Guide — Class F Fire Safety
Wet Chemical Extinguisher
Wet chemical extinguishers are specifically designed for Class F fires — burning cooking oils and fats. They are the only extinguisher type that cools and saponifies burning oil safely, preventing re-ignition. Required in every commercial kitchen in the UK.
Key point
A wet chemical extinguisher works by applying a fine mist of potassium acetate or citrate solution over burning oil. It cools the oil below its auto-ignition temperature and saponifies (turns) the surface into a soapy foam layer that seals the oil from oxygen — preventing re-ignition. No other extinguisher type achieves both effects on Class F fires.
Extinguisher type by fire class
| Type | Class F | Class A | Class B | Class C | Electrical | Typical use |
|---|---|---|---|---|---|---|
| Wet chemical (Class F) | Yes | Yes (limited) | No | No | No (unless 35kV tested) | Primary choice for commercial kitchens |
| CO₂ | No | No | Yes | No | Yes | Electrical panels, server rooms |
| Dry powder (ABC) | No | Yes | Yes | Yes | Limited | Outdoor/vehicle use |
| Water | No | Yes | No | No | No | Paper, wood, textiles |
| Foam (AFFF) | No | Yes | Yes | No | No | Flammable liquids |
How to use a wet chemical extinguisher
- Turn off the heat source if it is safe to reach the controls.
- Pull the safety pin from the handle.
- Stand back at least one metre — the lance is designed for standoff application.
- Aim above the burning oil, not directly into it — the spray must fall gently onto the surface.
- Apply in a slow circular motion, building a foam blanket across the entire surface.
- Continue until fully extinguished and the surface is covered. Do not remove the foam layer.
- Do not leave the area until you are certain re-ignition cannot occur.
Placement requirements
BS 5306-8 requires a wet chemical extinguisher to be sited within 30 metres of the cooking hazard. In practice, this means mounting one adjacent to (but not directly above) the cooking range — where it can be reached without passing through flame or smoke. It must not be mounted so close to the fryer that heat renders it inaccessible in an emergency.
For high-volume commercial kitchens with multiple deep-fat fryers, a fixed fire suppression system is required in addition to portable extinguishers. See our fire extinguisher types guide for a full comparison of all UK extinguisher colours and classes.
Maintenance and servicing
Wet chemical extinguishers must be serviced annually (basic service) and fully overhauled every five years (extended service) under BS 5306-3. See our fire extinguisher maintenance guide for a full servicing schedule, what each service involves, and how to keep records for your fire risk assessment.
Who needs a wet chemical extinguisher?
Any premises where cooking oil is used commercially — restaurants, cafes, takeaways, school kitchens, care home kitchens, hotel kitchens. Under the RRO 2005, the responsible person must provide appropriate fire-fighting equipment for the fire risks present. A kitchen with deep-fat fryers without a wet chemical extinguisher fails this duty. See the kitchen fire prevention guide for the full range of measures required.
Frequently asked questions
FAQ