Glossary / Transport
DOT hazard class
A DOT hazard class is the transport category assigned to a hazardous material under the U.S. Department of Transportation hazmat rules. It groups materials by their main danger, such as explosives, gases, flammable liquids, toxics or corrosives, and drives labels, placards and packaging.
Explanation
The DOT hazmat regulations are found in 49 CFR Parts 171-180. They sort dangerous goods into nine classes, and some classes are split into divisions. Class 3, for example, covers flammable liquids, and Class 8 covers corrosive materials. A material is placed in a class based on its most significant transport hazard, not on its workplace GHS classification.
This matters because the DOT class is not the same thing as a GHS hazard class. GHS is designed for workplace and consumer communication, while the DOT system is designed to protect carriers, the public and emergency responders during movement. The two systems overlap but use different categories, different symbols and different cut-offs. For flammable liquids, DOT Class 3 covers materials with a flash point of not more than 60 C (140 F), while combustible liquids have a flash point above 60 C and below 93 C (200 F).
The class works together with other shipping information. The UN number identifies the material, the Proper shipping name describes it, the Packing group shows the degree of danger within the class, and the class determines the diamond-shaped label and the Placard shown on a vehicle. Together these tell a driver or responder what they are dealing with before any container is opened.
A material with more than one hazard may carry a subsidiary hazard class in addition to its primary class. Shipping papers list the primary class first and the subsidiary class in parentheses.
What to do and watch for
- Check the class on the shipping paper against the labels on the package before it leaves your dock.
- Do not assume a GHS pictogram tells you the DOT class; look at the transport section of the SDS.
- Only trained, certified staff should classify and offer hazmat for shipment.
Where it appears on an SDS
- Section 14: Transport information. Lists the DOT hazard class, UN number, proper shipping name and packing group for ground transport, with equivalent entries for air and sea.
SDS content and wording vary by supplier. This page is general reference and does not replace the current SDS for your product.