In the event of a fire, your first instinct might be to grab the nearest fire extinguisher. However, using the wrong type of extinguisher on a fire can be ineffective and, in some cases, extremely dangerous, as it can spread the flames, cause an explosion, or lead to electrocution. The “material” that is burning dictates the “class” of fire, and each class requires a specific type of extinguisher.
Understanding this vital difference is a cornerstone of fire safety. This guide will break down the different fire classes, explain which materials they correspond to, and help you identify the correct extinguisher to use every time.
The Quick Answer
The correct extinguisher depends entirely on the material that is burning (the fire class). For Class A (Solids) like wood, paper, and textiles, use a Water (red label) extinguisher. For Class B (Liquids) like petrol or paint, use a Foam (cream label) or CO2 (black label) extinguisher. For live Electrical Fires, never use water; use a CO2 (black label) or Dry Powder (blue label) extinguisher. Finally, for Class F (Fats) like cooking oils, only use a Wet Chemical (yellow label) extinguisher.
Understanding the Fire Classes
Before you can pick an extinguisher, you must identify the fire. In the UK, fires are categorised into six main classes based on the fuel source.
What Are Fire Classes?
Fire classifications make it simple to identify the type of fire and the correct extinguishing agent. The main classes you’ll encounter are A, B, C, F, and electrical fires.
Class A Fires: Solid Materials
This is the most common fire class. It involves organic solid materials that burn to leave ash. These materials include wood, paper, cardboard, fabrics, textiles, and plastics, and they are found in any environment, from offices to homes and warehouses.
Class B Fires: Flammable Liquids
This class involves fires where the fuel is a flammable or combustible liquid. Common materials include petrol, diesel, paint, solvents, white spirit, and oils (but not cooking oils). These fires are common in workshops, garages, and manufacturing settings.
Class C Fires: Flammable Gases
These fires are fuelled by flammable gases such as propane, butane, methane, and LPG (Liquid Petroleum Gas). They are most likely to occur in kitchens, laboratories, and areas with gas boiler systems.
Class F Fires: Cooking Oils and Fats
This is a specialist class for fires involving deep-fat fryers or pans with cooking oils. The materials are items like cooking oil, lard, butter, and other fats, and these fires are found exclusively in kitchen environments.
Electrical Fires
This is not a formal “class” of fire, but a critical hazard. It refers to a fire started by or involving live electrical equipment. The electricity itself doesn’t burn, but it’s the source of ignition, and using the wrong extinguisher (like water) can cause a fatal electric shock.
Matching the Extinguisher to the Material
Each extinguisher type is designed to fight a fire in a specific way: by cooling, smothering (removing oxygen), or interfering with the chemical reaction.
Wood, Paper, and Textiles (Class A)
The correct extinguisher for these materials is a Water (Red Label) extinguisher. Water works by cooling the burning material to a point where it can no longer burn. It is highly effective, low-cost, and safe for this class. Foam extinguishers also work well on Class A fires.
Petrol, Paint, and Solvents (Class B)
For these flammable liquids, you should use either a Foam (Cream Label) or CO2 (Black Label) extinguisher. Foam smothers the fire, creating a blanket over the liquid to cut off its oxygen supply. CO2 is a gas that displaces oxygen and also “freezes” the fire. You should never use water, as it will splash the burning liquid and spread the fire.
Live Electrical Equipment
The correct extinguishers for electrical fires are CO2 (Black Label) or Dry Powder (Blue Label). CO2 is the ideal choice as it is non-conductive and leaves no residue, meaning it won’t destroy sensitive computer or medical equipment. Dry Powder is also non-conductive and very effective, but creates a huge, corrosive mess that can be difficult to clean up.
Cooking Oils and Fats (Class F)
The only extinguisher you should use on a chip pan or deep fat fryer fire is a Wet Chemical (Yellow Label) extinguisher. It works by spraying a fine mist that cools the oil and reacts with it (a process called saponification) to form a soapy blanket, smothering the fire. Using water on a fat fire is catastrophic, as it will cause an explosion of burning oil.
How to Identify Your Extinguisher
You don’t need to guess. All modern extinguishers are colour-coded for instant identification.
The Colour-Coding System
Under the British Standard BS EN 3, all extinguisher bodies must be red. A colour-coded label on the body identifies its contents. RED signifies Water (Class A only). CREAM signifies Foam (Class A and B). BLACK signifies Carbon Dioxide (CO2) (Class B and Electrical). BLUE signifies Dry Powder (Class A, B, C, and Electrical). YELLOW signifies Wet Chemical (Class F).
Reading the Label
The label is your most important guide. It will clearly state the type of extinguisher (e.g., “FOAM”), the fire classes it is safe to be used on (e.g., “For Class A and B fires”), and any fires it must NEVER be used on (e.g., “DO NOT USE ON LIVE ELECTRICAL FIRES”).
Your Legal Responsibilities
Knowing what to do is part of your legal fire safety duty.
The Fire Risk Assessment
The Regulatory Reform (Fire Safety) Order 2005 is the primary fire safety law in England and Wales. It states that the ‘Responsible Person’ for a building must provide “appropriate fire-fighting equipment.” Determining what is “appropriate” is a key part of your fire risk assessment, which must analyse the specific materials and hazards in your workplace.
Training and Maintenance
Simply having the correct extinguishers is not enough. The law also requires that they are properly maintained, as advised by organisations like the Fire Protection Association (FPA). Furthermore, your staff must be given adequate fire safety training on which extinguishers to use and, just as importantly, when not to fight a fire and to evacuate instead. The UK Fire Service also provides excellent resources on extinguisher choice and use.
Conclusion
Matching the extinguisher to the material isn’t just a recommendation; it’s a critical safety rule that can be the difference between a small, controlled incident and a disaster. Always check the label. The red, cream, black, blue, and yellow codes are your guide. For Class A (solids), use Water. For electrical, use CO2. And for kitchen fat fires, only use Wet Chemical. When in doubt, get out.
