Fire class B: How to extinguish liquid fires correctly

Class B fires are caused by flammable liquids or substances that become liquid when heated. These substances usually burn with an open flame, without embers.

Typical substances are

• Petrol, diesel, heating oil
• Varnishes, paints, solvents
• Alcohol (e.g. ethanol, spirits)
• Wax, tar, bitumen
• Liquid burning plastics (e.g. kerosene)
• Fats and oils (note: cooking oils belong to fire class F)

Such fires mainly occur where flammable liquids are being worked with, stored or cooked. Frequent locations are:

• Workshops and garages (e.g. oils, paints, cleaning agents)
• Petrol stations and vehicles (e.g. fuels such as petrol and diesel)
• Households (e.g. spirits, lamp oil, cleaning products)
• Industrial plants (e.g. solvents, chemicals)
• Camping areas (e.g. fuel paste, gas cartridges)

Class B fires must never be extinguished with water. Water can spread the flammable liquid and exacerbate the fire.

Suitable extinguishing agents are:

• Foam: Forms a dense blanket over the liquid and excludes oxygen. Ideal for many liquid fires.
• ABC powder: Very effective, interrupts the chemical reaction of the fire. Universally applicable, but with high contamination.
• BC powder: Especially for fire classes B and C, particularly useful for liquids.
• Carbon dioxide (CO₂): Displaces oxygen and therefore extinguishes flames. Particularly suitable in closed rooms and for sensitive technology.

Which fire extinguishers are suitable for fire class B?

Different extinguishers are suitable depending on the environment and risk:

• Foam extinguisher: Very effective on liquid fires, suitable for offices, storage rooms and workshops.
• ABC powder extinguisher: Versatile, extinguishes class A, B and C fires. Good for vehicles, garages and industry.
• CO₂ extinguisher: Clean, leaves no residue. Ideal for sensitive technology, e.g. in server rooms.

Class B fires require quick and considered action - especially because water is unsuitable as an extinguishing agent. With the right fire extinguisher and knowledge of the correct extinguishing agents, dangerous situations can be safely controlled.

Anyone who regularly works with or stores flammable liquids should keep suitable extinguishers to hand - and ideally know exactly how to use them in an emergency.