Friday 3rd April 2026
Disclaimer: This guide is for general information only. It does not constitute professional fire safety advice. Always consult a qualified fire safety professional and follow the latest UK regulations, including the Regulatory Reform (Fire Safety) Order 2005, when assessing fire risks or selecting fire safety equipment.
A class B fire is a fire involving flammable liquids, such as petrol, diesel, paint, solvents or methylated spirits. These fires are common in garages, workshops, industrial premises and anywhere flammable liquids are stored or used. The right extinguisher, used correctly, can suppress a class B fire effectively. You can browse suitable options in our CO2 fire extinguishers category.
Estimated reading time: 5 minutes
Key takeaways:
- A class B fire involves flammable liquids such as petrol, diesel, paint and solvents
- Class B fires are distinct from other fire classifications, which cover solids, gases and electrical hazards
- CO2 and foam extinguishers are the most effective types for class B fires
- Water extinguishers must never be used on a class B fire
- Class B fires are most common in garages, workshops and industrial environments
- Proper storage of flammable liquids is the most important step in preventing class B fires
What does a class B fire contain?
A class B fire contains flammable liquids. Common examples include petrol, diesel, oil, paint, lacquers, solvents and methylated spirits. These liquids produce flammable vapours that ignite easily and burn intensely. Class B fires spread quickly, particularly if the burning liquid spills or flows to a new area. That’s what makes them so hazardous in garages, workshops and storage facilities.
How does a class B fire differ from other fire classifications?
The UK follows the European fire classification system, which categorises fires by the type of fuel involved. Class A covers solid combustible materials such as wood, paper and textiles. Class B is for flammable liquids. Class C covers flammable gases, class D covers combustible metals and class F covers cooking oils and fats. There is also a separate category for electrical fires. Getting the classification right matters, because the wrong extinguisher can spread a flammable liquid fire rather than suppress it.
Which fire extinguisher is best for a class B fire?
CO2 extinguishers and foam extinguishers are both well suited to class B fires. CO2 extinguishers work by displacing oxygen and smothering the fire without leaving residue. They’re a good choice for enclosed spaces and areas with sensitive equipment. Foam extinguishers work by forming a blanket over the burning liquid, cutting off the oxygen supply and preventing re-ignition. Both types carry a class B rating. Always check the extinguisher label before use to confirm it’s rated for flammable liquids.
Can you use a water extinguisher on a class B fire?
No. A water extinguisher must never be used on a class B fire. Water can cause burning liquid to splash and spread, making the fire considerably worse. It can also cause steam burns. Dry powder extinguishers can tackle class B fires in some circumstances, but they leave heavy residue and reduce visibility, so CO2 or foam are the better choices for most environments.
Where do class B fires most commonly occur?
Class B fires are most common wherever flammable liquids are stored, handled or used. That includes garages and vehicle workshops, fuel storage areas, paint stores, industrial manufacturing premises and laboratories. They can also occur in domestic settings, for example where petrol lawn mowers, paint tins or cleaning solvents are kept in a garage or outbuilding. Any space containing flammable liquids needs an appropriate extinguisher nearby.
How do you prevent a class B fire?
Good storage practice is the most effective way to prevent a class B fire. Store flammable liquids in clearly labelled, sealed containers designed for the purpose. Keep them in a cool, ventilated area away from ignition sources such as naked flames, sparks or hot surfaces. Don’t store more than you need. Clean up any spillages immediately and dispose of them safely. In commercial and industrial settings, follow the relevant COSHH regulations and make sure staff are trained in safe handling procedures.
Are class B fires dangerous?
Class B fires are among the most hazardous fire types. Flammable liquids burn at high temperatures, spread fast and produce toxic smoke. Because the fuel is liquid, the fire can flow to new areas quickly if it’s not contained. CO2 and foam extinguishers, used early and correctly, can prevent a small fire from becoming a serious one. But if a class B fire takes hold, evacuate immediately and call 999.
We stock a full range of fire safety equipment at Safelincs. If you want to make sure you’re covered, take a look at our Ultrafire 2kg CO2 fire extinguisher and browse our complete range to find the right extinguisher for your needs.
All information correct at time of posting.
