The charring ability of polyethylene polymers was investigated also by Frache et al . They showed that the induction period preceding the ignition is the controlling factor for the fire protection of polymers. A non-pyrolyzable carbonaceous layer on the material surface could prevent the development of a sustained flame during this induction stage. Fire usually occurs when volatiles are formed in enough concentration and exceeds the self-ignition temperature. It was shown that thermo-oxidative dehydrogenation process competes with the thermal decomposition of polymers to produce volatiles. It was mentioned shown again that the presence of oxygen in the HFFR formulations interacts with the polymer chain and forms C-radicals. These radicals, in turn, results either into crosslinking or the formation of polycyclic structures resulting in char formation on the surface. The rate of char formation was reported for four different PE samples with high and low density in this study.