Shipping UN 3373 Biological Substances From Miami: Packaging, Paperwork and Cold Chain

Miami moves a lot of diagnostic material. Clinical trial samples, laboratory specimens, veterinary samples and research material flow through MIA to and from Latin America and the Caribbean constantly. Most of it travels as UN 3373, Biological Substance, Category B – and most of the rejections at the counter come down to the same handful of avoidable mistakes.

This is an operational overview. Always work from the current edition of the IATA Dangerous Goods Regulations and your carrier’s variations, since both change annually.

What UN 3373 covers – and what it does not

Category B (UN 3373) is infectious substance material that does not meet the criteria for Category A. In practice this is the great majority of diagnostic and clinical specimens: blood, serum, tissue, swabs, cultures for routine diagnosis.

Category A (UN 2814 / UN 2900) is material capable of causing permanent disability or life-threatening disease in otherwise healthy humans or animals. It has a far stricter packaging standard, requires a Dangerous Goods Declaration, and is a different shipping process entirely. If your material is Category A, stop and speak to a qualified DG specialist.

There are also exempt human and animal specimens – material with minimal likelihood of containing pathogens. These still need triple packaging and the “Exempt human specimen” or “Exempt animal specimen” marking, but they are not dangerous goods.

Classification is the shipper’s responsibility, and it must be made by someone qualified to make it. Getting it wrong in either direction causes problems: over-classifying creates unnecessary cost and delay; under-classifying is a regulatory violation.

Packing Instruction 650: the triple packaging rule

Category B material ships under Packing Instruction 650, which requires three layers:

1. Primary receptacle – leakproof, holding the specimen itself. Sealed, and wrapped in enough absorbent material to soak up the entire contents if it leaks.
2. Secondary packaging – leakproof, containing the primary receptacle(s). If multiple primaries are used, they must be individually wrapped or separated so they cannot contact each other.
3. Outer packaging – rigid, with at least one surface measuring 100mm x 100mm minimum, and the whole package capable of passing a 1.2 metre drop test.

An itemised list of contents goes between the secondary and outer packaging. For air transport, liquids in the primary receptacle are limited to 1 litre, and the total package to 4 litres; solids are limited to 4 kg.

Use pre-qualified P650 kits. Assembling your own compliant packaging from generic materials is possible but not worth the risk for routine shipments.

Marking and labelling

The outer package needs:

• The UN 3373 diamond marking – a square-on-point at least 50mm x 50mm with 2mm lines, with “UN 3373” inside.
• The proper shipping name “BIOLOGICAL SUBSTANCE, CATEGORY B” adjacent to the diamond, in letters at least 6mm high.
• Full shipper and consignee names and addresses.
• The name and phone number of a responsible person for air shipments.
• An orientation arrow if the primary receptacle exceeds 50ml of liquid.

No Dangerous Goods Declaration is required for Category B by air, which surprises people. But the air waybill must show “Biological Substance, Category B” and “UN 3373” in the nature and quantity of goods field.

Where dry ice complicates things

Most Miami-origin biological shipments need to stay cold, and that usually means dry ice – which is its own dangerous good, UN 1845, Class 9.

When you add dry ice, the shipment becomes a multi-hazard consignment. You now need:

• The Class 9 dry ice label with the net weight of dry ice in kilograms marked on the package.
• Packaging that vents – a sealed container with dry ice inside can rupture.
• The dry ice entry on the air waybill in addition to the UN 3373 entry.
• Carrier acceptance for the dry ice quantity, which some passenger aircraft limit.

Sublimation rate matters operationally. Dry ice sublimates continuously, and a shipment packed on Friday for a Monday delivery may arrive warm and empty. Our guides on shipping dry ice by air under PI 954 and dry ice logistics in Florida cover the quantity calculations.

If the material tolerates it, gel packs or a validated phase-change shipper avoid the dangerous goods layer entirely. That is often the cheaper and more reliable answer for 2-8 degree Celsius material.

Training – the requirement people forget

Anyone preparing UN 3373 shipments for air transport needs dangerous goods training appropriate to their function, with records retained. This applies even though Category B does not require a DG Declaration. Carriers do audit it, and a lab technician packing shipments without documented training is a genuine compliance gap.

Why Miami shipments get rejected

The recurring reasons, in rough order of frequency:

• Marking too small or wrong dimensions. The 50mm diamond and 6mm text are specific measurements, not guidelines.
• Insufficient absorbent material. It must absorb the entire liquid contents, not some of it.
• Dry ice weight not marked, or marked in pounds instead of kilograms.
• Sealed dry ice packaging that cannot vent.
• Missing responsible person contact on air shipments.
• Import permit missing at destination. Many Latin American and Caribbean countries require a health ministry permit for biological material. This is a destination-side requirement that no amount of correct US-side packaging fixes.

Getting it out of Miami reliably

Time-critical biological material out of MIA generally needs three things lined up: a compliant package, a confirmed flight with dry ice acceptance, and ground handling that does not leave the box on a hot ramp. For temperature-sensitive life sciences freight we handle the ground leg, cold storage and airport recovery together – see our pharma logistics and clinical trial logistics pages, or talk to our team about a specific lane.

Frequently asked questions

Do I need a Dangerous Goods Declaration for UN 3373?

No. Biological Substance, Category B shipped under UN 3373 does not require a Shipper’s Declaration for Dangerous Goods by air. However, the air waybill must state ‘Biological Substance, Category B’ and ‘UN 3373’, and the package must carry the UN 3373 diamond marking and proper shipping name. If dry ice is added, its details must also appear on the air waybill.

What is the difference between Category A and Category B infectious substances?

Category A material is capable of causing permanent disability or life-threatening disease in otherwise healthy humans or animals, and ships as UN 2814 or UN 2900 with strict packaging and a Dangerous Goods Declaration. Category B, shipped as UN 3373, covers material that does not meet that threshold – most routine diagnostic and clinical specimens. Classification is the shipper’s responsibility.

Can I ship UN 3373 with dry ice?

Yes, and it is common for temperature-sensitive specimens. Adding dry ice makes the shipment a multi-hazard consignment: you need the Class 9 label, the net dry ice weight marked in kilograms, venting packaging, and both entries on the air waybill. Carrier and aircraft limits on dry ice quantity apply, so confirm acceptance before you pack.