Class 4, Flammable Solids, has three divisions:
4.1 - A solid that under normal conditions of transport is readily combustible, or would
cause or contribute to fire through friction or from heat retained from manufacturing or
processing, or is a self-reactive substance that is liable to undergo a strongly exothermic
reaction, or is a desensitized explosive that is liable to explode if they are not diluted
sufficiently to suppress their explosive properties.
Commonly used in lacquers (example: naphthalene).
4.2 - A substance liable to spontaneous combustion, under normal conditions of transport, or when in contact with air, liable to spontaneous heating to the point where it ignites. Commonly used in rocket fuel (example: sodium hydrosulphite).
4.3 - A substance that, on contact with water, emits dangerous quantities of flammable gases or becomes spontaneously combustible on contact with water or water vapour. Commonly used in heat exchangers (valves) (example: sodium).
4.2 - A substance liable to spontaneous combustion, under normal conditions of transport, or when in contact with air, liable to spontaneous heating to the point where it ignites. Commonly used in rocket fuel (example: sodium hydrosulphite).
4.3 - A substance that, on contact with water, emits dangerous quantities of flammable gases or becomes spontaneously combustible on contact with water or water vapour. Commonly used in heat exchangers (valves) (example: sodium).
Packing Groups
Class 4 is separated into packing groups to indicate the amount of danger related to the substance. (Packing group 1 is the most dangerous.)