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Placards on tankers provide information concerning the hazard class of the material inside, but a great deal can also be learned about the physical characteristics and hazards of the material from the tank itself. For example, the MC/DOT 312/412 is used exclusively for the transport of corrosive materials. The tanker, however, may carry oxidizer, flammable, poison or corrosive placards.
Photo by Robert Burke
An MC/DOT 312/412 acid-hauling tanker. Notice the small tank and the heavy reinforcing rings around the outside. Such tankers may carry placards warning of the presence of oxidizers, flammables, poisons or corrosives.
Photo by Robert Burke
An MC/DOT 306/406 with multiple compartments. Notice the elliptical shape of the container.
Placards are placed on a vehicle based on the U.S. Department of Transportation (DOT) system of listing the most severe hazard. Corrosive materials, as with most hazardous materials, can have more than one hazard. If response personnel become familiar with the various types of bulk highway containers and the products they typically haul, they can better identify "hidden" hazards of materials involved in accidents.
The DOT defines a highway bulk cargo tank as "any tank attached to or forming a part of any motor vehicle or any bulk liquid or compressed gas packaging not permanently attached to any motor vehicle, which by reason of its size, construction or attachment to a motor vehicle, is loaded or unloaded without being removed from the vehicle." The term "bulk hazardous material" is defined by the DOT as "any container with over 119 gallons liquid capacity." Other vehicles are also used to transport dry bulk and liquid/dry mixtures.
Specifications for construction of highway transportation bulk tanks are in accordance with American Society of Mechanical Engineers (ASME) requirements. Additionally, the DOT stipulates procedures for manufacturing, maintaining, testing, inspecting and repairing bulk containers. Construction materials are also specified by the DOT, and include aluminum, carbon steel, high-strength/low-alloy, mild steel and stainless steel. Tanks are designed around the hazards of the materials they will be hauling.
DOT regulations and construction standards apply to both interstate and intrastate vehicles. The most common bulk containers used to transport hazardous materials are MC/DOT 306/406, 307/407, 312/412, MC 331, MC 338, dry bulk and tube trailers (MC stands for motor carrier and DOT stands for Department of Transportation). Since Aug. 31, 1993, the manufacture of vehicles with the MC 300 series specifications has not been allowed. Vehicles manufactured after the above date are required to conform to design specifications for the DOT 400 series. DOT 400 series tanks are built using stronger metals, are larger, and have a larger volume and a lower center of gravity. MC 300 series tanks will remain in service as long as they meet testing and inspection requirements.
The MC/DOT 306-406 tanker is primarily an atmospheric pressure non-insulated flammable liquid container that is hydrostatically tested to 3 psi. Capacities vary from 2,000 to 9,000 gallons. It generally has an elliptical shape, although some manufacturers make a round version, and is used to haul gasoline, diesel, aviation fuel and other flammable liquids. Materials used to construct these tanks include aluminum, steel and stainless steel. Baffles installed within the container limit product movement during transportation.
These tanks may have multiple compartments and may be carrying several different materials. Specification plates, usually located on the right frame rail of the trailer, are small and difficult to read. They may be of more use during training and pre-planning than during an incident. The plate contains information about the type of tank, manufacturer, construction material, date built, design and test pressures and number of compartments and capacities. Specification plates for other bulk tanks contain similar information and are located in the same general area.