Ignition characteristics of mixtures of micro-sized wood dusts and centimeter-sized flakes and fibers initiated by deposit fires

As a highly flammable biomass dust, the explosion potential of wood dust has been widely recognized. However, compared with wood dust, other larger-sized wood processing by-products, such as wood flakes and wood fibers, pose a lower explosion risk due to their difficulty in forming dust clouds. Nevertheless, their fire risk should not be underestimated. Accident case analyses have shown that the explosion risk may increase when wood dust is mixed with wood processing by-products like wood flakes. This study experimentally investigated the ignition characteristics of mixtures of wood dust, wood flakes, and wood fibers, with a focus on the effects of mixing ratios, particle sizes, and spatial confinement on explosion risk. Whether in confined or open spaces, smoldering wood dust (D50 = 137 μm) as an ignition source was found to be insufficient to trigger a dust explosion. In mixtures of wood dust with wood flakes or wood fibers, the mixing ratio played a significant role in explosion risk. When the wood dust content exceeded 50 wt %, explosions occurred at both 0.2 MPa and 0.4 MPa dispersal pressures, with the key factor being the contact between the fireballs generated by burning wood flakes or wood fibers and the wood dust cloud. Conversely, when the wood dust content was lower (25 wt %), no explosion occurred. This study provides experimental evidence for the safe management of wood processing and biomass fuels. It recommends that enhanced preventive measures be implemented during storage and handling, particularly for mixtures with a high wood dust content, to mitigate explosion risks.