Fire- What Is It?

Fire is a chemical reaction, called combustion, during which a fuel combines with an oxidizer to release energy and some byproducts. We see fire, because fire emits energy in the form of light. Sometimes you see products of this chemical reaction as smoke. If you are close enough, you can feel a fire’s released heat energy.

- Bert Fisher

A LOOK AT FLAMES

You see flames because of the electromagnetic energy emitted as light by the hot gases, in part as blackbody radiation from their overall temperature and in part by specific colors emitted by the heated gases. Some of this emitted energy is visible light. The color of visible light emitted by a flame depends on the temperature of the flame. Once flame temperature reaches 500ºC (932ºF), the flame emits a substantial amount of visible light and is termed “incandescent.” Viewed in darkness, the first visible light emitted by a flame appears ghostly gray, because the color-sensing “cones” in the human eye are not activated at such low light levels. If the blackbody radiation is the dominant source of a flame’s color, the flame may become red as its temperature increases. It then changes to yellow and, finally, to an intense bluish-white. Flames from a wood fire appear largely yellow or orange, but, at their base, they can be much hotter and appear blue. White flames emit a good deal of energy as ultraviolet radiation. In fact, fire can give you a sunburn.