The 9 Hazmat Hazard Classes and Divisions
Updated October 27, 2026
Every hazardous material is assigned to one of nine hazard classes, and some classes are split into divisions. The class drives almost everything else on the CDL hazmat test: the labels, the placards, the loading rules and the emergency response. Learn the class numbers, what each one means, and an example of each.
The nine classes
A division is a subdivision of a class, written as the class number, a decimal point and a second digit (for example, 2.1). The examples below are the ones the model CDL manual uses.
| Class | Division | Name | Example |
|---|---|---|---|
| 1 Explosives | 1.1 | Mass explosion hazard | Dynamite |
| 1.2 | Projection hazard | Flares | |
| 1.3 | Mass fire hazard | Display fireworks | |
| 1.4 | Minor explosion hazard | Ammunition | |
| 1.5 | Very insensitive | Blasting agents | |
| 1.6 | Extremely insensitive | Explosive devices | |
| 2 Gases | 2.1 | Flammable gas | Propane |
| 2.2 | Non-flammable gas | Helium | |
| 2.3 | Poisonous gas | Fluorine, compressed | |
| 3 Flammable liquids | Flammable and combustible liquids | Gasoline (flammable), fuel oil (combustible) | |
| 4 Flammable solids | 4.1 | Flammable solid | Ammonium picrate, wetted |
| 4.2 | Spontaneously combustible | White phosphorus | |
| 4.3 | Dangerous when wet | Sodium | |
| 5 Oxidizers | 5.1 | Oxidizer | Ammonium nitrate |
| 5.2 | Organic peroxide | Methyl ethyl ketone peroxide | |
| 6 Poisons | 6.1 | Poison (toxic) material | Potassium cyanide |
| 6.2 | Infectious substance | Anthrax | |
| 7 Radioactive | Radioactive material | Uranium | |
| 8 Corrosives | Corrosive material | Battery fluid | |
| 9 Miscellaneous | Miscellaneous hazardous material | Polychlorinated biphenyls (PCBs) |
Flammable or combustible?
Class 3 is split by flash point, the lowest temperature at which a liquid gives off enough vapor to ignite:
- Flammable liquid: flash point of 140°F (60°C) or lower. Example: gasoline.
- Combustible liquid: flash point above 140°F and below 200°F (93°C). Example: fuel oil.
The lower the flash point, the more easily the liquid catches fire.
One class per material
A material can meet the definition of more than one class, but it is assigned only one hazard class. Its other hazards are shown as subsidiary hazards, with extra labels and sometimes extra placards.
Packing groups
Within a class, packing groups show how dangerous a material is: I is great danger, II medium danger, III minor danger. The packing group appears in Roman numerals at the end of the basic description on the shipping paper.
Why the class matters for the test
- Placards: some classes and divisions are in placard Table 1 (any amount), the rest in Table 2. See hazmat placards.
- Loading: the segregation table says which classes may not ride together. See the segregation table.
- Smoking: the 25-foot no-smoking rule covers Class 1, Division 2.1, Class 3, Divisions 4.1 and 4.2, and Class 5.
Test yourself
-
Propane belongs to which division?Answer: APropane is the manual's example of a Division 2.1 flammable gas. Helium is the example for 2.2, and compressed fluorine for 2.3.
-
What hazard does Division 1.3 describe?Answer: BDivision 1.3 explosives, such as display fireworks, are a mass fire hazard. Division 1.1 is a mass explosion hazard, 1.4 a minor explosion hazard and 1.5 very insensitive.
-
Battery fluid is an example of which hazard class?Answer: CBattery fluid is a Class 8 corrosive. Class 3 is flammable liquids, Class 6 poisons and infectious substances, and Class 9 miscellaneous hazardous materials.
-
Potassium cyanide is the manual's example of which division?Answer: DPotassium cyanide is a Division 6.1 poisonous (toxic) material. Division 6.2 covers infectious substances such as anthrax.
-
A liquid has a flash point of 100°F. How is it classed?Answer: AA liquid with a flash point of 140°F or lower is a flammable liquid in Class 3. A combustible liquid has a flash point above 140°F and below 200°F.
-
What does Division 5.2 cover?Answer: BClass 5 has two divisions: 5.1 oxidizers, such as ammonium nitrate, and 5.2 organic peroxides, such as methyl ethyl ketone peroxide.
-
How many hazard classes do the hazmat rules use?Answer: CThere are nine hazard classes, numbered 1 to 9. Some of them are split into divisions.
-
In hazmat terms, what is a division?Answer: DA division is a subdivision of a hazard class, such as 4.1, 4.2 and 4.3 within Class 4. The division number is shown on labels and placards.
-
Which list correctly names the three divisions of Class 2?Answer: BClass 2 gases are Division 2.1 flammable gas, Division 2.2 non-flammable gas and Division 2.3 poisonous gas.
-
Which Class 1 division is "extremely insensitive"?Answer: CDivision 1.6 is extremely insensitive explosives (the manual's example is explosive devices). Division 1.5, such as blasting agents, is very insensitive.
Pass your hazmat endorsement test on the first try
- All 181 questions on hazard classes, shipping papers, placards, loading, cargo tanks, driving and parking rules and emergencies
- An explanation for every answer, from the CDL manual and the federal hazmat rules
- Unlimited full 30-question practice tests, scored like the real one (80% to pass)