Ammonium Phosphate??? Isn’t that fertilizer? It’s monoammonium phospate in an ABC Fire extinguisher and nothing gets activated by water Yes, it would make a mess but better to have a mess then a burned up truck. ABC units are for class A B and C fires which are A common combustibles like wood paper etc. B is flammable liquids and C energized electrical, you have all that on a truck. So yes better to have one then not.