Mark Lorch: In George RR Martin’s fantastic land of Westeros in Game of Thrones and House of the Dragon, the spectacle of fire-breathing dragons captivates its audience through a mix of myth and fantasy. For me, at least, there is also scientific curiosity.
The images of dragons unleashing flames in the new series House of the Dragon got me thinking: if dragons existed, what biological mechanisms and chemical reactions might they use in the real world?
But first, a summary of the chemistry. To ignite and maintain a flame we need three components; a fuel, an oxidizer – usually the oxygen in the air – and a heat source to start and maintain combustion.
Let’s start with the fuel. Methane could be a candidate. Animals produce it during digestion. The on-screen images of Westeros show that dragons like to eat sheep. However, our methane-powered dragons would have to have a diet and digestive system more like that of a cow to produce enough gas to burn down a city.
There is also a problem with storing sufficient amounts of methane gas. A typical methane cylinder can withstand a pressure of 150 atmospheres, while even an inflated intestine can only withstand slightly more than one atmosphere. So there is no biological basis for non-marine animals to store gases under high pressure.
A better option would be a liquid. Ethanol could be an option. Perhaps our dragons keep a vat of fermenting yeast in their intestines, or they may have a metabolic system similar to Devil’s Hole fry, which live in hot springs in Nevada, USA. Under low-oxygen conditions, these fish switch to a form of respiration that produces ethanol.
However, storage is again an issue. Ethanol quickly crosses biological membranes, so keeping it in high concentrations and ready for use on the ‘dracarys’ signal (which translates to ‘dragonfire’ in the fictional High Valyrian language) would require alien biology.
So if we’re going to stick with explanations with at least one foot in real-world biology, then my preferred option is something more oil-based. As anyone who has accidentally set a frying pan on fire knows, it can be a source of roaring flames. There is a biological basis for this in the petrel gull.
They produce energy-rich stomach oil that they regurgitate to feed their chicks. The oil also acts as a deterrent. When threatened, the petrel vomits the sticky, foul-smelling oil on predators. Fortunately, the seagulls have not yet developed a way to ignite their vomit.
Feeding the flames
Now that we have a fuel source, let’s turn our attention to the oxidizer. As with most fires, this will most likely be oxygen. However, it takes more than just oxygen in the surrounding air to generate a jet of pressurized flaming oil hot enough to melt an Iron Throne. And it should be well mixed into the fuel. The better the oxygen supply, the hotter the flame.
A dragon could draw on the chemistry used by the bombardier beetle. This insect has developed reservoirs adapted to store hydrogen peroxide (the stuff you might use to bleach your hair). When threatened, the beetle pushes hydrogen peroxide into a vestibule that contains enzymes that quickly decompose the hydrogen peroxide into water and oxygen.
This is an exothermic reaction, which transfers energy to the environment, and in this case increases the temperature of the mixture to almost its boiling point. The reaction is so aggressive that it is sometimes used to propel rockets.
The increase in pressure caused by the rapid production of oxygen and the boiling water forces the noxious mixture out of a vent in the beetle’s abdomen and toward its prey or threat.
When used by a dragon, this response has a few nice features. It would create the high pressure needed to drive the flow of oily fuel, the exothermic reaction would heat the oils making them more combustible, and most importantly it would create oxygen which would power the combustion reaction.
All the dragon needs is some kind of biological equivalent of a gasoline engine carburetor to mix the oil with the oxygen and create an explosive mixture. As a bonus, the erupting mixture would likely form a fine mist of oil droplets, like an aerosol, which would ignite all the better.
The spark
Finally, we need a spark to ignite the mixture. For this I am going to suggest that the dragons have evolved an electrical organ similar to that of many fish, especially electric eels.
These can generate short pulses of up to 600 volts, easily enough to create a spark across a short air gap. If these sparks travel through the channels in the back of a dragon’s mouth, they can ignite the high-pressure jet of oil and oxygen.
While we’ll never see a dragon unleash a sea of flame outside the realm of fiction, it’s intriguing to think about the science behind fantasy. So, the next time you witness a Targaryen’s command of ‘dracarys’, consider the biology behind that magical inferno.
Mark Lorch, Professor of Science Communication and Chemistry, University of Hull
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