What type of materials does DOT Hazard Class 4 include?

DOT Hazard Class 4 encompasses flammable solids, which are substances that can easily ignite through friction, heat, or moisture. These materials can pose significant risks during transportation and handling, as they can lead to fires that are difficult to control. Items in this class include many types of combustible solids, such as certain types of metals that are susceptible to ignition when finely divided or mixed with air.

The other options relate to different categories of hazardous materials. Flammable liquids belong to a different hazard class (Class 3), as they include liquids that can easily ignite and form flammable vapor. Organic peroxides are classified under Class 5, as they are compounds containing the bivalent -O-O- structure that can act as strong oxidizers. Finally, spontaneously combustible materials are categorized under Class 4 as well, but they are a specific subset that can ignite without an external ignition source, which is a distinct characteristic. Thus, the recognition of flammable solids as the correct answer is crucial for understanding the classifications under DOT regulations.