Is fire a solid, a liquid or a gas?

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The answer is none of the above. Contrary to what the ancient Greeks thought, not only is fire not one of four basic elements that make up everything in the universe, fire isn’t even a substance. It’s a process.

As any good Boy Scout knows, to light a fire, you need three things: fuel, heat and oxygen. Each type of fuel has what’s called an ignition temperature – for wood, it’s about 500F. This is the point at which molecules of the fuel break up because of the heat and become gases. These gases then react with the oxygen in the air and – presto chango – you get fire.

Fire will eventually burn itself out when it runs out of enough fuel, heat or oxygen. So it makes sense that traditional extinguishers work to remove at least one of these elements.

But here’s where it gets weird.

We’ve known since the 1900s that sound – yup, you heard me right – sound can extinguish fire. Although we still don’t exactly understand how this works – something to do with a drop in pressure leading to a drop in temperature – researchers are developing technology that uses this nifty technique. But for now, stick to the tried and true methods of fire extinguishing.

Critical thinking challenge: How do traditional fire extinguishers remove one of the elements necessary to make fire?