Because asbestos is amazingly flame proof, it has been used since ancient times for everything from protective clothing to magic tricks. It's just a real shame that that stuff will kill ya. Horribly. Asbestos, which not many people know is actually a naturally occurring substance that is mined like coal, is made up of tiny fibres.
When these fibres are breathed in by humans, all kinds of bad things happen to the lungs. Asbestosis is a fibrosis of the lungs that turns them into honeycomb (but significantly less delicious), calcified plaques will also build up in the lungs which can impair breathing and all forms of asbestos are considered to be carcinogenic.