Class 4.1: Flammable Solids or Substances.
IMO Classes Class 1. Explosives Class 2. Gases Class 3. Flammable Liquids Class 4.1. Flammable Solids or Substances Class 4.2. Flammable solids Class 4.3. Substances which, in contact with water, emit flammable gases Class 5.1. Oxidizing substances (agents) by yielding oxygen increase the risk and intensity of fire Class 5.2. Organic peroxides - most will burn rapidly and are sensitive to impact or friction Class 6.1. Toxic substances Class 6.2. Infectious substances Class 7. Radioactive Substances Class 8. Corrosives Class 9. Miscellaneous dangerous substances and articles
Class 4.1

Flammable Solids or Substances

Desensitized explosives that when dry are explosives of Class 1 and are specifically authorized by name or have been assigned a shipping name and hazard class by the Associate Administrator.

Self-reactive materials,which are thermally unstable and that can undergo a strongly exothermic decomposition even without participation of air.

Readily combustible solids that can cause a fire through friction and show a burning rate faster than 2.2 mm (0.087 inches) per second, or metal powders that can be ignited and react over the whole length of a sample in 10 minutes or less.