Hazard Classes
The nine federal hazard classes and what each one looks like in the field.
Endorsement: Hazardous Materials (H) · Source: FMCSA CDL Manual (public domain)
The federal hazardous materials regulations divide regulated materials into nine hazard classes, each with sub-divisions. Class 1 is explosives, divided 1.1 through 1.6 by mass-explosion hazard; the placards are orange. Class 2 is gases — 2.1 flammable gas (red), 2.2 non-flammable compressed gas (green), 2.3 poisonous gas (white). Class 3 is flammable and combustible liquids (red, white "3"). Class 4 is flammable solids (4.1), spontaneously combustible (4.2), and dangerous-when-wet (4.3). Class 5 is oxidizers (5.1) and organic peroxides (5.2). Class 6 is poisons (6.1) and infectious substances (6.2). Class 7 is radioactive materials, with three sub-categories I, II, and III by radiation level. Class 8 is corrosives. Class 9 is miscellaneous hazardous materials.
The CDL Hazmat exam tests both the class numbers and the visual placards. Each placard is a 10.75-inch diamond-shaped sign in a class-specific color and pattern with the hazard class number at the bottom. The four-digit UN/NA identification number for the specific material may also appear on the placard or on a separate orange panel adjacent to it. Drivers must be able to look at any placard and name the hazard class, and conversely look at a class number and pick the correct placard from a lineup.
The Hazardous Materials Table in 49 CFR 172.101 cross-references each material name with its hazard class, packing group, label requirements, packaging requirements, and any special provisions. While the exam does not require memorizing the entire table, it does test the highest-volume materials drivers encounter: gasoline (3, UN1203), diesel fuel (3, UN1202), liquefied petroleum gas (2.1, UN1075), anhydrous ammonia (2.2 with subsidiary 8, UN1005), and chlorine (2.3 with subsidiary 8, UN1017).
Key terms to memorize
- placard
- shipping paper
- Emergency Response Guidebook
- hazard class
- segregation table
- Safety Data Sheet
- TSA threat assessment
Other Hazardous Materials (H) topics
- Placarding Rules — When you must placard, what the placards mean, and where they go.
- Shipping Papers — What every hazmat shipping paper must contain and where it must live in the cab.
- Segregation and Loading — Which hazardous materials cannot be loaded together, and how to comply.
- Emergency Response — What to do in the first minutes after a hazmat incident.
Test what you learned
Now that you have the Hazard Classes material in your head, drill the Hazardous Materials (H) practice test. The questions are drawn from the same FMCSA source material this article paraphrases. For state-specific framing, jump to your state page and pick the Hazardous Materials (H) test for your jurisdiction.