Understanding DOT Class 4 Materials: Flammable Solids, Spontaneously Combustible, and Dangerous When Wet Materials

 

Definition of DOT Class 4: Flammable Solids, Spontaneously Combustible, and Dangerous When Wet Materials

Class 4 covers flammable solids, as well as spontaneously combustible and dangerous when wet materials.

The formal definition can be found at 49 CFR 173.124.

Class 4 Divisions

Class 4 materials are divided into three divisions.

Division 4.1

Division 4.1 materials are referred to under the name of Flammable Solids, and come in four groups.

• Desensitized Explosives
• Self-Reactive Materials, which are thermally unstable and capable of exothermic decomposition without oxygen
• Readily Combustible Solids
• Polymerizing Materials, which are liable to undergo an exothermic reaction under conditions normally found in transportation

Division 4.2

Division 4.2 materials are referred to under the name of Spontaneously Combustible Material. This includes both pyrophoric material and self-heating material.

Division 4.3

Division 4.3 materials are referred to under the name of Dangerous When Wet Material. This covers materials which are spontaneously flammable when in contact with water or give off flammable or toxic gas when in contact with water.

Relationship Between Class 4 and OSHA Hazard Classifications

Division 4.1 materials overlap with the OSHA Physical Hazard Flammable Solid category.

Division 4.2 materials overlap with the OSHA Physical Hazard Pyrophoric Solids category and the Self-Heating Chemicals category.

Division 4.3 materials overlap with the OSHA Physical Hazard "Chemical Which, In Contact with Water, Emit Flammable Gases" category.