What are the four primary categories of hazardous materials identified by DOT?

The four primary categories of hazardous materials identified by the Department of Transportation (DOT) encompass explosives, flammable liquids, gases, and hazardous substances. These categories are foundational in understanding how hazardous materials are classified and regulated for transportation.

Explosives refer to substances that can undergo a rapid chemical reaction, releasing energy in the form of heat, light, and pressure. Flammable liquids are those that can ignite and burn easily, posing significant risks during transport. Gases can be either flammable or non-flammable but often require specific containment and handling due to their inherent risks, including asphyxiation or the potential for explosions. Hazardous substances is a broad term that encapsulates materials posing a risk to health, safety, property, or the environment and includes a variety of other classifications, such as toxic and radioactive materials.

The other options, while they contain some hazardous materials, do not accurately reflect the DOT's primary categories, thus confirming that the choice highlighting explosives, flammable liquids, gases, and hazardous substances is the most accurate representation.