Labelling Dangerous Goods: UN Numbers, Hazard Labels and Vehicle Marking under the ADR

Under the European Agreement ADR and the national Dangerous Goods Ordinance for Road, Rail and Inland Waterways (GGVSEB), the labelling of dangerous goods is one of those obligations that admits no exceptions for ignorance. Chapter 5.2 ADR governs the marking of packages; Chapter 5.3 ADR governs the large-label marking of vehicles and containers. Incorrect or missing labelling constitutes an administrative offence under Section 10 GGVSEB for the consignor, the loader and, in certain cases, also the carrier.

This article systematically explains which labelling elements are required for packages and vehicles, how UN numbers, Kemler numbers and tunnel categories interact, and which special rules apply to limited quantities, excepted quantities and tank vehicles. For compliance officers and dangerous goods officers, it serves as a structured introduction to a complex, heavily regulated area.

The ADR distributes labelling obligations among multiple participants in the transport chain, each bearing independent responsibility. Subsection 1.4.2 ADR describes the consignor's obligations: they must ensure that packages are properly classified, packed, marked and labelled. Under subsection 1.4.3.2 ADR, the loader verifies whether the externally visible marking on the package complies with the regulations before the goods are handed over for transport.

This distribution of responsibilities has a practical consequence: errors made by the consignor in labelling may be identified and challenged by the loader — or may enter the transport chain undetected, where they are discovered during roadside checks by the Federal Office for Goods Transport (BAG) or the police. An inspection can trigger fines for several parties simultaneously, even where only one party caused the error. The loader's independent liability risk is therefore particularly significant.

The dangerous goods officer under Section 3 GbV has the task of ensuring within the company that labelling requirements are known, technically implemented and documented in the annual report under Section 7 GbV. Without systematic training of all employees involved — dispatch department, warehouse, drivers — labelling errors remain structurally unavoidable, as the ADR is complex and updated on a two-year cycle. Companies shipping dangerous goods for the first time should conduct structured introductory training for all employees involved, explicitly addressing company-specific substances and their labelling requirements.

Every dangerous good is assigned a four-digit UN number under the UN classification system. The UN number uniquely identifies the substance or group of substances and is the basis for all further regulations: packing group, quantity thresholds for exemptions, tunnel category, special provisions and exceptions. Subsection 5.2.1.1 ADR requires that the UN number be displayed in black numerals of at least 12 mm height on a white rectangle measuring at least 100 mm by 100 mm. For small packages whose surface area is insufficient for the standard size, the size may be reduced proportionally to the available area, provided the label remains fully legible.

The UN number need not be printed directly onto the package by the consignor; pre-printed labels and marking tapes are permissible, provided they adhere durably and remain legible. However, the applied UN number must correspond to the information in the transport document under section 5.4.1 ADR. Discrepancies between the transport document and the physical marking are a frequently cited violation during inspections.

For substances not individually listed in the ADR dangerous goods list (Chapter 3.2 Table A), generic collective entries with their own UN numbers apply. Employees in the dispatch department must master the correct assignment or use a verified reference tool. Misassignment of UN numbers is not merely a formal violation — it can impede emergency response in transport accidents, as rescue personnel make decisions based on the marking.

Hazard labels under ADR section 5.2.2 are diamond- or square-shaped labels with standardised graphic patterns that convey the hazard class of the goods at a glance. ADR 2025 recognises nine main classes with several subclasses: class 1 (explosives, subclasses 1.1 to 1.6), class 2 (gases, including flammable, toxic and non-flammable gases), class 3 (flammable liquids), classes 4.1 to 4.3 (flammable solids, self-reactive substances and water-reactive substances), classes 5.1 and 5.2 (oxidising substances and organic peroxides), classes 6.1 and 6.2 (toxic substances and infectious substances), class 7 (radioactive substances), class 8 (corrosive substances) and class 9 (miscellaneous dangerous substances and articles).

Subsection 5.2.2.1.1 ADR requires that hazard labels be affixed to a smooth, flat and solid surface of the package, parallel to the edges and in a clearly visible location. The minimum size is 100 mm by 100 mm. Substances with multiple hazardous properties receive primary and subsidiary hazard labels in accordance with the assignment rules in Chapter 3.2 Table A, column 5. In the case of combination packaging, each inner packaging must bear the appropriate label.

The most common error in practice is the missing subsidiary hazard label for substances with multiple hazards — for example a substance that is simultaneously flammable and toxic. During training sessions, the dangerous goods officer should explicitly highlight the obligation to apply subsidiary hazard labels and practise the assignment rules using the range of substances relevant to the company's operations.

Vehicle marking under ADR section 5.3.2 enables quick identification of the potential hazard for emergency services, police and inspection bodies before the transport document can be consulted. It consists of an orange rectangular warning panel 40 cm wide and 30 cm high with a reflective surface. The panel carries two lines: the Kemler number (also known as the hazard identification number) at the top, and the UN number of the goods being transported at the bottom. The panels must be affixed to the front and rear of the vehicle.

The Kemler number is a two- or three-digit code encoding the primary hazard and supplementary hazards. The first digit indicates the primary hazard (2 = gas, 3 = flammability, 6 = toxicity, 8 = corrosiveness, 9 = other hazard). The second and third digits describe supplementary hazard properties using the same key. A doubled first digit — for example 33 for highly flammable liquids or 66 for highly toxic substances — signals increased intensity of the primary hazard. A prefixed X means: do not extinguish with water.

For transports carrying multiple goods with different UN numbers, subsection 5.3.2.1.3 ADR applies: when carrying mixed consignments of different dangerous goods, orange panels without numbers are affixed, unless all goods share the same UN number. The dangerous goods officer should ensure that drivers are familiar with and can apply the combined loading panel under ADR Chapter 7.5 special provision CV33.

Large labels under ADR section 5.3.1 are the vehicle and container equivalent of hazard labels on packages. They are square with a minimum side length of 250 mm and correspond to the hazard labels for packages in terms of colour, pattern and numerals, but are designed for recognition at a distance. Chapter 5.3.1.2 ADR specifies which vehicle categories and container types require this marking: primarily tank vehicles, tank wagons, tank containers, UN large packaging and bulk containers.

Large-label marking for tank vehicles is technically complex: each class of dangerous goods transported requires its own large label. For multi-compartment tank vehicles carrying different substances in each compartment, all hazard classes of the tank contents must be represented with large labels on each long side of the vehicle; the arrangement follows the sequence of compartments. If the vehicle is travelling empty but has not been cleaned, the large labels for the most recently transported goods remain until proven cleaning has taken place.

Containers transported on vehicles are subject to their own requirements under subsection 5.3.1.3 ADR. If a container is positioned on a vehicle such that its long sides are not visible from the roadway, the vehicle must carry corresponding large labels on those sides. The dangerous goods officer should establish a standardised pre-departure checklist for tank vehicles documenting the completeness of large labels and warning panels. As part of regular company inspections, the dangerous goods officer should carry out random checks to verify that large labels are complete, clearly legible and not affected by contamination or mechanical damage.

The ADR provides for two quantity-threshold exemptions that significantly simplify labelling requirements. Transports in limited quantities under Chapter 3.4 ADR are exempt from hazard label marking on packages; instead, the diamond pattern for limited quantities — a black-and-white diamond label without a class numeral — suffices. Transports in excepted quantities under Chapter 3.5 ADR are permissible with virtually no special marking, provided the quantity thresholds per inner packaging and package are observed.

The quantity thresholds for limited quantities vary by substance and type of packaging and are set out in the ADR dangerous goods list (column 7a, maximum quantity per inner packaging or article). Even lower thresholds from column 7b apply to excepted quantities. If a single package exceeds the applicable threshold, the full labelling obligation under Chapter 5.2 applies immediately — there is no pro-rata exemption. Mixtures of excepted and standard quantities in one package are not permissible.

For tank containers and portable tanks, Chapter 6.7 ADR imposes special requirements regarding the durability of marking: it must be weather-resistant and legible for the entire service life of the container. Labels that detach when wet do not meet this requirement. As part of the annual operational audit, the dangerous goods officer should check the physical integrity of markings on tank containers and vehicles and document the results. The procedural instructions should also explicitly designate who within the company is responsible for deciding whether an exemption is to be claimed for a specific substance and packaging unit.

Marking and transport document form a legal unit under the ADR: every piece of information on the package or vehicle must correspond to the transport document, which is mandatory under subsection 5.4.1 ADR. The transport document must contain at least: the UN number preceded by the abbreviation "UN"; the official name for transport from the ADR list of substances; the hazard class; the packing group where applicable; and the total quantity of dangerous goods. Additional mandatory particulars apply for class 1 and class 7.

BAG inspections regularly verify consistency between the transport document and the physical marking. Discrepancies in the UN number or hazard class may lead to immediate objections and, in the event of serious discrepancies, to interruption of transport. The transport document must be accessible to the driver throughout the entire duration of transport and must be producible upon request; a digital version is permissible under subsection 5.4.0 ADR.

For companies with multiple dispatch points and different customers, a documented process is advisable: who creates the transport document? Who checks consistency with the physical marking before handing it to the driver? This consistency check should be built into the dispatch process as a mandatory step and its completion documented in an audit-proof manner with the date and reviewer. The dangerous goods officer is structurally responsible for this process. The transport document creation process should be underpinned by a four-eyes inspection and a checklist, so that discrepancies between the document and the physical marking are identified before departure.

ADR Chapter 8.6 regulates tunnel marking as an independent marking element. Each UN number in the ADR dangerous goods list (Chapter 3.2 Table A, column 15) is assigned to one of five tunnel categories A to E. The category determines which tunnels may be transited with the respective substance: category A means no prohibition in tunnels; categories B to E mean increasingly restrictive transit limitations, up to and including a transit ban in all classified tunnels in category E. The tunnel category need not necessarily be stated in the transport document, but must be known to the driver.

A practical obligation falls on the vehicle driver: they must know the tunnel category of the goods being transported for each journey and take it into account when planning the route. Standard navigation devices without a dangerous goods mode regularly direct drivers through prohibited tunnel sections, resulting in fines. Several EU states have national tunnel categorisations that go beyond the ADR minimum requirements; for international transport, these country-specific rules must also be checked.

The dangerous goods officer's annual report under Section 7 GbV should include statements on driver training regarding the tunnel categories of substances used in the company. If the report documents that drivers have no systematic information about tunnel restrictions for their transported goods, this constitutes a structural compliance deficit. A substance- and route-specific tunnel overview as a laminated document in the vehicle is a simple, effective remedial measure.

The correct labelling of dangerous goods is not a one-off project goal but an ongoing operational process. New substances, changed regulations in the ADR two-year update cycle, new employees, new transport routes and new customers — each of these factors can silently invalidate existing labelling routines. A structured dangerous goods compliance system ensures that regulatory changes are communicated promptly, training is kept current and labelling processes are documented in an audit-proof manner.

CIVAC supports this process with two complementary models: the workspace for the internally appointed dangerous goods officer and the external dangerous goods officer from the CIVAC partner network. Licence the workspace for your internal representatives or appoint our representatives. The workspace provides 37 ready-to-use audit templates, including specialised checklists for package marking, pre-departure vehicle inspection, transport document consistency checks and the annual report under Section 7 GbV.

Companies wishing to outsource the dangerous goods officer function benefit from the CIVAC SLA: order document, person and ongoing operation within two working days — rather than the conventional two to six weeks. Order document, signed, filed, verifiable. The auditor calls, the evidence is ready — annual report, training documentation, labelling records. Turn reading into action — write to info@civac.de or use the contact form on civac.de. The CIVAC concept of compliance platform and officer-as-a-service combines technical infrastructure with human expertise — a combination that purely software-based solutions without a qualified representative cannot replicate.