Fires are classified by the proper extinguishing agent.  While water is used on Class A fires, using water on a Class B fire (such as a grease fire) is extremely dangerous.[3][5] This is because burning grease is hotter than the boiling point of water (212 degrees Fahrenheit or 100 degrees Celsius); when water is placed on grease, it creates steam which expands rapidly and splatters, causing burns and spreading the fire).[3] Because of this, Class A fire extinguishers use water, while Class B fire extinguishers use dry chemicals (foam or powder),[5] such as aqueous film-forming foam, multi-purpose dry chemicals such as ammonium phosphate, and halogenated agents (such as Halon 1301 and Halon 1211).[6]  or highly pressurized carbon dioxide.[5] Some fire extinguishers contain chemicals designed to fight both Class A and Class B fires.[6]