Which of the following materials is typically considered combustible dust?

The correct choice is metal powders because they can readily ignite and sustain combustion under certain conditions, making them a significant hazard in industrial settings. When finely divided metal powders are dispersed in air, they present a substantial risk of explosion if an ignition source is present, as their increased surface area allows for rapid combustion.

Factors such as the size of the particles, the concentration in the air, and the presence of ignition sources contribute to the explosiveness of dust clouds formed by such materials. It's important to recognize that, unlike glass fibers or inert materials, which do not burn and thus do not present the same risks, metal powders can create dangerous conditions and require careful handling and control measures to prevent dust accumulation and ensure safety in environments where they are used.