Nature shows how dragons might breathe fire
No fantasy world is complete without a fire-breathing dragon. But if dragons were real, how might they get that fiery breath? Nature, it seems, has all the parts a dragon needs to set the world on fire. The creatures just require a few chemicals, some microbes — and maybe tips from a tiny desert fish.
Fire has three basic needs: something to ignite the blaze, fuel to keep it burning and oxygen, which interacts with the fuel as it burns. That last ingredient is the easiest to find. Oxygen makes up 21 percent of Earth’s atmosphere. The bigger challenges are sparking and fueling the flame.
All it takes to strike a spark is flint and steel, notes Frank van Breukelen. He’s biologist at the University of Nevada, Las Vegas. If a dragon had an organ like a bird’s gizzard, it could store swallowed rocks. In birds, those rocks help break down tough foods. Swallowed flint might rub against some steel inside the dragon, sparking a flame. “Maybe what you have is sort of scales that are flint-like and click together,” van Breukelen says. If the spark was close enough to a very sensitive fuel, that might be enough to ignite it.
But some chemicals don’t need that initial spark. Pyrophoric molecules burst into flame the instant they contact air. Consider the element iridium, says Raychelle Burks. She is a chemist in Texas at St. Edwards University in Austin. Iridium burns different colors when it becomes part of various molecules. One of them burns a warm orange or red. Another burns a violet-blue. (That’s one way to get the blue flame of the zombie ice dragon in George R.R. Martin’s Game of Thrones series.)
Unfortunately, iridium isn’t common, especially in biology. “There are a lot of cool elements on the periodic table, but [living things] only use a few,” Burks explains.
There are other pyrophoric chemicals that a dragon might find a little closer to home, notes Matthew Hartings. He’s a chemist at American University in Washington, D.C. Assume that dragons like caves, he begins. “If you’re living amongst a bunch of rocks, you’ll have access to a high amount of iron.”
Iron can react with another chemical, hydrogen sulfide. This is a flammable gas that smells like rotten eggs. It is found in crude oil. When hydrogen sulfide and iron get together — in a rusty oil pipe, for example — the result is iron sulfide. Combine it with air and you’ve got an explosive mix. Iron sulfide is sometimes the culprit when gas pipelines or tanks blow up.
Another explosive option comes from Anne McCaffrey’s series The Dragonriders of Pern. McCaffrey describes her dragons chewing on rocks containing phosphine — a chemical made of one phosphorus atom and three hydrogen atoms. In gas form, phosphine is very flammable and explodes on contact with oxygen. It’s also very toxic: Just seven drops of its liquid form can kill someone.
Fictional dragons often spout flaming gas. But a gas would present problems, Hartings says. Gas, he notes, expands to fill available space. To keep it contained, a dragon would have to keep that gas under pressure.
Chemicals like phosphine, therefore, aren’t the perfect dragon-fire solution, Hartings says. The boiling point for phosphine is -84° Celsius (-120° Fahrenheit). At room (or dragon breath) temperature, it’s a gas. “You’d have to really compress it,” he says, to make it a liquid that a dragon could store and use.
Also, Hartings notes, gases are difficult to control. If a dragon blew some fiery gas into the wind, the flames might wash back on the creature and singe its face. “You have a much better chance of controlling your flame spray if you’re pushing liquid rather than a gas,” he explains.
A liquid also would help a dragon avoid burning itself, Hartings notes. The liquid with its flammable gas would ignite as soon as it hit air. Speed is key. “As long as you are shooting it out fast enough, [the] particles don’t hit the air until they are far enough away from your face,” he notes.
A combination of liquid and gas might work even better, Burks suggests. In an aerosol spray, tiny liquid droplets are suspended in a pressurized gas, which spurts out when it is released. If a dragon were to shoot an aerosol spray, it could look like a gas, with some of the properties of a liquid. “In a fine aerosol spray, it would look like the dragon is spraying fire,” Burks notes. The aerosol would spread out, she says, “and the minute it hits air — kaboom!”
Something fiery, something fishy
Plenty of liquids in nature will burn. Living things already produce two of these that might work for a dragon: ethanol and methanol. Both are alcohols often burned as fuels.
“Certainly, we know that yeast makes ethanol,” Hartings says. These single-celled fungi transform sugars into alcohol. That’s why they’re used to brew beer and make other alcoholic beverages. A dragon with a bellyful of yeast is not as silly as it might appear. Yeast are part of the microbial community that lives on and in people and other animals.
Methanol first requires methane. Ruminants — including cows, goats, giraffes and deer — make methane during digestion. Certain bacteria can turn methane into methanol, Hartings notes. A dragon that got enough fiber in its diet to make methane could pass that gas on to its bacterial buddies, which would convert it into methanol.
But those bacterial coworkers might not even be needed. The Devil’s Hole pupfish doesn’t bother with them. It is a tiny, incredibly rare species found in Devil’s Hole — a single naturally heated pool in Nevada. This fish can whip up its own whisky in a pinch, van Breukelen and his colleagues have shown.
Temperatures in Devil’s Hole reach 33 °C (91 °F). There is very little oxygen in the water to start with. When it gets hot, the oxygen levels drop even lower — too low for the fish to breathe. So pupfish stop using oxygen. Instead, they produce energy anaerobically — without oxygen. In the process, their bodies make ethanol.
The fish produce 7.3 times more ethanol than fish living in cooler water, notes van Bruekelen. He and his colleagues published their fishy findings in 2015 in the Journal of Experimental Biology.
A dragon might be able to produce ethanol under similar circumstances. However, van Breukelen says, it’s not quite so simple. “I don’t think there’s a way to keep ethanol. I don’t think you could store it,” he says. The reason: It seeps through everything. Ethanol, he explains “goes right through membranes.” Those include the membranes that surround cells and organs. When pupfish produce ethanol, the chemical ends up throughout the fish. It would not pool as a concentrate in some pouch or organ. So any dragon that made ethanol would have trouble storing enough to get a decent flame going.
The pupfish won’t be setting the world on fire — nor will dragons. One is a tiny fish, and the other isn’t real. Both, however, offer an excuse to use our imaginations to apply science to the fantastic.
Technically Fiction is a blog that finds the science in the realm of the fantastic. Have a comment or a suggestion for a future post? Send an email to firstname.lastname@example.org.
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aerosol A group of tiny particles suspended in air or gas. Aerosols can be natural, such as fog or gas from volcanic eruptions, or artificial, such as smoke from burning fossil fuels.
anaerobic Occurring in the absence of oxygen. Anaerobic reactions take place in oxygen-free locations.
atom The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.
bacteria (adj. bacterial) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals).
biology The study of living things. The scientists who study them are known as biologists.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
chemistry The field of science that deals with the composition, structure and properties of substances and how they interact. Scientists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. People who work in this field are known as chemists.
colleague Someone who works with another; a co-worker or team member.
crude oil Petroleum in the form as it comes out of the ground.
diet The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health.
digest (noun: digestion) To break down food into simple compounds that the body can absorb and use for growth. Some sewage-treatment plants harness microbes to digest — or degrade — wastes so that the breakdown products can be recycled for use elsewhere in the environment.
element A building block of some larger structure. (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.
ethanol A type of alcohol, also known as ethyl alcohol, that serves as the basis of alcoholic drinks, such as beer, wine and distilled spirits. It also is used as a solvent and as a fuel (often mixed with gasoline, for instance).
fiber Something whose shape resembles a thread or filament. (in nutrition) Components of many fibrous plant-based foods. These so-called non-digestible fibers tend to come from cellulose, lignin, and pectin — all plant constituents that resist breakdown by the body’s digestive enzymes.
flammable Something that can burn (go up in flames) easily.
fuel Any material that will release energy during a controlled chemical or nuclear reaction. Fossil fuels (coal, natural gas and petroleum) are a common type that liberate their energy through chemical reactions that take place when heated (usually to the point of burning).
gizzard A thick-walled part of a bird’s stomach that is used for grinding food. It may contain grit or small stones to help the bird break down tough seeds.
hydrogen The lightest element in the universe. As a gas, it is colorless, odorless and highly flammable. It’s an integral part of many fuels, fats and chemicals that make up living tissues. It’s made of a single proton (which serves as its nucleus) orbited by a single electron.
iridium Discovered in 1803, its name comes from the Latin for rainbow. It’s a hard, brittle and corrosion-resistant metal in the platinum family. Slightly yellowish, the principle use for this element is as a hardener for platinum. Indeed, its melting point is more than 2,400° Celsius (4,350° Fahrenheit). The element’s atomic number is 77.
iron A metallic element that is common within minerals in Earth’s crust and in its hot core. This metal also is found in cosmic dust and in many meteorites.
journal (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.
membrane A barrier which blocks the passage (or flow through) of some materials depending on their size or other features. Membranes are an integral part of filtration systems. Many serve that same function as the outer covering of cells or organs of a body.
methane A hydrocarbon with the chemical formula CH4 (meaning there are four hydrogen atoms bound to one carbon atom). It’s a natural constituent of what’s known as natural gas. It’s also emitted by decomposing plant material in wetlands and is belched out by cows and other ruminant livestock. From a climate perspective, methane is 20 times more potent than carbon dioxide is in trapping heat in Earth’s atmosphere, making it a very important greenhouse gas.
methanol A colorless, toxic, flammable alcohol, sometimes referred to as wood alcohol or methyl alcohol. Each molecule of it contains one carbon atom, four hydrogen atoms and an oxygen atom. It is often used to dissolve things or as a fuel.
microbe Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
organ (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.
oxygen A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).
particle A minute amount of something.
phosphine A chemical made by combining one phosphorus atom with three hydrogen atoms. It is colorless, odorless, toxic and so flammable that it will catch fire in the presence of air.
phosphorus A highly reactive, nonmetallic element occurring naturally in phosphates. Its scientific symbol is P. It is an important part of many chemicals and structures that are found in cells, such as membranes, and DNA.
pressure Force applied uniformly over a surface, measured as force per unit of area.
pyrophoric An adjective for some chemical that bursts into flame when exposed to air.
solution A liquid in which one chemical has been dissolved into another.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
toxic Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.
waste Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.
yeast One-celled fungi that can ferment carbohydrates (like sugars), producing carbon dioxide and alcohol. They also play a pivotal role in making many baked products rise.