Editing UN number (section)

{{Short description|United Nations code for dangerous substances}}{{Multiple issues|
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[[File:Placard 1814.jpg|200px|thumb|A United States [[Placard#United States Department of Transportation|placard]] showing the UN number 1814, indicating [[potassium hydroxide]] solution, on a railroad tank car.]]
A '''UN number''' ([[United Nations]] number) is a four-digit number that identifies [[hazardous materials]], and articles (such as [[explosive]]s, [[flammable liquid]]s, [[oxidizer]]s, [[toxic]] liquids, etc.) in the framework of [[international trade]] and [[transport]]. Some [[hazardous substances]] have their own UN numbers (e.g. [[acrylamide]] has UN 2074), while sometimes groups of [[Chemical substance|chemicals]] or products with similar properties receive a common UN number (e.g. flammable liquids, not otherwise specified, have UN 1993). A chemical in its [[solid]] state may receive a different UN number than the liquid phase if its hazardous properties differ significantly; substances with different levels of purity (or [[concentration]] in solution) may also receive different UN number