What is Hazmat? A history of Hazmat, Hazardous Materials Placards and markings - also known as Dangerous Goods markings from the 1800s to present

What is HAZMAT?
Where did the numbers come from?

Starting in the 1950s, regulators began to suggest standard markings as these materials began being traded and transported internationally, especially in the emerging European market. The United Nations Economic Commission for Europe (UNECE) created a list of what they called Dangerous Goods, and assigned each material a four-digit number starting with 0004 and going up. The highest number is currently 3496. These are known as U.N. numbers. Possibly because all the numbers under 1000 pertain to explosives, the U.S. only adopted 1001 and higher from this list in their own numbering scheme, but added another series of numbers between 8000 and 9500 to describe materials not covered specifically enough in the U.N. numbers. These are known as N.A. numbers because they are almost exclusive to the U.S. and Canada.

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There are several basic classes of HazMat in common use:

Also, see our Hazmat Code page

References:
o Bureau of Explosives of the Association of American Railroads
o United States Fire Administration Hazardous Materials Guide for First Responders
     (Search from the HSDL homepage -- no direct link)
o United Nations Economic Commission for Europe (UNECE)
o UNECE UN Codes
o U.S. DOT CFR 49.172.101 (para 172.332, page 378-379)