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What is a Kemler code?
A Kemler code, officially the hazard identification number, is the two- or three-figure number in the top half of the ADR orange plate; the UN number goes underneath. Each figure signals a hazard (3 flammable, 8 corrosive), a doubled figure intensifies it, and an X in front warns that the substance reacts dangerously with water.
How do you read the orange plate?
The plate is a reflectorized orange rectangle, 40 × 30 cm, with a 15 mm black border (5.3.2.2.1). When it carries numbers, a black line divides it in two (5.3.2.2.2):
Example: 33 above 1203 = petrol (gasoline).
| Top half | Hazard identification number («Kemler»): 2 or 3 figures, preceded by an X where appropriate. Column (20) of Table A. |
|---|---|
| Bottom half | UN number of the substance: 4 figures. Column (1) of Table A. |
What does each figure mean?
| Figure | Hazard |
|---|---|
| 2 | Emission of gas due to pressure or to chemical reaction |
| 3 | Flammability of liquids (vapours) and gases or self-heating liquid |
| 4 | Flammability of solids or self-heating solid |
| 5 | Oxidizing (fire-intensifying) effect |
| 6 | Toxicity or risk of infection |
| 7 | Radioactivity |
| 8 | Corrosivity |
| 9 | Risk of spontaneous violent reaction |
The four reading rules
- Doubling a figure indicates an intensification of that hazard (33 = highly flammable).
- Where one figure is enough to indicate the hazard, it is followed by a zero (30, 80).
- An X in front means the substance reacts dangerously with water; water may only be used with the approval of experts.
- Some combinations have a special meaning (22, 323, 333, 362, 382, 423, 44, 446, 462, 482, 539, 606, 623, 642, 823, 842, 90 and 99): read them from the list in 5.3.2.3.2, not figure by figure.
Source: ADR 2025, 5.3.2.3.1.
Six real examples from Table A
| Plate | Substance | What the hazard number means |
|---|---|---|
| 33 / 1203 | Motor spirit / petrol | Highly flammable liquid (flash-point below 23 °C) |
| 30 / 1202 | Diesel fuel / gas oil | Flammable liquid (flash-point between 23 °C and 60 °C, inclusive) |
| 23 / 1978 | Propane | Flammable gas |
| 268 / 1005 | Ammonia, anhydrous | Toxic gas, corrosive |
| 80 / 1830 | Sulphuric acid (more than 51 % acid) | Corrosive or slightly corrosive substance |
| X423 / 1428 | Sodium | Solid which reacts dangerously with water, emitting flammable gases |
Source: ADR 2025, Table A of Chapter 3.2 (columns 1 and 20) and 5.3.2.3.2.
Kemler code — frequently asked questions
What does the X in front of a Kemler code mean?
That the substance reacts dangerously with water. For such substances, according to ADR 2025 (5.3.2.3.1), water may only be used with the approval of experts. Example: X423, sodium (UN 1428).
What does 33 on a truck mean?
Highly flammable liquid, with a flash-point below 23 °C (ADR 2025, 5.3.2.3.2). If 1203 is shown underneath, the vehicle is carrying petrol.
What is the bottom number on the orange plate?
It is the four-figure UN number of the substance, from column (1) of Table A. The hazard number goes on top and the UN number below, separated by a black line (ADR 2025, 5.3.2.2.2).
Do all ADR vehicles show numbers on the orange plate?
No. With packaged goods, the vehicle shows two plain orange plates, front and rear (5.3.2.1.1). Numbered plates are required on tanks and on bulk or unpackaged loads when column (20) of Table A gives a hazard identification number (5.3.2.1.2 and 5.3.2.1.4).
What about Class 1 explosives?
For Class 1 substances, the hazard identification number is the classification code in column (3b) of Table A: the division number followed by the compatibility group letter (ADR 2025, 5.3.2.3.1).
Where can I look up the Kemler code of a substance?
In column (20) of Table A of ADR 2025. Our free ADR Substance Lookup shows it, with the class, labels and tunnel code, from the UN number.
Information only: it assists the person responsible and does not decide for them. Always check each substance's number in column (20) of Table A of ADR 2025 and, if in doubt, ask your Dangerous Goods Safety Adviser.