Source: https://business.libertymutual.com/

What is aqueous film-forming foam?
Aqueous film-forming foam (AFFF) is a type of firefighting foam that is used to extinguish flammable liquid fires (Class B fires). AFFF has been used since the  1960s and is considered the gold standard to suppress Class B fires quickly and reliably.

AFFF has received scrutiny because it is manufactured with fluorosurfactants which may include per- and polyfluoroalkyl substances (PFAS), including  perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), which are known carcinogens. PFAS (also known as “forever chemicals”) do not break  down in the environment, can move through soils and contaminate drinking water sources, and bioaccumulate in fish and wildlife. PFAS exposure in humans  may affect reproduction, thyroid function, and the immune system, and injure the liver. When AFFF is used, discharged, or released to the environment,
containment and cleanup may be required to prevent adverse health or environmental impacts. Long-term exposure to AFFF is also a concern, particularly for  firefighters. Read more.