Under what circumstances can a coal dust explosion occur?

A coal dust explosion can occur when coal dust particles are suspended in the air, creating a cloud that can be ignited by a source of ignition, such as an open flame, spark, or high heat. This specific condition is crucial because, when coal dust is airborne, it has a greater surface area that can react with oxygen, and if ignited, the explosion can propagate rapidly throughout the mine. The configuration and concentration of the dust cloud play significant roles in the potential for an explosion.

Conditions involving water, a vacuum, or high pressure do not favor the formation of a coal dust cloud or the conditions necessary for combustion and explosion. For example, water often helps suppress dust and is used in mining operations to maintain a safer environment. In a vacuum, oxygen is limited, making ignition impossible. High pressure alone does not create the necessary conditions without the dust being suspended in the air and having an ignition source. Thus, the correct context for a coal dust explosion is the presence of a suspending air mixture with an ignition source.