This study experimentally investigated that the inerting effect of Ammonium Polyphosphate (APP) on characteristics of Polypropylene (PP) dust explosion. The results indicated that the maximum explosion pressure (P-max), the explosion index (K-st) and the minimum explosion concentration (MEC) of PP powders were 8 bar, 257 bar m/s and 25 g/m(3), respectively. Moreover, the minimum ignition energy (MIE) and the minimum ignition temperature (MIT) were 10 mJ and 335 degrees C, correspondingly for PP dust cloud. The explosion of PP powders could be inerted completely by 80 wt% APP. In addition, the MIE of PP powders increased when the mass fraction of APP increased. Furthermore, APP had a significant inerting effect on the MIT of PP dust cloud. The MIT of PP powders increased by 80 degrees C when the mass fraction of APP increased to 80 wt %. Thermal analysis results showed that the introduction of APP could improve the thermal stability of PP. Furthermore, thermogravimetric analysis/infrared (TG-IR) spectroscopy was employed to gain insights into the pyrolysis mechanism of the PP/APP mixtures. The TG-IR results showed that the volatilized products formed in the pyrolysis were H2O and NH3 which could dilute and consume oxygen in gas phase. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.