Fire Extinguisher Classes: Matching the Agent to the Risk

Extinguishers are classified by the type of fuel they are designed to fight. Using the wrong agent can be ineffective, and in some cases makes the fire worse.

The fire classes

• Class A — ordinary combustibles such as wood, paper, textiles
• Class B — flammable liquids such as petrol, oils, solvents
• Class C — flammable gases
• Class D — combustible metals
• Class F / K — cooking oils and fats

Electrical equipment is not a fuel class in itself. What matters is whether the agent is safe to use on live equipment.

Common agents

ABC dry powder covers a broad range and is the general-purpose choice for corridors, workshops and warehouses. The trade-off is heavy residue, which is why it is avoided around sensitive electronics.

Carbon dioxide leaves no residue and is used around electrical equipment and server rooms. It has limited cooling effect on deep-seated fires, so re-ignition is a risk. The discharge horn becomes extremely cold in use.

Foam suits Class A and B risks such as fuel stores and plant rooms.

Wet chemical is intended for cooking oil fires in commercial kitchens, where it reacts with the hot oil to form a sealing layer. A powder extinguisher is not a substitute here.

Beyond the extinguisher itself

Placement, visibility and signage decide whether an extinguisher is used in time. Mount units on the escape route, keep them unobstructed, and ensure the access path stays clear.

Servicing intervals, pressure checks and the condition of the hose and pin matter as much as the initial selection. An extinguisher that has not been inspected is an assumption, not a protection measure. Confirm the certification requirements applicable to your project and authority.