They should be fine. The only thing I think that might effect them is prolonged exposure to uv rays or high heat. I am only guessing about the uv thing, and heat should not be a problem in the winter, besides I am talking about open flame heat not a hot summer day kind of stuff.

One more advantage to carbons getting lost in the yard. You can run over them with you rider mower and as long as the blades don't catch them they will be fine. Try driving over an aluminum, or stepping on one in the grass for that matter, and see what happens.

Paul