Class A fires (‘’dry’’ type) originate from ember producing solid materials such as cellulose, wood, paper, textiles, filling materials, cotton, plastics, rubbers, etc. All of these materials are highly inflammable.

Class B fires (‘’greasy’’ type) are caused by liquids and liquefiable solids such as hydrocarbons, tar, asphalt, greases and oils, paint, varnish, alcohol, gasoline, ketones, solvents and various chemicals. All of these produce flames before extinguishing, but do not form embers (slow combustion) and smothering the fire entails its complete extinction. Flammability of the materials depends on their specific flash point (minimal temperature at which the emission of vapour combines with the ambient atmosphere to create a flammable environment). All of these products may re-ignite without warning (spontaneous combustion) as long as ambient temperature remains close to self-ignition point (temperature at which a vaporous compound auto-ignites without the presence of a flame or spark). Therefore, the complete extinction of such fires imperatively requires a cool-down period.

Class C fires are electrical type fires originating from live electrical equipments. You can never use fresh water to extinguish these fires, but the use of a droplet-forming water spray device is acceptable if the voltage is less than 1000v, as the spray is not conductive.

Class D fires pertain to metal fires. All D type extinguishing powders are specific to the particular combustible metal(s) found in some industrial environments. These fires are generally quite intense and highly luminous. Some metals, such as sodium, magnesium, potassium or phosphor may spontaneously self-ignite when in contact with the ambient atmosphere.

Class K fires characterize incidents related to oils and fats used in cooking appliances. Although these fires technically are part of the class B category, the presence of live electrical equipment nearby the ignition source has resulted in the development of specific extinguishing devices and agents better adapted to food environments, including the foam-forming extinguisher that smothers the fire by covering the surface of the fire source (saponification process). Furthermore, the use of water to put out class K fire is highly dangerous due to boil over risks.