Base on operation of metal machining machine, we found that an automatic fire extinguisher is an undetachable part of each metal machining machine. In term of machining, cutting blade (or drill tip) will make electric spark due to friction between blade and workpiece’s surface. Moreover, workpiece’s surface will also become hotter by operation of cutting blade. Cutting blade (or drill tip) is cooled by a coolant. Coolant and metal chip will fall into the collecting tank of machining machine. If metal chip is not remove frequently (as recommended by coolant’s manufacturer) and coolant is not replace periodically. Characteristics of coolant would be changed and ignited by electric spark.