Fires are grouped into classes by what's burning. Each extinguisher is labelled with the classes it can tackle.

  • Class A – ordinary solid materials: wood, paper, cardboard, fabric. Small plastic items count as Class A too, but larger amounts of plastic melt as they burn and can behave like a burning liquid (Class B). Worth bearing in mind where there's a lot of plastic stock or packaging.
  • Class B – flammable liquids: petrol, diesel, paint, solvents.
  • Class C – flammable gases: propane, butane, natural gas.
  • Class D – burning metals, such as magnesium, aluminium swarf, sodium and lithium metal. These need specialist extinguishers. Lithium-ion batteries are not Class D: they don't contain lithium in metal form. They now have their own class – see Class L below.
  • Class F – cooking oils and fats, for example in a deep fat fryer.
  • Class L – lithium-ion batteries. A new class, explained below.
  • Electrical– not a class as such, but shown with a lightning symbol on the label.
    • CO2 is the usual choice for fires in electrical equipment, and dry powder also works.
    • Many water-based ("wet") extinguishers – water, water mist, foam and wet chemical – have a special spray nozzle and have passed the BS EN 3 dielectric test. They're approved for use on live electrical equipment up to 1000 volts.
    • That means they're safe for most situations where the spray accidentally reaches electrical equipment – for example, a socket or cable near burning paper or furniture.
    • Check the label: it shows whether the extinguisher has passed the dielectric test, and the safe distance to keep from the equipment.

Class L – the New Class for Lithium-Ion Batteries

Class L was added in 2026 to the international standard for fire classes (BS ISO 3941:2026). It covers fires in lithium-ion cells and batteries – the kind found in e-bikes, e-scooters, laptops, power tools, electric vehicles and battery storage systems.

These fires get their own class because they behave differently. A damaged or faulty battery can go into "thermal runaway": it heats itself up, spreads from cell to cell, gives off toxic and flammable gases, and can reignite hours after it seems to be out.

Why You Won't See Class L on Extinguishers Yet

BS ISO 3941 classifies fires – it doesn't test extinguishers. Before an extinguisher can carry a Class L rating, there has to be an agreed test method, as there is for Classes A, B and F under BS EN 3. A new test standard for extinguishers used on small lithium-ion battery fires, BS EN 3-11, is being developed but, at the time of writing (October 2026), hadn't been published. Until it is, no extinguisher can be officially rated for lithium-ion battery fires.

Extinguishers sold for lithium-ion battery fires have been tested by their manufacturers using their own methods. Check the product information to see what each one has been tested on.

What the Numbers Mean

You'll see ratings such as "13A" or "70B". The number shows the size of test fire it put out – the higher the number, the bigger the fire it can handle. The letter is the class.

Good to know: with gas fires (Class C), the safest action is usually to shut off the gas supply, not to put the flame out while gas is still escaping.

Worth remembering… your fire risk assessment is what decides the equipment your premises need. This guide is general advice, not a substitute for it.

Not sure what you need? Get in touch with our team – we'll be delighted to help. No pressure. No sales patter.