The Essential Guide to Class F Fires: Prevention, Extinguishing, and Safety Equipment

A Class F fire involves cooking oils and fats, such as vegetable oil, animal fat, and grease used in deep fryers. These fires are particularly dangerous because they burn at extremely high temperatures (often above 340°C) and can re-ignite easily. Never use water on a Class F fire—it will cause a violent grease explosion. The only safe and effective extinguishing methods are a fire blanket for small fires and a wet-chemical fire extinguisher for larger fires.

Prevention is the best strategy. Never leave cooking unattended, control oil temperatures, and ensure you have the correct fire safety equipment—a wet chemical extinguisher and a fire blanket—readily accessible in your kitchen.

Introduction: Understanding the Danger of Class F Fires

Class F fires are among the most dangerous and complex fires to tackle. They involve cooking oils and fats and are a leading cause of property damage and injury in both domestic and commercial kitchens. Unlike other types of fires, Class F fires burn at extremely high temperatures, making them notoriously difficult to extinguish. Using an incorrect extinguishing method, such as water, can be catastrophic, causing a "grease explosion" that can spread the fire instantly.

This comprehensive guide will provide you with everything you need to know about Class F fires, from their causes and characteristics to the correct safety equipment and proven extinguishing techniques. Whether you are a homeowner, a professional chef, or a business owner, understanding Class F fire safety is essential for protecting lives and property.

What Is a Class F Fire? Definition and Key Characteristics

A Class F fire is a specific type of fire that involves cooking oils and fats. These fires are common in kitchens, from homes to large commercial restaurants, and are particularly dangerous because the fuels burn at extremely high temperatures.

Unlike flammable liquids like petrol, cooking oils need to reach a very high temperature—often over 340°C—before they will ignite. At this point, the oil can reach its autoignition temperature and catch fire without a flame or spark. This inherent property makes them notoriously difficult to extinguish with standard methods.

Key Characteristics of Class F Fires

• High Temperatures: Involves burning oils that can reach over 340°C, creating intense heat that is hard to cool.

• Rapid Spread: These fires can spread quickly, especially if the burning oil is spilled or splashed.

• Dangerous Re-ignition: Because of the heat involved, they can easily reignite after appearing to be extinguished if not cooled properly.

• Saponification Required: They require a specific extinguishing method called saponification, which turns the oil into a non-combustible soap.

Class F fires are classified separately from Class B (flammable liquids) because the high temperatures involved mean that extinguishers designed for petrol or other solvents are often ineffective and can be dangerous to use.

What Causes a Class F Fire?

Class F fires are almost always the result of human error or negligence in the kitchen. Understanding the primary causes is the first step in effective prevention.

Common Causes of Class F Fires

• Overheating Oil: This is the most frequent cause. When oil is left on a high heat, it can exceed its autoignition temperature and burst into flames spontaneously.

• Leaving Cooking Unattended: A pan left unsupervised for even a few minutes can easily overheat, leading to a fire.

• Spilling Oil on Hot Surfaces: If oil is spilled from a pan onto a hot stovetop or open flame, it can ignite immediately.

• Grease Buildup: Accumulated grease on cooking surfaces, in exhaust hoods, or in deep fryers can catch fire if exposed to high heat.

• Equipment Malfunction: Faulty thermostats or electrical failures in deep fryers and other cooking appliances can cause them to overheat and start a fire.

• Overfilling Pans or Fryers: Too much oil increases the risk of spillage and rapid fire escalation.

The Science Behind Class F Fires: Flash Point and Autoignition Temperature

Flash Point: The flash point of a substance is the lowest temperature at which it can vaporise to form an ignitable mixture in the air. For cooking oils and fats, the flash point is relatively high, meaning they need to reach a significant temperature before they can produce flammable vapours. However, once the flash point is reached, these vapours can ignite if exposed to an open flame or a hot surface.

Autoignition Temperature: This is the minimum temperature at which a substance will ignite spontaneously without an external ignition source, such as a flame or spark. For cooking oils and fats, the autoignition temperature is typically higher than the flash point—often above 340°C. If the oil reaches this temperature, it can catch fire without direct contact with an open flame.

Prevention of Class F Fires: Safety Tips for Home and Commercial Kitchens

Preventing Class F fires is far better than trying to extinguish them. Implementing consistent safety measures is key to protecting lives and property.

In Commercial Kitchens

• Install Fire Suppression Systems: Automatic fire suppression systems are essential. They can quickly detect and suppress a fire before it spreads.

• Provide Correct Equipment: Ensure you have the right fire safety equipment, including wet chemical fire extinguishers and fire blankets, readily accessible.

• Regular Staff Training: Train all kitchen staff on fire safety protocols, the correct use of extinguishers and fire blankets, and the importance of immediate action.

• Regular Cleaning: Promptly clean up oil and fat spillages and ensure a regular, deep clean of all cooking surfaces, exhausts, and ductwork.

• Equipment Maintenance: Ensure all cooking equipment is professionally installed and regularly maintained to prevent malfunctions.

• Use Drip Trays: Place drip trays under cooking equipment to catch any oil or fat drips, preventing them from reaching hot surfaces.

• Non-Slip Mats: Use non-slip mats in cooking areas to prevent accidental spills and provide a safer working environment.

In Home Kitchens

• Stay Attentive: Never leave cooking unattended. Stay in the kitchen when frying or using other methods involving oils.

• Control Temperatures: Be vigilant about maintaining proper cooking temperatures to avoid overheating.

• Keep a Lid and a Blanket Nearby: Have a fire blanket and a pan lid close at hand. In an emergency, turn off the heat and slide the lid over the pan or use the blanket to smother the flames.

• Avoid Overfilling: Do not overfill pans or fryers with oil. Keeping oil levels low reduces the risk of spillage and rapid escalation.

• Keep Flammable Materials Away: Store flammable materials, such as kitchen towels and curtains, away from cooking areas to prevent accidental ignition.

• Use Appropriate Cookware: Use cooking utensils and equipment designed for high-temperature cooking. Avoid using damaged or inappropriate cookware.

Essential Prevention Checklist

How to Extinguish a Class F Fire: A Step-by-Step Guide

If a small Class F fire occurs, taking the right action immediately can prevent a major disaster. Your safety is always the priority. If the fire is large or spreading, evacuate immediately and call 000.

Critical Warning: What NOT to Do

DO NOT use water, foam, powder, or CO₂ extinguishers. They are ineffective and will likely make the fire much worse.

• Water will evaporate instantly on contact with the hot oil, causing an explosion that can spread burning oil and cause serious injury.

• Foam extinguishers are not designed for high-temperature oil fires and can cause the oil to splatter.

• Powder extinguishers may temporarily suppress the flames but do not cool the oil, allowing the fire to re-ignite.

• CO₂ extinguishers do not cool the oil effectively and can cause the hot oil to splatter.

Step 1: Turn Off the Heat Source

If it is safe to do so, immediately turn off the stove, deep fryer, or any other heat source. Removing the heat is the first step in stopping the fire.

Step 2: Assess the Fire

Evaluate the size and type of fire to confirm the blanket's suitability for the situation. Fire blankets are designed for small fires involving cooking oils, fats, or ordinary combustibles. Do not attempt to use a blanket on large fires.

Step 3: Use a Fire Blanket for Small Fires

For a very small, manageable fire in a pan, a fire blanket is an excellent tool. Here is how to use it correctly:

1. Retrieve the Blanket Safely: Approach the fire blanket cautiously, keeping yourself at a safe distance from the fire.

2. Hold the Edges: Grasp the edges of the fire blanket to avoid direct contact with the flames or hot surfaces.

3. Cover the Fire: Gently place the blanket over the burning oil or fat, ensuring that it completely covers the fire source. Avoid unnecessary movement that may spread the fire.

4. Leave in Place: Once the fire is covered, leave the blanket in place to smother the flames. Do not attempt to move the blanket or uncover the fire prematurely.

5. Allow to Cool: After the fire is extinguished, allow the covered area to cool before removing the blanket to prevent re-ignition.

Step 4: Use a Wet Chemical Fire Extinguisher for Larger Fires

For larger fires, a wet chemical fire extinguisher is the only safe and effective solution. This is the only type of extinguisher designed specifically for Class F fires.

How to use a wet chemical extinguisher:

1. Pull the pin to break the tamper seal.

2. Stand back from the fire. These extinguishers have a long lance applicator.

3. Aim the lance at the base of the fire, just above the burning oil.

4. Squeeze the lever to discharge the agent. Use a gentle, sweeping motion.

Why it works: The wet chemical agent reacts with the hot oil in a process called saponification, turning the oil into a non-combustible, soapy foam that cools the fire and prevents re-ignition.

Step 5: Call Emergency Services

Report the fire to the appropriate authorities, even if you think it has been contained. Fire can spread quickly, and professional firefighters should always be alerted. Call 000 (Triple Zero) for fire emergencies in Australia.

Fire Safety Equipment for Class F Fires

Having the right equipment, installed and maintained correctly, is critical for managing Class F fire risks, especially in commercial environments.

Wet Chemical Fire Extinguishers

These are the first line of defence for Class F fires. They are specifically designed to tackle the unique challenges posed by cooking oils and fats.

Key Features:

• Easily identifiable by a red body with a yellow, beige, or oatmeal-colored band or label.

• Contain a potassium-based solution (like potassium acetate) designed for saponification.

• Certified to AS/NZS 1841.3 in Australia.

How They Work: The primary agent used in wet chemical extinguishers is a specially formulated solution that creates a barrier between the burning oil or fat and the surrounding air, suppressing the fire. The extinguisher not only cools the burning oil but also reacts with it to form a soap-like substance. This soap forms a layer on the surface of the oil, preventing the release of flammable vapours and cutting off the oxygen supply to the fire. This dual-action approach makes wet chemical extinguishers highly efficient in dealing with Class F fires.

Fire Blankets

Fire blankets play a vital role in fire safety, including the management of Class F fires involving cooking oils and fats. These blankets are typically made of fire-resistant materials such as fibreglass or specially treated wool. The primary purpose of a fire blanket is to smother and extinguish small fires by cutting off the oxygen supply.

Proper Storage and Accessibility: For fire blankets to be effective, they must be stored in a location that is easily accessible in case of an emergency. In kitchen environments, especially those prone to Class F fires, fire blankets should be strategically placed near cooking areas, preferably mounted on a wall or stored in a clearly marked and easily reachable location. Employees should be trained on the location of fire blankets and how to quickly access them in case of a fire.

Limitations:

• Fire blankets are most effective for small fires. In the case of larger fires or those that are spreading rapidly, other firefighting methods may be necessary.

• Users should prioritise their safety and evacuate the area if a fire becomes uncontrollable. Fire blankets are not a substitute for professional firefighting equipment.

• Regularly inspect fire blankets for damage, and replace them if necessary. Damaged blankets may not provide adequate protection.

• Proper training on the correct use of fire blankets is crucial. Users should be familiar with the steps to take and practice using fire blankets in a controlled environment.

Fire Suppression Systems

Commercial kitchens should have automatic fire suppression systems installed in exhaust hoods and over cooking appliances. These systems are designed to automatically detect a fire and discharge a wet chemical agent directly onto it, preventing it from spreading.

Benefits:

• Quick detection and suppression

• Automatic activation, no human intervention required

• Designed specifically for commercial cooking environments

• Reduces the risk of fire spreading to other areas

Equipment Comparison Table

Additional Fire Safety Measures

Vigilance Is Key

Vigilance is a critical aspect of fire safety in cooking environments, especially in areas where Class F fires involving cooking oils and fats are prevalent. Kitchen staff and individuals responsible for cooking should remain attentive and focused during all cooking activities.

Key aspects of vigilance include:

• Regular Monitoring: Consistently monitor cooking processes to ensure that temperatures are controlled and there are no signs of overheating or potential fire hazards.

• Avoiding Distractions: Minimise distractions in the kitchen to maintain concentration on cooking activities. Distractions can lead to oversight and increase the risk of accidents.

• Immediate Response to Issues: Address any issues or malfunctions in cooking equipment promptly. This proactive approach can prevent potential fire hazards before they escalate.

Potential Risks Beyond Class F Fires

While Class F fires involving cooking oils and fats are a significant concern, it's essential to recognise that other fire hazards may exist in various environments.

Common risks include:

• Electrical Fires: Malfunctions in electrical appliances or wiring can lead to electrical fires. Regular inspections of electrical systems and prompt repairs are essential.

• Combustible Materials: The presence of combustible materials, such as paper, cardboard, or textiles, can increase the risk of fires. Proper storage and maintenance of these materials are crucial.

• Flammable Gases: In some environments, the use of flammable gases or substances may pose a fire hazard. Proper storage, handling, and ventilation are essential to mitigate these risks.

Incorporating Comprehensive Fire Safety Equipment

Beyond specific measures for Class F fires, it's crucial to incorporate a comprehensive set of fire safety equipment to address various fire hazards:

• Fire Extinguishers: Install appropriate fire extinguishers based on the types of potential fires in the environment. This may include extinguishers suitable for Class A, B, E, and F fires.

• Smoke Alarms: Install smoke alarms in key areas to provide early detection of smoke, indicating the presence of a fire. Regular testing and maintenance of smoke alarms are essential.

• Fire Suppression Systems: In commercial settings, consider the installation of automatic fire suppression systems, such as sprinklers or mist systems. These systems can quickly suppress fires, preventing them from spreading.

• Emergency Exit Plans: Develop and communicate clear emergency exit plans to occupants. Regularly conduct fire drills to ensure that everyone is familiar with evacuation procedures.

• Training Programs: Provide fire safety training for personnel to ensure they understand how to use fire safety equipment effectively and respond appropriately in case of a fire.

Frequently Asked Questions About Class F Fires

What is a Class F fire?

A Class F fire involves cooking oils and fats, such as vegetable oils, animal fats, and the grease used in deep fryers. These fires are especially dangerous because they burn at extremely high temperatures.

What causes a Class F fire?

Class F fires are most commonly caused by leaving cooking unattended, overheating oil, spilling oil onto hot surfaces, or allowing grease to build up on cooking surfaces.

How do you extinguish a Class F fire?

Small Class F fires can be smothered with a fire blanket. Larger fires should only be fought with a wet chemical fire extinguisher. Never use water, as it will cause a dangerous grease explosion.

Can water put out a Class F fire?

Absolutely not. Water will evaporate instantly on contact with the hot oil, causing an explosion that can spread burning oil and cause serious injury.

What type of fire extinguisher is used for Class F fires?

The only safe and effective extinguisher is a wet chemical fire extinguisher. It cools the fire and chemically turns the oil into a non-combustible soap.

Are fire blankets good for Class F fires?

Yes, fire blankets are effective for very small, contained cooking fires. They work by smothering the flames to cut off the oxygen supply.

What is the autoignition temperature of cooking oil?

Cooking oil autoignition temperatures vary but are typically above 340°C, which is why they are so hard to extinguish and can re-ignite easily.

Why are Class F fires so dangerous?

They burn at extremely high temperatures, can spread rapidly, and are very difficult to extinguish without the correct equipment. Using the wrong method can make them much worse, potentially causing a grease explosion.

What is saponification?

Saponification is a chemical process where the wet chemical extinguishing agent reacts with the hot oil to form a non-combustible, soapy foam. This process cools the fire and prevents re-ignition.

What Australian standard applies to Class F fire extinguishers?

Wet chemical fire extinguishers for Class F fires should be certified to AS/NZS 1841.3 in Australia.

Can I use a Class F extinguisher on other types of fires?

While wet chemical extinguishers are designed for Class F fires, they may also be suitable for some Class A fires (ordinary combustibles). However, they are not effective for Class B (flammable liquids) or Class E (electrical) fires.

How often should I inspect my Class F fire safety equipment?

You should visually inspect your wet chemical fire extinguisher monthly and have it professionally serviced annually. Fire blankets should be visually checked every 6-12 months and replaced immediately after any use.

What should I do if a Class F fire is too large to handle?

If a Class F fire is spreading rapidly or is beyond your ability to control, evacuate immediately and call 000. Do not put yourself at risk trying to fight a large fire.

Conclusion: Why Understanding Class F Fires Matters

Class F fires represent a unique and significant fire risk in any environment where cooking oils and fats are used. Their high temperatures, rapid spread, and potential for re-ignition make them particularly dangerous. However, with the right knowledge, prevention measures, and equipment, these fires can be effectively managed.

Key takeaways:

• Prevention is the best strategy. Never leave cooking unattended and always control oil temperatures.

• Never use water on a Class F fire—it will cause a violent grease explosion.

• Always have the right equipment—a fire blanket for small fires and a wet chemical fire extinguisher for larger fires.

• Ensure equipment is accessible and that everyone in the kitchen knows how to use it.

• Regular maintenance and training are essential for both home and commercial kitchens.

By understanding the unique characteristics of Class F fires and implementing robust safety measures, you can significantly reduce the risk of fire and protect both lives and property.

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.

About Fire Products Direct

With years of experience in the Australian fire safety industry, Fire Products Direct is committed to providing expert guidance and high-quality fire protection solutions. We help businesses and homeowners navigate the complexities of fire safety to ensure they have the right protection for their specific needs.

Products Mentioned in This Guide

• 2L Wet Chemical Fire Extinguisher

• Fire Blanket 1.2m x 1.2m

• 2Kg CO2 Fire Extinguisher

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.