Fire & Fire Classification

by Faisal Javaid Safety

What is Fire?

Fire is defined as:

“A chemical reaction in which any fuel combines chemically with oxygen and gives out heat, and smoke.”

To start fire, these three elements must be present. The fire triangle was subsequently changed to a fire tetrahedron (also referred to as fire diamond, pyramid, or combustion triangle) to reflect the fourth element.

Elements of Fire

1.Fuel

Fire cannot start if there isn’t any material available to burn. Businesses and homes alike are full of flammable materials including fabrics, wood, oil, and paper. Any of these materials can serve as fuel for a fire.
Some of the materials burn more easily compared to others. Fuel is probably the hardest ‘side’ of the fire triangle you can remove, so it is advisable to ensure that they are appropriately stored so that they don’t become a fire hazard. Common examples are gasoline, wood, paper, natural gas etc.

Common Sources of Fuel around us:

  1. Liquid: Gasoline, Paints, Chemicals
  2. Solid: Wood, Paper, Trash, Plastic, Rubber etc.
  3. GAS: Natural Gas, LPG cylinders

2.Oxygen

The air we breathe has about 21% oxygen. Fire needs only 16% oxygen. Oxygen is needed to sustain the combustion reaction since it reacts with the burning fuel to release carbon dioxide and heat.
Some fire extinguishers and fire blankets remove the oxygen ‘side’ of the triangle by displacing or removing it thus causing suffocation and ceasing the combustion reaction.

Common sources of Oxygen around us

  1. Oxygen in atmosphere
  2. Oxygen supplies such as cylinders, piped supply etc
  3. Chemicals (Oxidizing agents)

3.Heat/Ignition Source

Any matchstick, hot surface, burning cigarettes, naked flame etc. A heat source is necessary for ignition to occur and different materials have different ‘flash points or the lowest temperatures at which they can ignite. Combustion reactions, however, also produce heat as they burn, which further increases the fuels’ temperature. The heat may be cooled by applying water, but this is only possible for some types of fire.

Common sources of Ignition around us

  1. Naked flame & burning cigarettes/lighters
  2. Fixed or portable heaters
  3. Stoves for cooking
  4. Electric equipment
  5. Hot processes e.g., welding

Types/classification of fire

Type of fire is determined by the type of Fuel:

Compatibility of Fire Extinguishers

Extinguishing Theory

Removing Heat, Removing Fuel, Reducing Oxygen will Inhibit Chemical Chain Reaction.