What classification includes hazardous materials that may spontaneously combust or create heat?

The classification that includes hazardous materials that may spontaneously combust or create heat is flammable solids. Flammable solids are substances that can ignite and burn quickly when exposed to heat, friction, or moisture. This class of materials is particularly concerning in HAZMAT operations because they pose an increased risk of fire or explosion under certain conditions. When dealing with these materials, awareness of their properties is essential for safe handling and mitigation of hazards.

The other classifications listed do not specifically address the characteristics of materials that can spontaneously combust or generate heat. Flammable liquids are substances that can ignite at relatively low temperatures but do not inherently exhibit spontaneous combustion like flammable solids do. Oxidizers are materials that can enhance the combustion of other substances but are not classified as spontaneously combustible themselves. Radioactive materials contain unstable isotopes but do not inherently involve rapid combustion. Thus, the focus on spontaneous combustion and heat generation aligns with the properties of flammable solids.