture of, of smoke everywhere. That is extremely difficult to remove because you don't have a forest that would move it to the place you would like it to be.

[00:48:51] So you either have to end up with very strong opposing flows. Basically move everything, to one side. But that probably will be difficult in a [00:49:00] habit habitat where you don't have excessive air from outside you can use to over ventilate your space. So I, I see this could be potentially quite challenging, uh, to combat.

[00:49:10] We, we once, uh, feel the whole sports arena with this smoke, and it took like three days to get rid out of it. so, so, so yeah, it, it, it may be a c. good advice to friends on, on the moon. If you go outside, don't take a deep breath because the, the dust is bad for

[00:49:26] your lungs.

[00:49:26] David Urban: exactly.

[00:49:28] Wojciech Wegrzynski: And what about Mars exploration missions, uh, long flights and, and habitat on Mars?

[00:49:34] How do you see special challenges with

[00:49:37] that?

[00:49:37] David Urban: Uh,

[00:49:37] Well, the it's a different gravitational

[00:49:39] level and we haven't really figured out, which is the most, is the

[00:49:43] highest, uh, flowability condition is believed to be somewhere in the lunar martian range. We haven't really

[00:49:48] pinned down, cuz of this competition between, uh, cooling and ventilation aspect of the flow.

[00:49:53] Uh, there's, um, the maximum flowability is somewhere in that range. So, and you would think Martian would be, tend to have [00:50:00] Stronger flames once ignited. Um, so those are all gonna be challenges. We don't really, we have not brought. Soil samples are, um, regular. It's called back from

[00:50:09] Mars. So we don't know with certainty how small the particles are, but there was a lot of water on Mars at one point, so maybe they're not as small as they're on the moon, but this really isn't known.

[00:50:18] So when expect that there's still a big dust problem on Mars. And, uh,

[00:50:23] so I think it's gonna be similar to the moon, but. with a difference in the flame intensity and, you know, the plume strength, uh, from a fire,

[00:50:31] Wojciech Wegrzynski: And for, we, we were talking only mant exploration, uh, so far. And for unmanned missions like James Webb based telescope is, is fire safety also something of a concern or,

[00:50:41] David Urban: essentially not because, uh, all

[00:50:44] those, uh, other spacecraft

[00:50:46] don't have an, know, environment with oxygen, any that they

[00:50:48] Wojciech Wegrzynski: Okay. Of course. Yeah.

[00:50:50] David Urban: They, they almost always designed them to be, um, not have any atmosphere in it. And they use other systems to cool their electronics, but, uh, if you were gonna have an atmosphere, [00:51:00] you'd naturally make it nitrogen or something else.

[00:51:01] Cause there's no reason to have, uh, oxygen present.

[00:51:04] Wojciech Wegrzynski: seems that, um, humankind and fires go hand by hand.

[00:51:08] In space, In space, exploration for sure.

[00:51:11] David Urban: we

[00:51:11] breathe the same thing.

[00:51:12] Wojciech Wegrzynski: we read the same, Essentially it's a very similar process. It's just the time scale and, uh, and chemical, uh, process a little different, but yep, it's, it's very much the same thing. Chemical, uh, release of heat. David, , one last thing I would like to ask you.

[00:51:27] Um, a lot of people are listening. A lot of them are young fire engineers. Do you think, uh, one day something like, uh, space fire engineer pathway will open? Maybe it's open already. like it sounds like such an exciting, thing. if I ask my younger self, Would you like to be a space fire engineer?

[00:51:47] Oh boy. Sure. I wonder, to what extent do you see this, like, in a way, a growing industry? Now, now we, we live in a different world than, than 50 years ago. We have private companies that regularly go to orbit. This, [00:52:00] this is amazing. Uh, who knows what will happen in 50 years.

[00:52:03] David Urban: Well, it's true. I think, uh, it's gonna grow. I don't think it will ever rise to the point of, uh, terrestrial fire engineering. Um,

[00:52:09] but we currently have a great group

[00:52:11] of,

[00:52:11] uh,

[00:52:12] Wojciech Wegrzynski: Engineering, that's, uh, I'm, I'm putting that in my, on my business card now.

[00:52:16] David Urban: Exactly.

[00:52:17] Wojciech Wegrzynski: Engineering,

[00:52:18] David Urban: We've got a great group of researchers, uh, with us at NASA and interact with excellent ones at the, you know, some of the commercial providers, et cetera. So there's really a one, you know, but know, that's all globally. We're a small group and there's also, we great fire researchers at other, the other space agencies.

[00:52:34] So there's really a tremendously um, Group of researchers engineers, although albeit small, but I think this is a growing opportunity. There's clearly gonna be more space, flight in the.

[00:52:43] future, so it is a future opportunity, and a very fun one.

[00:52:46] Wojciech Wegrzynski: I've, I suddenly have seen a fire engineer position for Spaceport fire safety at SpaceX some time ago. So, uh, that's already close enough to me

[00:52:58] to, to, even touch the, [00:53:00] the, this infrastructure. David, thank you so much for your time. This was an excellent conversation and, Wow. Uh, such a, such a different view on, on the fire science, fire problems, combustion fundamentals.

[00:53:12] It feels like, like rocket science now,

[00:53:14] David Urban: That's right. It's been this huge op fun opportunity for me as well. I really enjoy your podcast and I'm, I think, um, it's got a great information for lots of people on

[00:53:24] Wojciech Wegrzynski: I wonder too, how many people, it'll be relevant what we've talked today, but I think for everyone it'll be interesting. So, it's, uh, definitely has been a big pleasure and for me, uh, a very, very special thing to, to talk with someone from NASA about my own job. That's, that's, um, amazing. Thank you so much for that.

[00:53:42] David Urban: Uh, my pleasure. Thank you.

[00:53:44] Wojciech Wegrzynski: And that's it. Well, thank you, David. I was a fantastic discussion and I enjoyed it thoroughly.

[00:53:50] And I'm especially thankful. Well, you cannot know that, but we have to recall this twice, the first time because of a technical, problems I've lost the whole recording. [00:54:00] Of David. So we had to actually meet once again and the Rica the second I can say the second time was better. So. So in the end, you have a better product.

[00:54:09] In your ears. I hope you may enjoy that a lot. from the things that I took from this I took so many. Maybe I'll call in on a thing that we maybe touch them more in the first recording session that that was lost. And we didn't touch that much in the second one. The second one was, had so many items on it. So we didn't cover that that much, but the role of ventilation in the spacecraft and David mentioned that there's constant velocity flow of 20 centimeters per second in the whole cabin.

[00:54:38] So there is a move around the station. And when the fire is detected, they stop it. So now the consequences of stopping the ventilation in a spacecraft. It's completely different than stopping it in. On earth. In terrestrial fire system safety system. It would mean nothing if you just stop extracting, but in space, when you [00:55:00] stop moving the air.

[00:55:01] The air doesn't really have weight.

[00:55:04] To go into the flame. Like there's no way how the air. Would transport itself towards the flame. So you're essentially cutting out the oxygen supply to the, to the flame. That's interesting. Strategy there that stopping movement makes the fire like quench itself because it has to. Expense to burn the air. That's just standing around it. So let's say it's expanding in the form of a sphere and because the further it goes from the fuel, the less of the heat feedback there is to the fuel surface.

[00:55:34] Eventually it will. Radiate the energy way in and stop producing your fuel and It's super interesting mechanism that would never work on that. And, yeah, I would never think it could work like that. It's super, super interesting.

[00:55:48] And I hope you've found many of gold nuggets like this in the podcast episode. As mentioned before there's a SpeakPipe feature on the website now. So just go into ask me [00:56:00] anything. Part of the website. And just ask me a question, if you want to. Hear more about spacecraft and fires and maybe some aspects of this that we have not been touched on the era of the podcast and for now, that's it. Thank you very much for listening to this episode. And see you here next wednesday cheers