Co-authored by Jeffrey Karp and Edward Mahaffey
Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are found in firefighting foam used by the military since the 1970’s for training exercises and to extinguish liquid and gas fires. These compounds are part of a larger class of toxic chlorinated chemicals called per- and polyfluoroalkyl substances (PFAS). Similarly, airports and municipal fire departments have used the aqueous film forming foam (AFFF) for decades to extinguish fires caused by flammable liquids.
Firefighting foams are divided mainly into two classes. Class A foams are used to fight wildfires and structural fires. Class B foams are used to extinguish fires caused by flammable liquids. While not all Class B fire extinguishing agents contain PFAS, all AFFF does, and AFFF has special characteristics that make it difficult to find adequate replacements. When mixed with water, AFFF produces an aqueous spreading film that extinguishes burning hydrocarbon fuel and prevents reignition by cutting off oxygen from the fuel source.