In Great Britain every extinguisher body is red, and the type is shown by a coloured band or panel on it. That convention exists because somebody reaching for an extinguisher in a hurry has no time to read a label, and using the wrong type on the wrong fire can make things dramatically worse. The bands are the fastest thing on the unit to read.
The colours and what they mean
Red band or all red: water, for ordinary combustibles such as paper, wood and textiles. Cream: foam, for the same plus flammable liquids. Blue: dry powder, which covers most classes but leaves a mess and should not be used in a confined occupied space. Black: carbon dioxide, for electrical risk and flammable liquids, leaving no residue. Yellow: wet chemical, for cooking oils and fats. Those five are what a UK building will normally carry.
Which fires to use water on, and which to avoid
Water is for class A, the ordinary solids. It must not be used on live electrical equipment, because water conducts, and it must not be used on burning oil or fat, because it will turn to steam instantly and throw burning liquid out of the pan. A chip pan fire is the classic case where reaching for water makes an injury out of an incident.
Why CO2 and wet chemical exist
Carbon dioxide displaces oxygen and leaves nothing behind, which is why it sits next to server racks and switchgear. It does not cool much, so a fire can reignite, and the horn gets extremely cold in use. Wet chemical turns burning cooking oil into a soapy layer that seals the surface, which is the only practical way to deal with a deep fat fryer and the reason a commercial kitchen carries one.
Dry powder, and why it is not the universal answer
Blue band powder puts out most things, which is why it looks like the safe choice. Inside an occupied building it removes visibility almost instantly, it is an inhalation hazard, and the residue is corrosive to electronics. It belongs outdoors, in plant rooms and on vehicles, and a building fitted out entirely with powder units usually reflects a purchase decision rather than a risk assessment.
Getting the right mix
The fire risk assessment decides, not a catalogue. The questions are what will burn here, who will be using the extinguisher, and what happens to the room if they do. A small office usually needs water or foam plus CO2 near the electrics; a kitchen adds wet chemical; a workshop may need powder outside the occupied area.
Questions people ask about fire extinguisher colours
What do the fire extinguisher colours mean in the UK?
Red is water, cream is foam, blue is dry powder, black is carbon dioxide and yellow is wet chemical. The body is red and the band shows the type.
Which fires should you use water extinguishers on?
Ordinary combustible solids such as paper, wood and textiles. Never on live electrical equipment or on burning cooking oil or fat.
What is a blue fire extinguisher used for?
Dry powder, which covers a wide range of fires but removes visibility and leaves a corrosive residue, so it is generally kept out of occupied interior spaces.
What is a CO2 extinguisher used for?
Electrical risk and flammable liquids. It leaves no residue, which is why it is sited near electrical equipment, and it does little cooling so reignition is possible.