Class 4
Class 4 — flammable solids
Class 4 covers flammable solids, spontaneous combustibles, and substances dangerous when wet.
Class 4 is a family of solid hazards. Division 4.1 is flammable solids. Division 4.2 is substances liable to spontaneous combustion. Division 4.3 is substances that become dangerous when wet, often giving off a flammable gas.
These show up in boxcars, covered hoppers, and sometimes in tank cars for molten or special forms. The division number changes the hazard completely. "Flammable solid" is the wrong description for a 4.3 load.
As with the other classes, the four-digit identification number names the material. The class only names the kind of hazard.
Identification only. If a car is leaking or in a wreck, move away and call your local emergency number. Responders use the Emergency Response Guidebook. This page is not that book.