UN3373 Category B Packaging Explained: IATA PI 650, 95 kPa and What Inspectors Look For

Most human and animal samples that leave a Canadian collection site travel as UN3373 — Biological substance, Category B. The packaging rules for that classification are specific, compact, and frequently misunderstood. Getting them wrong is not a paperwork problem: it is the reason a sample leaks in transit, a courier refuses a shipment, or an inspector writes a finding during a laboratory assessment.

This guide sets out how Category B is classified, what Packing Instruction 650 requires, what the 95 kPa rating actually proves, and where inspections usually find gaps.

How do you decide between Category A and Category B?

Classification comes before packaging. Category A covers an infectious substance in a form capable of causing permanent disability, life-threatening or fatal disease in otherwise healthy humans or animals. Category B covers infectious substances that do not meet that threshold, which includes most patient specimens sent for routine diagnostic testing.

Cultures and laboratory stocks deserve a second look: a culture of a pathogen is assessed on its own, not on the patient it came from, and some cultures belong in Category A. If a sample is transported with the wrong assignment, the packaging that follows will be wrong as well. The WHO guidance on the transport of infectious substances is the reference used to make that decision, and it is the document a Canadian laboratory should be able to point to when a classification is questioned.

What does Packing Instruction 650 require for UN3373?

Category B substances travel under Packing Instruction 650 in the IATA dangerous goods regulations. The instruction describes a three-layer package and four performance requirements. What it does not require is equally important: a UN specification packaging or a shipper's declaration for dangerous goods, which is what makes Category B practical for daily laboratory transport.

For liquids, multiple primary receptacles may be placed in one secondary packaging provided the absorbent capacity and the quantity limits of the instruction are respected. Documentation travels outside the secondary packaging — a specimen bag with a separate document pocket exists precisely so the requisition never shares space with the sample.

What does the 95 kPa figure actually mean?

The pressure requirement is a performance test, not a product feature: the primary receptacle, or the secondary packaging enclosing it, must withstand a pressure differential of at least 95 kPa without leakage. In practice this addresses the pressure changes a package experiences during handling and air transport, and it is the reason a laboratory cannot substitute a generic zip bag for a validated specimen bag when the bag forms part of the packaging system.

Two consequences follow. First, the rating belongs to a tested design, so a supplier should be able to produce the test basis for the bag they sell, not just a claim on the catalogue page. Second, the rating is one element of the system. A 95 kPa bag inside a soft envelope is not a compliant package, because the outer layer still has to be rigid and to pass the drop test.

How does Canada apply the UN3373 rules?

For the ground leg within Canada, the Transportation of Dangerous Goods Regulations (SOR/2001-286) govern the consignment, and Category B substances carried domestically follow the same packaging logic as the international instruction. For anything moving by air, the IATA instruction applies for the whole journey. A courier's own terms apply in addition, and couriers commonly require their own packaging kit for Category B accounts.

Canadian laboratories also work to standards published by CSA Group for related facility and container requirements, which is why packaging documentation often sits in the same folder as the sampling procedure rather than in a shipping binder.

What do inspectors look for in a Category B shipment?

• A written procedure that names packaging components, absorbent material, markings and the quantities allowed per package, with training records for the people who pack.
• Traceability from the sample to the package and the courier handover, including time out and time in.
• Temperature control where the sample type requires it, with monitoring and a defined response when limits are exceeded.
• A rejection and incident log covering leaked packages, refused shipments and late arrivals — the record that shows the process genuinely runs.
• Supplier evidence that specimen bags and secondary packaging meet the pressure and containment requirements claimed for them.

The explainer on 95 kPa seal standards covers the bag side in more detail, and the clinic supplies collection lists the containment items laboratories stock most often.

Which packaging mistakes show up most often in assessments?

1. Using a generic bag as the secondary packaging because it seals, without a pressure rating or test basis.
2. Forgetting absorbent material, or using a pad too small to absorb the full volume of the primary receptacle.
3. Placing the requisition inside the sample bag instead of in the outer document pocket.
4. Shipping a culture as Category B without re-checking the classification.
5. Recording the sample as sent without recording who received it — the handover gap that turns a lost sample into a finding.

Fixing these is mostly a matter of writing the procedure around the instruction, stocking the components it names, and keeping the record. That means the whole chain of containment, not just the outer bag: leak-proof graduated specimen cups as primary receptacles, and individually wrapped swabs for environmental surface and equipment sampling. A 95 kPa specimen bag with an external document pocket covers the containment and the paperwork separation in one item; paired with a rigid outer container, it forms the working part of a Category B package.

Before standardising on one spore test format, request the 5-pack biological indicator trial and run it alongside your current product for a week.

How do I ship Category B infectious substances in Canada?

The shipment is built around the classification, not around the courier's paperwork: once a sample is correctly assigned to Category B, the packing instruction tells you exactly what the package must contain, and the Canadian and international rule sets agree on that much.

1. Confirm the classification first. Category B covers specimens that do not meet the Category A threshold; a culture is assessed on its own, and the WHO guidance on the transport of infectious substances is the reference a Canadian laboratory should be able to point to.
2. Assemble the three layers. A leak-proof primary receptacle, absorbent material sized to absorb the entire contents of that receptacle inside the secondary packaging, and a rigid outer package.
3. Mark the outer package. The UN3373 diamond and the words Biological substance, Category B, with the name and telephone number of a responsible person.
4. Use a courier that accepts Category B infectious substances. Courier terms apply in addition to the regulations, and some accounts require the courier's own packaging kit.
5. Keep the requisition outside the secondary packaging, in the document pocket, so the form never shares space with the sample.
6. Record the packing. Time out and time in, the courier handover, the components used and the packaging lot, so the consignment can be reconstructed from records.

For the ground leg inside Canada the Transportation of Dangerous Goods Regulations (SOR/2001-286) govern the consignment, and anything moving by air follows the IATA instruction for the whole journey. Neither leg requires UN specification packaging or a shipper's declaration for Category B, which is what keeps the process workable for daily laboratory transport.

What packaging is required to ship Category B biological specimens (UN3373)?

Three layers, in this order: a leak-proof primary receptacle such as the tube or vial; leak-proof secondary packaging holding enough absorbent material to absorb the entire contents of the primary receptacle; and a rigid outer package marked UN 3373 and labelled with a name and telephone number of a responsible person. Category B does not require UN specification packaging and does not require a shipper's declaration for dangerous goods. What it does require is the marking, absorbent capacity matched to the sample volume, and an outer package that passes the drop and pressure tests set out in Packing Instruction 650.

In daily clinic practice those three layers are usually two items: a 95 kPa specimen bag with a document pocket acting as secondary packaging with the absorbent wrap inside it, plus a rigid outer container. The failure that shows up most often in compliance write-ups is the absorbent pad rather than the bag — an under-sized pad passes a visual check and only fails the day a tube breaks. For capped cultures, dry swabs and low-volume samples the same three-layer logic applies with less absorbent material.

The UN3373 detail most summaries leave out: Category B is the dangerous goods entry where the package does not need UN specification packaging and the shipment does not need a shipper's declaration for dangerous goods. What replaces both is performance — absorbent capacity matched to the entire primary volume, and an outer package that passes the drop and pressure tests set out in Packing Instruction 650. That is why the under-sized absorbent pad, not the bag, is the failure that shows up most often in compliance write-ups.

Labs standardising the configuration across several collection sites can request a bulk quote for bags, absorbent and outer containers in one order.

Related Reading

• Specimen Shipping Compliance: Packaging Rules for Canadian Labs — the shipping view of the same requirements.
• ISO 15189 in Canada: What It Requires of Sample Transport and Lab Consumables — how packaging fits a laboratory quality system.
• Specimen Bag Labeling Requirements for Canadian Laboratories — what goes on the bag and the request form.
• Next in this series: a compliant specimen transport workflow — from the point-of-care site to the central laboratory.
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Frequently Asked Questions

What is the difference between UN3373 and Category A?

UN3373 is the entry for Biological substance, Category B: infectious substances that do not meet the Category A threshold of causing permanent disability, life-threatening or fatal disease. Category A substances are assigned to UN2814 or UN2900 and require UN specification packaging and a dangerous goods declaration; Category B does not.

Does Category B packaging need a UN specification box?

No. Packing Instruction 650 requires compliant three-layer packaging and markings rather than a UN specification packaging, and no shipper's declaration for dangerous goods is required. The outer packaging still has to be rigid and to meet the drop and pressure performance requirements.

What does the 95 kPa rating apply to?

It applies to the primary receptacle, or to the secondary packaging that encloses it, which must withstand a pressure differential of at least 95 kPa without leakage. A bag that carries the rating is only one component; the rigid outer packaging is still required.

How much absorbent material is required?

Enough to absorb the entire liquid contents of the primary receptacle or receptacles inside that secondary packaging. Undersized pads are one of the most common packaging failures found in practice, and they fail silently until a package leaks.

Where should the requisition form travel?

Outside the secondary packaging, in a separate compartment such as the document pocket of a specimen bag. Paperwork placed inside with the sample both risks contamination of the form and puts the sample at risk if the paperwork becomes wet.

How do I ship Category B infectious substances from a clinic in Canada?

Treat the shipment as UN3373: a leak-proof primary receptacle, absorbent material able to absorb the full contents of that receptacle, and a rigid outer package marked UN 3373 with a responsible person named. Use a courier that accepts Category B infectious substances, keep the requisition in a separate compartment outside the secondary packaging, and keep a packing record. No shipper's declaration for dangerous goods is required for Category B, and UN specification packaging is not required either.

Last updated: September 11, 2026. CliniEco Medical is a licensed medical device establishment (MDEL #35334).