Foam fire extinguishers, easily identified by their cream-coloured label, are one of the most common and versatile extinguishers found in UK workplaces. They are highly effective at tackling fires involving solid materials and flammable liquids. However, this versatility can create a dangerous sense of overconfidence. Using a foam extinguisher on the wrong type of fire can be ineffective at best, and at worst, it can be catastrophic, leading to electrocution or a violent fire explosion.
Understanding what a foam extinguisher cannot do is just as important as knowing what it can do. At Fire Response UK, we believe that correct fire safety knowledge is essential to prevent a bad situation from becoming a tragedy. This guide details exactly which materials and fire types you must never use a foam extinguisher on.
The Quick Answer
A foam extinguisher should never be used on live electrical equipment as the foam is water-based and a potent conductor of electricity, creating a high risk of fatal electric shock. It is also extremely dangerous to use on Class F cooking fat fires (e.g., a chip pan), as the water content will cause a violent explosion of burning oil, spreading the fire rapidly. It is also ineffective on Class C flammable gas fires.
Understanding Your Foam Extinguisher
What is a Foam (AFFF) Extinguisher?
The cream-labelled extinguisher contains Aqueous Film-Forming Foam (AFFF). When discharged, it works on two levels: first, the water content in the foam cools the fire, and second, the foam itself spreads over the surface of a liquid fire, forming a blanket. This blanket smothers the fire, cutting off its oxygen supply and sealing in flammable vapours to prevent re-ignition.
What Foam Extinguishers are Designed For
Foam extinguishers are excellent for Class A fires. These involve solid combustible materials like wood, paper, cardboard, and textiles.
They are the primary and most effective extinguishers for Class B fires. These involve flammable liquids such as petrol, diesel, paint, and solvents. The foam blanket is perfect for smothering these types of fires.
The Critical Dangers: Where Not to Use Foam
Live Electrical Equipment
This is the most significant danger associated with foam extinguishers. Because the foam is water-based, it is an excellent conductor of electricity. Spraying it onto live electrical equipment, such as computers, servers, machinery, or fuse boxes, will almost certainly cause a severe or fatal electric shock to the operator. It can also cause short-circuits, which may damage equipment and even start more fires. The correct extinguisher for electrical fires is always CO2 (black label). For more information on electrical safety, resources from Electrical Safety First are invaluable.
Class F: Cooking Oil and Fat Fires
This is the second major danger. Using a foam extinguisher on a burning deep-fat fryer or a pan of oil is a catastrophic mistake. The water in the foam instantly sinks to the bottom of the hot oil and flash-boils, erupting in an explosion. This explosion sends a fireball of burning oil into the air, spreading the fire across the kitchen and causing severe burns. The only extinguisher safe for Class F fires is a Wet Chemical (yellow label) extinguisher, as clearly advised by the London Fire Brigade.
Class C: Flammable Gas Fires
Foam is not designed for fires involving flammable gases like propane, methane, or butane. A foam extinguisher cannot “smother” a gas fire, as the gas is often under pressure and will simply push through the foam blanket. The priority for a gas fire is to turn off the gas supply at the source, if it is safe to do so. The specialist extinguisher for gas fires is Dry Powder (blue label).
Legal and Safety Implications
Your Responsibilities Under the Law
The Regulatory Reform (Fire Safety) Order 2005 (FSO) is the law governing fire safety in non-domestic premises. It states that the designated ‘Responsible Person’ must ensure that “appropriate fire-fighting equipment” is provided. Providing a foam extinguisher in a kitchen without a specific Wet Chemical extinguisher could be seen as failing this duty. Your provision of extinguishers must be guided by a thorough fire risk assessment.
The Importance of Fire Safety Training
This is precisely why professional fire safety training is a legal requirement. It is not enough to simply have extinguishers; your staff must be trained on which one to use, how to use it, and, critically, which ones to avoid for the specific risks in their environment. The National Fire Chiefs Council (NFCC) reinforces that a trained and aware workforce is a key part of any successful fire safety strategy.
Conclusion
Foam extinguishers are reliable and effective tools for Class A and Class B fires. However, their limitations are severe and non-negotiable. Always remember the two golden rules: never use foam on electrical fires due to the risk of electrocution, and never use foam on cooking fat fires due to the risk of explosion. Always check the label, and if in any doubt, get out, stay out, and call 999.
