Hazard class 4.1: Flammable solids, self-reactive substances, polymerizing substances and solid desensitized explosives
Self-reactive substances are thermally unstable substances liable to undergo a strongly exothermic decomposition even without participation of oxygen (air).
Polymerizing substances are substances which, without stabilization, are liable to undergo a strongly exothermic reaction resulting in the formation of larger molecules or resulting in the formation of polymers under conditions normally encountered in carriage.
Hazard class 4.2: Substances liable to spontaneous combustion
Hazard class 4.3: Substances which, in contact with water, emit flammable gases
Class 4.3 are substances which react with water to emit flammable gases liable to form explosive mixtures with air. They are easily ignited by all ordinary sources of ignition that produce a spark. They are often referred to as 'dangerous when wet'.
Packing groupsClasses 4.1, 4.2 and 4.3 have been assigned a packing group which indicates the degree of danger.
Packing Group I: Substances presenting high danger
Packing Group II: Substances presenting medium danger
Packing Group III: Substances presenting low danger