I'd urge you, my friend, to not use it, even when he does replace it.
If you do, read the instructions. People kill me with standing in front of the thing, and popping it open while it still running. The instructions clearly state to stay four feet from the thing when it on. Furthermore, when you open while it's still on a plethora of radiation comes out. You are supposed to wait a couple minutes after it's finished... Even typing this out sounds ridiculous, I don't know why people still use them. The thought of the end product that comes out, well, it's not food.