What is UN3373? Biological Substance, Category B: meaning, conditions, exemptions and misconceptions

Dangerous goods are given a four-digit UN number worldwide, so that everyone in the transport chain means the same substance. For road transport those numbers are in the ADR, the European agreement on the carriage of dangerous goods by road. UN 3373 sits in Class 6.2, infectious substances. The ADR describes infectious substances as substances which are known or reasonably expected to contain pathogens: micro-organisms such as bacteria, viruses, parasites and fungi, or prions, that can cause disease in humans or animals.

In the Netherlands the ADR is not only a rule for international transport. The Dutch Act on the Transport of Dangerous Goods applies to carrying, offering, accepting, loading, unloading and packing dangerous goods without regard to borders, and the regulation on the transport of dangerous goods by land makes the Dutch translation of the ADR applicable to road transport within the Netherlands. The same follows from the European directive on the inland transport of dangerous goods, which prescribes the ADR annexes for transport within and between the Member States. A ride from a collection point to a laboratory in the next town is therefore covered.

The ADR is revised every two years; the text in force now is the 2025 edition. In the Netherlands the Human Environment and Transport Inspectorate (ILT) supervises transport, loading and unloading, and packing.

The ADR divides infectious substances into two categories. Category A is an infectious substance which, in the form in which it is transported, is capable of causing permanent disability or life-threatening or fatal disease in otherwise healthy humans or animals when exposure occurs. Those substances are assigned UN 2814 (affecting humans and animals) or UN 2900 (affecting animals only). The ADR gives an indicative list of examples, such as Ebola virus, Lassa virus and Marburg virus; many other pathogens appear on that list only when transported as cultures. In case of doubt, Category A applies.

Category B is an infectious substance that does not meet the criteria of Category A. UN 3373 is intended for it, with the proper shipping name BIOLOGICAL SUBSTANCE, CATEGORY B. The World Health Organization writes in its guidance on the transport of infectious substances that most shipments can be transported as Category B.

The ADR also recognises the exempt human or animal specimen: a specimen with a minimal likelihood of containing pathogens. That is not a dangerous good within the meaning of the ADR, provided it is carried in a leakproof packaging marked 'Exempt human specimen' or 'Exempt animal specimen', in three layers with absorbent material, and with an outer packaging of which at least one surface measures 100 by 100 millimetres. The ADR gives as examples tests for cholesterol, glucose, hormones, PSA, organ function, pregnancy, and biopsies to detect cancer. Here too professional judgement is required, based on the patient's history, symptoms, circumstances and the local situation.

Patient specimens are, in the ADR, all materials collected directly from humans or animals, such as blood, urine, tissue and swabs, transported for research, diagnosis or treatment. Which of the three groups applies to a specimen depends on what it contains and on the circumstances. More on the requirements for specimen transport as a whole is in transporting medical specimens.

Classification is not the courier's job. Under the ADR the sender has to ascertain that the goods are classified and authorised for carriage, has to give the carrier the necessary information and documents, and may only use approved and properly marked packagings. The sender may rely on information provided by others, and whoever instructs the sender has to point out dangerous goods to them in writing. The ILT summarises it like this: the sender classifies the substance, provides information and documents and ensures correct packaging and marking; the sender may outsource those tasks, but remains responsible.

The WHO explains how that decision comes about: through sound professional judgement, by the sender, who has to be able to justify the classification. If the sender cannot reasonably conclude that the likelihood of pathogens is minimal, it is Category B. A carrier may advise, but the sender remains responsible for identification, classification, packaging, marking and documentation.

For a laboratory, collection point or practice this means there has to be an internal rule: who decides, on what basis, and where that decision can be found. How that works in the daily chain from collection to analysis is described in laboratory transport.

Packing instruction P650 applies to UN 3373. The packaging consists of at least three components: a primary receptacle, a secondary packaging and an outer packaging, of which either the secondary or the outer packaging is rigid. For liquids the primary receptacle and the secondary packaging must be leakproof, there must be enough absorbent material between them to absorb the entire contents, and the primary or the secondary packaging must withstand an internal pressure of 95 kPa. Solids must be packed siftproof. The complete package must pass a drop test of 1.2 metres.

The outer packaging carries a diamond-shaped mark of at least 50 by 50 millimetres containing UN3373, and next to it the proper shipping name BIOLOGICAL SUBSTANCE, CATEGORY B in letters at least 6 millimetres high. One surface of the outer packaging measures at least 100 by 100 millimetres. The manufacturer or distributor of the packaging must give the sender clear instructions on filling and closing.

For road transport P650 sets no quantity limit per package. The limits of 1 litre per primary receptacle and 4 litres per outer packaging that are often quoted come from the air transport rules (ICAO and IATA) and are not in the ADR. The full explanation of the packaging, with the mistakes that most often show at pickup, is in packing instruction P650; how the ADR applies in the Netherlands and which exemptions exist in ADR and medical specimens.

In the ADR's list of dangerous goods (Table A), UN 3373 carries special provision 319. It says that substances packed, and packages marked, in accordance with P650 are not subject to any other provision of the ADR. In practice that means: no dangerous goods transport document, no orange plates on the vehicle, no ADR training certificate for the driver and no other ADR equipment, as long as the packaging and the marking are correct. The WHO confirms that no dangerous goods transport document is required for UN 3373 packed under P650.

The exemption therefore depends entirely on the packaging and the mark. A shipment that is not packed or marked in accordance with P650 does not fall under it. Category A (UN 2814 and UN 2900) has no such exemption: packing instruction P620 applies there, with a transport document stating the technical name or the suspected Category A classification, and the other ADR provisions.

Anyone searching the ILT website for exemptions from the ADR will not find UN 3373 there. That is no omission: the exemptions listed there, for private individuals, limited quantities, the 1000-point rule and the like, do not apply to UN 3373, for which the limited quantity is zero. The route for UN 3373 is special provision 319.

When specimens are transported on dry ice, a second substance comes into play: UN 1845, carbon dioxide, solid. Dry ice is not subject to the ADR, except for the provisions of chapter 5.5.3 on coolants. These require, among other things, that the packaging can release the gas so that no pressure builds up, that the vehicle is well ventilated or otherwise carries a warning, that the people involved are trained in line with their responsibilities, and that the package is marked CARBON DIOXIDE, SOLID or DRY ICE with the words AS COOLANT, in an official language of the country of origin and, if that is not English, French or German, also in one of those. The WHO makes the same point: the packaging must be able to vent the carbon dioxide.

Refrigerated transport without dry ice, for example in a cool box with cooling elements, adds no further dangerous good. Which temperature a specimen needs is not an ADR question but a laboratory question; see temperature-controlled transport.

The carrier has its own duties under the ADR. It checks that the goods are authorised for carriage and that the prescribed information has been provided and the documents are on board, and it ascertains by visual inspection that the vehicle and the load show no obvious defects, leakage or cracks. The carrier too may rely on the information of the other participants. If it finds an infringement, it may not continue the transport until the provisions have been complied with.

For a UN 3373 shipment this comes down to: is the diamond mark present and legible, is the proper shipping name next to it, is the outer packaging intact and dry, and was the shipment announced as agreed? What is inside the inner packaging and whether the 95 kPa requirement was met, a courier cannot see at pickup. That is, and remains, the sender's responsibility.

'All blood samples are UN3373.' No. Besides Category B, the ADR recognises Category A and the exempt specimen. A tube of blood for a cholesterol test on a healthy patient can be an exempt specimen; a culture of a dangerous pathogen can be Category A. Classification follows from the contents and the circumstances, per shipment.

'The courier determines the classification.' No. The sender classifies and has to be able to justify it; the courier checks what is visible and may rely on the sender's information.

'A UN3373 shipment needs an ADR transport document and a driver with an ADR certificate.' Not when the shipment is packed and marked in accordance with P650: it is then exempt from all other ADR provisions through special provision 319. For Category A it is different.

'There is such a thing as a UN3373-certified packaging or courier.' The text of P650 contains no quality mark and no certificate. It contains requirements for the packaging and for the mark. A packaging supplier can show that its product meets P650, for instance with test reports; that is something other than a certification of the carrier.

'Category B means harmless, so no rules.' Category B is less dangerous than Category A, but P650 does impose requirements: three layers, absorbent material, pressure resistance, a drop test and marking. The exemption of special provision 319 only applies when those are met.

'The 4-litre limit per package applies everywhere.' That limit comes from the air transport rules. For road transport under the ADR, P650 sets no quantity limit per package.

Anyone offering specimens for transport prevents most mistakes with a short fixed routine.

How UrgentX transports UN3373 shipments and what we check at pickup is described under transport of laboratory samples.

• Record who makes the classification (Category A, Category B or exempt) and on what basis, so that you can justify it.
• Pack in accordance with P650: primary receptacle, secondary packaging with absorbent material, rigid outer packaging; follow the supplier's filling and closing instructions.
• Put the diamond-shaped UN3373 mark and the proper shipping name on the outer packaging; use the marking 'Exempt human specimen' for exempt specimens.
• Tell the carrier in advance what is being shipped, under which temperature condition, and who the contact person is.
• Hand over with name and time, so that the chain from collection to analysis can be traced afterwards.