Nine Hazmat Classes and Their Placards
The U.S. Department of Transportation (DOT) classifies hazardous materials into nine classes under 49 CFR Part 173. Class 1 — Explosives (six divisions: 1.1 mass explosion hazard through 1.6 extremely insensitive); placard background is orange with the explosion graphic. Class 2 — Gases: Division 2.1 Flammable Gas (red, flame graphic), Division 2.2 Non-Flammable Gas (green), Division 2.3 Poisonous Gas (white with skull and crossbones). Class 3 — Flammable Liquids (red, flame on diagonal stripe). Class 4 — Flammable Solids: Division 4.1 Flammable Solid (red and white vertical stripes), Division 4.2 Spontaneously Combustible (white over red), Division 4.3 Dangerous When Wet (blue). Class 5 — Oxidizers and Organic Peroxides: Division 5.1 Oxidizer (yellow), Division 5.2 Organic Peroxide (yellow with vertical red stripe). Class 6 — Toxic and Infectious: Division 6.1 Poison (white), Division 6.2 Infectious Substance (white with biohazard symbol). Class 7 — Radioactive (yellow and white with propeller trefoil). Class 8 — Corrosive (black and white, liquids dripping from containers). Class 9 — Miscellaneous (alternating black and white vertical stripes). Memorising the colour coding by class is essential for the CDL Hazmat endorsement exam — the exam frequently presents a placard description and asks which class it represents.