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Zinc Dust: Active and Explosive, How to Control It?

2025/03/19
Zinc Dust: Active and Explosive, How to Control It?

Zinc Dust: Active and Explosive, How to Control It?

Zinc is a light gray transition metal with excellent covering power, making it suitable as a pigment. It has strong anti-rust and atmospheric erosion resistance, making it an important component in anti-rust paints and strong reducing agents. Additionally, it is widely used in mercury-free batteries, chemical industry, dyes, medicine, pesticides, and other fields. However, zinc dust is highly active and often involved in explosion accidents. According to research, spherical zinc dust with a particle size of less than 47μm has an auto-ignition point of 460℃ and an explosion limit of about 500g/m³. If the fineness increases, its activity becomes stronger, and the ignition point and explosion limit decrease. Moreover, zinc dust not only easily ignites when exposed to open flames but also spontaneously heats and burns in humid air. Contact with water, acids, or alkali metal hydroxides can release flammable hydrogen gas, and reactions with oxidizers or sulfur can cause fires or explosions, making it a true "hidden bomb." Therefore, whether in production, transportation, or application, if the explosive nature of zinc dust is not effectively controlled, the consequences could be disastrous.

Transportation Scenario

Zinc dust during transportation is also a hidden bomb. In April 2018, a train carrying zinc dust caught fire on a highway. Besides screws and other items, the train was carrying 20 barrels (50 kg each) of zinc dust. Once leaked, the zinc dust dispersed in the air could easily be ignited by an open flame, causing a mixed explosion. Although the driver noticed the fire in time, they could not stop it from spreading, and two barrels of zinc dust were not rescued. Fortunately, the rescue team, after understanding the situation, prepared sand and dry powder fire extinguishers to put out the fire, and the two barrels of zinc dust were eventually found and safely transferred.

However, not every incident ends so luckily. In November 2013, a semi-trailer carrying about 36 tons of zinc dust and aluminum powder spontaneously combusted on a highway due to heavy rainfall. The prolonged exposure to rainwater soaked the tarpaulin covering the cargo, allowing water to seep into the zinc dust. Zinc, being an active metal, reacts with water to release a large amount of heat, causing multiple parts of the truck to smoke and catch fire. Although the truck owner had taken some waterproofing measures, they were clearly insufficient. Therefore, when transporting these materials in rainy weather, strict waterproofing measures must be taken to avoid combustion or even explosion.

Application Scenario

Metallic zinc is mainly used for the anti-corrosion of steel structures, with hot-dip galvanizing being the most common method. In July 2012, a company in Qingdao using zinc dust for thermal spraying experienced a spontaneous combustion accident during the dust removal process. The handling of the spontaneous combustion caused secondary dust dispersion, leading to a zinc dust explosion that injured several workers.

The thermal spraying process uses purified compressed air to propel zinc wire forward, with the molten part forming a mist that sprays onto the substrate metal surface to create a uniform coating. Another part of the zinc dust rebounds and scatters in the air and on the floor of the spraying room. To prevent zinc dust deposition, a vacuum dust removal system is installed, maintaining negative pressure in the spraying room through a fan. The air containing zinc dust is drawn into the dust removal system, where a bag filter separates the solids from the gas.

The spontaneous combustion of zinc dust was mainly caused by the failure to promptly handle the zinc dust accumulated at the exhaust vent. The zinc dust, exposed to air for a long time, continuously oxidized and reached a critical point, leading to spontaneous combustion. Therefore, preventing dust accumulation and overheating is the key technical aspect of dust remover design and modification.


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