Although the history of the modern canister type fire extinguisher dates back to the early 19th Century, Wet chemical fire extinguishers are very much the baby of the brood. British Standard 7937 was first published in the year 2000 and gives detailed specifications for portable fire extinguishers for use on cooking oil fires together with the establishment of a new Class F rating for extinguishers of this type.
Previous to the development of Class F fire extinguishers there was no satisfactory fire extinguisher alternative that could deal effectively with cooking fat fires which is a general term for any animal fats and vegetable oils like rapeseed, sunflower, palm and olive oil used in cooking.
Be aware that there are different types of “chemical” fire extinguisher that involve some kind of chemical reaction to suppress a fire, dry powders for example, but it is important to realise that only wet chemical extinguishers are effective on cooking fats and that no other type of extinguisher is approved for a cooking oil fire. The Class F extinguishers contain a “Wet Chemical”, typically potassium acetate, carbonate, or citrate that reacts with the fats through a process called saponification to form a soapy foam that smothers the fire. The chemical reaction is also endothermic i.e. it absorbs heat so lowering the surface temperature of the oil to prevent re-ignition.
Owners and operators of food processing and commercial catering and retail food outlets should be aware that you must provide a Class F fire extinguishers in any commercial premises having fryers containing more than three litres of cooking oil, as a legal requirement of the Regulatory Reform (Fire Safety) Order 2005. When it comes to buying a wet chemical extinguisher you should also ensure it conforms to British Standard BS7937-2000 and is CE marked if you want to satisfy a visiting Fire Safety Officer.
Class F fire extinguishers in common with other types of fire extinguisher have fire ratings according to their filled capacity to help you choose an extinguisher appropriate to the fire risk. The ratings on Class F extinguishers vary from 15F to 75F which as a rough guide you can translate in terms of the maximum number of litres of oil contained in any one fat fryer, e.g. a 75F rating equates to 75 litres of oil and requires a 6 litre wet chemical extinguisher to cover the risk.
Even more recently a multi-purpose Class ABF foam extinguisher has been introduced as a cost effective alternative for home and leisure use and in small mobile type food outlets. These use a foam additive solution rather than a potassium based wet chemical and can also be used on solid combustibles and petroleum liquid fires. It is horses for courses when it comes to making your choice but if your fire risk is primarily safeguarding cooking fires be aware that a typical 2 litre Wet Chemical is 60% more effective than the equivalent sized ABF extinguisher.