The safety of transporting hazardous materials has long been an area of concern to the Federal Government. Legislation regulating the transportation of explosives and flammable materials was first enacted in the mid-nineteenth century. In 1908, Congress passed the Explosives and Combustibles Act, authorizing the Interstate Commerce Commission to issue regulations covering the packing, marking, loading, and handling of explosives and other dangerous substances in transit.
The Federal statute known as the Hazardous Materials Transportation Act (HMTA) of 1974, signed into law in 1975, expanded the role of the U.S. Department of Transportation in regulating the safety of hazardous material transportation. The HMTA states that when the Secretary of Transportation finds that transportation of a commodity of a particular quantity and form poses an unreasonable risk to the health and safety or property of the public, the commodity is to be designated as a hazardous material.
The regulations identifying various commodities as hazardous materials and specifying the requirements for their transport are codified in the Code of Federal Regulations (CFR) Title 49 Parts 100 to 185. A table listing over 3,000 proper shipping names and corresponding hazmat identification numbers along with specific transportation requirements is shown in 49 CFR 101.
The hazmat identification number is a four-digit number (also known as the United Nations/ North American, or UN/NA number) and is assigned to each listed hazardous material in the hazardous materials table. The four-digit hazmat ID numbers are grouped into 21 divisions that are categorized by 9 distinctive Hazard Classes. This regulatory structure is now universal, having been developed and implemented by international committees organized under the authority of the United Nations.
Building on this existing detailed and hierarchical regulatory scheme—while at the same time collecting shipment data by the Standard Classification of Transported Goods (SCTG) codes—the CFS compiles a robust dataset of hazardous materials estimates by asking hazardous materials shippers to enter a four-digit UN/NA identification number on the CFS questionnaire. These data allow for the production of separate CFS analyses including a Hazardous Materials Report that displays hazardous material data sorted by hazard class, division, and selected hazmat ID numbers by the standard CFS characteristics of mode, value, tons, ton-miles, and distance shipped.
Although there are alternative data sources for obtaining data on hazardous materials shipments in the rail and water modes, CFS hazardous materials data is the only publicly available source of hazardous materials flow data for the highway and air modes, as well as multiple-mode combinations.