IMDG Class 4

IMDG Class 4 covers solids that present specific fire hazards beyond normal combustion: 4.1 flammable solids (e.g. matches, sulphur, some metals as powder), 4.2 substances liable to spontaneous combustion (e.g. yellow phosphorus, oily rags packaged with oxidising material), and 4.3 substances which on contact with water emit flammable gases (e.g. calcium carbide, sodium, some lithium compounds). Each sub-class has specific stowage and segregation requirements designed to manage the dominant hazard, including ventilation, dryness, and reactive-material isolation requirements.