Three ceiling materials from Zhongtong Bus, China, showed significant heat release within a minute at heat flux 25 kW/m2. The three materials consisted of a PVC covering with backing materials (1) polyethylene + polypropylene, (2) non-woven fibre + plywood and (3) rigid polyurethane foam. Heat release rate was highest for the backing material (1), but the PVCs in the materials also had different fire behaviours significantly influencing overall fire reaction. The authors note that ceiling materials can contribute to spread of fire through the whole bus, and that fire performance of both surface and backing materials are important.
3Pyrolysis characters and fire behavior of bus ceiling materials”, J. Wang et al., Journal of Thermal Analysis and Calorimetry 2020 https://doi.org/10.1007/s10973-020-10171-6
Burning bus picture: Adrian Beard