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Different fire classes

fire fighting
fire triangle

HOW A FIRE OCCURS?

Combustion is a chemical reaction in which a combustible material or fuel is oxidised by an oxidising agent in the presence of an energy source. A fire naturally occurs with the interaction of 3 elements, also known as the fire triangle. 

  • The combustible material could be wood, gasoline, ethanol, plastics…
  • The oxidising agent is usually oxygen from the air. It could also be chlorine, oxygenated water, nitric acid, chlorates, perchlorates...
  • The heat is produced by an energy source such as mechanical friction, electricity (lightning or static electricity), chemical reaction, solar energy...

The suppression of one of these elements can extinguish the fire. That’s why the fuel must be separated from the oxygen supply or cooled down below the ignition temperature.

WHAT ARE THE DIFFERENT FIRE CLASSES?

Fire classes are characterising the different types of fire depending on the combustion material.

European standard classified fire types:

  • Class A are combustible material fires such as wood, cardboard, paper, fabric, tyres…
  • Class B are flammable liquids fires such as fuel, gasoline, kerosene, white-spirit…
  • Class B are flammable gases fires such as ethanol, propane, butane, acetylene, hydrogen, methane…
  • Class C are electrical fires
  • Class D are flammable metals fires such as powdered aluminium, steel wool, magnesium…
  • Class F are cooking oils fires

The type of fire affects the choice of firefighting operation. Firefighting foams are mostly applied on class A and class B fires.

What is the definition of class A fire?

Class A fires are three dimensional fires or structural fires ignited from ordinary combustible such as plastic, wood, bush, paper, rubber, tyres, trash…

Class A fires could also include traffic accident, Waste treatment plant fires, Warehouse, wild fires, bush fires, residential buildings...

Class A fires can be extinguished with water. To extinguish fire faster, save water and improve firefighter autonomy, the use of specific class A foam is required. Class A foams have high wetting and expanding capabilities. They lower the surface tension of water and allow penetration deeply into the flammable material.

multipurpose fluorine free firefighting foam
hydrocarbon fire foam test

What is the definition of class B fire?

In the US fire classification, there are 2 types of class B fires:

Class B Hydrocarbon fires:

Flammable liquid fires such as fuel, diesel, kerosene, heptane, benzene... composed of carbon and hydrogen.

Class B hydrocarbon fires are mostly found in petrochemical industries such as refineries or tank storages, also on aircraft firefighting, marine industries.

Hydrocarbons are non-mixable with water.

Class B hydrocarbon fires require a specific class B firefighting foam which spreads rapidly above the fuel surface and seals vapours, preventing from reignition.

Class B polar solvent fires

Polar solvents are split into 7 main families:

  • Alcohols: methanol, ethanol, isopropanol…
  • Ketones and aldehydes: acetone, acetaldehyde, methylethycathinone, MIBK…
  • Esters: ethyl acetate…
  • Ethers: diethylether, MTBE, THF…
  • Glycols: a combination of ‘alcohol + ether’: MEG, MPG, Butoxyethanol, butylcarbitol…
  • Amines: trimethylamine…
  • Acids: acetic acid, propionic acid…

Class B polar solvents fires are those in petrochemical industries, power plants, distilleries, solvent and coatings processing plants (paintings, varnish, perfume, aroma, essential oils, fragrances..).

Polar solvents are hydrophilic (water attractive), they are water-mixable. Using AFFF on polar solvent fire will cause the foam to break down and will quickly mix with the fuel. This is why, class B Polar solvent fires require a class B alcohol-resistant foam concentrate. The foam forms a foam blanket which spreads rapidly above the fuel surface. It also creates a polymer layer resistant to solvents’ destructive ability and to vapours emissions.