Up In Flames: Background Briefing
For those of you not up-to-speed with my management style, I like to provide entertaining background information for any new science show I write and produce. I find it helps my staff with any curly questions they may get. It’s not required reading (I’m a big believer in being adequately compensated for your work!) but it’s there if they want it or need it.
This is the one I wrote for our brand new science show “Up in Flames”
This holidays we’re going to be delving into the world of FIRE and ICE. (Not that one… literal fire and ice).
So we’re finally introducing a dedicated FIRE SHOW. WOO.
Actual behind the scenes footage of me writing this show
On the surface, this is pretty simple. But if you take the time to really delve into the science of fire and how/why it burns, you’ll end up following me down a really long, dark, black hole… with fire at the end… ok maybe the hole is glowing a bit…
Let’s move on before this metaphor gets more tortured? Cool
First things first, we’ll take a closer look at the concept that underpins this entire show.
The Fire Triangle
The basis of this show is the Fire Triangle. It’s really simple: to make a fire, you need three things.
If you take one of these three things away, the fire goes out. Now for the purpose of this show, the above triangle is really as far as you need to go. BUT because here at Science Space we’re extra and love a good background briefing full of tasty facts, there’s a bit more to it than this.
If you spend more than 2 seconds googling the fire triangle, you’ll come across the fire “tetrahedron”. This includes “combustion” as the fourth component.
Listen, is it necessary? No? I mean I think it’s a given that the result of the fire triangle is fire… This is totally a bunch of chemists going “um, actually…” and inserting it because they felt it wasn’t technically correct.
It’s implied guys. Yeesh.
Anyway, to make a fire you need fuel, an oxidiser (most often oxygen) and heat to raise the fuel to its ignition temperature. If you remove a side of the triangle, it’s not a triangle any more and boom - no more fire.
Ok, so what is fire anyway?
We’ll start with what it’s NOT and that’s plasma.
It’s a really common misconception that fire is basically like what we find at the Sun - superheated and ionised gas. The thing is that the plasma in the Sun is at MILLIONS of degrees celsius. If that existed on Earth, we’d be instantly vapourised.
A whole planet filled with tiny suns on the surface would be an ISSUE.
Fire isn’t a plasma, but it’s not a solid, liquid or gas either. So what is it?
Well fire is the way we experience combustion. Which is science’s way of saying “yeah it’s not really a thing but it is a thing but it’s also not… it’s hot? And we feel it? So…. yeah.”
As far as I can tell, fire is complicated. It’s a by-product of a classic combustion. In the presence of heat, oxygen starts reacting with the fuel. When bonds within both of these reactants are broken, energy is released. Energy is directly related to heat in this case and so the fire becomes self-sustaining until someone comes in and goes “oh hey, that’s not supposed to be on fire!” and removes something in the fire triangle to extinguish it.
For those playing at home, here’s a combustion reaction:
CxHy (hydrocarbon) + O2 -> H2O + CO2 + Heat/light
So that explains why fire burns (kind of… ), but where does the light come from?
Fire glows for a few different reasons. I’m simplifying it a lot but it’s because of temperature and black-body radiation.
A black-body is an object that absorbs light and emits radiation without reflecting anything. These don’t actually exist in real life but you can approximate things (because physics) and guesstimate temperature based on their glow. Humans emit infrared radiation because we have a much lower temperature, but the Sun glows white because of its insanely high heat output.
So a flame glows because it’s hot… kind of.
Fuel also has by-products when it burns. Wood and candle flames glow a yellow colour because of their temperature but also because of soot and other particles.
Flames are a specific shape too because of gravity. Hot air rises when it burns and pulls the flame into a cone. If you look at flames in micro-gravity, they look more like little balls. So cute!
https://www.nsf.gov
The temperature of the flame also changes as it rises up above the wick. That’s why we get a weird colour change from blue (hotter) to yellow (cooler).
A note on fire extinguishers… because you might get questions… also this is kind of just good to know in everyday life.
There are a bunch of different types of fire and these depend solely on the type of fuel. There are five main categories of fuel:
Class A - wood, paper and textiles
Class B - Flammable Liquids
Class C - Flammable Gasses
Class E - Electrical fires
Class F - Cooking oils and fats
For those eagle-eyed viewers playing at home, you’ll notice there’s no class D - that’s because when you have a flammable metal fire, all bets are off and you’ve probably got bigger problems.
Your steel-making factory has exploded for example…
Each of these fires have specific types of fire extinguishers that work best. Like you should NEVER throw water onto an oil fire. That’s because oil and water don’t mix so the water droplets sink to the bottom of the oil, superheat and then EXPLODE. Not a good plan.
Each fire extinguisher works based on the fire triangle again. Remove heat, fuel or oxygen and the fire goes out.
For class A fires, wetting the fuel cools it down. Wet wood doesn’t burn. Job done.
Class B fires are flammable liquids. You add liquid to a liquid and you get… well more liquid. Water extinguishers are probably not going to work so much. Foam extinguishers smother the fire, removing oxygen. Job done.
Class C are flammable gasses. Speaking from experience, gas fires are tricky. I once turned around in a chemistry lab I was supervising to find my teaching partner holding the end of a gas tube that had previously been connected to an ignited bunsen burner. She was essentially holding a flamethrower, surrounded by shocked-looking first year students. It was a time. In that case we turned off the gas at the wall - remove the fuel and the fire goes out. We also could have used a powder fire extinguisher.
Powder extinguishers are the workhorses of the extinguishing world. They’re effective on multiple classes because they’re made of a powder that melts upon contact with heat. They basically cover the fire completely, cutting it off from its oxygen source. If you have a fire extinguisher in your house, there’s a good chance it’s filled with monoammonium phosphate powder.
The other likely candidate is Carbon Dioxide. This one’s used mostly on electrical fires but it can be used on a bunch of other flames because it does two things. First, it smothers oxygen and second, because it’s compressed gas and it’s COLD, it removes heat.
We’ve got a CO2 extinguisher and a fire blanket hanging on the wall in the science theatre. Hopefully you’ll never have to use them! Both are SUPER effective at breaking up that fire triangle.
Anyway, that’s all I can think of! Most of the time this won’t come up - you’ll be too busy picking jaws up off of the floor. If you do get extra questions though, please don’t hesitate to send me a message and I’ll see what information I can find!
Go forth and FIRE!
Safely.
Pls.
Science Space is a not-for-profit organisation at the University of Wollongong. The work presented here was written by me and should not be reproduced without Science Space’s permission.
