Influence of particle size, thickness and compaction on the ignition of poplar sawdust layers

Poplar wood is an important bioresource used in the manufacture of plywood, fibreboard, paper pulp, and a wide range of other products. The accumulation of poplar sawdust in industrial environments represents a significant hazard when exposed to hot surfaces. Despite the widespread use of this material, fire and explosion safety data for poplar dust remain notably scarce. The Minimum Ignition Temperature of a dust layer ( MIT L ) is a key parameter for assessing its susceptibility to ignition. In this study, a series of hot plate experiments was conducted on different fractions of poplar sawdust to investigate the influence of particle size, layer thickness and bulk density on the ignition temperature. The results indicate that MIT L decreased with increasing layer thickness, whereas particle size had little influence on ignition behaviour. The latter finding was not observed for samples of pine pellet dust, which followed the trend commonly reported in the literature. Compaction of the poplar samples reduced MIT L by 10 °C, thereby increasing their susceptibility to ignition, although one sample did not follow this trend. The results suggest that the process is heat-limited and that bulk porosity –or compaction– may play an important role, potentially explaining the contrasting behaviour of the two materials. In addition, the Frank-Kamenetskii thermal explosion model was applied to the experimental results to estimate the activation energy and extrapolate the MIT L values to thicker dust layers. The prediction for 50 mm-thick layers deviated significantly from the general recommendations for dust layers provided in the EN 60079-14 standard.