ABC dry powder extinguishers

ABC dry powder is mono-ammonium phosphate, and it works on Class A solids, Class B flammable liquids and Class C gases. That range is why it is the default extinguisher in a corridor, a society lobby, a shop or a workshop: whoever picks it up does not have to identify the fire class first, which is a realistic thing to design around.

It is not the right unit everywhere. Powder is messy and mildly conductive when damp, so a server room or a switchboard gets CO₂ or clean agent instead, and a commercial kitchen gets wet chemical. Placement, unit size and the mix of types across a floor come out of a survey against the risks on it — which is what the fire officer is checking when he walks the building.

Supply is the small part of this. The unit has to be mounted at the right height on the escape route, signed so it can be found, logged, checked at the interval, refilled after any use and pressure-tested on its cycle. We do that under an annual contract, with a service record per unit, because an extinguisher nobody has looked at for four years is a compliance problem rather than a fire precaution.