A substance or material may be classified as hazardous if the transportation of the material in a particular amount and form poses an unreasonable risk to health and safety or property. Hazardous materials are defined by the U.S. Department of Transportation in accordance with the Federal Hazardous Material Law and require special handling and documentation. For more general information, go to the U.S. DOT website at http://www.phmsa.dot.gov/hazmat.