Loading, Unloading, Segregation, and Cargo Securement
Loading and unloading
49 CFR 177.834 controls loading and unloading of hazardous materials. The vehicle's brakes must be set and wheels chocked when necessary to prevent movement. The engine should be shut off unless it must run for the loading or unloading operation. Packages must be secured against movement, and loading equipment must not damage packages or obscure labels. Smoking and open flames are prohibited around flammable or combustible cargo. The driver or a qualified representative must attend the operation when attendance is required, and unauthorized people should be kept away from the cargo area.
Segregation
49 CFR 177.848 contains the segregation table for hazardous materials loaded in the same transport vehicle. An "X" entry means the materials may not be loaded, transported, or stored together. An "O" entry means they may be loaded together only if separated by at least three feet horizontally or vertically. An asterisk refers to the Class 1 explosives compatibility table, which governs which explosive divisions and compatibility groups may travel together. Segregation is not optional paperwork: the load plan must physically keep incompatible packages apart or use separate vehicles.
Cargo securement
Under 49 CFR 392.9 and 177.834, cargo must be blocked, braced, tied down, or otherwise secured so it cannot shift, slide, or fall. Use dunnage and blocking that do not crush packages or cover hazard labels. Do not rely on the weight of the load alone to hold packages in place. Partial loads need attention because there may be no full wall of freight to brace against. Check securement after the first few miles and periodically during the trip.
Worked example
A load plan places 20 cases of Class 5.1 oxidizer beside 30 drums of Class 3 flammable liquid. The 177.848 segregation table marks the Class 3 versus Class 5.1 combination with an "X," so the plan is prohibited. The loader must remove one material from the vehicle or use separate vehicles. The reasoning: "X" is an absolute prohibition, not a spacing recommendation; only "O" permits loading together with at least three feet of separation.
Traps
Treating an "O" entry as a ban; measuring three inches instead of three feet; assuming labels alone satisfy segregation; forgetting that segregation applies to packages within the same vehicle, not just to bulk tanks; failing to secure a partial load; and loading or unloading with the engine running when it is not necessary.