Oh, and in response to all of this plastic crap:
Sealing your windows off with duct tape will not protect you. Your house is nowhere near airtight if the windows are sealed. Not even close. Think about a few things. First, your heater (if you don't live in Death Valley) has an exhaust pipe that feeds out of your house. Your house most likely sits on a foundation of some sort. It's not glued to it with a good seal, it just sits there. Bathroom fan exhausts, attic ventilation, insect holes (whether you see them or not), hell the place where your cable TV comes through the wall - these are all holes in your house. If you completely seal off your house to prevent chemical/biological weapons from leaking in, you will die anyway of asphyxiation (unless you live in a greenhouse with hundreds of plants, I guess) from the lack of oxygen (or the abundance of methane, in MazKid's case).