fire-tornado-9

Fire Tornado

A fire tornado is just like a tornado but made of fire instead of air.

When we picture a tornado, most of us imagine a whirling column of air poking down from the clouds. But this tornado-like effect is not just limited to air. Imagine what it might look like if winds could twist a ground level forest fire into an enormous fire tornado that dances across the tops of the trees. It’s not a special effect found in a movie—it’s a real-world danger that firefighters battle in the most extreme forest fires imaginable. This special demonstration is reserved for science teachers who want to share a small version of this amazing phenomenon.

WARNING! TEACHERS ONLY!
This demonstration write-up is provided for educational purposes only and should only be performed by properly trained science demonstrators. In other words, if you’re a kid and you want to see this in action, bookmark this page and share it with your middle or high school science teacher.

Experiment Materials

  • Lazy Susan (rotating tray)
  • Metal screen (You’ll want a mesh size that is similar to the screen found on your windows. The actual size of the piece of screen will depend on the size of the rotating tray.)
  • Wire or staples
  • Small glass dish
  • Glass dinner plate or something similar to cover teh fire
  • Pieces of sponge
  • Lighter fluid
  • Safety glasses
  • Fire extinguisher

Experiment Videos

Experiment

1

The key to making this demonstration work well is to test a number of circular rotating trays (commonly referred to as Lazy Susans) until you find one that suits you. It’s truly a matter of trial and error, but you’re bound to find one that functions perfectly.

2

Take a look at the photographs of the wire screen that is rolled into the shape of a tube. Find a friend to help you shape and hold the wire in place as you roll the screen into a cylinder that’s about the same diameter as the rotating tray. When you’re constructing this tabletop version of the Fire Tornado, it’s best to keep the height of the screen tube between 2.5 and 3 feet tall. Anything taller has the potential of falling over as you spin it. As you can see in the photographs, our wire cylinder rests on top of the tray and is just slightly smaller than the tray itself. Fasten the ends of the cylinder using wire or staples. Rivets or wire can be used to secure the center section.

3

Position the wire cylinder in the middle of the tray and give it a gentle spin. You should be able to make the cylinder spin slowly without having to physically fasten the screen to the tray. When you’re presenting the demonstration, you’ll need to be able to quickly remove the screen from the rotating tray and cover the fire with a plate to extinguish the flames.

IMPORTANT NOTE:
If the screen cylinder is not positioned in the very middle of the tray, the cylinder will spin off center and might even fall over. The more accurately you can get the screen centered, the more even the spin will be, which results in the best tornado possible.

4

Place the small glass dish in the middle of the rotating tray. It is best to find a small square of fire-resistant material (or a small plate or saucer) for the dish to sit on so as not to damage the Lazy Susan.

5

Cut up several pieces of sponge and place them in the dish. Squirt lighter fluid on the pieces of sponge so that each piece is completely soaked.

6

Put on your safety glasses. Light the fire but leave the mesh screen off of the rotating tray for now and gently spin the tray. Notice how the fire spins, but no tornado effect is created. Extinguish the fire by covering it with another small plate.

7

Reignite the fire and place the wire screen cylinder on the Lazy Susan. Gently spin the tray and watch as the fire twists into the shape of a tornado. The fire tornado will rise as the tray spins faster and faster.

8

Remove the screen cylinder from the tray and extinguish the fire.

How Does It Work

As you noticed, simply spinning the tray does not whip the fire into a twirling tornado. It’s only when you center the fire in the middle of the rotating screen that you create the perfect fire tornado. It all starts with the heat from the flame that causes the surrounding molecules of air to rise. Couple this with the rotational motion of the screen and you have the perfect storm, so to speak. The rotating screen gives the air molecules an initial spin (called angular momentum). The vertically rising hot air molecules collide with the rotating screen, and the angular momentum of the screen is transferred to the rapidly rising air molecules, giving them a “twist.” Fresh air fuels the fire from the bottom, and the flames twist into the shape of a tornado.

Take It Further

Experiment by making wire cylinders that are made from different types of metal screen—large mesh or small mesh constructed out of thin or thick wire. Each variation will produce a different effect. Don’t be surprised if the thick wire, large mesh screen doesn’t work at all. Why?

Visit your local thrift store, garage sale, or flea market in search of an old record player. With a little modification, you’ll be able to transform the turntable into the spinning platform needed for your experiment.

Safety Information

WARNING! TEACHERS ONLY!
This demonstration write-up is provided for educational purposes only and should only be performed by properly trained science demonstrators. In other words, if you’re a kid and you want to see this in action, bookmark this page and share it with your middle or high school science teacher.

Real-World Application

The rotating metal screen is a simple way to illustrate the way winds whip through the trees in the forest and collide with the warm updraft from the wildfire. These so-called fire tornadoes can measure 30–50 meters tall (100–200 feet). Some of the largest fire tornadoes have measured more than a kilometer in height. It’s easy to see how the rising column of twisting fire can dance along the treetops, causing the fire to spread easily.