These are suitable for fighting burning solids, liquids and gases (Class A, B and C fires). They work by the powder forming a crust which smothers the fire and stops it from spreading. Disadvantages are that the powder does not soak into materials and does not have an effective cooling effect on the fire, which can result in the fire re-igniting. The powder is hazardous if inhaled, so they should be used in well-ventilated areas and are not suitable for offices and domestic premises. The powder damages soft furnishings, machinery, etc, and needs a lot of cleaning up after use.