1. "Hazardous Materials" (known as hazmats,) is the U.S. wording for what are known in the rest of the world as "Dangerous Goods." The two terms are almost synonymous. The "Dangerous Goods" designation is slowly becoming assimilated into the American vocabulary.

2. Officially, hazmats are substances or materials determined by the Secretary of Transportation of the United States to be capable of posing an unreasonable risk to health, safety, and property, when transported in commerce, and which has been so designated. Hazardous waste materials are covered by the term, but that is far from being a complete list. Included also, are marine pollutants, and elevated temperature materials.

3. On the books also are the hundreds of often common materials that are designated as hazardous under the provisions of Code of Federal Regulations, Title 49 (known in the transportation industry as 49CFR, or Title 49, CFR); i.e. aerosols, paint, perfumery products, air bag modules, refrigerators, gas shocks, internal combustion engines, etc.

4. The official listing of hazardous materials for U.S. purposes can be found in 49CFR at 172.101. Specific references to the Department of Transportation's regulations for the correct identification, classification, description, packaging, marking, labeling and transporting of such materials are found there also.

5. Generally, hazmats fall into one of nine classes (In the real world, some items even fall into two or more classes, so that an item might easily have a major hazard and one or more secondary, "subsidiary" risks.):

Class 1,           Explosives

Class 2,           Gases

Class 3,           Flammable liquids

Division 4.1,     Flammable solids

Division 4.2,     Spontaneously combustible substances

Division 4.3,     Substances that are dangerous when wet

Division 5.1,     Oxidizing substances

Division 5.2,     Organic peroxides

Division 6.1,     Toxic (poisonous) substances

Division 6.2,     Infectious substances

Class 7,           Radioactive material

Class 8,           Corrosive materials

Class 9,           Miscellaneous dangerous goods (Items that do not readily fit into any of the 
                      other classes, i.e. Motor vehicles; consumer commodities; asbestos, white.)

Tip: Your definitive reference source is 49CFR starting at 172.101. (Parts of 49CFR may be downloaded (off the Department of Transportation's Washington, DC, website) by clicking on this hotlink: <http://www.myregs.com/dotrspa/>.)