Hazardous Materials Warning Labels Actual label size: at least 100 mm (3.9 inches) on all sides CLASS 3 Flammable Liquid CLASS 4 Flammable Solid, Spontaneously Combustible, and Dangerous When Wet: Divisions 4.1, 4.2, 4.3 Cargo Aircraft Only §172.405(b), §172.415, §172.416, §172.417 CLASS 5 Oxidizer, Organic Peroxide: Divisions 5.1 and 5.2Web