How the orange plate is laid out
Under ADR, the numbered orange plate is a reflective orange rectangle, 40 cm wide and 30 cm high, with a black border. The hazard identification number (often called the Kemler code) sits in the top half and the four-digit UN number in the bottom half. A petrol tanker, for example, shows 33 over 1203.
What each digit means
- 2 — gas given off by pressure or a chemical reaction
- 3 — flammable liquid (vapours) or gas, or a self-heating liquid
- 4 — flammable solid or self-heating solid
- 5 — oxidising (fire-intensifying) effect
- 6 — toxicity or risk of infection
- 7 — radioactivity
- 8 — corrosivity
- 9 — risk of a spontaneous violent reaction
The first digit is the main hazard; the following digits add secondary hazards. Three rules complete the system:
- A doubled digit means the hazard is intensified. 33 is a highly flammable liquid; 88 is a highly corrosive substance.
- A 0 as the second digit means one figure is enough. 30 is a flammable liquid with no further hazard to flag, such as diesel.
- An X in front means the substance reacts dangerously with water. Water may then be used only with the approval of experts.
Common codes you will meet
- 33 / UN 1203 — petrol: highly flammable liquid.
- 30 / UN 1202 — diesel fuel: flammable liquid.
- 336 / UN 1230 — methanol: highly flammable liquid, also toxic.
- 23 / UN 1965 — LPG (liquefied hydrocarbon gas): flammable gas.
- 268 / UN 1005 — anhydrous ammonia: toxic gas that is also corrosive.
- 22 / UN 1977 — refrigerated liquid nitrogen: refrigerated liquefied gas.
- 225 / UN 1073 — refrigerated liquid oxygen: refrigerated gas with an oxidising effect.
- 80 / UN 1830 — sulphuric acid: corrosive.
- 90 / UN 3082 — environmentally hazardous liquid.
- X423 / UN 1428 — sodium: a solid that reacts with water to give off flammable gas, so water must not be used.
Why the X matters so much
For most fires, water is the first tool firefighters reach for. On a vehicle marked with an X code, water can make the incident far worse — for sodium (X423) it releases flammable gas. That is why the X is printed before the number, where it is seen first, and why ADR exam questions on it are so common.
Co oznacza litera X przed numerem rozpoznawczym zagrożenia?
Litera X przed numerem rozpoznawczym zagrożenia na pomarańczowej tablicy oznacza, że materiał reaguje niebezpiecznie z wodą. Wody można użyć wyłącznie za zgodą ekspertów — przykładem jest X423 dla sodu (UN 1428). Podwojona cyfra oznacza nasilenie zagrożenia (33 — benzyna), a zero na drugim miejscu oznacza, że jedna cyfra wystarcza do opisu zagrożenia (30 — olej napędowy). Przećwicz to na teście ADR po polsku.
Test yourself
Hazard numbers are one of the most tested topics in the ADR driver exam. Try a free ADR driver practice test, with a basic course paper plus tank, Class 1 and Class 7 papers, or browse all workplace safety certification practice tests.
Frequently asked questions
What does the X mean on an ADR orange plate?
An X before the hazard identification number means the substance reacts dangerously with water, so water may be used only with the approval of experts. Sodium (UN 1428), for example, is marked X423.
What does 33 mean on a tanker?
33 means a highly flammable liquid: the doubled 3 shows the flammability hazard is intensified. It appears above UN 1203 on petrol tankers.
What is the difference between hazard number 33 and 30?
33 is a highly flammable liquid such as petrol (UN 1203). 30 is a flammable liquid whose hazard is adequately described by the single figure 3, such as diesel (UN 1202).
What is the top number on an orange hazard plate called?
It is the hazard identification number, often called the Kemler code. The bottom number is the four-digit UN number that identifies the substance.