Episode 8: Fueled by Fire

Announcer: Firing chain is armed, sound suppression water system is armed. Ten remaining to start - Eight, seven, six, five four…

[0:16] Narrator: Rockets use an explosive mix of chemicals to propel spacecraft and satellites off the surface of our planet. NASA’s Kennedy Space Center has many ways to prevent the launchpad from igniting, including using millions of gallons of water that both prevent flames from spreading and muffle the powerful sound waves of lift-off.

(sound FX: rocket launch)

One place you never want to see fire is inside a space vehicle. The International Space Station, or ISS, has three different fire extinguisher systems in case of accidents: one uses foam, another uses carbon dioxide, and the newest one uses an extremely fine water mist.

[1:07] To create such tools, you have to understand how fire behaves in the reduced gravity of space. But how can you run fire experiments in space without endangering the safety of the astronauts?

U.S. Commercial Cargo Ship Departs the Space Station Headed for a Destructive Reentry
Announcer: And that’s the beginning of the departure burn, now at 7:25 a.m. Central time.
Second Announcer: Departure burn is in progress. Continue to monitor to departure, step two and three…

Narrator: One solution to this dilemma is called Saffire – which sounds like an evil plan in a James Bond movie, but actually is a series of fire experiments that are run on unmanned Cygnus cargo shuttles that service the ISS.

U.S. Commercial Cargo Ship Departs the Space Station Headed for a Destructive Reentry, continued
Announcer: Cygnus cargo vehicle drifting further and further away from the station, as the International Space Station passes 252 statute miles above the west coast of Peru.

Narrator: Gary Ruff of NASA’s Glenn Research Center is the project manager for Saffire.

[1:58] Gary Ruff: “Saffire” is a mash-up of a “spacecraft fire experiment” – that’s how we came up with the name. The fires we’re burning in Saffire are larger than anything we've been able to burn in low gravity to date. Experiments that we’re conducting now on the ISS or ones on the Space Shuttle before that, they've all been rather small samples – the biggest material samples we’ve been able to burn are roughly the size of a three-by-five note card. And it’s just because they needed to be contained in a vessel to keep the crew safe -- keep them separated from the fire and any combustion products that are generated.

In Saffire, the samples are really on the order of… let’s say a T-shirt, if you held it up by the shoulders. It’s about 15 inches or so wide. The length can vary between 6 inches and 3 feet, depending upon the material and the number of samples we have on the sample card.

[2:53] The reason we’re conducting these tests on Cygnus is because Cygnus’s mission is to take supplies to the ISS and remove trash from the ISS. So by conducting our fire experiments there, we don't have to worry about people being in the vehicle or even cleaning it up when we finish burning. It’s just full of trash, and it's going to burn up in the atmosphere when it returns anyway.

Narrator: That’s right, NASA sets fire to trashcans in space.

[3:20] (music)

Narrator: Scientists on the ground send remote commands up to the experiment in the Cygnus spacecraft to get the fire started. These Space Age dumpster fires orbit Earth for about two weeks while the scientists run different kinds of tests, and then they download all the data before Cygnus begins its fiery return back down through Earth’s atmosphere.

Gary Ruff: Our experiment, and the samples that are burning, are actually inside a chamber that is inside Cygnus. So in the analogy of a dumpster fire, it's not like the whole dumpster is burning. We’re burning samples that are contained inside our Saffire hardware.

[3:59] Now, some of the samples are fabric, like a cotton, and we take a wire and literally weave it into the fabric in a sawtooth pattern. And whenever we want to ignite, we just run a current through it for a few seconds to get an ignition.

To put out the fire, we generally just turn off the fan, which stops the air flow. And once there’s no air flow, there’s no oxygen getting to the fire anymore, so the oxygen near the fire is consumed fairly quickly, and the flames will go out.

Narrator: On Earth, tongues of flames stretch upwards because hot air rises. But in space, without Earth’s gravity to provide a sense of up or down, fire stretches uniformly outwards as a flaming sphere. On a spaceship, however, the direction of a fire will tend to follow the flow of wherever air is coming out of vents.

The Saffire experiments began in 2016. There have been four conducted so far, and a fifth is on the ISS now and is ready to operate on the next available trash run.  The experiments do more than examine how fire behaves in reduced gravity.

(sound FX: fire)

[5:07] Gary Ruff: Saffire investigations are looking at the flammability of different materials under different conditions, and learning how those materials burn, and make measurements of the smoke particulate and combustion products that come off of that fire.  

When they close the hatch for Cygnus, we have the same atmosphere that they had on ISS – which is 21 percent oxygen and 14.7 PSI pressure. On our current flights, we're carrying along a bottle of oxygen, and conducting tests at higher oxygen concentrations and lower pressures.

One of the things that we’re really trying to get at is, if you have a fire on a spacecraft, you have to know how rapidly that fire grows. A spacecraft is a closed chamber; closed environment. And if a fire starts, it can start getting hot. It’s getting smoky, so you have difficulty seeing what’s going on.

[6:00] So we have to know how rapidly that fire grows, because those conditions are going to deteriorate while the crew is trying to respond to that fire. So we want to find out whether the rate at which that fire gets bad is different than the rate at which it would burn in normal gravity. We’re also testing out some of the air monitoring instruments and equipment to clean up the atmosphere that will actually be on some exploration vehicles to respond to a fire.

Narrator: The reason to test fire behavior under different kinds of oxygen and pressure conditions is not only because accidents might alter the standard levels, but also because some space missions and activities have different requirements. For instance, an astronaut’s spacesuit uses 100 percent oxygen and one-third atmospheric pressure.

(music)

[6:53] Gary Ruff: When an astronaut is going to do a spacewalk, they have to pre-breathe higher concentrations of oxygen at lower pressures for a while, to help get the nitrogen out of their system. They do that in an airlock. And they might be in that airlock for 2 hours or more, depending on upon what the environment is in the spacecraft.

It's actually the same kind of thing as when you’re scuba diving. Your blood absorbs nitrogen when you're breathing at depth underwater. And then when you come up, you're going from a higher pressure to a lower pressure, and that's where you can get the bends. And the bends is nitrogen that was dissolved in your blood coming out and forming bubbles inside your body. So the same thing can happen to an astronaut when they’re going into a spacesuit. So they’ve got to spend some time getting used to that pressure, to let their blood equilibrate again.

Now, if you're going to Mars, with the longer transit times that go with that, generally that vehicle would be at one atmosphere and 21 percent oxygen, because that's where human physiology is used to operating. And that trip’s going to be a long trip, so you want people to be comfortable.

[8:00] The place where you really get to some of the higher oxygen concentrations would be is if you were on the surface of the Moon or the surface of Mars, in a lander or a habitat. And you would want to be frequently going on a Moon walk or a Mars walk. So the habitats would want to be at a higher oxygen concentration and lower pressure, to reduce the length of time that the crew has to pre-breathe before they would go outside.

And it's not like every spacecraft is going to have that high oxygen and lower pressure, but for the kinds of tests that we want to do, we want to know that, if you do have to use those conditions, what kind of increased risk are you accepting because of the increased flammability of materials at those higher oxygen concentrations?

You know, we've run microgravity combustion experiments for quite a long time. The earliest experiments were in the mid-1960s. But we really started to run more experiments in the late 80s and 90s, as the vehicles and our capability to operate in space started to get much, much better.

[9:04] But, like many things, when you go to a new environment, like microgravity in space, you may think you know about a fire, and what's going to happen, but we're very frequently surprised by how that difference in gravity just changes something small, but makes the whole fire act completely differently.

To protect a crew of a spacecraft from an onboard fire, I think it's going to be really necessary to run enough of these large experiments in space and build up our knowledge base and confidence that we understand what’s going to happen. Yes, it’s unlikely that a fire will occur in a spacecraft, but if one does, we want to make sure that we’re giving the crew the right equipment and all of the right procedures so that they can respond to it, stay safe, and continue on with the mission.

(Intro music montage)

[10:29] Narrator: Welcome to “On a Mission,” a podcast of NASA’s Jet Propulsion Laboratory. I’m Leslie Mullen, and in this third season we’re traveling to the ends of the Earth with scientists who explore the many aspects of our complex world. This is episode eight: Fueled by Fire.

“Backdraft” movie:
Donald 'Shadow' Rimgale: In a word, Brian, what is this job all about? 
Firefighter Brian McCaffrey: Fire. 
Donald 'Shadow' Rimgale: It's a living thing, Brian. It breathes, it eats, and it hates. The only way to beat it is to think like it. To know that this flame will spread this way across the door and up across the ceiling, not because of the physics of flammable liquids, but because it wants to.

[11:36] (“Backdraft” music)

Narrator: In the 1991 movie, “Backdraft,” fire is described as a living creature. Fire has many qualities of life: it grows, it moves, it breathes, it consumes. It can reproduce through sparks into many more fires. But most of us don’t think of fire as a form of life, and scientists who search for life in the universe are guided by NASA’s definition of life as “a self-sustaining chemical system capable of Darwinian evolution.” Because fire doesn’t have genes to pass down inheritable traits from generation to generation, it doesn’t qualify as life. Instead, fire is a chemical reaction, a process of change.

Natasha Stavros is a JPL systems engineer who focuses on fire.

[12:26] Natasha Stavros: Fire doesn't have a consciousness, right? There're three ingredients for fire: fuel, oxygen and ignition. And so if you have those three things, then you can have a fire. And if you don't have those things, then fire will die. So yeah, from a technical perspective, I don't think fire is alive.

I think fire is really interesting though, and I've always really enjoyed studying fire because it is something that every single human being on Earth has experience with. Even when I'm just sitting on the airplane, if I say I study fire, everybody's got something to tell me. They want to share their personal experience or what they've learned about fire in their life. And I also think something that's interesting about fire is that it's really the only natural phenomenon that we think we can control, right? We're never like, "Oh, that hurricane, let's just turn that off."

[13:24] Whereas with fire, it's a tool. We've used it for millennia. I mean, Native tribes will use fire for nutrient cycling, to clear a landscape for agriculture. We see this still today down in the South American rainforest. In Australia and in parts of Africa, you'll see fire used as a way to flush out animals for hunting. And actually, what's interesting is there's birds who even do this; these birds in Africa who will take twigs from a fire and they'll move the flaming twig to start a fire in a new area. They’re predator birds, so they actually want the other birds to come out from wherever they're at, and then they’re easy picking.

Also, there’s a professor, Richard Wrangham from Harvard, and he argues that the thing that makes humans unique from all other species is that we can cook our food. That's actually how our brain evolved, because in cooking food, we can get more nutrients, which then help fuel our brain. And so, we even have a relationship with fire at a very small scale of putting it under a pot, or just having a bonfire cooking the food so that we can eat it.

[14:38] So we use fire in so many different ways, we think we can control it, and yet when it's on the landscape and you have a fire that is traveling 40 miles per hour and has flames that are 150 feet tall, it's not a tool for us anymore, right? It's a natural disaster. And so, that's another reason why I think fire is just so fascinating to study is that duality, or the conflict in our relationship with it.

News report: If you're worried about the weather in Europe, spare a thought for the Arctic Circle this year
Reporter: The current heat wave is a devastating cycle of cause and effect. Forest fires in Alaska and within the Arctic Circle haven’t just been caused in part by global warming, they’re also contributing to it. Vast swathes of woodland are burning in northern extremes in Russia, the US, and Canada -- an unprecedented wave of destruction in highly ecologically-sensitive regions of the planet.

[15:29] Narrator: Extreme fires have been in the headlines all this year, starting with fires in Australia that were so intense and widespread it became known as the Black Summer. Then came news of the Arctic Circle and Siberia burning. Massive fires also struck the Western United States, as well as South America and Indonesia. Many of these fires broke records in the amount of acreage burned, pollution produced, and the number of people who had to evacuate.

Natasha Stavros: The term that we call with extreme fire is “mega fire.” So you'll see “mega fire” in the headlines, and what's interesting about this term is that there's actually no single definition of it. A mega fire could be defined by the size of the fire. It can be determined by the growth of the fire. It can be determined by the destruction of the fire, so that would be houses lost, or I think the Camp Fire had 88 deaths and 18,000 homes burned.

[16:27] Another way of thinking about a mega fire could just be on downstream impacts, like shutting down all of the energy grid. Which is not necessarily like the fire created that, it's human’s reaction to that that created it, but that could constitute a mega fire. And so, there's a lot of different ways that we can think about this. The way that I define it for my research was by area burned.

One of the fires that I studied was the 2014 King Fire, which happened up in the Sierra Nevadas of California, and it grew 40,000 acres in one day. That's like almost 40,000 football fields in one day. Part of why it grew so fast was, yes, you had fuels, but also the fire creates its own localized weather. So when a fire is burning really hot, that hot air is rising up and it dries the fuels out in front of it, especially if you're in steep topography. And then that sort of propels the fire forward.

[17:31] You can actually see this in a candle. Have you ever watched a candle or a flame dance around? Well, that's a micro-scale version of what I'm talking about, because that flame is dancing because it is generating heat, and as that hot air is rising, there's a gap and the cool air is racing in. And that circulation from the hot air rising and the cool air coming in from below to fill that gap is what's making the flame dance around. And so you could imagine scaling this out onto the landscape.

(sound FX: fire)

Natasha Stavros: The Rubicon River Valley, which is where the King Fire burned, is very, very steep. And there's just no way any human being could climb out of this quickly. There was a story that I heard about a firefighter, he's in there, and all of a sudden the fire just – boom -- takes off.

(sound FX: fire)

[18:31] Natasha Stavros: It's coming at him and he's at the bottom of this. He's like, “I'm not getting out of here. I'm not out running this.” So he had to get down into the valley as fast as possible where there was a river. And it wasn't even a river, because it was like two years into the California drought. It's a very sparse river, but he just had to get down there and then he had to just lay down in the water while literally 150-foot flames are burning all around him.

I wish more people would hear that story, and hear the stories of what wild land firefighters go through, because they say, "I want to build my home in this beautiful remote location. Oh, and by the way, I want wild land firefighters to save my house." They're not thinking about what that means for the person who has to be in that environment at the end of the day, when the inevitable happens.

[19:31] Narrator: Scientists have been predicting for decades that as the climate warms, we should expect to see larger, more intense fires more often. Warmer temperatures for longer periods of time can make the landscape as dry as a tinder box, and encourage pests that kill trees. And just as the warming climate affects the frequency and size of fires, the fires will amplify other changes happening in the environment.

(music)

Natasha Stavros: When fire occurs across the landscape, you sort of wipe the canvas. And as climate changes, the species that were there before, the ecosystem that was there before may no longer prosper in this new climate. Then you add in humans bringing in the other species that may prosper just fine and you have invasives, then all of a sudden you've changed the ecosystem and it's no longer what it used to be.

[20:24] I think there's a lot of unknowns about what's going to happen going into the future. All the projections globally will tell you it's getting worse, and that's if you were to take everything into a lump sum. But that doesn't mean that it's going to be worse in your specific area. And I think that's an important distinction to make. Definitely in the Western United States, the size of the fires is growing. That's not necessarily true all over the world though.

One interesting study that recently came out of University of California, Irvine was that globally, the area burned by fire is actually declining. The interesting part of this is that they are increasing in certain parts of the world where there’s a lot of media attention, where there's a lot of population. So it's again, that human interaction. Another study out of University of Colorado, Boulder has recently shown that in the Western United States, 95 percent of these fires are happening around human infrastructure and are caused by humans. It's fire in relationship to us that's the problem, right? Is it jeopardizing our infrastructure? Is it jeopardizing lives?

[21:35] Narrator: Natasha’s world first became consumed by fire when a blaze threatened the lives of her family and community.

Natasha Stavros: I grew up in San Diego, and the early 2000s is really when extreme fires started happening more regularly. Before that we had extreme fires, but they were sort of a couple in five years, 10 years, like now they're every year. And so, when I was in high school, we were asked to evacuate our house.

Cedar Fire - October 2003: CBS 8 San Diego
Fireman: “Evacuate the area immediately!”
County official: “This is a very significant fire situation in the county of San Diego…”
Fire witness: “When the winds were up this morning, it was just outrageous. Flames shooting all the way up.”

Natasha Stavros: That was really scary. This sense of like, "Oh my childhood home." There was nothing we can do, right? You're sort of helpless. You're just told, “Evacuate.”

[22:28] When you don't study fire, all you have is what the news tells you. The news reports were like, "Oh, we're burning from Orange County down to the Mexican border." That's terrifying. What they aren't sharing on the news is that actually it doesn't burn continuously the whole way, right? It's in patches. And that's because you have embers that fly off one fire and start a fire a little bit further downwind.

And so, that was my first introduction to it. Then I went off to college, and then again my parents got evacuated. This time I wasn't there, I wasn't able to go through the process with them of evacuation. But I also had loved ones that I could do nothing about because I was very far away.

Narrator: While Natasha was at college working on her PhD, she tried to figure out how to predict extreme fire events.

[23:18] Natasha Stavros: When we start talking about how fire moves across the landscape, there's three ingredients for that. That's fuel, topography, and weather. There's the macro scale weather. Those are the things that we hear about like Santa Ana winds, winds coming from the desert moving out over the ocean and they're moving a vast distance. And then there's the localized winds, and weather that the fire is creating within its own environment, because it's such an extreme catalyst.

And a lot of the older fire behavior models didn't account for this. And back in the 50s, they weren't using satellite data for mapping Earth on the landscape. They were literally building a fuel lab in a room, in a warehouse with instruments, and they were lighting things on fire and measuring things and saying, "Okay, well that's how fire works!" And then they were trying to take these models and then apply them on the landscape.

Well now, the new models that we're working with, they are actually building in all of these dynamic processes that we're seeing and the fire generating their own wind. They're actually improving our ability to be able to predict how these extreme fires are going to grow.

[24:32] Narrator: Forecasting future fires has been a big part of what Natasha does in her work for NASA, using visual, infrared and microwave instruments on satellites to figure out where fires are most likely to ignite each year.

Natasha Stavros: One thing that managers need to do is predict seasonally where they expect resources to be needed most because they have to plan. They have to plan their budgets, resources, any temporary hires, especially during the fire season.

(music)

As we reach peak fire season, there are synchronous fires across the landscape. And so, at the national level, they have to make judgment calls about where they expect resources to be needed more than other places. Because if they send resources let's say to California, when really Washington State or Idaho are having more of the problems, they have to relocate those resources. That's time that's not spent fighting fires. That's also money that's not spent fighting fires; it's spent on mobilization of troops.

[25:38] And so, one of the things that I did here was I looked to find where the gaps were in their knowledge. What didn't they know when they were making this decision, and why didn't they know it?  We're trying to build a tool that can help them make their decisions in an educated and informed way. You're looking at broad patterns across the entire country. And so, you can give them just a map and they can generally say, "All right, Idaho's going to be our problem state this year, or Utah, or Arizona, or California, or wherever."

Some of the things to consider are fuel availability -- you know, grasses and shrubs and leaves that have fallen, they actually are more combustible than big logs. Think about building a bonfire. You can't start a bonfire without kindling, so those fine fuels are an important factor.

[26:31] So fuel availability, how combustible that fuel is -- that has to do with size, because the size will determine how dry it is. Grasses can dry out a lot faster than a big log, right? Again, go back to your bonfire example, you’re trying to build your bonfire, you're not going to put a big wet log on your fire. You typically want dried out kindling to start the fire.

And then there's what we would call flammability. This is very similar to combustibility, but it's much longer term. So this integrates in the seasonal cycle -- if it's really early and it's extremely wet, the ignition isn't going to spread. The kinds of hydrological variables we can measure from space are rainfall, humidity, soil moisture. We can even measure groundwater reserves. We can look at sort of “greenness” and how much fuel is accumulating on the landscape.

[27:30] And so, we wanted to consider these three factors in our algorithm. We used different proxies for fuel accumulation, flammability and combustibility to develop models based on different land cover types. The reason why this is important is because different land cover types have different fire regimes.

Fire regimes are essentially: how frequently does it burn? When it burns, does it completely scorch the landscape? Here in Southern California, when you see a fire and you drive through afterwards, there's nothing left. But in other parts of the world, when there's been a fire, there's still a lot of fuel leftover.

And another part is, what makes it burn in the first place? Typically, we can think of this on a spectrum from fuel-limited to flammability-limited. And so, if you think about Nevada -- it's hot, it's dry. Of course that's combustible. Ok, but what if there's no fuel? That's a fuel-limited system.

[28:32] On the other end of that spectrum, you have something like the Hoh Rainforest up in Washington state, which has tons of fuel, but it's wet and damp. That's not really where you want to start a fire. And typically those fires come -- now with climate change it's a different story -- but historically, those have been once every 400 years.

And on the fuel-limited system, they typically need to have rain in order to have a fire, which seems counterintuitive, right? Because that rain in the year previous is what builds fuel. Whereas in the flammability-limited system, you need to have a drought. You need to dry all that fuel out and not give it any moisture for a while. And so, we need to consider land cover type when we're building these models.

Narrator: In addition to building models that forecast future fires, NASA also uses different satellites and instruments to watch fires that are currently burning.

[29:29] Natasha Stavros: So we typically use the MODIS or the VIIRS satellite for detecting fires from space. And you can actually go online and you can look at maps. I mean, there are literally thousands of fires every single day all over the globe.

There's another component of active fire that we're interested in, and that's the smoke that's being generated. Last year the tropospheric composition research program at NASA launched an enormous airborne campaign called FIREX-AQ. They were measuring all of the emissions, and the chemical composition of those emissions, and how they were changing, so that we could better understand the dynamics that are happening in the atmosphere during an active fire.

(sound FX: fire)

Natasha Stavros: There's a couple of different chemicals that are the predominant emissions from fire. I think like 90 percent to 95 percent of those are either carbon dioxide or carbon monoxide. These are important because they are greenhouse gases. We can also produce particulate matter. Particulate matter is something that comes when a fire doesn't burn completely, so like microscopic particulate matter can end up in your lungs, it can cause eye irritation and other health effects. What you'll hear a lot in the news is, “Oh, there's this fire event. The health advisory is stay indoors,” right?

(sound FX: fire)

Natasha Stavros: Fire can burn in two different phases: flaming or smoldering. I'm going to take us back to a bonfire example.

When you're sitting around a bonfire and, all of a sudden, the smoke changes directions and it comes on you and you're just like, "I can't breathe. My eyes are going crazy." That smoke that you're experiencing is probably because your fire is not in a flaming state. It's in a smoldering state.

[31:32] And when it's smoldering, it's not combusting as completely. It's got a completely different set of fire emissions than if it was flaming. If it's flaming, you're going to get more of your CO2, it's going to have a different sort of reaction. The heat from the fire is going to inject it much higher up above our heads so that it's not going to affect our eyes.

The flaming fires get all the attention, right? They're big and they're scary, you know, there's a fear factor and it's outside of our control. Whereas a smoldering fire, it's within our control so we're a lot less afraid of it. But when you're thinking about purely from an air quality perspective, and even from a climate perspective, smoldering fires have much bigger impact.

[32:15] A really good example of this is the fires in South America in the Amazon, or in Indonesia in Southeast Asia where you have rainforests, they have a lot of dense peat -- peats are soils -- and someone's burning. The reason why this is a problem is because they might burn hot for a little while where they're flaming and then they will burn for weeks, sometimes months. I've even heard of some fires lasting years, where they're just in this smoldering state and they're constantly emitting. And we can't find them.

I mean, when there's a flaming fire, everybody knows. They're like, it's right there. But when it's smoldering, they're not burning hot enough for the sensitivity of the sensors that we have. And it's often covered by things. It could be smoldering in the peats underneath the canopy. So I mean, you just add all these factors together, and it's very hard. And then also, not only is it that we can't find the fire, but in a lot of those systems, we don't know how deep the peat actually is.

[33:19] And so, that's even more of a problem because not only do we not know where the fire is, but we don't know how much fuel is available for it to burn, and how much is going to come out of it. We know it's a problem, but there's so many factors around it that are unknown. And to me, that's almost more scary than a flaming fire where we actually have a lot of knowns.

Narrator: After fire has burned through a landscape, another aspect of Natasha’s work comes into play.

Natasha Stavros: So, after a fire is done and contained, I'll go out and collect data so that we can understand what happened. In a post-fire environment, you're looking at how many trees are still alive, how many burned, how much of the ground soil burned, how much what we call the duff, that's all of the litter, all the leaves that burn.

This actually is a very, very dangerous environment to work in because first of all, you have increased chance of landslides. What's interesting is when a fire burns a tree, especially if it's that smoldering state, the flaming fire may have moved on and the smoldering can move down the tree into the root system. And so it can burn out the entire root system. Also, if the root systems are being burned, trees can fall down. So you can have trees that just fall down on top of you.

[34:38] Those roots, they're like anchors. They help hold a lot of the surface soils and things like that in place. They can help prevent erosion. If you burn them, you're just more susceptible to having a landslide because the stability is gone. And then often post-fire we enter into the rainy season. That's when it's the most dangerous. It’s because we've removed all the vegetation, all the stabilization. And then we get flash floods, there's nothing there holding the hillsides in place. And so it all just washes into our waterways, and we can have landslides which can enter onto roads and houses and things like that.

[35:21] I had an incident on a fire where I was standing for a solid like two to three minutes, and then all of a sudden, the ground just dropped three feet. It was because the entire root system that was under that was gone. It was like being in an elevator when an elevator drops.

(sound FX: ground collapse)

Natasha Stavros: Free fall, boom! It was just a straight drop. My knees weren't bent. There was no shock absorption at all. "What just happened?" (laughs)

(music)

Narrator: At first glance, it seems like fire completely decimates and destabilizes an environment. But fire is actually a fundamental part of our planet’s elemental cycles.

For instance, because oxygen is consumed when fires grow, the levels of oxygen in the air are affected by how many fires are burning. And the oxygen levels, in turn, regulate fires. Studies have shown that fires don’t spread if oxygen levels in the atmosphere are below 16 percent, whereas at our current level of 21 percent oxygen, fires easily start and grow. If the oxygen level of the atmosphere was 23 percent or higher, fires would be much more frequent and destructive, because even damp things can burn if there’s enough oxygen to feed the flames.

[36:44] Earth’s oxygen levels have fluctuated up and down by several percentage points over the past 500 million years, and the reasons for this are many, but fire certainly would have played a part.

Fires also impact Earth’s carbon and phosphorus cycles in ways scientists are still trying to fully understand. Plants need phosphorus and carbon to grow, and they produce oxygen in the process. Fires feed on oxygen, and break down the phosphorus and carbon contained in the plants that they burn. Fire and plants are partners in an ancient dance of creation and destruction that has led us to the world we have today.

Some plants not only have adapted to regular episodes of fire, they’ve become dependent on them.

[37:31] Natasha Stavros: There are some plant species that actually can't reproduce without fire. It's what we would call serotiny. If you look at a pine cone, those are really tight and only under extreme heat do they open up. Other plants, like chaparral, it grows and then it gets really old and it has dropped seeds. But those seeds can't compete with the older generation of chaparral. And so, they're just kind of sitting there waiting. And then once the fire comes, it removes all the old generation and the seeds open up because of the heat and then they are able to establish themselves and start growing for the next generation of chaparral to come in. So there's a natural cycle there.

[38:22] Now, humans might influence that cycle. We might speed up that cycle and that might be a problem, right? Because maybe the chaparral hasn't reached an age where it's producing viable seeds and we've just burned it, burned it, burned it, burned it. This is where we go back to the concept of a fire regime. Every ecosystem has adapted through time to experiencing fire at a pace, a form of regularity. And if we disrupt that regularity, that's when there's a problem. But in general, there's a lot of ecosystems that actually benefit from having fire on the landscape.

(sound FX: wind)

Natasha Stavros: I remember, after a fire, it was so devastating. I mean, it was just charred toothpicks across the entire landscape. And it was so eerie and the fog rolled in and you heard the coyotes.

(sound FX: coyote howls)

Natasha Stavros: There was no food. Everything was gone, right? All the animals had disappeared. And so, the animals that had come back on the landscape were howling looking for food and it was echoing and it was just this eerie, dark, dystopia. And then six months later, in the Spring, was beautiful because after a fire you can just get phenomenal wildflower blooms.

[39:50] And it was just the juxtaposition. I think fire can represent destruction, and it can represent transformation and growth. If you start looking at other ideologies around the world, like in Hindu, right? They have a God, Shiva, who is the creator and the destructor, and they honor him. So it feeds back into that idea that people have had this relationship with creation and destruction for millennia. It's universal. It's part of being human.

(music: Firebird Suite, Igor Stravinsky)

[40:27] Natasha Stavros: Fire is embedded in so much of who I am. I'm an Aries, which is a fire sign. My husband's a film score composer and he got asked to score something for an orchestra. He picked this piece right before he met me, but it was called the Firebird. It was about the Phoenix from the ashes coming up after a fire. And I was just like, this is just too many coincidences! 

I think the thing that I like about the Phoenix story is just that life can feel devastating and destructive at times and there's still the potential and opportunity for growth. So we talked earlier about fire being a living thing. And fire will always come back, but life actually tries to prosper. Anywhere there's an opportunity for it, it will. It may transform and not be what it was before, but life comes back.

(music continues)

Narrator: If you like this podcast, please subscribe, rate us on your podcast platform, and share us on social media. We’re “On a Mission,” a podcast of NASA’s Jet Propulsion Laboratory.

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