Experimental investigation of the suppression effects of ammonium polyphosphate on explosion characteristics of unsaturated polyester resin dust

The suppression effects of Ammonium Polyphosphate (APP) with different mass fractions on the maximum explosion pressure (P_max), the explosibility index (K_st), the minimum ignition energy (MIE) and the minimum ignition temperature (MIT) of unsaturated polyester resin (UPR) dust were studied. Results indicated that the explosion severity and the ignition sensitivity of UPR dust decreased gradually when the mass fractions of APP increased. There existed a minimum inerting concentration (MIC), and the explosion of UPR dust could be suppressed completely by 60 wt% APP. Moreover, APP had a great inhibiting effect on the MIE of UPR dust cloud. The calculated MIE of UPR dust cloud increased from 10 mJ to 998 mJ when the mass fractions of APP increased to 30 wt%. Furthermore, the MIT of UPR dust cloud increased with the increase of the mass fractions of APP. When the mass fraction of APP increased to 80 wt%, the MIT increased by 290°C. The suppression mechanism of APP was studied according to thermogravimetry (TG) and differential scanning calorimetry (DSC) tests. Thermal analysis results showed that the addition of APP could increase the thermal stability of UPR. The suppression mechanism was reflected on the consumption of H and OH radicals.