Foam fire extinguisher (Class B fire)
Applied to fuel fires as either an aspirated (mixed & expanded with air in a branch pipe) or non aspirated form to form a frothy blanket or seal over the fuel, preventing oxygen reaching it. Unlike powder, foam can be used to progressively extinguish fires without flashback. Ensures maximum corrosion resistance. The most common type in portable foam extinguishers is the AFFF (aqueous film forming foam) as shown in the picture.