Classification, class properties and hazard identification
Who classifies and how
Classification is the consignor's duty (Chapter 1.4). The sequence is: look for an entry in Table A; if the substance is not named, apply the criteria in Part 2 and, where required, the UN Manual of Tests and Criteria; then assign class, classification code, packing group and any subsidiary hazard. There are nine classes, with divisions in Class 1 (1.1–1.6 plus compatibility groups A–S), Class 2 (2.1 flammable, 2.2 non-flammable non-toxic, 2.3 toxic) and Class 7 activity limits.
Class properties that drive the rules
Class 3 is defined by flash point (≤ 60 °C closed cup) with packing group taken from flash point and initial boiling point. Class 4.1 solids ignite readily, 4.2 spontaneously combustible, 4.3 evolve flammable gas on contact with water. 5.1 oxidise, 5.2 organic peroxides need temperature control, 6.1 are toxic by ingestion/inhalation/dermal, 6.2 infectious, 8 corrode skin or attack steel/aluminium. Class 9 covers substances not fitting elsewhere, including environmentally hazardous ones and lithium batteries.
Packing groups and precedence
PG I = high danger, II = medium, III = low. Where a substance meets criteria for several classes, the precedence table decides the primary class and the others appear as subsidiary risks.
Worked example
A liquid has a flash point of 23 °C and an initial boiling point of 45 °C. It is Class 3. Packing group: PG I needs IBP ≤ 35 °C - not met. PG II needs flash point < 23 °C - not met (23 °C is not below 23). PG III covers flash point 23–60 °C with IBP > 35 °C - met. Result: Class 3, PG III. The boundary at 23 °C is exactly the kind of hinge the exam tests.
Hazard identification
Label model numbers and placards identify the hazard; on RID tank-wagons and containers the orange plate shows the UN number, which is the reading key at an incident - RID plates do not carry an ADR-style hazard identification number.
Traps
Confusing PG with class; forgetting subsidiary labels; using a trade name instead of the proper shipping name; treating N.O.S. entries as complete without the technical name required by special provision 274.