Effect of the substrate on the results of the fire tests of thin layers of floor, wall, and ceiling coverings

In the fire tests of many building materials a thin sheet of the sample is mounted on a thicker substrate. The thermal properties of the substrate could have a considerable effect on the heating of a thin slab. This changes the ignition time, burning rate and other measured quantities, and could influence the conclusions from the fire test. Results from a simple linearized heat conduction model are reviewed and used to delineate regions in terms of Fourier and Biot numbers where that effect should be considered while designing fire tests for thin samples. The effective heat transfer coefficient is determined by an asymptotic approach devised here. Experimental evidence supports this linearized theory for steel plates on wooden substrates. CEN/TC127/WG1 has proposed standard substrates for the fire tests of surface products. These substrates should represent and cover well common usage. These theoretical and experimental results are used to make a new proposal for standard substrates for CEN/TC127/WG1.