Dry powder covers more fire classes than anything else in the range, which is why it is sold as the general purpose answer and why it turns up in so many vans and garages. It is also the extinguisher most fire safety guidance discourages inside an occupied building, for reasons that have nothing to do with whether it puts the fire out.
What it covers
General purpose ABC powder is rated for class A solids, class B flammable liquids and class C flammable gases, and is generally safe to use near live electrical equipment. That breadth is real and it is why powder is the standard choice for vehicles, forecourts, plant and external locations where one extinguisher has to answer several risks at once.
Why it is discouraged indoors
A discharged powder extinguisher fills the room with a dense cloud that destroys visibility instantly, which matters when people are trying to leave, and it is an inhalation irritant. The residue is corrosive to electronics and gets into everything, so the clean up after a small fire can cost more than the fire did. Guidance for occupied premises generally steers towards water, foam and carbon dioxide indoors and reserves powder for outdoor and vehicle use.
Class C and gas fires
Powder is the only common portable agent rated for flammable gases, but putting out a gas fire without stopping the gas supply creates an explosive atmosphere that will find an ignition source. The rule is to isolate the supply first, and only then deal with fire. An extinguisher rated class C is not permission to extinguish a gas fire and walk away.
Metal fires are different powder
Class D metal fires need a specialist powder designed for the specific metal, applied gently with an applicator rather than jetted. General purpose ABC powder is not class D rated and using it on burning metal can make matters considerably worse. If a site holds magnesium, sodium or lithium metal, the class D provision is a separate decision from the general extinguishers.
Fire extinguisher powder is not one agent
Nearly. Most blue panel units contain ABC powder, a monoammonium phosphate based agent rated for solids, liquids and gases, and that is what a general purpose powder unit means. Two specialist powders exist and are not interchangeable with it: a BC powder for liquid and gas risks only, and a class D powder for burning metals, which is a specific purchase for a specific process. If a unit is on site for a metal risk, its label will say so and a general ABC unit will make that fire worse rather than better.
Where dry powder extinguishers belong, and where not
Outside, and in places where a discharge cannot blind anybody: forecourts, plant and boiler houses, external tanks, vehicles, and some workshops. Not in offices, corridors, kitchens or any small enclosed space, because a discharge fills the air with fine dust in seconds, takes the visibility with it and gets into anything electronic. That is the whole reason the office standard moved to foam plus carbon dioxide. If powder units are inside a building, the assessment should say which risk put them there.
A blue label fire extinguisher is powder, and a blue coded fire extinguisher means the same thing
The colour code is the panel on the red body, and blue is dry powder in every case. Two words people mix up: label and code mean the same panel, and it carries the agent's colour, the ratings and the service date on the same sticker. What the blue panel does not tell you is WHICH powder, since a general ABC unit, a BC unit for liquids and gases and a class D unit for metal fires all wear blue. That is written in the text beside the panel, and on a site with a metal risk it is the line that matters most.
A fire extinguisher ABC powder unit is the general purpose one, and the least suitable indoors
It is the most widely rated and the least suitable indoors, which is the trade off. ABC powder handles ordinary combustibles, flammable liquids and gases, which is genuinely useful on a forecourt, in a plant room, on external tanks and in a vehicle. Inside a building the discharge fills the air with fine dust in seconds, taking the visibility and getting into electronics, so the escape route you were standing in disappears. That is why the office standard is foam plus carbon dioxide, and why an ABC unit indoors should be there because the assessment identified a specific risk.
Questions people ask about dry powder fire extinguishers
What colour is a dry powder extinguisher?
Blue. A red body with a blue band or panel identifies dry powder contents.
Why is powder not recommended indoors?
A discharge destroys visibility in the room people are trying to leave, irritates the airway, and leaves a corrosive residue that is expensive to clean up. Water, foam and carbon dioxide are preferred inside occupied premises.
Is ABC powder suitable for metal fires?
No. Class D metal fires need a specialist powder and an applicator. General purpose ABC powder is not rated for them and can make a metal fire worse.
What colour panel indicates a dry powder extinguisher?
A blue panel or band on a red body. The body of every portable extinguisher sold in the UK to the current standard is red, and a coloured panel of limited area identifies the agent inside: blue for dry powder, cream for foam, black for carbon dioxide, canary yellow for wet chemical, and a plain red body with no panel for water. That is the whole code, and reading it is not the same as choosing a unit, because the blue panel tells you the extinguisher is powder and says nothing about whether powder is appropriate in the room you are standing in.
Is an ABC powder fire extinguisher the right general purpose unit?
It is the most capable on paper and the least suitable indoors, which is why it has largely left offices. ABC powder handles solids, liquids and gases, which is genuinely useful on a forecourt, in a boiler house or on a vehicle. Discharged in a room it fills the air with a fine dust that destroys visibility in seconds, gets into electronics and takes a specialist clean to remove, so the escape route you were standing in disappears. Indoors the modern answer is foam plus carbon dioxide, with powder kept for external and specific plant risks.
Is a powder extinguisher the right fire extinguisher car owners should carry?
For a vehicle, yes, and small ABC powder units are what most motor factors sell for the purpose, because a car fire can involve fuel, plastics and electrics at once and powder covers all three. Two honest caveats. Powder discharged in a confined space destroys visibility, which matters more in a garage than at the roadside, and a unit rolling loose in a boot for five years may not work, so it needs a mounting bracket and a look at the gauge when the car is serviced. And the priority in a vehicle fire is getting everybody away from it, not saving the car.