So a lot of people don’t know that there are two ways to say fire in Korean. The common way of saying “불” just refers to the flame or object of fire. So if you’re camping or cooking on the stove, 불 would be appropriate to call the flame you see burning.
However for 화재, it is used to convey the meaning of a disaster caused by a fire. You would see this term on the news a lot to refer to a building that has caught fire and probably has been destroyed.
불 can also be used to refer to electric lights/lamps.
불이 붙다 (bul-i but-da) means to catch fire.
불을 켜 주세요 (bul-eul kyeo ju-se-yo) means to turn on the light.
불을 꺼 주세요 (bul-eul kkeo ju-se-yo) means to turn off the light.