What Do Hazmat Placards Mean?

They show the hazard class of what is being shipped. Federal hazmat rules say a hazardous material's hazard class is indicated by its class or division number or its class name, and list nine classes, 1 explosives, 2 gases, 3 flammable and combustible liquids, 4 flammable solids, spontaneously combustible and dangerous when wet materials, 5 oxidizers and organic peroxides, 6 poisonous materials and infectious substances, 7 radioactive material, 8 corrosive material and 9 miscellaneous hazardous material.

PHMSA's 2024 Emergency Response Guidebook says placards identify a material's class or division, that the class or division number must be displayed in the lower corner of a placard, and that hazard words such as CORROSIVE are shown only in the US and are not required except on Class 7 placards. It says a 4-digit ID number may be shown on the diamond-shaped placard or on an adjacent orange panel on the ends and sides of a cargo tank, vehicle or rail car.

Under 49 CFR 172.504, unless an exception applies, each bulk packaging, freight container, unit load device, transport vehicle or rail car containing any quantity of a hazardous material must be placarded on each side and each end. For materials in the rule's second table moved by highway or rail, placards are not required on a transport vehicle or freight container with less than 454 kg, or 1,001 pounds, aggregate gross weight of those materials, except for bulk packagings and materials covered by section 172.505.

For emergencies, PHMSA says its Emergency Response Guidebook, published in a 2024 edition, contains an indexed list of hazardous materials and their associated ID numbers, the general hazards they pose, and recommended safety precautions.