UN 3373 and Packing Instruction P650 Explained

UN 3373 looks like a dangerous goods classification and in one sense it is, but it comes with the broadest exemption in ADR. Get the packaging right and a Category B sample travels as an ordinary secure consignment. Get it wrong and you are moving infectious substances with none of the driver, vehicle or documentation controls that class 6.2 otherwise demands.

What does UN 3373 mean on a package?

UN 3373 is the UN number for BIOLOGICAL SUBSTANCE, CATEGORY B — a substance containing or suspected of containing a pathogen that does not meet the criteria for Category A. Road carriage in Great Britain is governed by Packing Instruction 650 of ADR.

The practical meaning for a sender is narrower than the classification suggests. Pack and mark the consignment in accordance with P650 and, in the Department for Transport's words, no other requirement of ADR applies to your consignment. That means no ADR-qualified driver and no placarded vehicle for a movement that would otherwise be a class 6.2 dangerous goods job.

Everything therefore rests on the packaging being right. Get P650 wrong and you are not carrying an exempt consignment with a minor paperwork defect; you are carrying infectious substances outside the exemption, with the driver, vehicle and documentation requirements that attach to class 6.2.

Who decides whether a sample is Category A or Category B?

The consignor does, and the Department for Transport's guidance says so explicitly: classification of patient samples remains the responsibility of the consignor. A carrier cannot classify your sample for you and should not be asked to.

That split matters because the two categories travel completely differently. Category A substances take UN 2814 or UN 2900 and Packing Instruction P620, with UN-approved packaging and the full weight of ADR behind them. Category B takes UN 3373 and P650, with the broad exemption above.

If there is genuine doubt about which category applies, the question belongs with whoever took the sample, not with the courier booking screen. See UN numbers for how the four-digit codes work across the other classes.

What does P650 triple packaging actually require?

At least three components: a primary receptacle, a secondary packaging and an outer packaging. Either the secondary or the outer must be rigid — the instruction does not say which, and that flexibility is deliberate.

The Department for Transport's worked example is a sealed plastic bag as the primary, a sealed plastic bag as the secondary, and a suitably closed cardboard box as the outer. That is compliant, because the cardboard box supplies the rigidity.

Primary receptacles must be packed so they cannot break, be punctured or leak into the secondary under normal carriage. Secondary packagings are secured in the outer with cushioning material, and any leak must not compromise that cushioning or the outer. The guidance is specific about fragile items: glass vials loose in a plastic bag are only acceptable if each vial has its own cushioning, whereas the same vials individually located in a plastics box are well protected.

Does P650 packaging have to be UN approved or drop tested?

No to both, and this is where most unnecessary cost enters a sample-transport contract.

P650 does not reference ADR 4.1.1.3, the provision requiring successfully tested UN design-type packagings, so the Department for Transport's reading is that packaging under P650 does not require design-type approval. You are not obliged to buy certified UN packaging for Category B samples.

On testing, paragraph 6 requires the completed package to be capable of passing a drop test at 1.2 m — not to have passed one. VCA guidance is to either run an in-house test and keep a record of what was done, or compile an evidence folder: records of previous shipments, comparisons with similar packagings used without problems, with due regard to whether the contents are solid or liquid and to the mass of the package. An evidence folder is a legitimate answer to an inspector's question.

What are the marking requirements for UN 3373?

The mark is a square set at an angle of 45 degrees — a diamond, not a square — with minimum dimensions of 50 mm by 50 mm, a line width of at least 2 mm, and letters and numbers at least 6 mm high. It goes on the external surface of the outer packaging against a contrasting background.

Adjacent to it, the proper shipping name BIOLOGICAL SUBSTANCE, CATEGORY B must appear in letters at least 6 mm high. At least one surface of the outer packaging must measure a minimum of 100 mm by 100 mm, which is in practice what stops a sample travelling in a padded envelope.

The mark does not have to be pre-printed. It can be drawn directly onto the box in thick black pen, applied as a sticky label, or pre-printed — provided the dimensions are met and it is applied as a diamond. A square-applied label is a defect even when the artwork is otherwise correct.

What changes when the sample is a liquid, a solid, or frozen?

One useful interpretation sits behind the liquid row: if there is no free liquid present, it is not treated as a liquid substance. A sample completely absorbed into cotton wool is not a liquid for P650 purposes. Where dry ice is the coolant the separate obligations of ADR 5.5.3 attach — see shipping dry ice for what that means for the vehicle.

Does a UN 3373 consignment need a dangerous goods transport document?

No, where the exemption applies. Paragraph 11 of P650 puts it beyond doubt: a UN 3373 consignment packed and marked to the instruction is not subject to any other requirement in ADR, and the transport document under ADR 5.4.1 is one of those requirements.

That does not make paperwork pointless. A sample movement still needs a consignment record for the receiving laboratory, a chain-of-custody trail for the clinical audit, and a temperature record where the sample is temperature-sensitive. Those are contractual and clinical obligations rather than dangerous goods obligations, and they do not disappear because ADR has stepped back.

The distinction is worth drawing with whoever audits you, because the two sets of requirements are often conflated. Compare dangerous goods note for what a consignment outside the exemption has to carry — the contrast is stark, and it is the reason P650 compliance is worth getting right rather than treating as optional best practice.

Can other dangerous goods travel inside the same package?

Only where they are needed to keep the sample viable, stabilise it, prevent degradation or neutralise its hazards — and then only in small amounts. Up to 30 ml of dangerous goods in Classes 3, 8 or 9 may be packed in each primary receptacle containing infectious substances.

Within that limit, no other requirement of ADR has to be met for the added substance, and it does not need to be separately identified. A fixative or a preservative in a specimen pot is the ordinary case. Anything beyond 30 ml per primary receptacle takes the consignment out of this allowance and into mixed dangerous goods territory, which is a different conversation and a different document — see ADR.

Complete marked packages may also be placed inside an overpack for easier handling. There is no restriction on how many, but the required marks must either remain clearly visible or be reproduced on the outside of the overpack.

What does T&C Logistics need before collecting UN 3373 samples?

The classification, confirmed by you as consignor, and packaging already compliant with P650. We carry ADR competence across classes 2, 3, 4, 5, 6, 8 and 9 — we do not carry class 1 explosives or class 7 radioactives — but for a properly packed UN 3373 consignment the exemption means the job runs as a standard secure movement rather than a placarded one.

We are not an MHRA-licensed wholesale dealer and we are not GDP-certified; where a movement requires GDP conditions it runs through GDP-authorised partner carriers. Our biological samples courier page sets out the handling, and shipping IVF embryos covers the cryogenic case, which is governed differently again.

If a leak occurs in a vehicle, the vehicle cannot be reused until it has been thoroughly cleaned and, where necessary, disinfected or decontaminated, and other goods carried in it have to be examined for contamination. That is why we want the packaging standard settled before the first collection, not after an incident. Tell us the route and the sample type and we will confirm what we need in writing.