Whether you gather twigs, leaves and sticks to build a campfire or cook up hot dogs on a backyard grill, fire is the chemical reaction that gives us heat, light and energy. But how does it work? And where does the energy that drives it come from? The answer is a bit complicated. Fire is made up of three essential ingredients – fuel, oxygen and heat. Take away any one of them, and the flame won’t go up. But put them all together, and the chain reaction keeps on going.
The first step is applying the heat to the fuel. That makes the molecules in the fuel expand and break free of the bonds that hold them together. They then vibrate until they get so hot that the atoms that make them up start to sputter and glow. The unbound atoms then form gases that mix with oxygen in the air and produce the spooky blue light of a flame.
But that’s just the beginning of what happens in a fire. The same heat that breaks apart hydrogen and carbon atoms in the fuel also breaks apart oxygen molecules in the air, producing more gas and more sputtering. This produces more flame and more heat, and so on. The chain reaction continues until the fuel runs out of atoms to heat up, or there’s no more oxygen in the air to combine with them.
Once the burning starts, it doesn’t stop unless you deliberately extinguish it. That’s usually done by pouring water over it. But even if the flames go out, the heat from them will keep remaining fuel at its ignition temperature and ignite gases that are being emitted. It’s a process known as backdraft, and it can be dangerous to people and pets.
Fire has been used for thousands of years to cook food, clear land and provide warmth in caves and hovels. But it has also been used to smelt metals, make glass and create pottery. It can even be used to generate power, as it is in most modern industrial processes. In power plants, the burning of fossil fuels such as coal, oil and natural gas releases chemical energy that is converted into mechanical work in turbines that spin electric generators. This power can then be used to run motors and other appliances in homes, businesses and factories. A fire’s other important role in nature is to clear brush and dead organic material from the ground, which otherwise would choke out other plants. This is often accomplished through a controlled burn called a prescribed fire. The heat produced by the burning of these materials and the resulting gases can quickly restore nutrients to the soil. It’s this benefit that farmers have exploited for centuries.