Infrared radiation. While thin sheet metal may not be able to stop a propagating flame for long, it will do a damn fine job of blocking radiating heat from melting the fuel lines...

Try taking a thinnest piece of sheet metal and putting it in front of your face while you stand next to a campfire and you'll see what I mean. [/b]


So in essence, your saying two layers of sheet metal or other materials are what they want for addition safety? Why would they want to use a material such as plastic which would only contribute as an additional fuel for the fire?