Fire Hazard of Fire-Resistant Cables Below the Ignition Point

I have previously proposed the introduction of so-called hazard classes, which follow the real-life classification of cables exposed to different thermal stresses. My experience has shown that the causes of fires, i.e. temperatures, can be classified into three ranges, which also cover the mechanism of action on plastics, i.e. the type of damage. Accordingly, cables should be tested in three temperature ranges according to the high operating temperatures that can be expected in the application environment. Temperatures below the flash point can be ensured by radiant heat rather than flame. The heat load is usually expressed in literature in terms of heat flux (W/m2) rather than temperature. So, following the professional protocol, we built a radiant source and measured the heat load on the cables with a Gardon pyrometer. The polymer sheaths of the cables showed typical degradation characteristics (fouling, smoke formation, sheath rupture) well below the ignition point (range 150–220 °C).