United Nations (UN) Numbers are four-digit numbers used world-wide in international commerce and transportation to identify hazardous chemicals or classes of hazardous materials. These numbers generally range between 0000 and 3500 and are ideally preceded by the letters "UN" (for example, "UN1005") to avoid confusion with other number codes. North American (NA) Numbers are identical to UN numbers. If a material does not have a UN number, it may be assigned an NA number; these are usually 4-digit numbers starting with 8 or 9 such as 9037 (or ideally, NA9037), the NA number for hexachloroethane. UN/NA numbers are required for the shipment of hazardous materials. You have probably seen placards (such as the one on the right) that bear a UN/NA number on railway cars, trucks, shipping containers etc.