Firefighting foam is a foam used for fire suppression for Class B fire or for aviation industries. Its role is to cool the fire and to coat the fuel, preventing its contact with oxygen, resulting in extinguishing the fire through suffocation.
There are many types of foam – low expansion form and high expansion foam. Low expansion foam can be of premixed type stored in a tank for immediate use during emergency. Or foam concentrates can be stored in a tank and be introduced through induction method through a water jet during firefighting.
Low-expansion foams such as AFFF, have an expansion rate less than 20 times are low-viscosity, mobile, and can quickly cover large areas. These are best used for liquid fire and for aircraft firefighting purpose.
Medium-expansion foams have an expansion ratio of 20–100.
High-expansion foams have an expansion ratio over 200–1000 and are suitable for enclosed spaces such as hangars, where quick filling is needed. Or extinguish a basement fire. High-expansion form need to be generated with a fan and a ductwork and could fill up a room.
Alcohol-resistant foams contain a polymer that forms a protective layer between the burning surface and the foam, preventing foam breakdown by alcohols in the burning fuel. Alcohol-resistant foams are used in fighting fires of fuels.