Dry Powder Fire Extinguishers

For classes B and C, a dry powder is used. There are two main dry powder chemistries in use:

BC powder is either sodium bicarbonate or potassium bicarbonate , finely powdered and propelled by carbon dioxide or nitrogen. Similarly to almost all extinguishing agents the powders acts as a thermal ballast making the flames to cool for the chemical reactions to continue. Some powders also provide a minor chemical inhibition, although this effect is relatively weak. These powders thus provide rapid knockdown of flame fronts, but may not keep the fire suppressed. Consequently, they are often used in conjunction with foam for attacking large class B fires. BC extinguishers are often kept in small vehicles since they provide good knockdown of a rapidly flaring class B fire, from a small package.