What is fire? How does it work? According to the American Heritage
Dictionary, 2nd College Edition, fire is,
"A rapid, persistent chemical reaction that releases heat
and light, especially the exothermic combination of a
combustible substance with oxygen."
That's a mouthful. Before we explain that definition, let's
look way back in history.
Right after the sun, fire is the oldest form of energy used by man.
Fire can be extremely dangerous and destructive, like shown in the photo on the right.
But it can also be beneficial when used properly.
In L'Escale Cave in southeastern France, a layer of ash
was found on the roof of the cave that dates from 700,000 to
400,000 BCE (Before the Common Era).
This layer is viewed by some scientists as the earliest known
evidence of fire used by hominids in Europe, although it
cannot be established that the ash is not the result of naturally
Middle Pleistocene humans controlled fire (burning wood) as
early as 500,000 BCE. Direct evidence was found outside a
cave at Chou k'ou-tien, China. Here charcoal was found along
with traces of a stone toolmaking industry in an open gully
deposit. This deposit appears to be slightly older than the
cave deposit itself, which contained the bones of Homo erectus, early man.
Fire was treated as a gift from the gods. Usually fire
was found naturally from a lightning strike or near
volcanic areas. Fire helped early
man cook food, provided warmth and kept wild animals away.
Today, fire is used in homes to do much the same...except
for maybe keeping the animals away.
Let's explain what fire is...
Fire is a chemical process. Three things are needed for this
process: oxygen, heat and fuel. Without one of these elements
a fire cannot start or continue.
In a chemical process, the molecules rearrange themselves.
Energy is either released or absorbed. The process in a
fire is called oxidation, where oxygen atoms
combine with hydrogen and carbon to form water and carbon
dioxide. Oxidation is the same chemical process
that turns iron into rust. But with iron, the reaction is
VERY slow. So, the heat energy that is released is VERY low.
With certain things, like paper or wood, the oxidation rate
of the molecules can be very fast. If the heat cannot be
released faster than it is created, then combustion happens.
Besides heat, there must also be flames or smoldering
present during the chemical process for it to be called
fire. Exhaust gases also are produced. If the burning
process is very clean, you don't see the exhaust gases. If
some of the particles of the fuel are not completely burned,
you see smoke. Smoke is made up of evaporated water, carbon
dioxide and unburnt particles of the fuel.
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