The most familiar warnings are displayed on placards, the colored signs on the outside of trucks which provide a readily visible warning of hazardous materials. Each group of hazardous chemicals (flammable liquid, flammable gas, non- flammable gas, explosives, corrosive materials, oxidizers, poisons, radioactive materials) are represented by a particular color. Placards may also contain a symbol describing the type of hazardous material being transported. Labels are miniature placards attached to individual boxes, cylinders, or containers of hazardous materials. In addition, truckers are required at all times to have shipping papers, which describe the hazardous cargo. Individual shipping containers should also have the name of the chemical written on them; certain materials will have the marking, "Inhalation Hazard."