Fire

Fire is the visible appearance of heat and light produced by rapid oxidation (a chemical reaction between a substance and oxygen). When the reaction begins, it releases heat, light, and new gases such as carbon dioxide and water vapour. The visible part of fire is called a flame, which is hot gas that emits radiation.

Fire requires three things to exist simultaneously: fuel (a substance that can burn), oxygen, and heat reaching the ignition temperature of the fuel. These three are often called the fire triangle. If any one of them is removed or reduced, combustion stops—this is the basis of fire suppression.

How combustion occurs

When solid or liquid material is heated, it releases vapour or gas. That gas mixes with oxygen in the air, and when the temperature reaches a certain level, a chain reaction begins. This reaction releases more heat than it started with, so fire sustains itself until the fuel or oxygen runs out.

Colour and temperature

The colour of a flame depends on the temperature and the material burning. Yellow or red flames usually indicate incomplete combustion, involving material with unburned carbon particles. Blue flames typically indicate complete combustion with abundant oxygen, as seen in kitchen gas burners.

Human use

The use of fire is among the fundamental steps in human history. It was used for cooking food, heating homes, lighting, and metalworking and smelting. Today, combustion of fossil fuels remains a major source of energy and is also linked to greenhouse gas emissions.

Fire suppression

Various methods are used to stop combustion: water (which cools the flame), foam or powder (which blocks oxygen), and specific chemicals that break the chain reaction. The type of fire determines the appropriate method; for example, water is not suitable for oil fires or electrical fires.