Fire Safety in Commercial Kitchens: Wet Chemical Extinguishers and Fire Blankets Explained

Why Commercial Kitchens Are a High Fire Risk

Commercial kitchens are one of the highest fire-risk environments found in any workplace. The combination of intense heat, large volumes of cooking oil, naked flames or high-power induction equipment, and busy working conditions creates conditions where fire can start quickly and escalate rapidly.

Cooking oils and animal fats are classified as Class F fires under UK and European fire classification standards. Class F fires are unique: cooking oil does not simply burn — it can reach its flash point at temperatures around 340°C without producing visible smoke, meaning a fryer can catch fire without obvious warning. Once ignited, burning oil releases enormous quantities of heat and can re-ignite after it appears to have been extinguished.

This behaviour makes Class F fires fundamentally different from other commercial fire risks, and it means that equipment appropriate for other areas of a building is often entirely wrong — or actively dangerous — in a kitchen environment.

Why Standard Extinguishers Are the Wrong Choice

It is essential that kitchen staff and responsible persons understand why conventional extinguisher types should never be used on a cooking oil fire:

• Water: Contact between water and burning oil causes an almost instantaneous and violent conversion to steam. The expanding steam hurls burning oil droplets outward as a fireball. A single litre of water applied to a burning chip pan can create a fireball several metres wide. This is one of the most dangerous mistakes possible in a kitchen fire.
• CO2: CO2 displaces oxygen and can temporarily suppress the flames, but it cools the oil only minimally. The oil remains above its flash point, and re-ignition as soon as the CO2 disperses is common. CO2 also creates significant blast pressure when discharged close to a fryer, which can scatter burning oil.
• Dry powder: Powder can briefly smother a Class F fire but does not cool the oil. Re-ignition is highly probable, and powder creates a dense cloud that severely impairs visibility in the kitchen, making evacuation and further fire-fighting more dangerous.
• Foam: Standard foam extinguishers are not rated for Class F fires. Foam contains water and applying it to a burning oil fire carries similar risks to water.

Wet Chemical Extinguishers: How They Work

Wet chemical extinguishers are specifically engineered for Class F fires. The agent used is a potassium-based solution — typically potassium acetate, potassium citrate, or potassium carbonate — that works through two simultaneous mechanisms:

1. Saponification: When the wet chemical contacts the burning oil, it reacts chemically to convert the surface layer of fat or oil into a thick, soapy foam. This foam forms a stable crust over the oil surface, cutting off oxygen and preventing re-ignition.
2. Cooling: The solution has a significant cooling effect, reducing the temperature of the oil below its flash point and preventing re-ignition once the crust forms.

The discharge is designed as a fine, gentle spray applied at a distance — this is critical. Direct high-pressure discharge onto burning oil, even with the right agent, can cause splashing. The long lance and low-velocity spray head on a wet chemical extinguisher is an integral part of how it works safely.

Wet chemical extinguishers are certified to BS EN 3 and rated using an F-rating system: a unit rated F5 is tested against a 5-litre test fire (approximately equivalent to a 5-litre fryer), while an F75 rating indicates the unit can handle a 75-litre fryer capacity.

How Many Wet Chemical Extinguishers Do You Need?

The number and rating of wet chemical extinguishers required is determined by the fire risk assessment. BS 5306-8 provides guidance, and the RRO 2005 requires the responsible person’s assessment to specify appropriate provision where deep-fat fryers exceed 3 litres of capacity — at which point a wet chemical extinguisher becomes the standard expectation.

As a general sizing guide:

• A 2-litre wet chemical extinguisher is typically rated to cover approximately 34 litres of oil capacity (e.g. a single medium-capacity fryer)
• A 6-litre wet chemical extinguisher is typically rated to cover approximately 75 litres of oil capacity (e.g. a commercial bank of fryers)

The fryer manufacturer’s maximum oil capacity and the F-rating of the extinguisher must be matched. Where a kitchen operates multiple fryers or a fryer with very high oil volume, multiple extinguishers or a higher-rated unit may be required. Your fire risk assessment should specify this clearly.

Fire Blankets in Commercial Kitchens

A fire blanket is a sheet of fire-resistant material used to smother small fires by cutting off the oxygen supply. In a commercial kitchen, fire blankets serve two purposes:

• Smothering a small pan fire at source before it escalates (where the blanket can be placed safely without risk to the user)
• Wrapping around a person whose clothing has caught fire

Kitchen fire blankets must comply with BS EN 1869:2019 and should be a minimum of 1.0m x 1.0m for kitchen use — smaller blankets intended for domestic use are not suitable in a commercial environment. A 1.2m x 1.2m blanket is often recommended for additional margin.

The key rule with a fire blanket on a pan fire is to place, not throw: lay the blanket gently over the pan to avoid disturbing the burning oil, then leave it in place until the pan has cooled fully. Removing a fire blanket too early will allow re-ignition.

Positioning and Placement

The positioning of kitchen firefighting equipment requires careful thought:

• Extinguishers and fire blankets should be within reach of the cooking area but not mounted directly above or beside cooking equipment, where they could be obscured by steam, grease, or heat, or become inaccessible if a fire breaks out at the cooking station
• Positioning should allow staff to access the equipment without having to pass through the fire or its immediate heat zone
• Fire blankets should be wall-mounted in a prominent, easily identifiable location, ideally at eye height, and clearly labelled
• Extinguishers should be positioned on the exit route from the kitchen, allowing staff to discharge them while retreating rather than having to advance into the fire

Inspection and Servicing

Wet chemical extinguishers must receive an annual service by a competent person in accordance with BS 5306-3. At the five-year extended service interval, the unit must be fully discharged, internally inspected, and recharged with fresh agent. Given the caustic nature of the wet chemical agent, this work must only be carried out by a trained engineer.

Monthly visual checks should confirm that the pressure gauge is in the green zone, the safety pin and seal are intact, and the unit is undamaged and correctly positioned.

Fire blankets should be inspected monthly: check that the blanket is fully enclosed in its quick-release container, the container is undamaged, and the blanket has not been deployed or disturbed. Once a fire blanket has been used, it must be replaced — it cannot be refolded and reused. The same applies if the blanket is found to be damaged or the packaging has been opened.

Browse Cocus’s range of wet chemical extinguishers, fire blankets, and general fire safety equipment at our fire safety equipment collection, or view our full fire extinguishers range for all types and sizes. All equipment supplied meets the relevant British and European standards for commercial kitchen use.