Ignition risk analysis of common building material cylindrical PMMA exposed to an external irradiation with in-depth absorption

Abstract

The Poly methyl methacrylate (PMMA) material with a cylindrical shape are widely used for the building components. Under external irradiation, it may be ignited by a pilot ignition. Previous studies focused more on a flat surface sample, while for a cylindrical configuration, the heat flux distribution, solid-phase temperature profile and ignition time establishes different aspects induced by the cylinder curvature. Therefore, this study investigated the ignition behaviors of the cylindrical PMMA samples with various radius exposed to an external irradiation by experimental and numerical methods. Firstly, decomposition gases of PMMA samples under the irradiation were observed to evidently accumulate on the top surface of the cylinders, after which an incipient ignition occurred in conjunction with blue flames, quickly followed by sustained ignition. With varied cylinder radius, the characteristic parameters of solid-phase temperature profile and thermal penetration depth changed, which are dependent upon sample radius. While for thermal-thick slabs, these parameters have no changes to be independent of the sample thickness. Furthermore, two absorption heat flux coefficients were introduced to analyze the in-depth heat absorption by considering the effects of angle and sample radius. Finally, the critical mass flux and ignition time were given. The cylindrical samples were easier to be ignited than slab samples. With smaller sample radius, the ignition time is established to be shorter. With increasing sample radius, the critical mass flux is lower. This investigation will provide a tractable way to obtain a comprehensive evaluation of fire risk of the commonly used cylindrical components in construction and buildings.