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Last updated on April 17, 2014 at 1:21 EDT

What Is Fire?

March 26, 2013

Hi, I’m Emerald Robinson, and in this “What Is” video, we’ll answer the question, “What is Fire?”

Fire is scientifically defined as a chemical reaction that results in heat, light, and smoke. We call this type of chemical reaction “oxidative combustion,” that is, the reaction requires oxygen, and actively burns fuel. Fire is also an “exothermic reaction,” because it gives off heat.

When we think of fire, we picture a flame, a mass of burning ionized gas or vapor. If the flame is hot enough, it may ionize the gas into the state of matter known as plasma.

Pyrologists, scientists who study fire, have defined four conditions required for a fire to burn:

First, there must be fuel; Second, there must be oxygen. Third, there must be an initial source of heat to ignite the fire, and fourth, there must be conditions for a “chain reaction,” events that occur when a reaction’s products automatically start the reaction all over again. In fire, the key product is heat, which turns more fuel to vapor, enabling it to burn, which then produces more heat, and so on.

A fire’s “life cycle” has four phases:

• Ignition, when fuel, oxygen, and a source of heat combine and start the chemical reaction,

• Growth, which happens when the fire’s flames begin the chain reaction, igniting more fuel,

• Full development, when most of the fuel is being consumed, and

• Decay, which happens when the fuel is mostly consumed, the fire’s heat is decreasing, and the fire is “burning out.”

A fire is put out, or “extinguished” when one or more of the components is removed. For example, fire extinguishers remove the source of the oxygen by replacing it with carbon dioxide, while dumping water on a campfire removes its heat.

Fire can be destructive, but it’s been used by humans for almost a million years to cook our food, provide light and keep us warm.