Every day, tens of thousands of cargo tank trucks transport hazardous materials classified as flammable liquids (primarily gasoline and fuel oil) for sale in the United States. This involves some safety risk because of the volatile nature of flammable liquids, the volume of liquid transported (up to 9,200 gallons per truck), and the numbers of trucks and passenger vehicles on the road. Tank trucks that carry flammable liquids have three main components-the truck, the trailer, and the cargo tank. The tank may be divided into several compartments-usually four or five-allowing the truck to carry different petroleum products in a single trip, such as different grades of gasoline and diesel fuel. Although the design of cargo tank trucks can vary depending on the model and manufacturer, the components in figure 1 are common features.