Combustible dust can be defined as:

Combustible dust is specifically characterized as finely divided solid materials that pose fire or explosion hazards under certain conditions. This definition emphasizes the critical aspects of particle size and the potential for ignition, highlighting that when these materials become airborne and are mixed with an adequate amount of oxygen, they can ignite and result in combustion.

The focus on "finely divided solid materials" means that particles are small enough to remain suspended in the air, creating an environment where they can ignite more easily. This information is important for understanding safety procedures and risks related to various industrial processes that handle or produce dust. Recognizing the hazards associated with combustible dust is essential for preventing explosive scenarios in workplaces, particularly in industries like agriculture, food processing, and manufacturing.

Other choices do not accurately define combustible dust in a fire safety and explosion context. Some refer to characteristics unrelated to combustion risk, while others limit the scope of ignition sources without considering the broader potential risks associated with combustibility.