Being fat doesn ' t mean being unhealthy just like being slim doesn ' t mean being unhealthy . Great double standards . Is awful to discriminate against some but perfectly fine with others . <| sep |> AFFF is made from water the A is for Aqueous , although I don ' t know to what degree that comes into play with the other chemicals involved and a quick google was not all that effective for me . Lots of firefighting manuals and such . That said , AFFF is for mainly class B fires , meaning liquids that will just spread if you spray water on them . Magnesium is a Class D . Sadly you ' re a little late to the party so the real experts probably won ' t chime in here . My training was more focused on the what to do rather than why to do it not completely but it was just training and not chemistry class and also took place 10 years ago with minimal refreshing because I was in a job eventually that involved pretty much no time on a ship .