The UN Recommendations on the Transport of Dangerous Goods are contained in the UN Model Regulations prepared by the Subcommittee of Experts on the Transport of Dangerous Goods of the United Nations Economic and Social Council (ECOSOC).
"Dangerous goods" (also known as "hazardous materials" or "HAZMAT" in the United States) may be a pure chemical substance (e.g. TNT, nitroglycerin), mixtures (e.g. dynamite, gunpowder) or manufactured articles (e.g. ammunition, fireworks).
The most common dangerous goods are assigned a UN number, a four digit code which identifies it internationally.
[1] From 1996, the Recommendations were effectively split into two parts: the Model Regulations, which form a suggested drafting for laws and regulations on the transport of dangerous goods; and the Manual of Tests and Criteria, which contains technical information about methods of testing products to ascertain their hazards.
The package testing is based on the packing group (hazard level) of the contents, the quantity of material, and the type of container.