A large share of the chemicals traded internationally are classified as dangerous goods for transport. Flammable solvents, corrosive acids, oxidisers, toxic reagents and even dry ice used to keep samples cold all fall under transport regulations. Shipping them correctly protects the people who handle them and prevents costly rejections, delays and penalties. This article introduces the key concepts.
The regulatory framework
Dangerous goods rules are harmonised internationally through the UN Recommendations on the Transport of Dangerous Goods, often called the Orange Book or Model Regulations. Each transport mode then applies them through its own instrument:
- Sea: the International Maritime Dangerous Goods (IMDG) Code, published by the International Maritime Organization and updated in two-yearly amendments
- Air: the ICAO Technical Instructions, applied through the IATA Dangerous Goods Regulations, published annually
- Road and rail: regional and national rules, such as ADR and RID in Europe or 49 CFR in the United States
Section 14 of the Safety Data Sheet summarises a product's transport classification across these modes.
The nine hazard classes
| Class | Hazard | Examples |
|---|---|---|
| 1 | Explosives | Certain nitro compounds, picric acid when dry |
| 2 | Gases | Compressed nitrogen, aerosols, liquefied gases |
| 3 | Flammable liquids | Acetone, methanol, ethyl acetate, hexane |
| 4 | Flammable solids. Spontaneously combustible. Dangerous when wet | Sulfur, sodium metal, some metal powders |
| 5 | Oxidisers and organic peroxides | Potassium permanganate, hydrogen peroxide solutions, benzoyl peroxide |
| 6 | Toxic and infectious substances | Sodium cyanide, many pesticides |
| 7 | Radioactive material | Radioactive isotopes |
| 8 | Corrosives | Hydrochloric acid, sodium hydroxide, sulfuric acid |
| 9 | Miscellaneous | Dry ice, environmentally hazardous substances |
A substance may have a primary class and one or more subsidiary hazards, for example a flammable liquid that is also toxic.
UN numbers and proper shipping names
Each dangerous substance, or group of substances, is assigned a four-digit UN number and a proper shipping name from the Dangerous Goods List. Acetone is UN1090, methanol UN1230, hydrochloric acid UN1789, sodium hydroxide solid UN1823 and dry ice UN1845. Where no specific entry exists, a generic or not otherwise specified (n.o.s.) entry is used, with the technical name added in brackets. The UN number is the key used to look up the rules that apply.
Packing groups
Most classes are divided into three packing groups according to the degree of danger:
- Packing Group I: high danger
- Packing Group II: medium danger
- Packing Group III: low danger
For flammable liquids, the criteria are based on flash point and initial boiling point: PG I for an initial boiling point of 35 °C or below. PG II for a flash point below 23 °C with a boiling point above 35 °C. PG III for a flash point from 23 °C to 60 °C. The packing group determines packaging performance, quantity limits and some documentation requirements.
UN-specification packaging
Dangerous goods must generally travel in packaging that has passed UN performance tests, such as drop, stacking, leakproofness and hydraulic pressure tests. Approved packaging carries a UN mark, for example:
UN 1A1/Y1.4/150/25/IND/...
- 1A1: packaging type, here a steel drum with a non-removable head
- Y: performance level, where X covers PG I to III, Y covers PG II and III, and Z covers PG III only
- 1.4: maximum relative density for liquids
- 150: hydraulic test pressure in kPa
- 25: year of manufacture
- IND: country authorising the mark, followed by the manufacturer's code
Laboratory quantities are often shipped as combination packaging: glass or plastic inner bottles cushioned with absorbent material inside a UN-rated outer box.
Limited and excepted quantities
Small quantities can often travel under relaxed conditions. Limited quantity provisions allow small inner packagings, such as up to one litre for many PG II flammable liquids by sea or road, with simplified marking. Excepted quantity provisions allow very small amounts, typically millilitres or grams per inner package, with a special mark and minimal documentation. Air transport rules for limited quantities are stricter than for sea and road. These provisions are useful for samples and reference standards.
Sea freight under the IMDG Code
- A Dangerous Goods Declaration signed by a trained person, listing UN number, proper shipping name, class, packing group, quantity and emergency information
- A Container Packing Certificate confirming correct loading and securing
- Correct labels and placards on packages and containers, and marine pollutant marks where applicable
- Compliance with segregation rules that keep incompatible classes apart on board
- Emergency response information, referenced through EmS codes
Air freight under the IATA DGR
Air rules are stricter. Some substances are forbidden entirely, many are permitted only on cargo aircraft, and per-package net quantity limits apply. A Shipper's Declaration for Dangerous Goods is required, and staff preparing shipments must be trained. Express courier networks accept only a limited range of dangerous goods, so some samples must go through specialist air freight forwarders.
Common reasons for rejected shipments
- Missing or mismatched UN number between SDS, labels and declaration
- Packaging whose performance level does not cover the packing group
- Exceeding per-package quantity limits for air
- Undeclared dry ice in sample shipments
- Incorrect or missing orientation arrows and hazard labels
- Shipper's declaration signed by an untrained person
FAQs
What does packing group mean?
It indicates the degree of danger within a hazard class: PG I high, PG II medium and PG III low. It determines packaging performance and quantity limits.
Is dry ice a dangerous good?
Yes. Dry ice is UN1845, Class 9. It must be declared, and packages must allow carbon dioxide gas to vent.
Can dangerous chemicals be sent by courier?
Only some, in limited amounts and through couriers that accept dangerous goods. Many require specialist air freight or sea shipment.