Due to amount of chloride PVC (57%) (There is a composition of chlorine in the chain ring or in each monomer molecule) this substance with plastic alloy is in fact very difficult to burn.  Chlorine itself prevents the burn. This characteristic of PVC provided one substance preventing another fire.

With BK IV protection against fire and RK2 classification of smoking and by adding antimony tri oxide BK V and RK I can be produced very easily.