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| Literally rocket science. "Fire Breathing Dragon" by san dara [deviantart] |
Dragons are riveting creatures. They have been a staple of fiction and mythology for all of written history, captivating our wonders and fears for millenia. The mere mention conjures imagery of massive scaly beasts alighting dark caverns with the bodies of over-zealous knights. From ancient works like Beowulf to modern works like George RR Martin's A Song of Ice and Fire, dragons are known to spew fire "hot enough to weld steel or crack stone." But one part of the lore remains a fundamental mystery and topic of debate. What is dragon's fire? What is it made of and what makes it possible? A simple explanation is that the fire stems from their magical nature- but what if dragons really existed? What would it take to make dragons and their iconic fire-breathing real? Let's explore what it might take to make dragons possible- the chemistry, biology, and physics of this mythic beast.
A somewhat knowledgeable person might suggest that fire breath could be created by a pyrophoric compound. Pyrophoric compounds are certain chemicals that spontaneously burn in air and moisture. That, on the other hand, oversimplifies a more complicated question- how could a pyrophoric molecule possibly be made and moved within the body without resorting to some sort of magical or exotic material? It couldn't. With the exception of certain microscopic extremophile bacteria, the chemistry of living things is carried out in watery environments. This would mean the chemicals would burst into flame inside the dragon's body. Luckily, there exists within nature a model for small scale explosions within an animal.
This lucky little bug is called the bombardier beetle! These beetles use a mix of hydrogen peroxide (the same as the drug store disinfectant) and a chemical called para-hydroquinone. When mixed in the presence of catalysts called enzymes, these two chemicals undergo a reaction that produces a ton of heat and steam! Enzymes are proteins that act like little machines to help chemical reactions happen in the body. Though its result is certainly impressive, this little jet only reaches the boiling point of water though- it's no flame!
To melt steel, crack stone, or burn flesh we need something REALLY hot, so lets get back to basics. Any firefighter will tell you that you need three things for a fire: fuel, oxygen, and a source of ignition. For a fire to come out of a dragon, this rule still needs to hold true, but where do we find such a combination? The bombardier beetle gives us an interesting starting point- take two materials in separate sacs, mix them together and create a chemical reaction that is quick and violent.
Another class of materials serves this exact purpose, hypergolic chemicals. Hypergolic chemicals automatically burst into flame when they come into contact with the right material. As shown in the video below, reactive nitrogen oxides provide a really neat example of the ignition of an organic (carbon containing) molecule with dinitrogen tetroxide. Nitrogen oxides of many different types are used as liquid propellants for rockets because of their high energy density and reactivity with various fuels.
But if these reactive nitrogen oxides burst into flame in contact with anything organic, how could they exist inside the dragon's body he'll be hurt by it? Production of these chemicals inside the body would not be favored by evolution, so we'll have to find a way to quickly make these chemicals on demand. Fortunately, the two components of nitrogen oxides- nitrogen and oxygen- are incredibly abundant in the air! But how would such stable molecules, which exist in the atmosphere without complication, react to form these extremely reactive molecules? Simple!
Using an enzyme inside of an internal air sac, the dragon could take nitrogen and oxygen gasses from the air and convert them into nitrous oxide N2O. You'd know this compound better as laughing gas- the same that you would get from the dentist! When N2O comes in contact with more oxygen, it gets converted into nitric oxide, NO. This is a very reactive molecule that would react with still more oxygen very rapidly to form nitrogen dioxide, NO2. This is where the chemistry gets exciting.
NO2 can react with itself to form dinitrogen tetroxide N2O4, and normally a balance between these two molecules exists within a sample. Both are known to react explosively with organic matter (hydrocarbons) like you see in the video above. So this brings us to the next point- what do we use for fuel?
Dragons are voracious meat eaters and would therefore consume plenty of fats and oils. If they were known to eat vegetables, we could throw sugars and fiber into that mix as well, but we don't ever see dragons passing up a tasty horse for a salad now do we? These fats and oils from the dragon's meat intake, if combined with dinitrogen tetroxide serve as a perfect vehicle for lighting up the knight! If we leverage the dragon's serpentine nature and connect its digestive tract to a special sac inside the dragon's skull (like a snake's venom sac), the dragon could "exhale" the nitrogen oxide compounds, squirting a jet of grease would create the necessary environment to mix with air and ignite the fire!
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| Dragon Fire Anatomy, original sketch by Sara Spath |
Combining biochemistry with fire clearly has never happened under any circumstances that science knows of at the moment, but if such a creature were to evolve or be engineered a la Jurassic Park, my bet would lay with a creature similar to this. Certain bacteria in the soil already produce nitrous oxide from the air, but it's obviously in very small amounts. I, for one, am thankful that we don't live in constant fear of a gigantic, reptilian, fire-breathing beast. I'm glad that (for now) they exist solely in works of fiction. But what if...?
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Author’s notes:
Thanks to those who contributed conversation, expertise, and input on this post!
Thanks to those who contributed conversation, expertise, and input on this post!
Previous examples[1] of this supposition[2] exist elsewhere, where the former example focuses on the ignition of methane and oxygen in the presence of a spark and the latter on platinum from the dragon's diet catalyzing a hydrogen flame. Clearly, no scientific consensus exists on the matter about what it is dragons breathe.
I suggest this version over those provided in the earlier explanations for a variety of reasons. In the SciKat post, she suggests an actual spark be produced by the jaw or a “piezoelectric crystal” that ignited the flame inside the throat. Not only is this dangerous to the dragon, no real biological analogs exist for us to build from. It works on the idea of “exotic materials” too much for me. In the Animal Planet discussion, they use a platinum ore catalyst with hydrogen to produce the flame. It’s chemically accurate…but that would require the dragons to consume an amount of material that simply wouldn’t be sustainable for a healthy system. It’s why microbes eat rock, not animals.
There are some cool chemicals to look at that produce the hottest carbon-based flames, cyanogen NCCN and dicyanoacetylene NCCCCN (respectively), that I would have loved to include but there isn't any biologically applicable way of including them.
[1] http://sciencedaydreams.wordpress.com/2011/08/29/hello-world/
[2] http://www.animalplanet.com/tv-shows/other/videos/dragons-fire-breathing-dragons-explained.htm
[3] http://en.wikipedia.org/wiki/Dicyanoacetylene
