Class 4.2 — substances liable to spontaneous combustion
Substances that can heat up and ignite on contact with air, without any external ignition source, including many pyrophoric materials.
- Packing groups
- I–III
- UN entries
- 108
What belongs in this class?
Class 4.2 covers two kinds of substance. Pyrophoric substances — liquids or solids that, even in small quantities, ignite on contact with air within five minutes — are the ones most liable to spontaneous combustion. Self-heating substances and articles are liable to warm up on contact with air without any energy supply, but ignite only in large amounts and after long periods (hours or days). (ADR 2.2.42.1.1)
Self-heating is a process in which a substance reacts gradually with the oxygen in air and generates heat. If heat production outpaces heat loss, the temperature rises and, after an induction time, can lead to self-ignition. (ADR 2.2.42.1.3)
Classification rules
- ADR 2.2.42.1.2
The classification code splits by properties — S for substances liable to spontaneous combustion (organic/inorganic, liquid/solid, organometallic, articles), SW for those that also emit flammable gases in contact with water, SO oxidizing, ST toxic and SC corrosive.
- ADR 2.2.42.1.5
Certain self-heating substances are exempt at small package volumes — no more than 3 m³ (no combustion or rise above 180 °C at 120 °C in the 10 cm cube), or no more than 450 litres (no combustion or rise above 160 °C at 100 °C).
- ADR 2.2.42.1.5
Organometallic substances can fall in Class 4.2 or 4.3 with additional subsidiary hazards, so a dedicated classification flow chart applies to them.
- ADR 2.2.42.1.6
Where admixtures shift a substance into a different hazard category than its named entry, the mixture is classified on its actual degree of danger.
Packing groups in this class
How many UN numbers in this class fall under each packing group.
Class 4.2 substances are assigned to packing group I, II or III on the basis of the self-heating and pyrophoricity tests in the Manual of Tests and Criteria. (ADR 2.2.42.1.8)
- PG I — pyrophoric substances (those that ignite spontaneously). (ADR 2.2.42.1.8)
- PG II — self-heating substances that, in a 2.5 cm sample cube at 140 °C, self-ignite or rise above 200 °C within 24 hours. (ADR 2.2.42.1.8)
- PG III — slightly self-heating substances that show the effect only in the larger 10 cm cube at 140 °C, not the 2.5 cm cube. (ADR 2.2.42.1.8)
Class 4.2 in Table A
Transport categories, tunnel codes and quantity reliefs across the 108 Table A entries of this class.
Transport categories
The category feeds the 1.1.3.6 calculation — the lower the number, the stricter the limit.
Tunnel codes
The column 15 code decides which tunnel categories the load may pass.
Limited quantities (LQ)
entries allow LQ
of 108 in the class
For the rest there is no relief — the full ADR applies to any quantity.
Excepted quantities (EQ)
entries allow EQ
of 108 in the class
For the rest there is no relief — the full ADR applies to any quantity.
Marking and signs for Class 4.2
What must be on every package — and what the transport unit carries on the road.
On the package
Every package carries the danger label of its Table A entry and the UN number with the letters "UN" (ADR 5.2.1, 5.2.2).
On the transport unit
Orange plates at the front and rear — and for tanks and bulk also enlarged placards 250 × 250 mm on the sides and rear (ADR 5.3.1, 5.3.2).
Limited quantities
Goods packed under Chapter 3.4 carry the LQ mark instead of the danger label and UN number (ADR 3.4.1, 3.4.7).
Class 4.2 specifics
- ADR 5.2.1.10.1
If the inner packagings of a combination packaging contain liquids, the package must bear orientation arrows — a general rule that applies to goods of all classes.
Transport document
What must be written in the transport document when you ship Class 4.2 goods.
- ADR 5.4.1.1.1
The transport document entry shows the packing group, which may be preceded by the letters PG — for example, UN 1378, METAL CATALYST, WETTED, 4.2, PG II, (D/E).
- ADR 5.4.1.1.6.2.1
For empty packagings, uncleaned, the information of the goods last loaded may be replaced by "WITH RESIDUES OF " followed by the classes and subsidiary hazards in the class numbering order.
Reliefs and restrictions
How much may travel under lighter regimes — and where tunnels restrict the route — is set per UN entry in Table A.
Limited quantities (LQ)
Column 7a caps each inner packaging. Within Chapter 3.4 most ADR requirements fall away, including the driver certificate.
ReadExcepted quantities (EQ)
E codes in column 7b let very small inner receptacles travel with almost no ADR overhead (Chapter 3.5).
ReadTunnel restrictions
Column 15 assigns the tunnel restriction code — it decides which tunnel categories the load may pass.
ReadLook up a Class 4.2 UN number
Get the full ADR profile for any UN number in this class.
Typical UN numbers
All 108 entries
Help with Class 4.2 shipments
Not sure this class applies to you?
A DGSA can confirm the classification before your next load leaves the yard.
Train your team
Awareness training under ADR 1.3 for everyone who consigns, packs or loads dangerous goods.
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