What do UN identification numbers indicate about a chemical?

UN identification numbers serve as a critical tool for identifying hazardous materials in transport, particularly in international shipping. These numbers are assigned by the United Nations and cover a vast range of chemicals and substances that pose various risks during handling and transport. When a chemical is assigned a UN number, it indicates that the substance can be safely and systematically transported, allowing for international standardization and safety protocols.

A key aspect of these identification numbers is that they enable emergency responders and transport personnel to quickly recognize the potential hazards associated with a material, ensuring appropriate precautions and measures are taken. Since UN numbers are recognized globally, they facilitate international trade and transport of hazardous materials, affirmatively indicating that the chemical in question may be shipped internationally under the regulations established for safe transport.

The other options do not accurately reflect the purpose of UN identification numbers. They do not exclude substances from transport or indicate non-hazardous statuses, nor are they limited to domestic use. Instead, they are fundamentally tied to international shipping protocols, which focus on safety and compliance for hazardous materials in transport.