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The Chemical Formula for Fire, Transmission and Types of Fire (SO1-AC2)
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Oxygen, heat, and fuel are referred to as the “fire triangle”. Add in the fourth element, the chemical reaction, and you actually have a fire “tetrahedron.”
The important thing to remember is, to take any of these four things away, and you will not have a fire or the fire will be extinguished.
Methods of Fire Transmission
Convection: The most common cause of fire spreading in domestic and commercial buildings. When a fire is burning large amounts of hot gases and smoke are produced. These will travel through the building in hot air currents often igniting more combustible materials and causing the fire to spread.
Conduction: Refers to the spread of fire through direct contact between materials. Some materials are better conductors of heat than others, metal is a good example.
Radiation: Refers to the emission of energy in rays or waves. Heat moves through space as energy waves. As the firefront gets closer, the amount of radiant heat received is increased.
Click here to view a video that explains how convection fires spread.
Click here to view a video that explains how conduction fires spread.
Click here to view a video that explains how radiation fires spread.
Types of Fire
There are actually five main types of fires.
Fires can be classified in five different ways depending on the agent that fuels them:
Class A, Class B, Class C, Class D, and Class K. Each type of fire involves different flammable materials and requires a special approach.
Class A: Suitable for wood, paper and regular combustible fires - pressurised water.
Class B: Suitable for gasoline or oil fires and is usually a dry chemical.
Class C: Suitable for electrical fires and is halon or CO2.
Class D: Used for water-reactive metals (laboratories) such as burning magnesium, and is in the form of a powder that must cover the material to extinguish it.
Class K: Special purpose wet chemical agents for use in kitchen fires and deep fryers.
Many fire extinguishers will work on a combination of fire classes. We will need to decide what type of fire we have, and ensure that our fire extinguisher is compatible with the fire we are attempting to extinguish. An all-purpose ABC dry chemical (5kg extinguisher) is a safe choice for most fires on construction sites.
Causes of Workplace Fires
