What Is UN Number Marking? Regulatory Basics For U.S. Shippers

UN Number Marking A package marking displaying the applicable four-digit UN identification number for a dangerous good. This marking links the packaged material to the official UN identification number used in emergency response, documentation, and modal regulations.

The U.S. Hazardous Materials Regulations incorporate UN identification numbers as a primary method to identify dangerous goods across road, rail, air and sea. A correctly applied UN Number Marking helps carriers, first responders, and receiving facilities determine hazards quickly and comply with transport rules found in 49 CFR and international modal codes.

What The Marking Must Include

At minimum the marking must show the letters "UN" immediately followed by the assigned four-digit number (for example, UN1203 for gasoline). The marking is distinct from the proper shipping name and hazard class labels — it is the numeric identifier intended to be machine- and human-readable for emergency and regulatory use.

• Identification: The letters "UN" plus four digits representing the UN number assigned to the substance or article.
• Durability: The marking must be durable and remain legible through normal transport conditions and reasonably foreseeable handling.
• Visibility: It must be on the outside of the package, overpack, or unit load where it can be readily seen without moving the load.

Why It Matters

UN identification numbers are a universal shorthand that reduces ambiguity in the supply chain. When emergency responders arrive at an incident, the UN number provides immediate access to hazards, firefighting measures, and isolation distances in emergency response guides. For shippers and carriers, the number also determines packaging standards, segregation rules, and documentation requirements.

How It Varies By Mode

The baseline requirement to display a UN number is consistent, but additional specifications differ by modal code. Air transport (IATA DGR) and maritime transport (IMDG Code) adopt the UN system and add size, placement, or wording requirements. Multimodal shipments should meet the strictest applicable requirement for each segment to avoid noncompliance during mode transfer.

Who Pays/Applies The Marking

• Shipper: Generally responsible for determining the proper shipping description, UN number, and applying required markings before offering the package to a carrier.
• Carrier: Responsible for accepting properly marked packages and may refuse shipment or require corrective actions when markings are missing or illegible.
• Consignee/Warehouse: Must preserve markings during storage, handling, and any repackaging operations.

Practical Example

A manufacturer ships drums of toluene by truck. The shipper assigns the proper shipping name "Toluene," the UN number UN1294, and marks each outer drum with "UN1294" in a durable, contrasting format. The carrier verifies the marking during tender; the receiving warehouse stores drums in accordance with segregation rules linked to the UN number and retains the marking through any subsequent repacking.

Tips For Compliance

• Cross-check: Verify the UN number against the proper shipping name, SDS, and modal rules before marking.
• Durable Materials: Use permanent ink, printed labels, or plates suited to weather and abrasion for shipments that may be exposed to the elements.
• Modal Rules: Confirm additional air or sea requirements (IATA/IMDG) that may dictate size or placement beyond domestic DOT rules.
• Documentation Match: Ensure the UN number on the physical package matches the number on the shipping papers and emergency response information.

In short, the UN Number Marking is the numeric link between a package and the regulatory/emergency guidance for that dangerous good. For U.S. shippers, apply the correct UN number visibly and durably, align the marking with modal regulations, and keep documentation synchronized to avoid delays and fines.