On the burning behavior of thermoplastics at large scale: Uncartoned unexpanded plastic commodity

Abstract

Large-scale tests were conducted to understand the burning process of thermoplastic high-density polyethylene pallets, a representative commodity in warehouse fire scenarios. Large-scale experiments of two stacks of eight plastic pallets showed that initially small fires can easily travel through the open structures, leading to rapid fire growth following an initially slow pre-heating phase. The plastic deforms and melts during the tests and this is most prominent for thin elements of the plastic pallets. In a second set of experiments involving one stack of plastic pallets, the liquid pool was accumulated in a collection pan and detailed measurements of temperature and heat flux were performed with an array of probes. The results show that 52–74% of the total pallet mass loss is accumulated in the burning liquid pool and that this fraction reduces with an increasing fire size. Radiative heat transfer is the dominant heat transfer mode for the plastic pallet fire, resulting in significant preheating ahead of the fire front. Spectral measurements were used to calculate an absorption coefficient of approximately 0.7 m-1 (only considering soot) for a 1.5 MW fire. These results will feed-forward into the development and validation of a numerical model for the thermoplastic pallet commodity.