Dry powder is the most capable portable agent on paper and the most restricted in practice. Its panel is blue. The common type is described as ABC because it is rated for class A solids, class B liquids and class C gases, and it is additionally marked as safe for use near live electrical equipment. That combination is why it dominates vehicle and forecourt provision and why it is largely absent from offices.
What the powder does
The powder interrupts the chemical chain reaction in the flame rather than cooling the fuel. That is why it knocks a fire down so quickly and why re-ignition is a real risk: the flame stops before the fuel has cooled, so a deep seated class A fire can come back several minutes later in a room that looks resolved.
Why it is refused in occupied interiors
A discharge fills the space with a dense cloud that removes visibility almost instantly, which is a direct problem for escape. The residue is mildly corrosive, gets into every seam of every machine in the room and is very difficult to clean out of soft furnishings. Guidance for occupied premises therefore steers powder outdoors or into plant rooms.
Where it is the right answer
Vehicles, forecourts, external plant, loading areas, and anywhere a gas risk exists and there is no realistic alternative. The open air removes the visibility objection, and the equipment in those places is usually robust enough that the residue is an inconvenience rather than a loss.
Sizes and the monobloc question
Powder units come in very small sizes that are sold for cars and caravans. A small unit has a short discharge time and a small rated capability, and buying one because it is cheap and mounting it in a workshop is how a building ends up with a provision that looks complete on a plan and cannot do anything.
Questions people ask about dry powder extinguisher colour panel
What is an abc powder extinguisher rated for?
Class A, class B and class C, with an electrical marking. The letters on the label are the rating; a unit sold as ABC that does not carry all three on its own label is not one.
Is a blue extinguisher always powder?
In the current standard a blue band means dry powder. On a pre-standard all-over blue body it also means powder, so this is one of the codes that did not change meaning.
Why is there a class D powder as well?
Metal fires need a different powder formulated for the specific metal and applied gently with a scoop or a low velocity applicator. It is a specialist provision, not a general one, and it is not interchangeable with ABC.