Wet Chemical Extinguisher vs Foam Extinguisher | London City Fire | London

Key Takeaways

• Wet chemical extinguishers are the required solution for Class F fires (cooking oils and fats), while foam extinguishers are suited to Class A (solids) and Class B (flammable liquids) fires.
• Both extinguisher types must be selected, installed, and maintained in accordance with BS 5306-3:2017, which covers the commissioning and maintenance of portable fire extinguishers in the UK.
• Foam extinguishers offer more versatility across different fire classes, but using a foam extinguisher on a cooking oil fire can be extremely dangerous and is not recommended.
• Under the Regulatory Reform (Fire Safety) Order 2005, responsible persons must ensure that appropriate fire-fighting equipment is provided and kept in good working order for their specific premises risk profile.
• Annual servicing is required for both extinguisher types, and extended service intervals apply at manufacturer-specified intervals, typically every five years.

What is a Wet Chemical Extinguisher?

A wet chemical extinguisher works by discharging a fine mist of potassium-based solution onto burning cooking oils or fats. This solution reacts with the burning oil through a process called saponification, creating a soapy foam layer that seals the surface of the oil, starves the fire of oxygen, and prevents re-ignition. The fine mist also helps to cool the oil rapidly, which is critical given that cooking oils burn at extremely high temperatures. This dual-action mechanism makes wet chemical extinguishers uniquely effective where other extinguisher types would fail or make the situation significantly worse.

Wet chemical extinguishers carry a Class F rating and are considered the industry-standard choice for commercial kitchens, catering vans, restaurants, and any premises where deep fat fryers or large volumes of cooking oil are in use. They are typically finished with a yellow label in line with BS EN 3 colour-coding conventions. If you are weighing up alternatives for kitchen environments, our guide on Wet Chemical Extinguisher vs Water Mist Extinguisher, Which is Right for You? explores another option worth considering for certain catering settings.

What is a Foam Extinguisher?

Foam extinguishers work by smothering a fire with a blanket of aqueous film-forming foam (AFFF) or synthetic foam, cutting off the oxygen supply and preventing flammable vapours from reaching the flame. They are effective against Class A fires involving solid combustible materials such as wood, paper, and textiles, and against Class B fires involving flammable liquids such as petrol, diesel, and paint. The foam also has a cooling effect, which helps prevent re-ignition once the fire has been suppressed. Most foam extinguishers carry a cream-coloured label, again in accordance with BS EN 3 identification standards.

Foam extinguishers are a popular general-purpose choice for offices, retail units, warehouses, hotel lobbies, and mixed-use commercial buildings where the likely fire risks span more than one fire class. They are not suitable for use on electrical equipment above 1,000 volts, on cooking oil fires, or on fires involving flammable metals. For a broader look at how foam extinguishers compare with other common options, the comparison between Water Extinguisher vs Foam Extinguisher, Which is Right for You? provides a useful reference point for buildings where liquid fire risks are not a primary concern.

Head-to-Head Comparison

Costs and specifications vary, so contact London City Fire for a site-specific assessment to ensure you select the right extinguisher type for your premises.

Which is Right for You?

If your premises includes a commercial kitchen, staff canteen with deep fat fryers, or any catering operation involving cooking oils, a wet chemical extinguisher is not simply a preference but a practical necessity. Using a foam or water extinguisher on a burning oil fire can cause a violent fireball, putting lives at serious risk. In these environments, the wet chemical extinguisher should be sited close to the cooking area, and staff should receive appropriate training on its correct use. Wet chemical extinguishers can also address Class A fire risks in the same space, which makes them a practical dual-purpose solution for kitchen environments.

For offices, retail units, warehouses, hospitality venues, and other commercial spaces where cooking oils are not a significant hazard, foam extinguishers offer solid broad-spectrum coverage at a typically lower unit cost. They handle the most common fire scenarios found in these environments, covering both solid combustible materials and flammable liquids, and are widely understood by building occupants. If electrical equipment is a concern, pairing a foam extinguisher with a CO2 extinguisher is a common approach. For a comparison of those options, the guide on CO2 Extinguisher vs Foam Extinguisher, Which is Right for You? covers that decision in detail.

In many buildings, particularly larger or mixed-use properties, the correct answer is not one or the other but a combination of both, positioned strategically to address different fire risks in different zones. The right approach will always depend on a thorough review of your specific fire risk profile, occupancy, and layout. A qualified fire safety professional can carry out a fire risk assessment and recommend the correct extinguisher provision under the requirements of the Regulatory Reform (Fire Safety) Order 2005. We strongly recommend seeking that professional advice before making a final decision.

Why Choose London City Fire?

London City Fire has been protecting commercial and residential properties across London for over 20 years. Our team of IFSM-registered assessors and certified engineers brings deep practical knowledge of fire safety compliance to every project, from single-site retail units to large residential blocks and mixed-use developments. We supply, install, and service both wet chemical and foam extinguishers in accordance with BS 5306-3:2017 and the wider requirements of UK fire safety legislation. Every recommendation we make is based on a genuine assessment of your premises, not a one-size-fits-all approach.

We work with landlords, managing agents, property developers, and facilities managers across the capital, providing clear documentation that supports audit readiness and ongoing compliance. Whether you need a straightforward extinguisher supply and service, or a broader fire safety review covering fire risk assessments, fire door inspections, and emergency lighting, London City Fire offers a comprehensive service under one roof. To discuss your extinguisher requirements or arrange a site visit, please contact us and a member of our team will be happy to help.

Frequently Asked Questions