What the plates are for and why they are so strict
The signage on a dangerous goods truck is not decoration: it is an emergency warning at a glance. If there is an accident, a firefighter or officer must know within seconds — without opening the box — what you are carrying and how that load may react. That is why ADR, the European agreement governing these goods, sets down to the millimetre which plates to carry, in what colour, size and position.
Two things are worth not confusing: the orange plates, which state with numbers what hazard and what substance you carry, and the hazard labels (the coloured diamonds), which show the class of risk with symbols. Getting them wrong, or not carrying them, is a serious offence and, at a roadside check, grounds to immobilise the truck until it is fixed.
The orange plate: the number plate of the hazard
It is the rectangular orange plate everyone recognises. It measures 40 cm wide by 30 cm high, is reflective and has a black border. It can appear in two ways, and knowing which one applies to you comes first.
Plain orange plate (no numbers)
It goes at the front and rear of the vehicle when you carry packages of several different dangerous goods. It says "dangerous goods here" without specifying which, because a mixed load could not fit a single number. The detail of each product goes in the documentation and on each package's labels.
Numbered orange plate (tankers and bulk)
When you carry a single identifiable substance — a tanker, a bulk load — the plate shows two numbers: on top the Hazard Identification Number (Kemler code) and below the UN number. They go on the sides of the tank (one per compartment on multi-compartment tanks), plus front and rear.
How to read the plate: the two numbers
The two numbers are read together and tell the whole story of the load. Understanding them is what separates a trained driver from one who just "has the plate on".
The top one: the Hazard Identification Number (Kemler)
Two or three digits stating the type of hazard. The first digit is the primary hazard and the following ones are added hazards: 2 gas, 3 flammable liquid, 4 flammable solid, 5 oxidiser, 6 toxic, 8 corrosive, 9 miscellaneous. If a digit is doubled, that hazard is intense (33 = highly flammable liquid). And if there is an "X" in front, take note: it means the substance reacts dangerously with water — a vital warning for anyone fighting a fire.
| Kemler code | What it means | Example (UN) |
|---|
| 33 | Highly flammable liquid | 1203 (petrol) |
| 30 | Flammable liquid | 1202 (diesel) |
| 80 | Corrosive | 1789 (hydrochloric acid) |
| 268 | Toxic and corrosive gas | 1017 (chlorine) |
| X423 | Solid that releases flammable gas with water | 1428 (sodium) |
The bottom one: the UN number
Four digits that identify the exact substance. 1203 is petrol, 1202 is diesel, 1017 is chlorine. With that number, emergency services pull the product's data sheet and know how to act. It is, so to speak, the load's ID card.
The coloured diamonds: the class labels
Besides the orange plate, the vehicle and packages carry hazard labels shaped like diamonds. The symbol and colour tell you the class of risk at a glance. Package labels are at least 10×10 cm; vehicle and container labels, 25×25 cm.
| Class | Risk | Diamond colour |
|---|
| 1 | Explosives | Orange |
| 2 | Gases | Red, green or white by type |
| 3 | Flammable liquids | Red |
| 4.1 / 4.2 / 4.3 | Flammable solids / spontaneously combustible / water-reactive | Red-white / red-white / blue |
| 5.1 / 5.2 | Oxidisers / peroxides | Yellow / red-yellow |
| 6.1 / 6.2 | Toxic / infectious | White (skull / biohazard) |
| 7 | Radioactive | White-yellow (trefoil) |
| 8 | Corrosive | White top, black bottom |
| 9 | Miscellaneous | White with black stripes |
Where each plate goes (no guesswork here)
Carrying the right plates is not enough: ADR requires placing them where they belong. A well-printed but badly positioned plate is still an offence, so it pays to be clear.
The orange plates
They go vertically, front and rear, clearly visible. On single-substance tankers and bulk, add the numbered plates to both sides. And a detail that gets forgotten: if you run with the tank empty but uncleaned and not degassed, the signage must stay up, because dangerous residues remain.
The labels (the diamonds)
Each package carries the labels for every risk class that applies to it. Large containers, tankers and full loads carry the 25 cm diamonds on both sides and the rear, so the risk can be read from any angle.
Other marks that sometimes apply
Depending on the load, extra marks are needed: the environmentally hazardous mark (the fish and tree), the elevated temperature mark (the red thermometer) for hot cargo, and the special marking for limited quantities (LQ). Each has its own shape and size.
What the inspector will ask for, besides the plates
The plate is the visible part, but the inspector will want to see the whole set. Keep this in the cab at all times.
The documents in the cab
You need the transport document with the goods' official name (its ADR proper shipping name and UN number), the instructions in writing — the what-to-do-in-an-emergency sheets — and your valid ADR licence for the class you carry. This all sits within the dangerous goods transport regulation.
The vehicle equipment
ADR requires carrying the protective and emergency equipment listed in the instructions in writing (extinguishers, wheel chocks, breakdown warning, personal protection). The inspector may check it, and the company's safety adviser is responsible for it all being in order.
What happens if something is wrong
At a check, signage is the first thing looked at, even before papers. A missing plate, a wrong code or labels that do not match the load are penalised and can end in immobilisation of the vehicle until the defect is fixed.
Frequently asked questions about ADR signage
The top one (Kemler code) states the type of hazard; the bottom one (UN number, four digits) states exactly which substance. For example, 33/1203 is petrol: a highly flammable liquid.
That the substance reacts dangerously with water. It is a key warning for emergency teams, who must avoid water to smother or contain it.
Plain when you carry packages of several different goods. Numbered on single-substance tankers and bulk, where it can be identified with one Kemler/UN pair.
Not while it is uncleaned and not degassed: it still holds dangerous residues, so the signage must stay up until it is fully decontaminated.