Shoot, I don't know. With all the junk they put in concrete to stabilize it, fast-cure it, de-grongilize it, fordilnok it, etc., I'd hate to think of what might be vaporizing in the heat and flames and ending up in my chow.
I could be wrong, though. Been wrong before. Or so they say.
Terry, 230RN
ETA: Dammit, AJ DUal beat me to it with a similar comment, but about its degradation under heat.