Inhibition effect of inert powder on secondary explosion of accumulated zirconium powder induced by hydrogen deflagration

Secondary dust explosion is a typical and hazardous disaster phenomenon in industrial dust safety, which is defined as the secondary combustion and explosion behavior of suspended combustible dust clouds excited and induced by the shock wave and thermal effect of the primary explosion. The inert powder suppression technology is recognized as one of the most efficient and feasible measures to mitigate and restrain dust explosion hazards. To reveal effective suppression routes for secondary explosions of high-reactivity metal dust, three typical inert suppressants including sodium bicarbonate (NaHCO₃), ammonium dihydrogen phosphate (NH₄H₂PO₄) and sodium chloride (NaCl) were selected. A series of contrastive experiments were carried out to investigate the suppression characteristics of four different mass fractions (33.3 wt%, 50 wt%, 60 wt%, and 75 wt%) of inert powders on hydrogen deflagration-induced secondary explosion of accumulated zirconium dust in an open space. The explosion overpressure, flame morphology evolution, flame propagation velocity and flame temperature duration characteristics were systematically analyzed. Experimental results demonstrate that inhibitors dominated by physical effects such as NaCl are more efficient and reliable for active zirconium dust. In contrast, chemically based inhibitors exhibit inconsistent concentration-dependent suppression performance. Specifically, NaCl powder relies on pure physical suppression mechanisms including heat absorption and flame blocking; it does not participate in chemical combustion reactions or generate secondary harmful by-products, thereby delivering outstanding suppression stability. The 60 wt% NaCl condition achieves the optimal comprehensive suppression effect, which can markedly reduce explosion overpressure, limit flame propagation range, lower flame temperature and shorten the duration of high-temperature zones. The suppression capacities of NaHCO₃ and NH₄H₂PO₄ cannot be continuously enhanced with the increase of doping mass fraction. Moreover, thermal decomposition products of NH₄H₂PO₄ even exert a certain catalytic effect on the combustion of zirconium dust. By comparison, 50–60 wt% NaHCO₃ presents relatively balanced suppression performance, whereas NH₄H₂PO₄ is not applicable to the suppression of zirconium dust explosion. Distinctions between physical and chemical inhibition mechanisms governing zirconium dust secondary explosions are identified, supplying reliable experimental datasets and technical support for explosion prevention and safety control of highly reactive metal dust in industrial production and storage processes.