Placards should be used:
Any time a vehicle is carrying hazardous materials.
If there is open space in the truck.
If the amount of hazardous materials in the truck exceeds 200 pounds.
If the hazardous materials create an inhalation hazard.
Placards must be placed on the outside of vehicles carrying hazardous materials. They identify the specific class or classes of materials being carried and warn others of relevant hazards.