The ADR orange plate: how to read the hazard identification number and UN number

In brief

• An orange-coloured plate measures 40 × 30 cm and has a black border. The upper part is the hazard identification number (2-3 digits, sometimes with the letter X), the lower part is the four-digit UN number.
• The first digit of the hazard identification number is the primary hazard, the following digits are subsidiary hazards. A doubled digit means an intensified hazard, a zero means no subsidiary hazard.
• The letter X in front of the number means the substance reacts dangerously with water.
• Vehicles carrying packages have blank plates. Numbers appear for tanks and carriage in bulk.
• Below you will find a decoder that reads any pair of numbers.

What an orange plate looks like under ADR

People often call it a "Kemler plate", but the regulations use the name orange-coloured plate. Its appearance is described in ADR 5.3.2.2: the plate is reflective, 40 cm wide and 30 cm high, with a black border 15 mm wide. A black horizontal line, also 15 mm wide, may run across the middle.

The digits are black, 100 mm high with a 15 mm stroke. The hazard identification number is in the upper part and the UN number in the lower part. The plate and digits must stay in place and legible after 15 minutes in fire, and a dimensional tolerance of ± 10% is allowed.

If the vehicle is too small for the full size, the plate may be reduced to 300 × 120 mm with a 10 mm border. This is sometimes the case with small delivery vehicles. On tank-containers and portable tanks, a self-adhesive sheet or paint may replace the plate if it meets the other requirements.

Markings on an ADR plate: what the upper number means

The hazard identification number consists of two or three digits. Each digit indicates a type of hazard (ADR 5.3.2.3.1):

The first digit shows the primary hazard, the next ones the subsidiary hazards. On top of this come three rules that are enough to read most plates on the road.

Zero, a doubled digit and the letter X

Zero is added when a single digit describes the hazard adequately. 30 is a flammable liquid with no subsidiary hazard, 80 is a corrosive substance.

A doubled digit means an intensified hazard. 33 is a highly flammable liquid with a flash-point below 23 °C, while 30 is a flammable liquid with a flash-point between 23 °C and 60 °C, inclusive. You can therefore see the difference between petrol and diesel straight away from the plate.

The letter X in front of the number means the substance reacts dangerously with water. Water may then only be used with the approval of experts. For a firefighter, this matters more than the name of the substance itself.

Combinations with a special meaning

Some combinations cannot be read digit by digit. ADR lists them explicitly: 22, 323, 333, 362, 382, 423, 44, 446, 462, 482, 539, 606, 623, 642, 823, 842, 90 and 99. For example, 22 is a refrigerated liquefied gas, asphyxiant, 44 is a flammable solid in the molten state at an elevated temperature, and 90 is an environmentally hazardous substance or miscellaneous dangerous substances. The full meanings are in the list in ADR 5.3.2.3.2, and the decoder below uses that list.

In class 1 (explosive substances and articles), a classification code such as 1.1D appears on the plate instead of a hazard identification number.

The lower number: the UN number

The UN number is the four-digit number of a substance or group of substances on the United Nations list. In ADR you will find it in column (1) of Table A in Chapter 3.2, and the hazard identification number for that substance in column (20).

The same UN number can have different hazard identification numbers if the substance occurs in different packing groups. This is why you should always read both numbers together. The pairs 30/1993 and 33/1993 are the same UN number (flammable liquid, n.o.s.), but a different degree of hazard.

Orange plate decoder

Enter the numbers from the plate or choose an example. The decoder shows the meaning according to the list in ADR 5.3.2.3.2 and, for common UN numbers, also the name of the substance and the data from Table A.

The most common plates on Polish roads

The pairs below come from Table A in Chapter 3.2 of ADR 2025. I chose those most often seen on fuel, gas and chemical tankers.

When a plate is blank and when it has numbers

Every transport unit carrying dangerous goods has two plates: at the front and at the rear (5.3.2.1.1). If it carries packages, that is, drums, jerrycans, cylinders or cartons, the plates are blank. A blank plate only tells the emergency services that there are dangerous goods inside. The details are in the transport document and on the danger labels.

Numbers appear for tanks and carriage in bulk. A tank-vehicle additionally has numbered plates on the sides of each tank or compartment (5.3.2.1.2). When the whole unit carries only one dangerous substance and no other goods, the numbers can be on the front and rear plates, and the side plates are then not needed (5.3.2.1.6).

Fuel tankers have a rule of their own. If the compartments contain only UN 1202, 1203, 1223, 3475 or aviation fuel UN 1268 or 1863, side plates are not required, provided the front and rear plates show the numbers of the most dangerous substance, that is, the one with the lowest flash-point (5.3.2.1.3). This is why a tanker with petrol and diesel in different compartments usually travels with a 33/1203 plate.

An empty tank and no plates for small quantities

An empty, uncleaned tank keeps its plates (5.3.2.1.7). On the other hand, a vehicle carrying quantities within the 1.1.3.6 exemption does not need plates at all, because Chapter 5.3 does not apply in that case. I explain how to calculate this limit in my article on the ADR 1.1.3.6 exemption and 1000 points.

What to do if you see an incident with a plated vehicle

If you witness an accident involving a tanker or a vehicle with orange plates, keep your distance and do not approach any leak or vapour cloud. Move so that the wind blows from you towards the vehicle, not the other way round. Do not smoke or use a naked flame.

When you call 112, give both numbers from the plate and the location of the incident. The pair 33/1203 or 268/1005 tells the dispatcher more than "a tanker has overturned". If the plate is blank, say so. The driver has the instructions in writing and the transport document in the cab, and the emergency services will get the rest from them.

Most common mistakes with plates

The same problems keep coming up in inspections and audits:

• plates not removed or covered after unloading, although the vehicle is no longer carrying dangerous goods,
• covering a plate with tape or cardboard that will not last 15 minutes in fire,
• interchangeable digits falling out of the frame or shifting during the journey,
• the wrong pair of numbers, for example 30/1203 instead of 33/1203 after a change of product in the tank,
• a faded plate that is no longer reflective.

Several participants are responsible for marking at the same time, which is why loading staff and drivers should be able to read plates as well as they read the transport document. It is one of the topics of Chapter 1.3 training, and I check the state of the marking in every ADR audit.

Legal basis: ADR 2025 (Polish text: Dz.U. 2025 item 642): section 5.3.2 (5.3.2.1.1-5.3.2.1.8, 5.3.2.2.1-5.3.2.2.4, 5.3.2.3.1, 5.3.2.3.2), Table A in Chapter 3.2, columns (1), (2) and (20), sub-section 1.1.3.6.

If you want the people on your loading bay to read plates and labels without looking up the regulations, book a free consultation. I will prepare a short training session using your own goods as examples.