Combustion dynamics and thermal suppression of aluminum powder fires using an expandable graphite–zinc borate formulation

Fires involving finely divided aluminum powder pose serious hazards due to their high reactivity, rapid heat release, and intense flame behavior. Conventional suppression methods often fall short in such scenarios, necessitating the development of more effective alternatives. This study investigates the fire suppression performance of an EGZB (expandable graphite–zinc borate) blend in controlling aluminum powder fires. Experiments were conducted using a fabricated fire test setup, where aluminum powder was ignited and treated with the EGZB suppressant. Zinc borate contributed to suppression through endothermic decomposition that released water and formed a glassy residue, while expandable graphite expanded under heat to produce an insulating char that smothered the flame and restricted oxygen access. The combined effect of both components led to a marked reduction in extinguishing time and thermal output. Results showed that EGZB achieved the shortest extinguishing time (13 s), outperforming EG (18 s) and ZB (29 s), and also exhibited the highest suppressant extinguishing index and fastest cooling rate. The EGZB composite not only reduced extinguishing time but also decreased the peak flame temperature to 923 °C, enhanced the cooling rate to 7.3 °C s⁻ 1 , and achieved the highest SEI 0.0952 (sg)⁻ 1 , among the tested suppressants. These findings demonstrated that the EGZB blend effectively reduced fire intensity and duration while maintaining thermal stability and environmental safety. The formulation also exhibited non-toxic properties, making it suitable for use in fire-prone environments involving reactive metal powders. This study supports the potential of EGZB as an efficient and eco-friendly suppressant for aluminum powder fires in industrial and laboratory settings.