What is Class B Fire Understanding Causes, Risks, and Safety Measures

Key Takeaways

Aspect	Details
Definition	Class B fires involve flammable liquids such as petrol, diesel, oils, and paints. These substances can ignite easily and spread rapidly.
Common Causes	Spills or leaks of flammable liquids, improper storage, and exposure to ignition sources like open flames or electrical sparks.
Suitable Extinguishers	Foam and dry powder extinguishers are effective for Class B fires. Foam extinguishers smother the fire by forming a seal over the liquid, while dry powder extinguishers interrupt the chemical reaction.
Unsuitable Extinguishers	Water extinguishers should not be used on Class B fires as they can spread the flammable liquid, exacerbating the fire.
Safety Precautions	Ensure proper storage of flammable liquids in appropriate containers, maintain good housekeeping to prevent spills, and keep ignition sources away from flammable substances.

Understanding different types of fires is essential for staying safe and responding effectively during emergencies. A Class B fire involves flammable liquids or gases, such as petrol, oil, alcohol, and solvents. These fires spread quickly and require specific methods and extinguishers for safe handling.

If you work in environments where such substances are present, knowing the risks and proper response can make all the difference. You’ll find that not all extinguishers work on this type of fire, so it’s important to be prepared with the right knowledge and equipment to protect yourself and others.

Understanding Class B Fires

Class B fires are unique because they involve specific fuel sources that require careful handling. Addressing these fires calls for an understanding of their makeup, how they differ from other fire classes, and what typically ignites them.

Definition and Characteristics

A Class B fire results from the ignition of flammable liquids and gases rather than ordinary solids. Typically, this class includes substances like petrol, oil, paraffin, alcohol, oil-based paints, solvents, and even some types of wax and grease. These materials can ignite at low temperatures and spread flames quickly, increasing the risk of rapid escalation.

You will often encounter Class B fires in locations where these liquids are stored or used, such as garages, workshops, laboratories, or industrial plants. Class B fires do not involve materials that produce embers or char, such as those in Class A fires. Instead, they are defined by their lack of solid fuel and the volatility of their vapours.

Fire extinguishing methods for Class B fires differ because water is generally inappropriate, as it may spread the burning liquid. Instead, foam, powder, or carbon dioxide extinguishers are more effective at interrupting the fire tetrahedron — specifically, by removing oxygen or disrupting the chemical reaction sustaining combustion. 

Comparison with Other Fire Classes

The main difference between Class B fires and other types of fires lies in the fuel involved. Class A fires arise from ordinary combustibles like wood, paper, and textiles. Class C fires are those fed by flammable gases, while Class D fires involve combustible metals such as magnesium or aluminium. In commercial kitchens, Class K fires result from burning cooking oils and fats.

Unlike Class B fires, most other fire classes do not readily spread with the same intensity as flammable liquids and gases. The suppression methods you use must match the fire class. For example, using water on a Class B or Class K fire can cause the fuel to splatter or the burning oil to flare, worsening the situation. 

Common Causes

Frequent causes of Class B fires include spills or leaks of flammable liquids near ignition sources, such as open flames, electrical sparks, or hot surfaces. Improper storage, handling, or disposal of flammable liquids can also contribute significantly. An unsecured fuel container, a knocked-over can of solvent, or a poorly ventilated workshop increases the chance of vapour build-up and accidental ignition.

Industries that use oil-based paints, lacquers, or solvents face higher risks. Vehicle refuelling stations, manufacturing plants, and garages are common sites for these fires. Awareness and proper handling of hazardous materials are crucial for prevention.

The causes highlight the need for vigilance whenever you work with or store combustible liquids and gases.

Flammable Liquids and Combustible Materials in Class B Fires

Class B fires involve specific fuels such as flammable and combustible liquids, along with gases like propane and natural gas. Their properties, risks, and the unique hazards they present require a detailed understanding for effective prevention and response.

Types of Flammable Liquids

Class B fires are defined by the presence of flammable liquids as a primary fuel source. These include substances like petrol, diesel, paraffin, turpentine, ethanol, and oil-based paints. Flammable liquids have a low flash point, meaning they can ignite at relatively low temperatures.

You may also encounter solvents, lacquers, and petroleum greases, all of which pose significant fire hazards due to their ability to evaporate and form combustible mixtures in air. Some, like petrol and spirits, are particularly volatile and may ignite easily from small sparks.

Common gases associated with Class B fires include propane and natural gas. Both liquids and gases can spread fire rapidly and are harder to contain than solid fuels.

Role of Combustible Materials

Combustible liquids differ from flammable liquids by having higher flash points, but they can still burn under the right conditions. Examples include some lubricating oils and certain types of paint. While less volatile, these materials become dangerous if heated or exposed to open flame.

Your workplace, garage, or home may contain significant quantities of both flammable and combustible materials. Oil-soaked rags, paint thinners, and cleaning agents can all contribute to the spread of a Class B fire if not stored or handled correctly.

Other combustible materials, such as packaging or rags contaminated with flammable liquids, can help the fire travel between different fuel sources. This can increase the severity and reach of an incident.

Hazards and Risks

Class B fires are hazardous due to fast flame spread and the potential for explosive vapour-air mixtures. Exhaustion or inhalation of toxic fumes is a key risk, particularly in enclosed spaces where ventilation is poor.

You must account for the potential of flashback, where invisible vapours ignite and fire travels back to the source. This outcome is common with spilt petrol or leaking propane.

Firefighting water can spread flammable liquids, worsening the hazard. Only suitable extinguishing agents like foam, dry powder, or CO₂ should be used for maximum fire safety.

Class B fires often result in rapid escalation if hazards are underestimated. Recognising associated risks is crucial to preventing widespread damage and harm.

Extinguishing Class B Fires

Class B fires involve flammable liquids or gases such as petrol, oils, solvents, and alcohols. Choosing the correct extinguisher and using the proper technique is essential because using the wrong agent can make the situation worse.

Selecting the Right Fire Extinguisher

For Class B fires, not all fire extinguishers are suitable. Water fire extinguishers should never be used, as water can cause flammable liquids to spread, increasing the risk. Instead, your options include foam (AFFF) extinguishers, CO2 fire extinguishers, dry powder fire extinguishers, and in some cases, ABC extinguishers.

You will often see foam and CO2 extinguishers in garages, workshops, or areas where flammable liquids are in use. Portable fire extinguishers that are easily accessible increase your ability to respond quickly. While halon extinguishers were previously common for this type of fire, their use is now restricted in the UK due to environmental regulations.

When selecting an extinguisher, look for the letter “B” on the label. This indicates that it is effective for flammable liquid fires.

Recommended Extinguishing Agents

The most effective extinguishing agents for Class B fires include foam (AFFF), carbon dioxide (CO2), and certain dry powder formulations. Foam extinguishers cool the fire and create a seal to prevent re-ignition, making them very effective for liquid pool fires. CO2 extinguishers work by displacing oxygen, which helps to suffocate the flames without leaving residue.

ABC extinguishers containing dry powder are versatile and can also tackle flammable liquid fires, but may not prevent re-ignition as effectively as foam. Wet chemical fire extinguishers are generally not recommended for Class B fires, as they are more suitable for kitchen oil fires. Choose an agent that matches the type of liquid or gas involved for the best results.

Extinguishing Techniques

To tackle a Class B fire, aim the extinguisher at the base or front edge of the flames. For liquid pool fires, use a sweeping motion from side to side, gradually advancing until the fire is out. Avoid aiming directly at the centre, as this can splash burning liquid and spread the fire.

Always keep yourself upwind and maintain a safe distance. Move closer only as the flames recede. Do not try to extinguish large fires on your own—evacuate immediately and call emergency services.

With portable extinguishers, remember the PASS technique: Pull, Aim, Squeeze, and Sweep. This ensures effective and safe application of the extinguishing agent. Practice and knowledge of these techniques can make a critical difference in an emergency.

Fire Safety and Prevention Strategies for Class B Fires

Class B fires involve flammable liquids such as petrol, oil, alcohol, and certain solvents. Effective prevention and protection depend on careful handling, regular inspections, and clear safety procedures for both work and home settings.

Workplace and Home Safety Precautions

To prevent Class B fires, keep ignition sources away from flammable liquids and vapours. Do not smoke, use matches, or operate open flames in areas where these substances are present. Ensure rooms are well-ventilated to reduce the risk of flammable vapour accumulation.

Install approved fire extinguishers suitable for Class B fires and make sure they are easily accessible. Conduct monthly inspections of extinguishers and fire safety equipment to confirm they are in proper working order. Train staff and household members in the use of fire extinguishers and evacuation protocols.

In kitchens, avoid leaving cooking appliances unattended, especially when using oils or other flammable substances. Clean up fuel spills promptly and dispose of rags or cloths used with flammable liquids in metal containers. Post clear warning signs in storage and usage areas to remind occupants of fire hazards.

Handling and Storage of Flammable Liquids

Always store flammable liquids in tightly sealed, approved containers. Use dedicated storage cabinets or rooms that are ventilated and isolated from ignition sources. Keep the amount of flammable liquid stored on site to a minimum by ordering only what is needed.

Label all containers clearly with their contents and hazard symbols. Follow specific handling procedures, such as transferring liquids by using anti-static pumps, to prevent sparks. Store containers away from direct sunlight or heat sources, and never near electrical equipment or cooking appliances.

Establish a routine for regular inspection of storage areas for leaks, corrosion, or damage. Ensure spill kits and personal protective equipment are easily available nearby. Educate all users on emergency response procedures and the safe disposal of unused or expired liquids.

Frequently Asked Questions

Class B fires involve flammable liquids that can ignite quickly and spread rapidly. Using the right extinguisher and following safety procedures is essential for effective management of these incidents.

What types of combustibles are involved in a Class B fire?

Class B fires result from the ignition of flammable liquids such as petrol, oil, diesel, alcohol, paint, and paraffin. These substances can be found in vehicles, workshops, and many industrial settings.

Liquids involved in Class B fires are often highly volatile and produce flammable vapours that can ignite at low temperatures.

How does a Class B fire extinguisher function?

A Class B fire extinguisher works by cutting off the fire’s oxygen supply or by interrupting the chemical reaction of the fire. Most often, foam, dry powder, or carbon dioxide extinguishers are used.

Foam extinguishers create a barrier over the liquid surface, while CO₂ removes oxygen and cools the fire. Dry powder smothers the flames and interrupts combustion.

Can you describe an example of a Class B fire scenario?

A common example would be a spillage of petrol in a garage that comes into contact with a hot engine or an electrical spark, leading to a sudden fire.

In kitchens, a spill of cooking oil or burning spirits can also cause a Class B fire if exposed to an open flame.

What safety protocols should be followed during a Class B fire emergency?

Do not try to extinguish the fire with water, as this can spread the flammable liquid and worsen the situation. Use the correct type of fire extinguisher, and only attempt to fight the fire if it is safe to do so.

Evacuate the area immediately if the fire is spreading or cannot be controlled. Alert emergency services as soon as possible.

What distinguishes a Class B fire extinguisher from a Class C version?

A Class B extinguisher is designed specifically for flammable liquid fires, while a Class C extinguisher is intended for fires involving flammable gases such as propane or butane.

Selection should be based on the material fuelling the fire, with Class B covering liquids and Class C focusing on gases. For more detail, refer to this guide to fire classes.

How should one respond to a Class B fire outbreak effectively?

Immediately assess the situation for personal safety and the safety of others nearby. Use a suitable Class B extinguisher, aiming the nozzle at the base of the flames.

If the fire cannot be controlled, evacuate via the nearest exit and contact the fire brigade. Do not re-enter the area until it is declared safe.