Influences of surface material on the fire behaviors of two-layer combustibles under autoignition conditions

Upholstered furniture usually has a typical two-layer structure with an ultra-thin surface layer. The surface layer can significantly affect the overall fire behaviors of the upholstered furniture. A series of experiments were carried out to investigate the fire behaviors of six two-layer combustibles based on a cone calorimeter. An empirical model was proposed to predict the heat release rate of two-layer combustibles. The predictions of the model are fitting quite well with experimental data. It was also known that the ignition time of the two-layer combustibles is controlled by those surface fabric materials. The shrink rate and the properties of the residues of those surface fabrics show obvious influences on the combustion processes. Comparing to those uncovered natural latex foam samples, it was known that the peak heat release rate decreases about 26.9% and 11.7% for the samples with natural and synthetic species covers, respectively; and the duration of the burning process increases about 41.7% and 15.4%, respectively. A combustion factor was proposed and a heat transfer model was developed to reflect the contribution of the surface and the second layers to the combustion processes. The combustion factor is within 0.7-0.9 for the six types of surface fabrics.