Segregation and Loading
Which hazardous materials cannot be loaded together, and how to comply.
Endorsement: Hazardous Materials (H) · Source: FMCSA CDL Manual (public domain)
Some hazardous materials cannot be transported together because their reactivity creates an unacceptable risk of fire, explosion, or toxic release. The FMCSA CDL Manual reproduces the segregation table from 49 CFR 177.848, which specifies forbidden, separated, and away-from combinations across the nine hazard classes. The Hazmat exam tests both the structure of the table and a handful of high-frequency rules.
Class 1 explosives generally cannot be loaded with most other classes. Class 8 corrosive liquids must be loaded below or away from foodstuffs (because of contamination risk if a leak occurs). Class 5 oxidizers cannot be loaded with Class 3 flammable liquids (oxidizer fire-acceleration risk). Class 7 radioactive packages have separation requirements based on the package transport index that limit how many packages can ride near the cab to limit driver exposure.
Loading rules also include practical safety requirements. The engine must be off before loading or unloading flammable liquids, the parking brake must be set, and the driver must be in attendance unless the vehicle is in a designated and secured area. Smoking is prohibited within 25 feet of any vehicle containing Class 1 (explosives), Class 2.1 (flammable gas), Class 3 (flammable liquids), Class 4 (flammable solids), or Class 5 (oxidizers). Drivers must use chocks under the wheels of cargo tank vehicles loading or unloading by gravity. The exam frequently tests these distance and procedure rules; memorize the 25-foot smoking rule, the engine-off rule, and the in-attendance rule.
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
- Hazard Classes — The nine federal hazard classes and what each one looks like in the field.
- 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.
- Emergency Response — What to do in the first minutes after a hazmat incident.
Test what you learned
Now that you have the Segregation and Loading 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.