Shipping UN3373: Requirements guide for biological substances, Category B

When shipping biological materials across borders, precision and compliance are everything. Whether you need to ship samples for research, diagnostic testing, or clinical trials, understanding the UN3373 Biological Substances, Category B classification ensures your shipment reaches its destination safely and efficiently. This guide walks you through what UN3373 is, the packaging standards required, and how DHL Express can help to ensure your sensitive shipments meet international standards.

What are UN3373 biological substances

UN3373 refers to Biological Substances, Category B, which are infectious materials that do not meet the risk threshold of Category A (those capable of causing life-threatening infections).¹ These substances are regulated under Hazard Class 6.2 and are also subject to simplified Dangerous Goods (DG) requirements.

Examples include:

• Blood or urine samples sent for routine diagnostic testing
• Tissue samples or nasal swabs used in COVID-19 or influenza detection
• Human or animal body fluids collected for research or investigational purposes

Is UN3373 considered a Dangerous Good?

Yes, but it’s managed differently from highly infectious Category A materials (UN2814/UN2900). Shipments under UN3373 follow a simplified declaration process while maintaining strict packaging and labeling standards.

UN3373 vs. Exempt Human Specimen

An exempt human specimen refers to samples with minimal likelihood of infection, such as cholesterol, hormones, or pregnancy tests. However, if a professional deems there to be any suspicion that a pathogen may be present, the sample can no longer be considered exempt and must be classified as UN3373 Biological Substance, Category B.

UN3373 requirements for air transport (IATA PI 650)

All shipments containing UN3373 substances are required to comply with the IATA (International Air Transport Association) Packing Instruction 650 (PI 650) to ensure safe handling and international transport compliance. DHL Express fully supports the transport of UN3373 substances via our Air Express Network, adhering to IATA PI 650 for biological materials as well as PI 954 when dry ice is used as a refrigerant.

Key documentation requirements:

• Air Waybill (AWB): The “Nature and Quantity of Goods” box must clearly state ‘UN3373 Biological Substance, Category B’ and the number of packages (unless these are the only packages within the consignment).
• Emergency contact: The name and phone number of a responsible person must be included on the package or the AWB.

Quantity limits:

• Liquids: Primary receptacle maximum of 1 L; outer package maximum of 4 L
• Solids: Except for packages containing body parts, organs, or whole bodies, the outer packaging must not contain more than 4 kg. This quantity excludes ice, dry ice, or liquid nitrogen when used to keep specimens cold.

Compliance with PI 650 exempts shippers from formal DG declarations, provided all packaging and labeling requirements are met.

How to triple package UN3373 properly

To ensure safety during transport, UN3373 shipments must follow the triple packaging system — a core part of IATA PI 650.² This structure protects against leaks, contamination, and environmental exposure.

1. Primary receptacle:
   • Leak-proof (for liquids) or sift-proof (for solids).
   • If multiple fragile receptacles are placed in a single secondary packaging, they must be individually wrapped or separated to prevent contact between them.
2. Secondary packaging:
   • Another leak-proof or sift-proof container, such as a biohazard bag.
   • Include enough absorbent material to soak up all liquid in case of breakage.
   • For air transport, the primary receptacle or the secondary packaging must be capable of withstanding an internal pressure of 95 kPa without leakage for liquids.
3. Rigid outer packaging:
   • A strong fiberboard or plastic box with at least one surface measuring 100 mm x 100 mm.
   • Must withstand standard handling and stacking conditions during international shipping and be capable of passing a 1.2 m drop test without leakage.

If dry ice (UN1845) is included, it must be placed outside the secondary packaging but within the outer box. The packaging must also be designed and constructed to permit the release of carbon dioxide gas, preventing any pressure build-up that could rupture the package.

UN3373 packaging checklist

Use this checklist before scheduling a pickup to ensure your shipment meets all UN3373 packaging and labeling requirements:

This checklist acts as both a compliance tool and a quality assurance step, helping you pre-empt shipping delays or customs issues.

UN3373 labeling and marking requirements

Proper labeling ensures visibility for couriers and customs, reducing the risk of shipment rejection or delays.

• UN3373 diamond mark: A black-bordered diamond with the text ‘UN3373’ inside, displayed on a contrasting background. Minimum side length: 50 mm.

• Proper shipping name: The words ‘Biological Substance, Category B’ must appear next to the diamond mark in letters at least 6 mm high.

• Orientation arrows: For liquid shipments exceeding 50 ml, place two arrows on opposite sides of the outer packaging to indicate upright positioning.

• Additional markings (if applicable): If the shipment includes dry ice, the package must also display UN1845, the net weight of dry ice, and the ‘Dry Ice’ label.

Ship UN3373 biological substances securely with DHL Medical Express

Shipping biological substances requires precision, compliance, and care. DHL Medical Express offers end-to-end solutions designed specifically for transporting UN3373 Biological Substances, as well as clinical samples and research materials.

Why choose DHL Express for UN3373 shipments:

• End-to-end visibility: Track every step with real-time monitoring and temperature logging.
• Temperature control: Choose from ambient, controlled room (15–25 °C), chilled (2–8 °C), or frozen (< –20 °C) packaging with Pharmacool Cassettes, coolant wraps, or dry ice to maintain stability during transit. Optional Smart Sensor tracking is also available for real-time monitoring.
• Expert compliance support: Access Dangerous Goods specialists in Singapore who can review your documentation and packaging before pickup.
• Global reach: With DHL’s Air Express Network, your samples can reach over 220 countries and territories safely and efficiently.

Transporting Category B Biological Substances requires a firm grasp of international regulations and packaging protocols. By following IATA PI 650 standards, completing the right documentation, and using the triple packaging method, shippers can avoid costly delays and ensure regulatory compliance.

With DHL Medical Express, you gain a trusted partner who combines compliance expertise with reliable international transport for critical medical and research materials.