The temperature that butter ignites is around 300 F for regular butter and 400 F for clarified butter, which means that butter can catch fire more easily than some refined oils.
Butter is considered a grease fire when the butter catches fire.
Butter acts like a cooking oil, fat or grease when heated and so butter can indeed cause a grease fire if the butter is overheated.
When the butter is overheated, the milk solids in the butter burn and potentially ignite the fat, which require the same careful smothering methods of a normal grease fire, like using a lid or blanket.
Never try to put out a grease fire including a fire from butter with water as it can and will make the fire spread farther.
Butter has a lower smoke point than most grease, which is around 300 F for butter and 400 F for clarified butter, which means that butter can catch fire more easily than some refined oils.
Butter is primarily made of fat and fats and oils ignite when they reach their auto ignition temperature.
Unclarified butter also contains milk solids that burn at a lower temperature, which is around 250 F, which also contributes to the ignition.
Butter also contains water, which, when heated rapidly in a very hot pan can also cause sputtering and steam which indicates that the butter is getting dangerously hot.
To prevent butter and grease fires never leave the butter or grease unattended when cooking and remain with the food that is cooking.
If the butter or grease catches fire, turn off the heat or stove immediately and slide a metal lid, baking sheet or fire blanket over the pan to cut off the oxygen.
But never use water on a butter or grease fire or oil fire as the water makes the grease fire, oil fire or butter fire explode and spread.
For small grease fires, small oil fires or small butter fires, a large amount of baking soda can help, but not flour.