It's red, yellow or orange. It's hot, bright and wants to burns everything it touches. It also gives light, warmth and cooks your food.
Everybody knows about fire, but what starts it?
What is fire?
Simply put, fire is a chemical reaction resulting from something getting too hot in the presence of oxygen.
Typically, this chemical reaction is between oxygen in the atmosphere and some sort of fuel (wood or gasoline, for example). Of course, wood and gasoline don't catch on fire on their own just because they're surrounded by oxygen. For the combustion reaction to happen, the fuel needs to reach its ignition temperature.
Now the ignition temperature of any material is the point at which it will catch fire. Let's try to understand this with an example of wood catching fire:
Wood gets heated to a very high temperature. The heating can come from different sources - a lit match, focused light, friction, lightning or even something else burning nearby.
When the wood reaches about 300 degrees Fahrenheit (150 degrees Celsius), the heat decomposes some of the cellulose material that makes up the wood.
Some of the decomposed material is released as volatile gases. We know these gases as 'smoke'.
When these volatile gases are hot enough (about 500 degrees F (260 degrees C) for wood), the compound molecules break apart, and the atoms recombine with the oxygen to form water, carbon dioxide and other products. In other words, they burn.
And it keeps on burning because
What sustains a fire is the fact that the chemical reactions in a fire generate a lot of new heat. The heat of the flame itself keeps the fuel at the ignition temperature, so it continues to burn as long as there is fuel and oxygen around it. The flame heats any surrounding fuel so it releases gases as well. When the flame ignites the gases, the fire spreads.
A fuel's heat production depends on how much energy the gases release in the combustion reaction and how quickly the fuel burns. Even the fuel's shape affects burning speed. Thin or sharp pieces of fuel burn more quickly than larger pieces because a larger proportion of their mass is exposed to oxygen.
In this way, fires from different fuels are like different species of animals - they all behave a little differently. Experts can often figure out how a fire started by observing how it affected the surrounding areas. A fire from a fast-burning fuel that produces a lot of heat will inflict a different sort of damage than a slow-burning, low-heat fire.