Iron and aluminum powder explosibility in 20-L and 1-m3 chambers

Metallic dusts with low values for maximum pressure P-max and volume-normalized maximum rate of pressure rise K-st, as determined in bench-scale apparatus have been labeled as "marginally explosible." These dusts pose unique challenges because they may be shown to be explosible using standardized bench-scale apparatus, yet they may not be found to be explosible using larger standardized test chambers. Furthermore, some metallic powders produce higher K-st values with increasing test scale. Results and preliminary analysis stemming from a comprehensive experimental campaign involving selected iron and aluminum powders of varying specific surface area are presented. Fine-, medium-, and coarse-particle size iron powder with Siwek 20-L K-st values less than 45 bar.m/s were also found to be explosible in the Fike 1-m(3) vessel. The coarse iron was only found to be non-explosible with the sub-75 mu m fraction removed. The fine, medium, and coarse iron powders produced lower maximum rates of pressure rise across all concentrations in the 20-L chamber compared to the 1-m(3) vessel. Fine-, medium-, and coarse-particle aluminum powders were also tested. The coarse aluminum powder could be exploded under the corresponding experimental conditions of 20-L chamber but not under the corresponding experimental conditions of 1-m(3) chamber. The volume-normalized maximum rate of pressure rise for the finest aluminum powder was found to be overdriven in the 20-L vessel using an ignition energy of 10 kJ compared to tests performed with the same ignition energy in the 1-m(3) vessel. An ignition energy of 5 kJ was found to be more appropriate for testing fine aluminum in the 20-L sphere. In contrast, the medium-particle size aluminum produced a K-St value substantially higher in the 1-m(3) vessel compared to the 20-L chamber.