<P> UN numbers (United Nations numbers) are four - digit numbers that identify hazardous materials, and articles (such as explosives, Flammable Liquids to oxidizing solid or toxic liquids, etc .) in the framework of international transport . Some hazardous substances have their own UN numbers (e.g. acrylamide has UN 2074), while sometimes groups of chemicals or products with similar properties receive a common UN number (e.g. flammable liquids, not otherwise specified, have UN1993). A chemical in its solid state may receive a different UN number than the liquid phase if their hazardous properties differ significantly; substances with different levels of purity (or concentration in solution) may also receive different UN numbers . </P> <P> UN numbers range from UN 0004 to about UN 3534 (UN 0001--UN 0003 no longer exist) and are assigned by the United Nations Committee of Experts on the Transport of Dangerous Goods . They are published as part of their Recommendations on the Transport of Dangerous Goods, also known as the Orange Book . These recommendations are adopted by the regulatory organization responsible for the different modes of transport . </P>

On which corner of a placard is the un hazard class number present