What hazard classification system number indicates a container of flammable solids?

The classification of flammable solids falls under the hazard classification system number 4. This classification reflects the properties of substances that can ignite and burn when exposed to an ignition source and can contribute to the fire load in an environment. Flammable solids, which might include materials that are combustive or have the ability to spontaneously ignite under certain conditions, are identified under this specific category.

Understanding this classification is crucial for emergency responders in hazardous materials operations, as it allows them to communicate effectively about the potential risks and appropriate safety measures required when handling such materials.