How Fire Works

Creating fire was possibly the most important human discovery, but it's easy to take for granted. But. Josh and Chuck get to the bottom of the chemistry of fire in their quest to explain everything in the universe.

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Episode Transcript

Speaker 1 (00:01):
Welcome to you stuff you should know from house stuff
works dot com. Hey, and welcome to the podcast. I'm
Josh Clark. With me is always as Charles w chuckle
Bryant said, and uh, this is stuffy snow, Josh. We
let me stand next to your fire. Sure, okay, come

(00:27):
over here right now? Okay, sorry, Well it's nice and
warm over here, isn't it. I'm feverish and it's smoky
and there. I feel like there's chemical reactions taking place
before my very eyes. There are. That's why there's fire.
If fire is nothing if not a chemical reaction. Yeah,
I got so. Okay. Have you heard of the Winecoff Hotel? Yeah,

(00:52):
but born and raised here, Yeah? Uh the Ellis Hotel?
Was that the hotel fire? Yeah? Yeah, you know that.
It's now the l Hotel. It's at the corner of
Peach Tree and Ellis, nice refurbished hotel. Back in nine
it was called the wine Cough Hotel and it was
the site of the most disastrous casualty wise hotel fire
in US history. In December d nineteen people died right

(01:17):
right here in a very sty four. Just under forty
four years later, in Las Vegas, Nevada. The MGM Grand
had a hotel fire. People died. Do you remember the
MGM fire GM Grand fire? It was a big deal.
Not at all you you. I'm surprised because I kind
of remember, like seeing footage of that. When was this?

(01:38):
Oh no, I don't remember. So both of these fires
and all the loss of life associated with them were
the direct result of hubris towards fire. The wine cough
their fire exits one stairwell for the whole building. I
think it was like nineteen stories or something like that. Um,

(01:58):
the MGM Grand, they they didn't put up like sixty
dollars for a fire detection system in this one part
of the hotel that would have saved everyone's lives. A
part Hubrist, part financial shenanigans. Right, But isn't that kind
of based on Hubrists. My point is is that if
there's one thing that we shouldn't have, hubris towards its

(02:19):
fire agreed. We do. You think we might control fire
thanks to Prometheus being given it by the gods, yea,
But fire controls us when it really comes down to it.
That's right. You gotta face off a tete a tete
with fire. You're gonna lose buddy because you're combustible. Yeah.
So also we should say here that this fire as

(02:41):
um it should be a prequel to the how wildfires
work and how um spontaneous human combustion works. Those two
episodes are great. I agreed, this will seal up our
triumvirate and now we're gonna explain how fire works. Yeah.
I do have a couple of quick stats. We're talking about.
The deadly nature of fire does kill more people than

(03:01):
any other force of nature. I couldn't find that any
source for that, but I saw I was searching for it,
and it brought up like a handful of plagiarized versions
of this article on the internet. Yeah. Those are always fun,
especially when it's your own. This one is not mine.
This is a Bill Harritt, Tom Harris, Tom Harris. Um.
But I do have some stats in the US, at

(03:21):
least in two thousand ten for residential building fires, over
people died that year. And that's sort of in the
wheelhouse that fluctuates between about thirty two hundred a year
from building fires. Uh, cooking is far and away the
leading cause of the building fire and arsonist number two huh,

(03:44):
which I would have thought like falling asleep with a
cigarette would would be above arson um and then total
in two thousand nine, and I guess this counts like
any kind of fire in the US, they were close
to thirty deaths that year, so that you know, that's
a lot. Yeah, I mean that's more than um, I'm

(04:05):
sure killed by volcanoes in the US every year. I think,
you know, that's just one or two people falling into
kill aweya from getting too close. Have you seen that
footage of that scientists going, Um, he's collecting some sort
of I guess magma from an active volcano in Hawaii,
and um, it was really nerve racking because he goes up,

(04:26):
takes a sample. He's climbing up the rim and then
climbs back down and right when he steps away from it,
the magma comes up over the rim exactly where he'd
just been climbing like five minutes before, and so it
would have like just just completely disintegrated him. I imagined,
what did he say? I don't know, like, holy crap,
did that Well? The guy who was filming it was

(04:48):
like narrating like this is so stupid. Yeah, it's very cool.
I don't know what you'd search, but it's up there
on the internet somewhere search WU and that should do it,
so Chuck. The Greeks thought that fire was one of
the four elements earth wire, water, wind and fire. Earth
wind and fire and water and nash and young silly Greeks. Uh.

(05:14):
The reason why that doesn't really hold up is because um, earth, fire, air,
these are elements. They're matter, Yeah, they're made up of atoms.
Fire is the physical manifestation of matter changing form. It's
pretty cool, like when you think of it that way.

(05:34):
And we're going to describe how this happens, all right,
I can tackle some of this. Chemistry is not my
forte but it is a chemical reaction at its core
between oxygen and um fuel, which I mean, we'll probably
let's talk about like a camp fire. Let's go with wood.
Wood fire is probably easiest way to describe it. But

(05:55):
the wood is the fuel. The wood is the fuel.
Oxygen's found in the air, that's right. But for these
things to uh make fire, you gotta have something called combustion, yeah,
and which means you're gonna have to have some sort
of a spark um. Well, actually not always, because as
we find out, some things can combust without a spark.
I think if they get hot enough, Like the heat

(06:16):
is just so intense that it doesn't need any spark, right,
But for wood, you have to get it up to um.
Uh it's ignition temperature, which is about three hundred degrees fahrenheit,
which is where you're gonna start seeing some smoke because
that is cellulose burning away. Uh. And it just occurred

(06:37):
to me reading this today, like where there's smoke, there's fire.
Not true, Yeah, because things can smoke without there being
a fire. Yeah, actually a byproduct of fire. You know,
um doesn't smoke. So I guess in order to if
you're one of the people that now says bottom of
the totem pole or instead of top of the totem pole,

(06:58):
then we can for they reinforce this obnoxious quality by
encouraging you to say, where there's smoke, there is ignition
temperature of a combustible fuel, there's volatile gases. It's nice
way to go chucked, all right? Thanks? So yeah, heat
is heat decomposes fuel where will to say wood, And
in the case of wood specifically, it decomposes the um

(07:21):
volatile gases contained in the solid matter, Right, so these
volatile gases start to heat up themselves, and while they're
doing that, the cellulose, the solid stuff, is decomposing and
turning into what's called char. Yeah, I got a little
thing on cell cellulotional quest and then you can just
take it home. No man, because that's where I get confused.
I'm confused to cellulose about of wood is cellulose, and

(07:47):
that's what like, that's where you make paper, that's what
you make paper from. That's what you make cellulosic ethanol from, too,
and it's what you make cellophane out of. Cellophane is
regenerated cellulose. So it's it's like it looks like plastic,
but it's not. I had no idea. It is a
man made as I'm sorry, it's a natural polymer. Plastic

(08:08):
is manmade obviously, So cellophane is nothing more than regenerated
paper in a way. Wow, like they had some other
stuff to it. But that's why it's biodegradable. And I
always wonder why, like supposedly cellophane is biodegradable. It's like
that's impossible. It's plastic, but it's not plastic. There's this

(08:28):
old telephone and from like the fifties maybe, and it's
like good things coming twos and it's like this, this
pair of twins wrapped in cellophane and they're just like
kind of looking around. But yeah, you can imagine they
only have them in there for a few seconds before
they snout the picture. I did not know that about cellophane.

(08:48):
Back to the podcast right there, and I don't know
about that. Hats off to you, all right back to you.
I know what the fact of the podcast is. You're
gonna save it for when it comes. We can't save it, okay, okay.
So um, you've got the cellulose, the solid matter of
wood separating now from the volatile um gases that are
starting to lift off. That's smoke, right, Okay, the wood,

(09:12):
the solid matter is starting to turn into char um.
And that is basically if you if you burn would
if you heat it up and you separate the gases,
which are the smoke, what remains is carbon and what
what charcoal is is charred wood that's had the volatile
gases burned out of it, which is why when you

(09:33):
have a charcoal fire, you don't have smoke, yeah, or
not much at least, Yeah, because the gases have already
been burned off. Yeah, and charcoal too. That got that
kind of got me on charcoal filtering because these charcoal
is a filter, and I think that is a scrubber
two on smoke stacks. And uh, if you're like I
did some of those survival articles at one point, and

(09:55):
one of the things you can do to purify water
is take your char from your fire, put it in
like you know, cool it down obviously, and then put
it in, then put it in like a hanky, and
then running creek water through that to collect it underneath.
That's awesome. And uh, and there's like real charcoal filters too.

(10:16):
But apparently charcoal has a quality because once it's pure
carbon like that, it um has a knack for filtering
out things like impurities like chlorine and letting other stuff
get through. So that's why it's used as a filter. Yeah,
because essentially what you're making is a carbon filter. Yeah,
charcoal is like basically pure carbon with all the impurities

(10:38):
burned off. Yeah, those impurities burned off as smoke. They're
volatile gases, So that's pretty neat. Yeah, that's pretty awesome.
Little survival tip man, you're killing it today. Well now
that this is when I go to sleep though. Okay, So, um,
the third component of burned wood. You've got the volatile
gases smoke, you have the char, the charcoal which is carbon,

(10:59):
and then you have ash, which is unburnable minerals like um,
calcium or phosphorus. I believe. Yeah. And if you like
you ever cook with briquettes, charcoal briquettes, you're gonna get
a lot more ash with that because it has a
lot of more like byproducts in it. Then if you
use like real wood charcoal, right, but they're not gonna smoke,
They're just not gonna burn. You're just gonna be left over,
like you can't get rid of it. You can pounded

(11:19):
into oblivion, but it's still there. Yeah. But if you
use the real wood coal then char, then you'll notice
you don't get a lot of that stuff. Oh is
that right? Yeah? Okay, but the brackettes aren't as nasty
synthetic briquettes. No, they're made from char and like binding
agents and stuff like that. And saw that. No. I
actually used to hear that like, oh, you can't cook

(11:40):
with briquettes are so nasty, But they're really I look
into it. It's not super nasty. I mean you probably
should cook somewhere in between nasty and super nasty. Yeah,
well it's not It's not as bad as I thought.
I thought it was like a bunch of chemical agents
and glue and cement. And that's not the case I got.
It's not the hot dogs of King materials. That's the

(12:02):
corn dog. Okay, um, okay, So we've got the components,
right um. As these volatile um gases continue to heat
up um to about five degrees fahrenheit two d six
degrees celsius, they the molecules break apart, and when they

(12:23):
break apart, they go to combine with oxygen oxidation. Right um.
And the same thing happens with the carbon in the wood,
but this takes place in place much more slowly. But
one of the the stars of this chemical reaction, this
change of breaking down to these molecules and then the
recombining into other things like carbon dioxide, carbon monoxide. Water.

(12:46):
Isn't that weird that fire produces water? Um, That's why
sometimes you have steam coming from a fire. Right um.
The star of all this chemical reactions, all these chemical reactions,
is heat is produced. He the energy is released, which
allows us to cook and be comfortable and feel secure
and all the good stuff that comes with fire. And

(13:08):
because of the heat that's released as these things are
heated up, um, it is sustainable. That means the fire
is sustainable so long as there's fuel and there's oxygen present. Yeah.
That was the kind of creepy part. And not creepy,
but it's self perpetuating, like that flame is gonna heat
up any fuel near it to the point where it
can release those gases to recombine with oxygen. It's pretty

(13:32):
elegant and think about it. Yeah, another big star of
fire besides heat is light and part of that is
from the same um the carbon atoms right, yeah, that
are combining, that are being torn apart, the molecules that
UM form up the char breaking down in their constituent

(13:53):
carbon atoms when they combine with oxygen, right recombine, Yeah,
I think that would make carbon monoxide. But as they
change UM, they they're electrons will go up, an energy
level will change orbit and when they come back down
they admit they release some of that energy that they

(14:14):
have and they release it in the form of photons.
They produce light UM and yeah, it's it's heat producing light.
Like we talked about bioluminescence, where basically you heat up
a filament in a light bulb and it glows. That's
the same thing with the fires, the same based on
the same principle, which is incandescence. Pretty awesome, and depending

(14:36):
on the temperature, Uh, different colored light is going to
be produced. Yeah, Like, uh, you remember the buns and
burners back in chemistry class and how the buns and
burners have little slots on the side that you can
vary the amount of like oxygen getting in there. You know,
there's the little flickering orange flame of a buns and burner.
Then if you let a lot more oxygen in, it's

(14:58):
going to be more it's gonna be more hot. And
that's why that's when it's gonna be that blue jet
the same as when you see like a jet plane,
like right next to where the flame comes out, it's
gonna be like really blue and then it gets more
orange and yellow, you know, like the batmobile. You know
what I'm saying, I know exactly the original batmobile. No. Um,

(15:18):
we've seen a bunch of batmobiles recently. There's a documentary
about the batmobile. That's what all those were there for
a comic con. Okay, we had and I had her
picture taken with it with which one the new one,
the tumbler, that's what they called the new one, is it? Yeah?
The chrystalin one is called the tongue. The chrystal was Yea,

(15:39):
it's awesome, it's pretty cool. Uh so yeah. The the
reason why the blue one happens to be a different
color and hotter is because there's more energy being released,
that's right. Uh The lower energy and slightly less hot
part of the flame that glows orange yellow is at
the top. And the reason of flame is pointed. This

(16:01):
is this is pretty awesome, not the fact of the podcast.
The space part is Okay, I think, all right, go ahead. Then,
So a flame is pointed and it burns upward because
the gases that are burning what you're burning right there
are volatile gases. They're being burned off right. Um. As
they as they burn, they're they're hotter, but they're also

(16:23):
less dance and they're moving upward towards the less dense
air above it, which causes it to be pointed. But
if you were to light you take it for granted,
but it's kind of cool to know how that works. Yeah,
that's why it always burns upward. It tends to burn upward. No,
it always does, always burns upward. And that's also why

(16:43):
it's pointed too, because the air around it is dense
and it's pushing it in right. Pretty awesome, But if
you were to light a fire in zero gravity, it
would burn as a sphere. I want to see this.
I mean, can it be done if we go into
zero Yeah? But I mean they have zero gravity environments,
is do they? At Tech? Surely someone has started a

(17:05):
fire in one of those just to see this. I
think it's a really bad thing if a fire starts
in the zero gravity environment, I guess. So that's I
just gotta think that someone's tried this. I'm sure. I'm
sure there's a video of it on YouTube. Now there's
probably a good reason why. And someone's gonna write and
some hute dummies. Don't you understand that when you start
a fire in zero gravity that we all die? That's right? Okay?

(17:27):
So steam, let's talk about steam, because because we talked
about the recombination of atoms, when these gases are released,
the same thing happens when you boil water. You know,
you get this this gas mixing with oxygen the air,
but it's not going to combust, thank thankfully, or cooking
would be much more dangerous. Um. It's because some of

(17:48):
these atoms aren't as attracted to each other. In the
case of water, for sure, they're tepid towards one another. Yeah.
If you're talking fire, though, they have carbon and hydrogen
which are really attractive to oxygen, and so they like
to get together and uh, combine, recombine more easily. Right,
pretty simple. Uh. And then we've been talking mostly about

(18:09):
wood as a fuel, but tons of things are fuel.
Gasoline is a good fuel. Gasoline doesn't produce char. Basically,
heat vaporizes gasoline into nothing but volatile gases which burn. Yeah,
that's so there you go. And I always heard too
that gasoline ignites like the vapor ignites, not the liquid.

(18:29):
Is that true. Yeah, it's not the it's not the liquid,
it's the gas. But heat causes all that liquid to
turn into the gas, which. Um, So different fuels are
going to catch at different temperatures, and no matter what
the fuel, it'll have a piloted ignition temperature and an

(18:52):
unpiloted ignition temperature. Basically, the piloted ignition temperature is that
um that point that temperature where the volatile gases are
being released and they're heated up to the point where
if you introduce a spark it would blow up. That's right.
One of the defining characteristics of a volatile gas is

(19:13):
that UM. It basically disperses at room temperature. I believe UM,
so at some point, introducing a spark is gonna set
that off at some temperature, which I guess means that
like if you have gasoline cooled to enough of a temperature,
just lighting a match next to it won't set off

(19:34):
the gas. I don't know if this is a question
we should be raising a general audience. Don't try this.
I'm curious, so we'll have to check that out. But
the unpiloted ignition temperature is basically when something gets hit
by lightning and the heat is so intense that there's
no need for a spark. It just heats it up
the point where now it's on fire, where it come bust.

(19:54):
Pretty cool, And I try to get to the origin
of pilot like a pilot light, which is the same
thing I guess I couldn't find it. I don't know
where that came from, because, yeah, I think about it,
You've got the gas burning and that it's glowing, yeah,
and then you just hit the spark and then bam,
you just ignited the gas. So it's at the pilot
the piloted ignition temperature in your hot water heater. But

(20:16):
I'm sure someone knows the answer that, so if you
do send it in. We're raising a lot of questions
in this one and giving some answers. Um the shape,
and by shape usually they mean like surface area of
a of a fuel effects how efficiently it burns and
how easily it burns too. Yeah, I mean this is

(20:38):
pretty basic. Like if you have a big thick log
obviously you're gonna have way less surface area exposed and
combustible then if you had like a toothpick. Yeah, and
they can absorb a lot more heat too, big thick
log um. But yeah, if you have a bunch of
little pieces of wood, it's gonna burn more quickly catch
more easily because there's more exposed surface surface temperature, and

(20:59):
more of that fuels is exposed to the heat than
a big Like you said, a big log or something. Yeah,
and that's why when you're starting. You know, if you
ever watched a bear grills do this thing or or
less stroud, they try to get the little like tiny
little shavings from the inside of h like you peel
away the bark on a tree and then get the
shavings off of the tree itself. And that's the stuff

(21:20):
that's gonna like really combust easily through friction with like Uh,
you know, there's different ways of doing the little I've
never been I've never done that. Have you? Have you
started a fire using like friction? Have you? Really? That's impressive.
I do that stuff when I go camping now for fun,
like in front of the real fire. You know that
we started with our big lighters and I'm sitting there

(21:43):
with my beer in my Southern comfort and my comfy
chair and the steak is on the grill. I'll do
some little survival stuff just kind of for fun, you know,
until I get tired of it and give up. But yeah,
it's fun. Um, Well, hats off to you for no
how to do that? Well, it's pretty easy. I mean
there's different ways. There's the plow method or the little bow, uh,

(22:05):
where you make the little string to bow. Yeah, and
do that little number. Yeah, I've seen that one. There's
the castaway one. Yeah, that's the plow method. Oh that's plow. Yeah,
that makes sense to be called that. Do you got
anything else? I don't think so, do you think Do
you feel like we explain this correctly? And well? Yeah,
I mean it's it's pretty basic chemistry. We're basically heat

(22:27):
breaks down a fuel so that it can combine with
oxygen and ignite. Yeah, and then burned. That's right. And
it's self sustaining so long as there's fuel and oxygen.
And then all you need is a bear skin rug
and some cinemax and you're all set for Friday night. Awesome.
If you want to know more about fire, you can
type fire into the search bar at how stuff works

(22:49):
dot com and that will bring up this article and
plenty of other stuff too. Um, maybe even some survival
stuff by one Charles W. Bryant. Uh, And I said
search bar. So it's time for a listener mail, Chuck. Yes,
we should tell everybody about something very special and due
to our hearts New York City. That's right. We are

(23:12):
going to Comic Con and we will be doing a
live podcast on Friday, October twelve at Comic Con at
the jab At Center. It's like our new thing. We
did San Diego, now we do in New York. That's
right next up Albuquerque. So if you are going to
Comic Con, you should come back and see that. But
after Comic Con, we have one of our famous that's
famous to us, All Star Trivia Nights. Um, where is

(23:36):
it gonna be the Cutting Room. It is at the
grand reopening of the Cutting Room in the flat Iron District,
which is what's the address? It is forty four East
thirty second Street in New York. And uh, it's in
the flat Iron you said. And doors open at seven thirty.
Trivia goes down to eight thirty. And what is first come,
first serve? Right? Free free, free, first come, first serve.

(23:58):
We will have a bar there that you can buy
a drinks. Yeah, you can buy us drinks. That's right.
We're gonna basically be having a really good time if
you if you're not familiar with our trivia nights, like,
just come out and check it out. It'll be worth
your while, absolutely, and stay tuned for info on Facebook
and Twitter about the makeup of the All Star team.
We're filling that out as we speak, but we will

(24:18):
have some special guests that you will want to meet. Yeah,
and at the very least you can come take on
me and chuck right, yeah, okay, it's just fun. So
what is that? That's Friday, October twelfth, right, yep, the
panels that went. The panel is at at beleave okay,
and then we're gonna be at the cutting room starting
at thirty. Trivite starts at eight thirty doors at seven thirty.
Be there, be square. You're good at this, Thank you?

(24:40):
All right? The time for listener mail. I'm gonna call
this email bad to the Bone, so Jocelyn Stone here
in Victoria, BC, Canada apparently hates bad to the Bone
just as much as I do. So we are we're
friends in that way, uh, she says. A few years ago,
my partner, or Tim, discovered that he could set anything

(25:02):
on his heart desired on his alarm clock for his
cell phone. He searched for the perfect song and decided
on bad to the Punt. Uh. Tim believed, in order
to slowly get himself ready for the day, he needed
alarms at five am, five thirty and six. I on
the other hand, wake up without an alarm at six
thirty without fail, which is what I do all right. Um.

(25:23):
Every morning I was shocked by the full volume darronn
or an airn Air. I would there's the way to
wake up right. I would blast up to a sitting
position in bed, my heart exploding out of my chest,
and look next to me at Tim, who was sleeping
through the whole event. I would punch him, get up,
turn off the alarm myself, and then repeat this two
more times. What kind of business partners are these? I

(25:45):
don't think their business partners. That was like an American
beauty remember that? Oh yeah, It's like I'd like you
to meet my partner. He's like, oh, what line of
work you guys? That was a quantum bleat meeting lone star?
Huh wow? Yeah, what could you um? For some reason,
no matter how much I begged him, he wouldn't change
the song or let me turn down the volume. If

(26:06):
I secretly changed it before bed, he would change it back.
But I tried to turn it off and hide his phone,
he would find it and turn it back again. If
I turned the volume down while he was sleeping, his
spidy sense would start tingling and he'd wake up and
turn it back on. It turned into a game that
lasted a full year, finally ending when I told him
the slipper of amusement I found in the game was
gone and I would throw his phone into the ocean

(26:27):
if he didn't change it. So eventually she just had enough.
It's like, this isn't fun anymore. I ended up buying
an alarm clock radio, which he also sleeps through. Now
thanks to Tim, every coming here bad at the bone
in public, I immediately leave the area lest I explode
in a muddy, scalding rock going rage like the Wamano
guys er, Well nice, yeah so, And then she said,

(26:50):
ps do a podcast on accordions after all that? Who's that?
Jocelyn from Victoria? Duci can thank you and Tim? Tim,
good luck, Tom and Jocelyn. I help you guys find
a yes song you can both agree on. Agreed? And Tim?
Just get up, dude? Is it time? For some people?

(27:11):
It's hard. I never understood the snooze because wouldn't you
rather to sleep that time? No, I'm with you, but
I'm saying like, instead of being woken up everything, that's
not that easy to just wake right up and right
eyed and bushy tail and to accept others as they are. Uh,
let's see what do we what do we want? Um? Geez,

(27:33):
I don't know. I don't know either. We'll have to
figure it out. Yeah, um yeah, send us anything. I
guess this is the it's a generic call out. You
can send us anything via Twitter at s Y s
K podcast. You can join us on Facebook dot com
slash stuff you should know and send us an email
containing anything. And if you send us an email it

(27:55):
just says anything like, you'll be one of five thousand
people that do that, so just stop. Um. You can
send that email that doesn't just say anything to Stuff
podcast at discovery dot com for more on this and
thousands of other topics. Is it how stuff works dot

(28:16):
com mhm