Class B Fires: What They Are, Examples & How to Extinguish Them
Class B fires involve flammable liquids. Common examples include petrol, diesel, kerosene, solvents, paints and other flammable liquid products.
Because burning liquids can spread quickly across a surface, Class B fires require the correct extinguishing agent. Using water incorrectly can spread burning liquid and make the situation more dangerous.
This guide explains what a Class B fire is, common examples and causes, which fire extinguishers can be suitable, why water should not normally be used, and how Class B fires differ from other fire classes in Australia.
Safety first: Only attempt to extinguish a small fire if you have the correct extinguisher, a safe escape route and the fire is still within manageable limits. If the fire is spreading, producing heavy smoke or threatening people or escape routes, evacuate immediately and call 000.
What Is a Class B Fire?
A Class B fire is a fire involving flammable liquids.
Common Class B fuels include:
Petrol
Diesel
Kerosene
Paints
Solvents
Thinners
Alcohol-based flammable liquids
Some petroleum-based products and fuels
The main characteristic of a Class B fire is that the burning fuel is a liquid rather than an ordinary solid combustible such as wood or paper.
Flammable liquids can create vapours that ignite readily. A spill can also allow the fire to spread across a larger area, which is why selecting the correct fire extinguisher is important.
Class B Fire Examples
Class B fires can occur anywhere flammable liquids are stored, transported, used or transferred.
Petrol Fires
Petrol is highly flammable and can produce vapours that ignite readily. Petrol fires can occur around vehicles, fuel storage areas, workshops and during fuel handling.
Diesel Fires
Diesel is less volatile than petrol but can still produce a serious Class B fire when ignited.
Paint and Solvent Fires
Paints, thinners, cleaning solvents and other chemical products may contain flammable liquids. Poor storage, spills or contact with an ignition source can result in fire.
Kerosene and Other Fuels
Kerosene and other petroleum-based fuels can also present Class B fire risks when they are ignited.
What Causes Class B Fires?
Class B fires generally require three things: a flammable liquid, an ignition source and conditions that allow the fire to develop.
Common causes include:
Fuel spills or leaks
Smoking near flammable liquids
Open flames
Sparks from electrical or mechanical equipment
Hot surfaces
Welding or cutting near flammable materials
Incorrect storage of flammable liquids
Poor handling or transfer of fuels and solvents
Many Class B fire risks can be reduced through appropriate storage, handling and housekeeping procedures.
What Fire Extinguisher Is Used for a Class B Fire?
The correct extinguisher depends on the particular fuel, fire size, location and required fire rating.
Common extinguisher types that may be suitable for Class B fire risks include foam, dry powder and CO2, depending on the application and extinguisher rating.
Dry Powder Extinguishers
Appropriately rated ABE and BE dry powder extinguishers can be suitable for Class B fires involving flammable liquids.
Dry powder is commonly selected where multiple fire risks need to be covered by one extinguisher.
For a range of ABE dry powder extinguishers, see our ABE dry chemical powder fire extinguishers.
Foam Extinguishers
Foam extinguishers can be suitable for many Class B flammable-liquid fires. The foam can form a layer over the liquid surface, helping suppress flames and reduce the release of flammable vapours.
Foam extinguishers are commonly used for suitable fuel and flammable-liquid risks, but the extinguisher's rating and manufacturer's instructions should always be checked.
CO2 Fire Extinguishers
CO2 extinguishers can be suitable for certain Class B fires, particularly smaller fires involving flammable liquids.
CO2 does not leave the powder residue associated with dry chemical extinguishers and is also commonly used around electrical equipment.
For more information, see our guide to CO2 fire extinguisher uses.
F-500 Extinguishers
Some specialised extinguishing agents, including F-500 products, are designed for particular fire risks and may have Class B applications depending on the product's certification and rating.
The appropriate extinguisher should always be selected according to its actual label, rating and intended application rather than assuming one agent is suitable for every Class B fire.
Can You Use Water on a Class B Fire?
A standard water extinguisher should not normally be used on a flammable-liquid fire.
Water can fail to control the burning liquid and, depending on the circumstances, can cause the fuel to spread and increase the area of the fire.
This is why the extinguisher must be selected according to the fuel involved.
Never assume that because water is effective on some fires it is suitable for every fire.
Class B vs Class F Fires
Class B and Class F fires can both involve liquids, but they represent different fire risks.
Class B fires involve flammable liquids such as petrol, diesel, solvents and paints.
Class F fires involve cooking oils and fats, particularly in commercial kitchens and deep fryers.
A standard dry powder, foam or CO2 extinguisher should not automatically be assumed to be suitable for a Class F cooking-oil fire. A wet chemical extinguisher is specifically designed for this type of fire.
Choosing the correct extinguisher for the actual fuel is essential.
Class B vs Class C Fires
Class B and Class C fires are also different.
Class B: flammable liquids, such as petrol, diesel, solvents and paints.
Class C: flammable gases, such as LPG, propane and butane.
This distinction is important because the hazards and appropriate firefighting approach can differ.
If a fire involves a gas supply, the priority should also be to isolate the gas supply if this can be done safely.
Class B Fires and Electrical Equipment
A Class B fire is defined by the fuel involved, but a fire can also involve electrical equipment.
If electrical equipment is energised, it creates an additional electrical hazard. The extinguisher must therefore be suitable for use around energised electrical equipment.
For more information about selecting an extinguisher for this situation, read our guide to a fire extinguisher for electrical fires.
Where it is safe to do so, isolate the electrical supply before attempting to extinguish the fire.
How to Extinguish a Class B Fire Safely
If a fire is small enough to tackle safely and you have the correct extinguisher:
Raise the alarm and make sure people nearby know there is a fire.
Call 000 if the fire presents a significant danger or cannot be safely controlled.
Make sure you have a clear escape route behind you.
Select an extinguisher with a rating suitable for the Class B fuel.
Follow the manufacturer's instructions for operating the extinguisher.
Keep a safe distance from the fire.
Aim the extinguishing agent at the appropriate area of the burning liquid rather than putting yourself unnecessarily close to the flames.
Stop immediately if the fire grows, spreads or becomes unsafe.
Continue monitoring the area after apparent extinguishment because re-ignition can occur.
Never allow the fire to place you between the flames and your escape route.
How to Prevent Class B Fires
Many Class B fire risks can be reduced through good storage and handling practices.
Store Flammable Liquids Correctly
Keep petrol, solvents, paints and other flammable liquids in appropriate containers and storage areas.
Keep Ignition Sources Away
Keep open flames, cigarettes, sparks and other ignition sources away from flammable liquids and their vapours.
Clean Up Spills
Deal with spills promptly using appropriate procedures and materials.
Maintain Equipment
Inspect fuel lines, containers, pumps and other equipment for leaks or damage.
Provide Suitable Fire Extinguishers
Make sure appropriate fire extinguishers are accessible wherever Class B fire hazards are present.
Commercial and industrial premises should select and position extinguishers according to the hazards present and the applicable Australian requirements.
Frequently Asked Questions About Class B Fires
What is a Class B fire?
A Class B fire involves flammable liquids such as petrol, diesel, kerosene, solvents, paints and other flammable liquid products.
What are examples of Class B fires?
Examples include petrol fires, diesel fires, kerosene fires and fires involving suitable flammable paints, solvents and thinners.
What causes Class B fires?
Class B fires can be caused by spills or leaks of flammable liquids coming into contact with an ignition source such as an open flame, spark, hot surface or other source of ignition.
What fire extinguisher is used for a Class B fire?
Depending on the fuel, fire size and application, appropriately rated foam, dry powder or CO2 extinguishers can be suitable for Class B fires. Always check the extinguisher's rating and manufacturer's instructions.
Can you use a powder extinguisher on a Class B fire?
Yes. An appropriately rated ABE or BE dry powder extinguisher can be suitable for Class B fires involving flammable liquids.
Can you use a CO2 extinguisher on a Class B fire?
CO2 extinguishers can be suitable for certain Class B fires, particularly smaller fires involving flammable liquids. Always check the extinguisher's rating and intended application.
Can you use water on a Class B fire?
A standard water extinguisher should not normally be used on a flammable-liquid fire because water can spread the burning liquid and make the fire more difficult to control.
What is the difference between Class B and Class F fires?
Class B fires involve flammable liquids such as petrol, diesel and solvents. Class F fires involve cooking oils and fats, such as those found in commercial deep fryers. Class F fires require an appropriate wet chemical extinguisher.
What is the difference between Class B and Class C fires?
Class B fires involve flammable liquids, while Class C fires involve flammable gases such as LPG, propane and butane.
Can a Class B fire involve petrol or diesel?
Yes. Petrol and diesel are common examples of fuels that can be involved in Class B fires. The appropriate extinguisher should be selected according to the fuel, fire rating and application.
Final Thoughts
Class B fires involve flammable liquids and can develop rapidly when fuels such as petrol, diesel, solvents or paints are ignited.
The correct extinguisher depends on the specific fuel, fire rating and circumstances. Appropriately rated dry powder, foam and CO2 extinguishers can all have applications for Class B fire risks.
Do not use a standard water extinguisher on a flammable-liquid fire, and never attempt to fight a fire if doing so would put you or others at risk.
Understanding the fire risk and having the appropriate fire extinguisher available can form an important part of a broader fire-safety plan.
This article provides general information only and is not a substitute for professional advice. It is not customised for any individual's specific situation. Always consult with a qualified professional for personalised guidance.
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