Fireproof material (8)
I believe the answer is:
asbestos
'fireproof material' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for asbestos that I've seen before include "Firewall material" , "Fire-resistant material dangerous to health" , "Fireproof material, dangerous to health" , "'Fireproof substance, dangerous to health (8)'" , "Fire defence" .)