Metal waste dusts from mechanical workings - explosibility parameters investigation

The reactivity of metal scraps or fine particles, typical residual wastes of mechanical workings, is significantly high to cause violent deflagration when particles disperse in the air in the form of clouds. However, literature information is scarce regarding the explosive risks of mixtures of pure metals, oxides and other impurities (like waste dust) whereas the form the bulk of materials in abatement systems and bag filters in the metal industry. Mechanical working could produce a different type of dust, depending on the process, the source material, and the operating conditions, main differences are in the particle size distribution, oxide content and morphology of samples. The present study investigates several samples of metal/oxide dust mixtures. The results of this work help to recognize the most hazardous dust in term of ignition sensibility when dispersing in clouds. The dust from sanding and welding processes fall into this group, while dust from laser-cutting does not ignite with standard ignition sources (like an electric arc or a hot wire). The work also aimed to establish a correlation between sample properties and explosibility parameters, like KST and Pmax. The results indicate a direct proportionality between these values and the particle size distribution of samples (in particular with the d-tenth percentile of the mass distribution) and with the metal oxide content. Additional research is needed to assess the influence of other variables (morphology, chemical composition) and the actual hazards related to different mechanical workings to prevent and mitigate explosive events.