A 1981 report, prepared for the EPA, estimated that 96% of the 264 million tn of hazardous wastes generated each year were disposed at the site where they were generated. By 1989, the National Solid Wastes Management Association (NSWMA 1989) stated that trucks traveling over public highways move over 98% of hazardous wastes that are treated off-site. Another perspective can be gained from statistics for hazardous materials transportation. Rail transportation moves about 8% of the hazardous materials shipped, but 57% of the ton-miles of hazardous materials shipped (U.S. Office of Technology Assessment 1986).
The highway transport mode is regarded as the most versatile, and is the most widely used. Tank trucks can access most industrial sites and TSD facilities. Rail shipping requires expensive sidings, and is suitable for very large quantity shipments. Cargo tanks are the main carriers of bulk hazardous materials; however, large quantities of hazardous wastes are shipped in 55-gal drums.
Cargo tanks are the main carriers of bulk hazardous materials over roads. Cargo tanks are usually made of steel or aluminum alloy, or other materials such as titanium, nickel, or stainless steel. They range in capacity from 4,000 to 12,000 gal. Federal road weight laws usually limit motor vehicle weights to 80,000 lb gross. Table 11.10.2 lists DOT cargo tank specifications for bulk shipment of common hazardous materials and example cargos.
As stated above, rail shipments account for about 8% of the hazardous materials transported annually, with about 3,000 loads each day. However, the proportion of hazardous waste shipments is unknown.
The major classifications of rail tank cars are pressure and nonpressure (for transporting both gases and liquids). Both categories have several subclasses, which differ in test pressure, presence or absence of bottom discharge valves, type of pressure relief system, and type of thermal shielding. Ninety percent of tank cars are steel; aluminum is also common.
DOT tank car design specifications are detailed in 49 CFR Part 179. Rail car specification numbers for trans
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