Two kinds of products are used for firefighting: conventional dry chemical (BC) and multi-purpose dry chemical (ABC).
When the product is discharged on the flames, the compound released is combined with free radicals avoiding the combustion to carry on. Dry chemical brings thermal radiation shielding effect when the powder cloud is projected over the fire. In addition, it produces some kind of cooling because dry chemical absorbs heat (this effect is negligible).
Dry chemical ABC acts by suffocation. When it decomposes by heat, meta-phosphoric acid is generated all over the combustion surface and isolates the combustible from oxygen of air.