Learning to manage this chemical reaction

What actually is fire? How does it start? How and why does it behave in different ways? How can we prevent it from starting or reduce its destructiveness?

This resource provides explanations of the key concepts encountered when investigating fire – the ‘basics’ that every student should understand.

Carbon dioxide and carbon monoxide

These toxic, colourless and odourless gases are products of combustion. Carbon dioxide (CO2) is an incombustible gas. Carbon monoxide (CO) is highly poisonous and is a product of incomplete combustion.

Chemical reaction

A process in which one or more substances are changed into different substances. In the context of fire, the chemical reaction occurs between oxygen in the air and some sort of fuel when heated to ignition temperature. For example, methane gas when ignited reacts with oxygen gas in the air to produce mostly carbon dioxide and water vapour.

Complete combustion

A chemical reaction that involves the process of burning. It occurs when fuel reacts with oxygen to release energy (light and heat) producing gases like water vapour and carbon dioxide. The flame is typically blue. For this to happen, there needs to be enough oxygen to combine completely with the fuel gas.

Ignition temperature

The lowest temperature at which combustion can begin and continue, for example, wood needs to be heated to between 250–300°C before it will ignite.

Incomplete combustion

If there is not enough oxygen available during a chemical reaction, incomplete combustion occurs and products such as carbon (C) and carbon monoxide (CO) as well as water and carbon dioxide are produced. In incomplete combustion, the burning flame is typically yellow or orange and there is smoke.

Fire retardant

A substance that interferes with the combustion process. This could be a substance like water. Wool and leather are also examples of fire retardants. They are difficult to ignite and burn slowly. Chemical fire retardants are chemicals that are used in fabrics and foams (in furniture) to slow down combustion in the event of a fire.

Flammability

How easily something will burn or ignite. Note that flammable and inflammable mean the same.

Fuel

A combustible substance that provides energy. A fuel load is the amount of fuel available for burning.

Heat energy

A form of energy that flows between two samples of matter because of their differences in temperature.

Heat transfer

The transfer of heat from a hotter substance to a cooler one. This can occur through conduction, convection or radiation.

    Published 9 November 2009