Wet chemical fire extinguishers are the new kids on the fire extinguisher scene, developed specifically for use on deep fat cooking fires. The first such extinguisher on the market was the Chubb FryFighter, and its appearance gave rise to a new fire class, Class F and a new British Standard, BS 7937: 2000.
Wet chemical fire extinguishers are red with a yellow panel above the operating instructions.
How Wet Chemical Fire Extinguishers Work
Normal fire extinguishers are worse than useless in a deep fat fire, since they cannot cool the oil and cause hot oil to splash up on contact with the extinguisher’s agent. Fat can burn at 340 degrees, and an average fat fryer holds up to 75 litres of oil.
Unfortunately, until the invention of the wet chemical extinguisher, many commercial kitchens were supplied with foam or powder units with the occupants falsely thinking these could be used on the fat fryers. The cost can also be high compared to other extinguishers but the risks are much higher in the kitchen and, if bought online at a discounted, the costs are not high these days.
The active ingredient in a wet chemical fire extinguisher is potassium acetate, often with added potassium citrate or potassium bicarbonate. When operated, a wet chemical extinguisher creates a fine mist, which cools the flames and prevents splashing.
The potassium salts then have a saponification effect on the oil’s surface, creating a thick, slippery foam layer that smothers the fat and prevents re-ignition. The chemical foam will also cool the fat over a prolonged period of time.
Unlike other extinguishers, the idea is to completely empty the contents into the fat fryer to enable the cooling process to begin.
A point to note is that the contents can be corrosive so the quality extinguishers are made from stainless steel. Beware of the cheap Middle-Eastern imports made from mild steel as the lifespan will not be as good and the linings could be affected.
Saponification: Here’s the Science
Saponification is the same process used to create soap from fats and oils as a result of a reaction with a metallic alkali, or base. The base acts on the oil to convert it into hydrolyzed acid and alcohol. Essentially, a wet chemical fire extinguisher converts the surface of the cooking oil or fat into a non-combustable soap.
An added benefit is that the soap-creation process is endothermic, meaning it absorbs heat energy from the oil, cooling the oil down in the process.
Using a Wet Chemical Fire Extinguisher
Like other specialist fire extinguishers, the wet chemical fire extinguisher has a long lance, allowing the user to stand well back from the fire and to spray the agent gently and evenly over the fire’s surface. As with all specialist extinguishers, full training should be given in the proper and effective use of this extinguisher, a common sight in commercial kitchens and food manufacturing environments.
Just Fats, Please
Wet chemical fire extinguishers only work with animal fats and vegetable oils, so they cannot be used on Class B fires involving flammable liquids such as petrol or diesel.
They have usually been tested to a 13A Class A rating but should not be specified for anything other than a kitchen.
Wet Chemical Fire Extinguishers and Electricity
Wet chemical fire extinguishers are not designed for use on electrical equipment, but in the modern kitchen environment, it is hard to avoid electricity cables. Hence, the lance of a standard wet chemical fire extinguisher is non-conductive, and passes the BSi 35kv conductivity test.
Other Fire Extinguishers in the Commercial Kitchen
Wet chemical fire extinguishers have a very specific function, and are not suitable for other fire types except Class A fires if no other extinguisher is available.
Most Fire Risk Assessments would recommend that wet chemical extinguishers are kept in proximity with other fire safety items such as a CO2 extinguisher for electrical items, and a substantial fire blanket such as a 1.8m x 1.2m size. Fire blankets should be used to smother small pan fires, not to deal with commercial fryer fires.
A small fire blanket is a useful fire safety device for any kitchen, commercial or domestic. Simple to use, yet effective, it should be used to smother a fire and then LEFT ALONE for a considerable length of time to ensure the fire is completely extinguished. If in doubt, smother, get out, stay out and call the Fire Brigade.