Almost burnt the house down

I hate how forgful I am. Almost burnt the house down. I put a plastic plate with bacon on it into the oven this morning to keep house flies off it. We heat the oven up to 425 this evening for garlic bread and when the oven alerts that it's at 425, that's when I open the oven to see the melted plate. Had to clean all that melted plastic off the racks and the bottom of the oven.