Laboratory Investigation of Flammability of Two Decking Slabs Used in the Wildland–Urban Interface ^†

During a wildfire, combustible exterior building materials, like decking assemblies, may be ignited and cause severe damage or total loss of a dwelling [1]. Therefore, in high fire risk areas, such as Wildland–Urban Interface (WUI), the flammability studies of exterior materials are a major issue in order to reduce construction vulnerabilities. Given these findings, we propose a study at material and product scales of the flammability of two kinds of decking slabs, made of wood and thermoplastic material by focusing on radiant exposure.

At material scale, the two slabs were cut in order to obtain an exposed surface of 36 cm². The samples were placed under a calorimeter cone and were exposed to heat fluxes ranging from 8 to 50 kW/m². Ignitability, combustibility and fire performance were analysed with the critical heat flux, ignition time, ignition temperature, different phases of combustion, heat release rate (HRR) and smoke production. The results demonstrated a greater ignitability of wooden slabs compared to thermoplastic ones. However, the latter are more combustible and emit more smoke.

At product scale, the whole slabs were used (40 × 40 cm²). A 500 × 500 mm² radiant panel modelled an impacting flame front. For the wooden slabs, two configurations were studied: the first with the slat of the slabs oriented parallel to the radiant panel and the second one for which the slat were oriented perpendicularly. The same criteria as previously were analysed, as well as the rate of spread and the flame height of the resulting fire. A greater ignitibility and combustibility were obtained for the perpendicular configuration, due to a greater exposed surface. At this material scale, we observed that the combustibility of the thermoplastic slabs was greater than that of the wooden slabs.