Fires take on the characteristics of the fuel causing it to blaze. Note that paper fires burn differently from electrical and petrol fires, which is why they’re extinguished differently. Here’s a quick rundown of the different fires and the right type of extinguisher to use if such a scenario happens.
A Class A fire is your everyday kind of fire: paper, wood, and plastic as fuel. When extinguished with water, they’ll leave ash.
A Class B fire burns flammable liquids and gases such as petrol and natural gas. Water, being heavier than petrol and gas, won’t work well against a Class B fire; in fact, it may just spread out and burn further. Dry powder, foam, and carbon dioxide extinguishers deprive Class B fires of their fuel by bonding with the latter’s molecules.
A Class C fire involves flammable gases such as butane, propane, and methane. Dry powder extinguishers are the most effective for Class C fires.
A Class D fire is caused by combustible metals. While a slab of steel may not ignite, steel filings surely can. A Class D fire is more common in workshops and factories that work with or store metals, namely magnesium, titanium, and zirconium. Extinguishing a Class D fire with water is ill-advised because you’ll end up feeding the metal fire with hydrogen and oxygen to combust. Specially formulated M28 or L2 dry powder extinguishers are recommended.