Class F Fire Guide – Extinguishers & Prevention

Class F fires must be handled carefully with the right extinguisher so that they are put out safely and swiftly.

Using the wrong type of fire extinguisher on a fire can increase the risk of injury to the person discharging it. Oil and grease fires can be particularly dangerous if an unsuitable extinguisher is used.

Class F Fires are oil or grease fires which burn at very high temperatures.

Each fire class has specific characteristics which cause them to behave differently. All of the different types of fire involve a different fuel and you must use the correct extinguisher to deal with the fire. If you use the wrong extinguisher, the consequences can be explosive.

Our guide looks at what class f fires are, how to extinguish them, and what type of equipment should be used to fight them.

What is Burning in a Class F Fire?

A class F fire involves the ignition of high temperature cooking oils and fats. These fires burn very intensely and can intensify suddenly.

They are technically similar to Class B fires which also involve flammable liquids. However, the extremely high flash point compared with Class B fires makes them unique. This difference is recognised as being important enough to warrant a separate fire category.

F type fires typically start when oils and fats reach high temperatures very quickly in equipment such as deep fat fryers. Oils and fats have a flash point of 315 degrees and once 340 degrees is reached, autoignition can occur. This type of fire happens quickly and has the potential to spread rapidly.

Fires involving oils and fat are common in kitchens and food preparation areas. They may break out around chip pans or deep fat fryers.

These types of fire are very dangerous because of the high temperatures involved and the potential for rapid spread.

What is the Class F Fire Symbol?

The class F fire symbol will have an image of a frying pan with a flame and an F in the top right corner of the symbol.

About Class F Fire Extinguishers

All commercial kitchens which use deep fat fryers should have the correct fire extinguisher for oil fires (Class F). Using the incorrect extinguisher can aggravate the fire making it worse, and posing a risk to those around it.

You must solely use wet chemical fire extinguishers for class F fires. This is the only way an oil fire can be dealt with in a controlled and safe manner.

No other type of extinguisher is suitable for this fire class. You should never use a water extinguisher, or throw water on a fire caused by oils and fats.

Using water in extremely hot and greasy conditions can cause the fire to explode out of control.

Wet Chemical Fire Extinguishers

Wet chemical fire extinguishers are used to put out fires caused by flammable cooking oils and fats and are the only type suitable for this class of fire.

The size of extinguisher needed varies depending on your business. For example, a mobile catering business will need a smaller one than an industrial kitchen with very large deep fat fryers.

Wet chemical fire extinguishers work by putting a layer on top of the fire which stops oxygen from reaching the flames and reduces its ferocity.

The extinguisher’s liquid is partly made up of potassium salts which removes the fire’s oxygen content and cools the flames.

Wet chemical fire extinguishers have a yellow label on a red cylinder marked  “Wet Chemical”.

See Also: Colour of Fire Extinguishers – how to identify all UK extinguisher types via their label colours.

Fire Blankets

Fire blankets can be used for class F fires if the fire is fairly small and not spreading to other areas quicker than you can handle.

Blankets should be stored where they can be easily and quickly accessed when needed. Made up of fire-resistant material, the blanket is positioned on top of the fire and smothers it.

Commercial kitchens and childcare settings have fire blankets ready in the event of a kitchen fire.

How to Extinguish a Class F Fire?

All fires comprise of oxygen, fuel, and heat. To extinguish any fire, you must remove one of these elements. 

In the case of Class F fires, this means you need to reduce the heat of the burning oil below its flashpoint. The very high temperatures involved in oil fires make this very difficult to do.

This is why A Class F fire needs a wet chemical extinguisher to safely deal with the flames. Using other types of extinguisher can be dangerous.

How to Use a Wet Chemical Extinguisher on an Oil Fire

You should direct the extinguisher in a circular motion above the fire but ensure you remain at a safe distance yourself.

This type of fire involves a risk of being splashed by burning fat or oil, which can cause serious burns. Wet chemical extinguishers feature a long hose to enable those using them to keep as far away from the fire as possible. Make sure you remain as far away as possible.

By spraying on top of the fire you are subduing the fire’s oxygen which ensures it doesn’t worsen. If the fire is too big to manage then step away and call the fire services.

Once the fire is out, make sure you ventilate the area thoroughly.

Types of Extinguisher That Should Not Be Used

Most ordinary fire extinguishers will be ineffective against bringing an oil or grease fire under control. Some extinguishers will worsen a fire, and should not be used on a class F fire.

  • Water Extinguishers  – Using a water extinguisher could cause an explosion. When water is put on an oil fire it becomes superheated, and will explode.
  • CO2 Fire Extinguishers – Although rated for use on class B fires (flammable liquids) CO2 extinguishers can spread oil fires. This is because the freezing cold discharge can splash the burning oil, and spread the flames.
  • Dry Powder Fire Extinguishers –  Dry powder extinguishers put out flames by forming a barrier between the fire’s fuel and it’s source of oxygen. They do not cool the fire. The high flashpoint of class F fires means they’re likely to reignite. Dry powder extinguishers also have corrosive and abrasive properties, meaning they can cause extensive damage to the environments they are used in.

Class F Fire Prevention

There are practical steps you can take to help prevent class f fires from happening in the first place which we’ve outlined below.

  • Keep watch over oils and fats at all times and never leave these hot pans unattended.
  • When oil spits or spills onto the surfaces, clean it up as soon as possible, without burning yourself.
  • Smoke means the oil is heating up too quickly so if you see this, you need to either reduce the heat or take it away from the heat source and let it cool before trying again.
  • Appliance flames should only be used when heating something and should be switched off at all other times.
  • Keep any flammable materials well away from the naked flames.
  • Carry out regular fire risk assessments and make sure everyone understands their role in keeping the kitchen a safe environment.

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