Flashpoint and burning of thin molten plastic pool above hot boundary

• Published in: Applied thermal engineering Vol. 215; p. 118931
• Main Authors: Sun, Peiyi, Huang, Xinyan, Xu, Cangsu
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2022
• Subjects: Burning dynamics; Flame extinction; Hot plate; Molten thermoplastics; Pool fire; Flame extinction; Molten thermoplastics; Pool fire; Burning dynamics; Hot plate
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2022.118931

•The ignition and burning dynamics of thin thermoplastic pool fire are explored above a hot boundary.•Flashpoints of both PE and PP plastic pools are measured to be about 60 °C below its pyrolysis point.•Three burning patterns, (I) near-limit flame, (II) transitional flame, and (III) intensive flame, are found.•Different burning features between conventional liquid fuels and plastic fuels are compared. The melting and dripping of burning thermoplastics can cause a new ignition and form a plastic pool fire, resulting in a significant fire risk. This work investigates the burning dynamics of polyethylene (PE) vs polypropylene (PP) pools fully melted at 380–410 °C on a hot plate with a controlled area and initial temperature. For PE, three burning patterns are observed and defined under different bottom boundary temperatures. When the boundary temperature is lower than the melting point of thermoplastic, burning Pattern I (near-limit flame) appears shortly and extinguishes quickly. Above the melting point of PE, the flame becomes stronger and can last for the longest period before quenching (Pattern II: transitional flame). PP does not have this transitional-flame stage due to a higher melting point and lower pyrolysis point. When the plastic pool temperature exceeds its flashpoint of about 300 °C (∼60 °C below its pyrolysis point), the flame becomes intense and quickly burns out the molten pool (Pattern III: intensive flame). The burning processes of molten thermoplastics show a clear difference from the burning of ethanol and paraffin wax. This study promotes the understanding of the melting and burning of plastics in real fire scenarios and helps quantify the hazards of dripping and flooring fires.