Air pressurized water

Although only effective on Class A fires, they have the advantages of being inexpensive to build and maintain, and leaving no special chemical residue when used.

[1] A standard APW extinguisher in the United States contains 9.5 litres (2.5 US gal) of water in a stainless steel tank.

The water is discharged by means of a 13 mm (1⁄2 in) hose, with a smooth-bore nozzle attached to the tip.

APW extinguishers are easily refilled by unscrewing the top and filling the cylinder with water about three-quarters of the way up.

Typically, the tip of the smooth-bore application nozzle is then cut off to allow the foam to properly expand.