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Dangerous goods classes — exam reference

Summarised from ADR Part 2 (Classification). Each card links hazard type, typical loads and placarding notes. Expand for chapter references.

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Use the primary class on the transport document. Subsidiary hazards appear in brackets — e.g. 6.1 (3) toxic with flammable subsidiary. Mixed loads take the most restrictive tunnel code (ADR 8.6.3.2).

Class 1 — Explosives

Explosive substances and articles. Divided into divisions 1.1–1.6 and compatibility groups (A–S). Highest scrutiny for HGV drivers carrying fireworks, ammunition or blasting agents.

Examples: Fireworks (1.4G); Detonators; Ammunition; Propellants

Exam focus · ADR 2.2.1

Know divisions: 1.1 mass explosion hazard; 1.2 projection hazard; 1.3 fire/minor blast; 1.4 no significant blast; 1.5 very insensitive; 1.6 extremely insensitive. Compatibility groups control mixed loading. Separate Class 1 training module required in UK.

Placarding: Orange placard with division number and compatibility group. High-consequence explosives trigger strict tunnel codes (e.g. B1000C, C5000D).

Subsidiary hazards: May also present toxic or corrosive subsidiary hazards depending on substance.

Class 2 — Gases

Compressed, liquefied, dissolved or refrigerated gases. Three divisions: flammable, non-flammable non-toxic, toxic. Common in cylinders, MEGCs and tankers.

Examples: LPG / propane; Oxygen; Chlorine; Refrigerated LNG

Exam focus · ADR 2.2.2

Gas definition: vapour pressure >300 kPa at 50 °C or fully gaseous at 20 °C / 101.3 kPa. Divisions 2.1 flammable, 2.2 non-flammable, 2.3 toxic. Tank module covers fixed tanks and MEGCs for gases.

Placarding: Division-specific placards; tankers also carry orange plates per 5.3.2.

Subsidiary hazards: Some gases have oxidising or corrosive subsidiary risks.

Class 3 — Flammable liquids

Liquids (or mixtures) with flash point ≤60 °C (closed cup) or ≤65.6 °C (open cup). Packing groups I–III by flash point and boiling point.

Examples: Petrol; Diesel (when classified); Paints/solvents; Ethanol

Exam focus · ADR 2.2.3

Flash point thresholds, packing groups, and vapour collection during loading. Mixed loading prohibitions with oxidisers (Class 5.1). Tank carriage uses Ch. 4.3 provisions.

Placarding: Red flame symbol placard. Tunnel codes often (D) or (D/E) for bulk/tank loads.

Subsidiary hazards: Toxic or corrosive liquids may show subsidiary class numbers.

Class 4 — Flammable solids & reactive

Three parts: 4.1 flammable solids/self-reactive/desensitised explosives; 4.2 spontaneous combustion; 4.3 dangerous when wet.

Examples: Matches; Metal powders; White phosphorus; Sodium batteries

Exam focus · ADR 2.2.4

4.3 substances react with water — keep dry, specific stowage. Self-reactive 4.1 and organic peroxides 5.2 need temperature control (7.1.7).

Placarding: Division-specific labels; 4.3 uses blue-red flame symbol.

Subsidiary hazards: Cross-classification table in 2.1.3 resolves primary vs subsidiary class.

Class 5 — Oxidisers & organic peroxides

5.1 oxidising substances; 5.2 organic peroxides. Intensify fire — strict segregation from flammables.

Examples: Ammonium nitrate fertilisers; Hydrogen peroxide; Pool chemicals

Exam focus · ADR 2.2.5

Mixed loading bans with Classes 3, 4.1, 4.2, 4.3 (7.5.2). Organic peroxides need specialist packing (4.1.7).

Placarding: 5.1 yellow oxidiser flame; 5.2 red/yellow organic peroxide symbol.

Subsidiary hazards: Some oxidiser mixtures may meet Class 1 criteria — rejected if explosive.

Class 6 — Toxic & infectious

6.1 toxic substances; 6.2 infectious substances (Category A/B). PPE and spill response critical.

Examples: Pesticides; Clinical waste; Diagnostic specimens

Exam focus · ADR 2.2.6

6.2 packing instructions P620/P621. Inhalation toxicity vs oral — packing group drivers. Infectious substances need triple packaging.

Placarding: 6.1 skull-and-crossbones; 6.2 biohazard label.

Subsidiary hazards: Many 6.1 liquids are also flammable (subsidiary 3).

Class 7 — Radioactive

Radioactive material with activity limits, category (I–III), transport index and criticality safety. Separate UK training module.

Examples: Medical isotopes; Industrial gauges; Depleted uranium

Exam focus · ADR 2.2.7 / 1.7

Radiation protection programme, category limits, exclusive use, segregation distances. Part 1 Ch. 1.7 and 5.1.5 Class 7 provisions.

Placarding: Trefoil label; category and TI on documentation. Yellow II/III labels when required.

Subsidiary hazards: Radioactive goods with other hazards follow 1.7.5 rules.

Class 8 — Corrosives

Substances destroying skin/eyes or corroding metals. Acids and alkalis in packages and tankers.

Examples: Sulphuric acid; Caustic soda; Battery electrolyte

Exam focus · ADR 2.2.8

Packing groups by corrosion severity. Segregation from foodstuffs (7.5.4). Tank cleaning after unload (7.5.8).

Placarding: Corrosive symbol — liquids/solids variants.

Subsidiary hazards: Corrosive flammable liquids classified per precedence table (e.g. UN 2734 → Class 8 primary).

Class 9 — Miscellaneous

Dangerous goods not meeting other classes but still regulated — lithium batteries, asbestos, environmentally hazardous substances, elevated temperature materials.

Examples: Lithium batteries; Dry ice; PCBs; Magnetized material

Exam focus · ADR 2.2.9

UN 3077/3082 environmentally hazardous marks (5.3.6). Lithium battery packing instructions. Elevated temperature mark (5.3.3).

Placarding: Class 9 placard when required; environmentally hazardous mark for marine pollutants on road when applicable.

Subsidiary hazards: May carry subsidiary hazards from other classes.

Hazard label diagrams 5.2.2

Official ADR label models — see full diagram gallery or chapter text.

ADR Class 1 explosive label with division 1.4 and compatibility group S — Figure 5.2.2.2.1 — Class 1 label (division & compatibility group)

ADR Class 2 flammable gas placard model — Figure 5.2.2.2.1 — Class 2 flammable gas placard

ADR Class 3 flammable liquid diamond label — Figure 5.2.2.2.1 — Class 3 flammable liquid label

ADR Class 4.1 flammable solid label — Figure 5.2.2.2.1 — Class 4.1 flammable solid label

ADR Class 4.3 substances which emit flammable gases when in contact with water — Figure 5.2.2.2.1 — Class 4.3 water-reactive label

ADR Class 5.1 oxidizer label — Figure 5.2.2.2.1 — Class 5.1 oxidizing substance label

Ch. 5.2 Marking & labelling

Classification principles (ADR 2.1)

Substances and articles are assigned to Classes 1–9 per criteria in Chapter 2.2.
Mixtures use the precedence table (2.1.3) to decide primary class and packing group.
UN numbers and proper shipping names come from Table A (Chapter 3.2) — Column 15 gives tunnel restriction codes.
Packing groups I (high danger), II (medium), III (low) apply to many classes — shown on documents and labels.