What category includes hazardous materials that can ignite and sustain fire?

The category that includes hazardous materials that can ignite and sustain fire is flammable solids. These materials are characterized by their ability to easily catch fire and continue burning, which poses significant risks in various environments, especially during firefighting operations.

Flammable solids can include a wide range of materials such as certain metals, organic compounds, and plastics. Their ignition can occur through various means, including friction, heat, or exposure to other flames, which allows them to not only start burning but also maintain their combustion under specific conditions.

Understanding the characteristics of flammable solids is crucial for first responders, as it enables them to implement appropriate safety measures and tactics when dealing with incidents involving these materials. In contrast, the other categories listed—oxidizers, gases, and radioactive materials—each have distinct properties and risks but do not focus primarily on the ability to ignite and sustain fire in the same manner that flammable solids do.